1, 2, 3

Cognitive How we think about ourselves, other people, and the world, as well as the assumptions we make and the strategies we use for solving problems and interact- ing with others are the keys to understanding differences between people. The particular language we learn and use shapes our way of thinking and perceiving. Memory formation is not a passive process but is shaped by our experiences, attitudes, and personalities. In short, what we do is shaped by how we think and perceive the world.

Sociocultural/Cross-Cultural The immediate (micro; family, friends) and larger (macro; region and nation) environments impact and mold a person's personality from birth on. One can't understand people without understanding the place and context in which they grew up. Cultures differ along particular dimensions—such as collectivism- individualism or masculinity-femininity—and these cultural differences influence the thought and behavior of individuals within each culture. Psychological outcomes can also be compared between cultures and there are both similarities and differences across cultures.

In one sense, you have been a psychologist for most of your life. Every time you ponder why you think and feel in particular ways, you are thinking psychologically. Every time you try to explain what someone else is doing—and why—you are thinking psychologically. You do it when you say your friend dominates conversations because he is self-absorbed. You also do it when you conclude that your big sister is bossy because she is older and always gets what she wants. We think and live psychology every day. Psychology Defined Many fields of study aim to understand people's thoughts and actions. Literature helps us understand people through storytelling, character exploration, development of setting, and use of imagery. History helps us understand people through description and analysis of past events and artifacts. Anthropology is the study of human culture and origins. Sociology seeks to understand people in terms of large-scale social forces and group membership rather than individuals. Psychology is unique in that it is the science of understanding individuals—animals as well as people. Formally defined, psychology is the scientific study of thought and behavior. The root word psyche comes from the Greek for "mind," but modern psychology is as likely to study the brain and behavior as it is the "mind." You might be thinking, Don't psychologists treat people with mental illness or try to help us figure out how our parents messed us up? Yes, they do these things too. Some professional psychologists practice, or apply, psychology to diagnose and treat problems of thought and behavior. In fact, psychology is both a clinical practice and a science. The clinical practice side encompasses the services provided in therapists' offices, schools, hospitals, and businesses. Without fail, when we (the authors of this text) tell people that we are psychologists, they immediately think we are clinical psychologists and are analyzing their every move, looking for hidden meaning in everything they do. You can also find popular psychology in homes, on radio talk shows, on Internet news sites, and in TV news reports. What sets scientific psychology apart from popular psychology—known as pop psychology—are the methods used in each. As you will see in the chapter "Conducting Research in Psychology" and again in the chapter "Treatment of Psychological Disorders", the methods of scientific and clinical psychologists are quite different from people in general, who sometimes draw from an unreliable body of knowledge known as common sense. psychology The scientific study of thought and behavior. Challenge Your Assumptions True or False? If you are a psychologist, you diagnose and treat mental disorders. False: Some psychologists diagnose and treat mental illness but others conduct scientific studies on human thought and behavior. Psychology is both a practice and a science. What Is Psychology? 5 Psychology in the Real World Why Psychology Is Important to My Life Yvette Szabo, University of Louisville For me, studying psychology has meant so much more than learning concepts for an exam. Every day I see how it applies to my life. Material from class and the textbook come alive in my daily encounters. For instance, I now understand what affects my own productivity and what increases my motivation. I know that stress sometimes serves as a major stimulant for me and activates me to work, but it also wears down my immune system. Also, too much stress impairs the quality of my work. From Intro Psych, I learned that these experiences are consistent with what research on motivation, stress, and health tells us. I have also noticed how patterns of behavior repeat themselves within families or groups of friends. When I learned about the effects of birth order on personal- ity, for example, I was able to connect the concept to my sister and me. I am the younger sister, and I am more rebellious and open to new ideas. In contrast, my elder sister is more agreeable and has a more cautious personality. When I learned in Intro Psych that younger- born children are "born to rebel" [see the chapter "Personality: The Uniqueness of the Individual"], I was amazed to discover that the pattern I see with my sister and me is a common one. This has helped put my own life in a larger context of human behavior. As a curious student, I always enjoy understanding something new. One thing I appreciated with this class is how all of the fields of psychology overlap and interconnect. For example: Different people see and perceive events differently. In other words, social and personality psychology are closely connected to memory, sensation, and perception. What we perceive and remember overlaps with our social environment and our personality. Perceiving and remember- ing is almost like a camera lens, but the lens has filters—your personality and previous experiences filter what you take in, what sense you make of it, and what you recall. Additionally, for me, connections between the subfields are clearer when I look at an area that interests me—diagnoses and treatments for depression. In order to understand both the causes of and treatments for depression, you need to appreciate how the biological origins of depression, such as hormones and neurotransmitters, are affected by life experiences, such as stress and trauma. If we don't integrate the biological and social approaches to understanding disorders, then we won't be very successful at diagnosing and treating them. Moreover, psychology often explores the roles of nature and nurture in shaping behavior and personality. This book in particular does a great job of emphasizing how nature and nurture work together to create who we are and who we become. I have seen this firsthand. My cousin, adopted by my uncle and his wife, developed mannerisms similar to those of her family members. And yet, I've also learned in class that twins separated at birth will likely 6 CHAPTER 1 Introduction to Psychology Perhaps because of the ubiquity of popular psychology, most people you talk to on the street don't think of psychology as a science; rather, they probably think of it only as a clinical practice. The editors of Scientific American, for instance, commented that "whenever we run articles on social topics, some readers protest that we should stick to 'real science' " ("The peculiar institution," 2002, p. 8). As we will see throughout this text, not only is psychology a science, but it is also considered a core science, along with medicine, earth science, chemistry, physics, and math. Core sciences are those that have many other disciplines organized around them. Why Should You Study Psychology? Reasons for studying psychology vary from person to person. Maybe your adviser suggested it would be a good course to take, or maybe you're taking the course because it satisfies a general education requirement. Psychology is considered part of a good general education because its content is useful to many fields. It is also relevant to your life. Adopting a scientific perspective on human behavior helps you develop a curiosity for how behavior works. It also fosters an appreciation for how much of have similar interests and characteristics. These examples both show that nature and nurture are intertwined. My knowledge of psychology provides constant explanations for the kinds of relationships I see all around me. For example, as I learned in my psychology courses, research shows that children who were bullied at home will be more likely to befriend someone meek so they can achieve dominance. Sure enough, a close friend of mine recently admitted she was a bully in grade school because it was the one place she was tougher than those around her. At home she was picked on, and so she wanted to dominate when she could at school. Psychology allowed me to better understand this not-so-desirable behavior in my friend. Similarly, I learned that people who do not receive much human contact and were not held as children will likely have difficulty forming bonds and close attachments as adults. I have seen this play out among numerous friends and acquaintances. Both of these cases show the importance of caregiving behavior in the formation of social relationships. By turning what I learn in my classes outward, I can better understand the actions of others. I am more effective at motivating others and myself, because I better understand individual differences and different types of motivation that stem from internal and environmental sources. I am more conscious about what motivates me. Sometimes I am more motivated by an internal source, such as when I participate in a sport because I enjoy the game. Other times, I am more motivated by external sources, such as when I work to earn a high grade in a class. Most importantly, the things I learned in Introduc- tory Psychology have laid a foundation for all my future studies in psychology and even other courses. As I have studied more about the clinical applications of psychology, I have become more conscious of the role of a listener and speaker and have greatly improved my listening skills. Psychology has taught me techniques for learning, like scheduling study time over several days, getting a good night's sleep, rehearsing material, and making information personal and relevant. Intro Psych can help you not only to understand other people but also to do well in college. Psychology has helped me so much in my everyday life that I want to continue to take as many psychology classes as I can and then pursue a doctoral degree in psychology. My motivation to learn more than what is required originated from the sampling of fields covered in introductory psychology. It is only in Intro Psychology where you learn about everything in psychology—from the brain and genet- ics to learning, memory, and perception; from development and aging to social groups and disorders of the mind. Intro Psych has been a wonderful foundation for understanding my own and other people's thought and behavior—and after all, isn't that what psychology is all about? Yvette Szabo, University of Louisville. Used by permission. human thought and behavior cannot be explained from one perspective. As you move through this text, you will find that many of the concepts you learn, such as memory, have several definitions depending on how you look at them. Memory, for instance, can refer either to a specific recalled event (such as your memory of last summer's vacation) or to the process by which we recall such information. Studying psychology not only makes you more aware of how people work in general, but it also makes you more aware of how you work—very practical knowledge to have in many settings. Understanding others' thoughts, feelings, and motives—as well as your own—may help you be a more effective doctor, lawyer, businessperson, or friend. Understanding how children learn, think, reason, and play will help you if you become a parent or a teacher. To learn how one recent college graduate has applied her knowledge of psychology in her life, read the "Psychology in the Real World" feature. The study of psychology is as old as the human species. Before people wondered about the stars, rocks, and planets, no doubt they tried to figure out themselves and others. They did, after all, form relationships, have children, and protect their families. Human babies could not survive without others to care for them. Perhaps that is why people fascinate us. From our very first days, we humans are inherently interested in other humans—for survival. Newborns prefer faces to almost any other object. Our very existence is social, and as you will learn, our brains have evolved mechanisms and structures that allow us to understand others in a re- markably complex way (Dunbar, 1996; Frith & Frith, 2010). As you begin your study of psychology, you will learn just how broad the field is. You may even find a subfield that dovetails with another interest you have already developed.

As a science and a practice, psychology is divided into various areas of investigation. Just as this book consists of chapters on different topics in psychology, the field of psychology is divided into more than 25 distinct, but increasingly interrelated, subdisciplines. Figure 1 gives a breakdown of the percentages of doctorates awarded in 2014 in each of the major subdisciplines we discuss (Doctorate Recipi- ents, 2016). It is noteworthy, that 71% of all PhDs in psychology in 2014 were earned by women. Each subdiscipline in psychology had more than 50% women PhDs, and the only two subfields with less than 60% were experimental psychology and cognitive/psycholinguistics. It is also worth noting that more PhDs were awarded in psychology in 2014 than all the other social sciences combined (anthropology, economics, political science, and sociology) (Doctorate Recipients, 2016). Cognitive psychology is the study of how we perceive information, how we learn and remember, how we acquire and use language, and how we solve problems. For example, a researcher who is concerned with how people visualize objects in their minds is studying cognitive psychology. Those who do research on cognition and learning are often referred to as experimental psychologists, be- cause they conduct laboratory experiments to address their research questions. Developmental psychology explores how thought and behavior change and show stability across the life span. This developmental perspective allows us to appreciate that organisms—human or otherwise—change and grow. Develop- mental psychologists ask such questions as these: How do our reasoning skills or emotional skills change as we age? How does parent-infant bonding affect adult relationships? Does old age bring wisdom? Behavioral neuroscience studies the links among brain, mind, and behavior. Neuroscience cuts across various disciplines and subdisciplines of psychology. One can study the brain functions involved in learning, emotion, social behavior, and mental illness, to name just a few areas. The more general subdiscipline of biological psychology includes research on all areas of connection between 8 CHAPTER 1 Introduction to Psychology bodily systems and chemicals and their relationship to behavior and thought. An example of research in biological psychology ap- pears in the chapter "Stress and Health", where we discuss the effects of stress on hormones and behavior. Neuroscience and biological psychology overlap substantially. Biological psychology is an older term that is being replaced by behavioral neuroscience in contemporary psychology. Using noninvasive advanced imaging techniques and electrical recordings, behavioral neuroscientists study the structure and functions of the living brain. Personality psychology considers what makes Industrial/ Organizational people unique, as well as the consistencies in people's behavior across time and situations. Personality research addresses questions such as whether our personal traits and dispositions change or stay the same from infancy to child- hood to adulthood. A question from this area, for example, might be whether the tendency to be friendly, anxious, or hostile affects one's health, career choice, or interpersonal relationships or whether a friendly or anxious child will necessarily have the same characteristics as an adult. Social psychology considers how the real or imagined presence of others influences thought, feeling, and behavior. Research on prejudice and racism, for example, looks at how a person of one group perceives and treats people in other groups. Social psychologists ask such questions as these: How does the presence of other people change an individual's thoughts, feelings, or perceptions? Why is someone less likely to help a person in need when there are many people around than when there is no one else around? Why are we attracted to particular kinds of people? Clinical psychology focuses on the diagnosis and treatment of mental, emotional, and behavioral disorders and ways to promote psychological health. Some clinical psychologists also con- duct research and teach. Clinical psychologists work in universities, medical settings, or private practice. As you can see from Figure 1, clinical psychology is the single largest subdiscipline in psychology. In the United States, since the late 1940s, the main approach to train- ing in psychology has been the scientist-practitioner model, in which people with PhDs in clini- cal psychology should be both therapists and researchers—or at least be trained to be both (Benjamin, 2007). Psychology is FIGURE 1 PERCENTAGE OF PhDs AWARDED IN THE SUBFIELDS OF PSYCHOLOGY IN 2014. (Adapted from Doctorate Recipients, 2016) personality psychology The study of what makes people unique and the consistencies in people's behavior across time and situations. social psychology The study of how living among others influences thought, feeling, and behavior. clinical psychology The diagnosis and treatment of mental, emotional, and behavioral disorders and the promotion of psychological health. Challenge Your Assumptions True or False? Psychology is made up of many different subfields. True: Psychology has many subfields and is not just one overall discipline. Each subfield examines an important component of thought and behavior, such as cognition, personality, or social influence. Educational/ School Neuro/ Physiotherapy Health Other Experimental Social Clinical Counseling Cognitive/ Psycholinguistics Developmental/ Child/Family ©Matthias Rietschel/AP Images The woman wearing goggles and headgear is being prepared for a neuroimaging exam in a neuroscience lab. a practice as well as a science. A related field is counsel- ing psychology. Counseling psychologists tend to work with less severe psychological disorders than clinical psychologists. They treat and assess relatively healthy people and assist them with career and vocational interests. Training for counseling psychologists is more likely to occur in schools of education than in psychology departments. Other professionals who provide therapy include clinical psychologists who have obtained a PsyD (a professional degree oriented toward nonresearch clinical careers); social workers; marriage and family therapists (who generally have master's degrees); and psychiatrists. Psychiatrists have training in medicine and an MD degree; in addition to offering therapy, they can prescribe drugs. Health psychology examines the role of psychological factors in physical health and illness. Topics in health psychology range from studies of how stress is linked to illness and immune function to studies on the role of social factors in how people interact with health care professionals. Some health psychologists work in disease prevention, treatment, and rehabilitation; thus, this area involves clinical practice as well as research. Educational psychology draws on several other areas of psychology to study how students learn, the effectiveness of particular teaching techniques, the dynamics of school populations, and the psychology of teaching. This field also attempts to understand special populations of students, such as the academically gifted and those with special needs. Educational psychologists are usually academics, theorists, or researchers. School psychology is a related field generally practiced by counselors in school settings. Approximately 9% of the doctorates in psychology were awarded in school psychology in 2005-2006. Industrial/organizational (I/O) psychology is an applied science, mean- ing that it involves understanding real-world rather than laboratory behavior. The industrial and organizational sides focus on two distinct sets of problems. The industrial side involves matching employees to their jobs and uses psychological principles and methods to select employees and evaluate job performance. For this reason, the industrial side of I/O psychology is also some- times referred to as personnel psychology. The organizational side of I/O aims to make workers more productive and satisfied by considering how work environments and management styles influence worker motivation, satisfaction, and productivity. I/O is one of the fastest-growing subdisciplines in psychology, with a nearly 50% increase in the number of PhD programs between 1986 and 2004 . Two of the smaller and newer disciplines in psychology are sports psychology and forensic psychology. Sports psychology examines the psycho- logical factors that affect performance and participation in sports and exercise (Weinberg & Gould, 2007). For instance, sports psychologists might focus on improving athletic performance through techniques such as relaxation and visualization. Forensic psychology is a blend of psychology, law, and criminal justice (Adler, 2004). Forensic psychologists make legal evaluations of a person's mental competency to stand trial, the state of mind of a defendant at the time of a crime, the fitness of a parent to have custody of children, and allegations of child abuse. Occasionally, they develop criminal profiles of the type of person who might have committed a particular crime. As you study the chapters of this text, you may find that one area of psychology especially excites you. Keep in mind, however, that psychology is about how humans think and behave. Thus, all of the topics are useful, many of them are closely intertwined, and there are many reasons for studying psychology, even if you don't become a psychologist. The field of psychology is the outcome of millions of years of humans' interest in their fellow human beings (Feist, 2006). As we will see next, however, the formal history of the field is not quite so old. In this section, we look briefly at the origins of the two main forms of psychology: clinical practice and science. The practice of psychology has deeper roots in human history than does the science of psychology. The prehistoric record offers evidence of efforts to heal people's suffering from disturbances of the mind, often in ways we now find alarming. The foundations for psychology as a science date back to the ancient Greeks, and the modern science of psychology originated in the 1870s (Robinson, 1995). First, we consider the practice of psychology, that is, clinical psychology. Disorders of thought and behavior are no doubt as old as humans—indeed, there is evidence that primates (monkeys and apes) are afflicted with psychological disorders such as depression, anxiety, repetitive and functionless behaviors, and self-injuries (Maestripieri et al., 2006; Novak, 2003; Troisi, 2003). Thus, research suggests that these behaviors go back to the ancestors of both spe- cies, in this case approximately 6 million years. Prehistoric Views As far back as the Stone Age (7,000 years ago and maybe even as long as 50,000 years ago), humans tried to cure one another of various mental problems. Most prehistoric cultures had medicine men or women, known as shamans, who treated the possessed by driving out demons with elaborate rituals, such as exorcisms, incantations, and prayers. Some of these shamans appeared to have practiced the oldest of all known surgical procedures, trephination. Trephination involves drilling a small hole in a person's skull, usually less than an inch in diameter . Some of these surgeries may have been for medical reasons, such as an attempt to heal a brain injury. Some may also have been performed for psychological reasons, to release the spirits and demons they believed possessed the afflicted person. Anthropological evidence suggests that a surprisingly large percentage of people survived such surgeries—which today's scientists can confirm by identifying bone growth after the procedure—and the surgeons must have had moderately sophisticated knowledge and understanding of the brain. Ancient Views Around 2600 BCE (Before the Common Era), the ancient Chinese moved away from supernatural explanations of psychological disorders toward natural and physiological explanations. Specifically, they made connections between a person's bodily organs and emotions. The heart housed the mind; the liver, the spiritual soul; the lung, the animal soul; the spleen, ideas and intelligence; and the kidneys, will and vitality. The ancient Egyptians and Greeks also sought natural explanations for psychological disorders. In the second century BCE, the ancient Egyptians apparently used narcotics to treat pain (Finger, 1994). The Greek physician Hippocrates (460-377 BCE) was the first to write about a man suffering from a phobia of heights—now called acrophobia. shamans Medicine men or women who treat people with mental problems by driving out their demons with elaborate rituals, such as exorcisms, incantations, and prayers. ©SSPL/The Image Works The hole in this skull may have been created by trephination, a prehistoric practice believed to release spirits or demons responsible for psychological disturbances.

Fraud or errors are one thing but ethical issues also arise in the treatment of participants and animals. For example, the classic series of studies by Stanley Milgram in the early 1960s. Milgram's landmark research on obedience is dis- cussed in more detail in the chapter "Social Behavior", but we mention it here for its pivotal role in the development of ethical guidelines for human psychological research. Milgram, like many other social psychologists of the mid-20th century, was both fascinated and horrified by the atrocities of the Holocaust and won- dered to what extent psychological factors influenced people's willingness to carry out the orders of the Nazi regime. Milgram predicted that most people are not inherently evil and argued that there might be powerful aspects of social situations that make people obey orders from authority figures. He designed an experiment to test systematically the question of whether decent people could be made to inflict harm on others. Briefly, Milgram's studies of obedience involved a simulation in which participants were misled about the true nature of the experiment. Thinking that they were part of an experiment on learning, they administered what they thought were electrical shocks to punish the "learner," who was in another room, for making errors. In spite of protests from the learner when increasingly intense shocks occurred, the experimenter pressured the "teachers" to continue administering shocks. Some people withdrew from the study, but most of the participants continued to shock the learner. After the study, Milgram fully ex- plained to his participants that the learner had never been shocked or in pain at all (Milgram, 1974). Milgram's study provided important data on how easily decent people could be persuaded by the sheer force of a situation to do cruel things. What is more, Milgram conducted many replications and variations of his findings, which helped build knowledge about human social behavior. Was it worth the distress it exerted on the participants? One could ask the same of the Stanford Prison Experiment. Zimbardo ap- pears to have coached the guards by suggesting behaviors they could do and these are the one's they ended up doing. Although the prison experiment led to some reform in U.S. prisons, it is hard to know whether the deception of the par- ticipants and the emotional breakdowns some of them experienced was worth it. What do you think? The Milgram study is one of the most widely discussed studies in the his- tory of psychology. A number of psychologists protested it on ethical grounds (Baumrind, 1964). The uproar led to the creation of explicit guidelines for the ethi- cal treatment of human subjects. Today all psychological and medical research- ers must adhere to the following guidelines: Informed consent: Tell participants in general terms what the study is about, what they will do and how long it will take, what the known risks and benefits are, and whom to contact with questions. They must also be told that they have the right to withdraw at any time without penalty. This information is provided in written form and the participant signs it, signifying consent. If a participant is under the age of 18, informed consent must be granted by a legal guardian. Informed consent can be omitted only in situations such as completely anonymous surveys. 2. Respect for persons: Safeguard the dignity and autonomy of the individual and take extra precautions when dealing with study participants, such as children, who are less likely to understand that their participation is voluntary. 3. Beneficence: Inform participants of costs and benefits of participation; minimize costs for participants and maximize benefits. For example, many have argued that the Milgram study was worth the distress (cost) it may have caused participants, for the benefit of the knowledge we have gained about how readily decent people can be led astray by powerful social situations. In fact, many of the participants said that they were grateful for this opportunity to gain knowledge about themselves that they would have not predicted (Milgram, 1974). Privacy and confidentiality: Protect the privacy of the participant, generally by keeping all responses confidential. Confidentiality ensures that participants' identities are never directly connected with the data they provide in a study. 5. Justice: Benefits and costs must be distributed equally among participants. In Milgram's study, participants were led to believe they were taking part in a learning study when, in fact, they were participating in a study on obedience to authority. Is this kind of deception ever justified? The answer (according to the American Psychological Association, APA) is that deception is to be avoided whenever possible, but it is permissible if these conditions are met: It can be fully justified by its significant potential scientific, educational, or applied value; it is part of the research design; there is no alternative to deception; and full debrief- ing occurs afterward. Debriefing is the process of informing participants of the exact purposes of the study—including the hypotheses—revealing any and all deceptive practices and explaining why they were necessary to conduct the study and ultimately what the results of the study were. Debriefing is required to minimize any negative effects (e.g., distress) ex- perienced as a result of the deception. Deception comes in different shades and degrees. In the Stanford Prison Experiment, all participants were fully informed about the fact that they would be assigned the roles of a prisoner or a guard. In that sense there was no deception. They were not informed of the details and the extent to which being in this study would be like being in a real prison world. They were not told upfront that, if they were assigned to the "prisoner" role, they would be strip-searched. When they were taken from their homes, the "prisoners" were not told this was part of the study. Not informing participants of the research hy- potheses may be deceptive but necessary to prevent biased and invalid responses. Not telling participants that they might experience physical pain or psychological distress is a much more severe form of deception and is not ethically permissible. Today, to ensure adherence to ethical guidelines, institutional review boards (IRBs) evaluate proposed research before it is conducted to make sure research involving humans does not cause undue harm or distress. Should Mil- gram's study have been permitted? Were his procedures ethical by today's stan- dards? To this day, there are people who make strong cases both for and against the Milgram study on ethical grounds, as we have discussed. It is harder to justify what Zimbardo did in the prison experiment. Ethical Treatment of Animals Human participants are generally protected by the ethical guidelines itemized in the previous section. What about animals? They cannot consent, so how do we ethically treat animals in research? The use of nonhuman species in psychological research is even more con- troversial than is research with humans. There is a long history in psychology of conducting research on animals. Typically, such studies concern topics that are harder to explore in humans. We cannot, for instance, isolate human children from their parents to see what effect an impoverished environment has on brain development. Researchers have done so with animals. The subfields of biological psychology and learning most often use animals for research. For instance, to determine what exactly a particular brain structure does, one needs to compare individuals who have healthy structures to those who do not. With humans this might be done by studying the behavior of individuals with accidental brain in- jury or disease and comparing it to the behavior of normal humans. Injury and disease, however, never strike two people in precisely the same way, so it is not possible to reach definite conclusions about the way the brain works by just look- ing at accidents and illness. Surgically removing the brain structure is another way to determine function, but this approach is obviously unethical with humans. In contrast, nonhuman animals, usually laboratory rats, offer the possibility of more highly controlled studies of selective brain damage. For example, damage could be inflicted on part of a brain structure in one group of rats while another group is left alone. Then the rats' behaviors and abilities could be observed to see whether there were any differences between the groups. Animals cannot consent to research, and if they could, they would not likely agree to any of this. Indeed, it is an ongoing debate as to how much animal re- search should be permissible at all. Because animal research has led to many treatments for disease (e.g., cancer, heart disease), as well as advances in under- standing basic neuroscientific processes (such as the effects of environment on brain cell growth), it is widely considered to be acceptable. Animal research is acceptable, that is, as long as the general conditions and treatment of the animals is humane. If informed consent is the key to ethical treatment of human research par- ticipants, then humane treatment is the key to the ethical use of animal subjects. The standards for humane treatment of research animals involve complex legal issues. State and federal laws generally require housing the animals in clean, sanitary, and adequately sized structures. In addition, separate IRBs evaluate proposals for animal research. They require researchers to ensure the animals' comfort, health, and humane treatment, which also means keeping discomfort, infection, illness, and pain to an absolute minimum at all times. If a study re- quires euthanizing the animal, it must be done as painlessly as possible. Despite the existence of legal and ethical safeguards and the importance for medical research in humans, some animal rights groups argue that any and all ani- mal research should be discontinued, unless it directly benefits the animals. These groups contend that computer modeling can give us much of the knowledge sought in animal studies and eliminates the need for research with animals. In addition, cur- rent brain imaging techniques, which allow researchers to view images of the living human brain, reduce the need to sacrifice animals to examine their brain structures. As is true of all ethical issues, complex and legitimate opposing needs must be balanced in research. The need to know, understand, and treat illness must be balanced against the needs, well-being, and rights of participants and animals. Consequently, the debate and discussion about ethical treatment of humans and animals must be ongoing and evolving.

Technology in general—wearable devices, laptops, desk- tops, and tablets—is transforming how we learn, think, remember, interact, and behave. More specifically, social media such as Instagram, Facebook, YouTube, and Twitter keep us constantly connected to family, friends, and oth- ers. Together, these technologies are changing how we think, feel, and behave, and therefore make a perfect topic to bring together all the major ideas discussed in the chap- ter—the nature of science, research methods, and research ethics. Descriptive Research Designs Descriptive research aims to simply observe and describe behavior and historically, this research has involved watching people behave in a real world setting. The "real world," however, is becoming increasingly the online world. Park and colleagues (2016) for example analyzed the language use of more than 65,000 Facebook volunteers. Park and colleagues found that when updating their status on Facebook, women were more likely to use friendlier, warmer, and more socially oriented language compared to men. For example, women more often than men used words such as "wonderful," "happy," "excited," "baby," "daughter," and "thankful." Men, by contrast, were more likely to use words about sex, work, money, politics, video games, or sports, such as "freedom," "government," "win," "lose," "xbox," or "enemy." Men were also more likely to use crude, sexual language than women. In short, women were more likely to discuss social topics and men more likely to dis- cuss activities or things. Correlational Research Designs Correlational research makes predictions about whether or not two or more variables are related to each other. Karpinski and colleagues (2012) addressed the question of the relationship between social network site (SNS) use per day and academic performance and whether multitasking disrupts or facilitates studying. The sample consisted of 590 undergraduate students and 285 graduate students in the United States and Europe. They found a negative relationship between social network site use and multitasking and GPA— meaning the more overall time spent on SNS and the more multitasking spent per day was associated with lower GPAs. Unsurprisingly, they also found that studying more is associated with higher GPAs. Studies sometimes combine research strategies. For example, Rosen et al. (2012) combined observational and correlational strategies in a study on Facebook use and academic performance. Researchers went to the homes of more than 250 middle school, high school, and college stu- dents and observed whether and how much students used social media while studying. Researchers also collected more general data via questionnaire on social media use and academic performance (GPA). On average, students lasted no more than 6 minutes on studying before switch- ing to social media, and those who went to social media most had the lowest GPAs. Like Karpinski and colleagues, the main finding from this study was that staying on task (not multitasking) and not accessing FB while studying was correlated with a higher GPA. Experimental Research Designs From a scientific perspective, the study of distraction and cell phone use lends itself easily to the experimental method, because cell phone use can be easily manipulated as the independent variable. Probably the oldest and most established research on the effects of technology on behavior focus on how cell phone use affects driving. In general, the results are clear: Using any kind of device, in- cluding hands-free, has costs in terms of attention and reaction times while driving (Delgado, Wanner, & McDonald, 2016; Engelberg, Hill, Rybar, & Styer, 2015; McDonald & Sommers, 2015). Moreover, using a cell phone while driving decreases awareness that one's driving is impaired (Sanbonmatsu, Strayer, Biondi, Behrends, & Moore, 2015). Using an experimental design, Papadakaki and colleagues (2016) had 50 professional (taxi) drivers go through a driver simulator under four different conditions: control (drive only), talking on cell phone, reading a text, and answering a text. Outcome measures were how much their steering deviated from a center line, how much they changed their speed, and whether they were able to main- tain a 3-second distance behind a car. The researchers found that reading and sending a text impaired steering, ability to maintain a constant speed, and following distance. Speaking on the phone diminished the driver's ability to maintain a constant speed and steering. Other similar exper- imental research has reported that driving while talking on a hands-free phone is as dangerous as driving with a blood alcohol content (BAC) level of 0.08, the legally drunk level in all 50 U.S. states (Strayer, Drews, & Couch, 2006). ©Hero Images/Getty Images RF Social network site (SNS) use while studying disrupts and interferes with the learning process. Students who do this regularly tend to have lower grades. How much time do you spend on social networks while studying? Ethics in Studying Technology and Behavior Big Data in particular raises questions about ethics, given that people often do not even know their data are being collated and analyzed by researchers. For instance, in 2014 psychological researchers at a U.S. university col- laborated with a Facebook data analyst and tested the hypothesis that positive Facebook feeds about friends' lives actually lowers the recipients' mood—that is, that moods can be contagious (Kramer, Guillory, & Hancock, 2014). On close to 700,000 Facebook users the re- searchers manipulated their likelihood of receiving posi- tive and negative feeds (based on the kind of words in the post). Different users had positive or negative mood posts decreased or increased. The researchers found that when positive mood posts were increased, people tended to post fewer positive mood posts. Likewise, a decrease in negative mood posts led to an increase in positive mood posts. The problem is not with the study in itself but the fact that researchers at a university bypassed informed consent and went by Facebook data use policy that did not explicitly stipulate that Facebook data can be used for research purposes. Private companies like Facebook can and do use data without users' knowledge for commercial purposes. But university researchers have a different stan- dard that requires "informed consent" and approval by the university's "Institutional Review Board"—neither of which happened in this study. Although the researchers were technically correct and were collaborating with a data scientist at Facebook, there was a public outcry over the study's borderline ethical violations. Four months after the study was conducted, Facebook changed its data use policy to include the word "research." People now have an opt-out policy for research on their Facebook data use policy. Science is about empirically testing our ideas and learning whether our understanding of the world is correct. • The key attitudes of science are skepticism, openness to new ideas based on evidence, and intellectual honesty. • The scientific method by which research is conducted can be summed up by OPTIC: Observing, Predicting, Testing, Interpreting, and Communicating. Scientists start with observations of the world, make predictions once they see a pattern, devise a study to test predictions, interpret results with the aid of statistics and decide whether the prediction was correct, and publish their work to clearly describe findings to others. These new findings lead to new predictions, and the whole process begins anew. • Pseudoscience lacks cumulative progress, disregards empirical facts, lacks skepticism of its own assumptions, RESEARCH DESIGNS IN PSYCHOLOGY • Psychologists use three types of research designs to test their ideas: descriptive designs, correlational designs, and experimental designs. • In descriptive designs, researchers simply observe and describe what they see. They address the question "What is X?" They don't manipulate anything or have any predictions to test. • In correlational designs, researchers measure two or more things carefully to see whether or not they are related. They address the question "Is X related to Y?" These designs use correlational statistics to interpret the results and to make and test hypotheses, but they do not allow researchers to draw any conclusions about causality. • Researchers use correlation coefficients to assess the strength and direction of association between two variables. ©Jane Underwood/My.Third.Eye Photography/Moment Select/Getty Images and vaguely describes how it came to its conclusions, which often stem from loose and distorted logic. • In experimental designs, researchers randomly assign participants to conditions and carefully manipulate the predicted cause (independent variable), then look for differences in outcome (dependent variables). True experiments address the question "Does X cause Y?" • In experimental designs, researchers randomly assign participants to conditions and carefully manipulate the predicted cause (independent variable), then look for differences in outcome (dependent variables). True experiments address the question "Does X cause Y?" • Meta-analysis is a quantitative method for combining the results of all the published and even unpublished results on one question and drawing a conclusion based on the entire set of studies on the topic. • Big Data consists of the extremely vast amounts of information from websites and apps that is collected and analyzed by unusually large and sophisticated computer programs. CHALLENGING ASSUMPTIONS IN THE OBJECTIVITY OF EXPERIMENTAL RESEARCH • Researchers can unintentionally affect the outcome of • In order to lessen these effects, double-blind procedures, results if they are aware of the study's hypotheses. in which both the participant and the experimenter are blind to the study's hypotheses, need to be implemented. COMMONLY USED MEASURES OF PSYCHOLOGICAL RESEARCH • Psychological researchers draw on several types of tools to measure variables relevant to their research questions. These measures fall into three major categories: self-report, behavioral, and physiological. • Self-reports are people's written or oral accounts of their thoughts, feelings, or actions. • Behavioral measurements involve systematic observation of people's actions in either their normal life situations (naturalistic observation) or laboratory situations. • Physiological measures include various types of measures of bodily responses. Each measure has strengths and weaknesses. By employing multiple measures, researchers offset the limitations of any given measure. 72 CHAPTER 2 Conducting Research in Psychology MAKING SENSE OF DATA WITH STATISTICS • Descriptive statistics organize data for interpretation and help researchers evaluate their hypotheses. The mean is the arithmetic average of a set of data. The median is the score that separates the lower half of scores from the upper half. RESEARCH ETHICS • Ethics are standards of right and wrong that guide people's behavior. • Professional ethics have been developed to protect the rights of humans and animals that participate • Variability is the spread between the lowest and highest values in a set of data; it is measured in terms of the standard deviation around the mean. • Inferential statistics go beyond describing data and allow researchers to test hypotheses and rule out chance as an explanation for the findings. in psychological research. Researchers must obtain informed consent from human participants before a study begins. Animals cannot provide informed consent, but strict ethical guidelines ensure humane living conditions and treatment. BRINGING IT ALL TOGETHER: MAKING CONNECTIONS IN PSYCHOLOGICAL RESEARCH • Research on how technology affects thought, feelings, and behavior is becoming more and more common in psychology. For example, studies using descriptive, correlational, and experimental methods have examined how multitasking while studying or driving leads to lower academic performance or impairs reaction time and steering ability while driving. Key Terms behavioral measures big data case study confounding variable control group correlational designs correlation coefficients debriefing demand characteristics dependent variable descriptive designs descriptive statistics double-blind studies effect size ethics experiment experimental group experimenter expectancy effects fabrication falsification fraternal twins frequency gene-by-environment interaction research hypothesis identical twins independent variable inferential statistics institutional review boards (IRBs) interviews longitudinal designs mean measures median meta-analysis mode naturalistic observation normal distribution physiological measures placebo plagiarism population pseudoscience qualitative research Quick Quiz Answers Quick Quiz 1: 1.d; 2.b; 3.a; 4.c Quick Quiz 2: 1.a; 2.b; 3.d; 4.c; 5.b Quick Quiz 5: 1.d; 2.a; 3.a Quick Quiz 6: 1.c; 2.e; 3.b quantitative research quasi-experimental design random assignment rationalism reliability replication representative sample research designs samples sampling scientific method scientific thinking self-fulfilling prophecy self-reports single-blind studies social desirability bias standard deviation statistics t-test theory twin-adoption studies validity variable Quick Quiz 3: 1.b.; 2.b Quick Quiz 4: 1.b; 2.a; 3.d

There are nearly a dozen ways a person can interact with others electronically—via email, blogs, phone calls, chat rooms, texting, instant messaging, audio or video chats, gaming (either solo or multiplayer), videos, photos, bulletin boards, and social network sites (SNSs). Humans have taken to electronic forms of interaction like fish to water. As a form of behavior that is evolving at a rapid pace, elec- tronic social interaction holds great interest for psycholo- gists in all of the subfields you read about in this chapter. Let's consider how psychologists from some of these areas might study electronic communication and its effects on human behavior and thought. Cognitive scientists typically are interested in how we learn, speak, remember, think, and reason. They are also interested in attention. The widespread use of mobile devices has sparked a number of research questions. The most obvious one concerns how drivers can pay attention to driving while talking on a mobile device. Researchers who have examined the effect of talking on a hands-free mobile device while driving report that a person's ability to operate a car while doing so is significantly impaired and is even similar to the ability to drive while drunk (Caird et al., 2008; Strayer, Drews, & Couch, 2006). In addition, attitudes and beliefs about how dangerous and how common mobile phone use is while driving predict using phones while driving (Hafetz et al., 2010; Zhou et al., 2009): Those who think most about receiving phone calls and think about their phones while they are off are most likely to have accidents while driving (O'Connor et al., 2013).

Developmental Psychology Developmental psychologists study how we change over the life span. They might ask questions like these: At what age is a person too young to form electronic social networks? At what age does participation in Internet social networks peak? Will they always be for the younger generation, or will people 60 and older use them? Does gender affect interest and participation in SNSs? How have mobile phones and other electronic methods of communicating changed the way teenagers interact with others? Researchers have already given us answers to some of these questions. Some suggest that older teen- age girls and young women are more likely to participate in social networking sites than are boys and young men (Boyd, 2007; Hargittai, 2008). A recent study found that 13-year-olds check social media up to 100 times a day, with one 13-year-old girl saying "I would rather not eat for a week than get my phone taken away. It's really bad. I literally feel like I'm going to die" (Hadad, 2015, p. 1 ). Moreover, 50% of teens admit to being "addicted" to their cell phones (Felt & Robb, 2016). College men are more likely to use SNSs to begin new relationships, whereas college women are more likely to use them to maintain existing relationships (Muscanell & Guadagno, 2012). Electronic interactions are popular with adolescents because of psychological factors: identity, autonomy, inti- macy, and sexuality (Subrahmanyam & Greenfield, 2008; Walsh, White, & Young, 2009). One reason the popularity of electronic interactions declines with age may be that these issues decline in importance as one moves from early adulthood to middle and late adulthood (Erikson, 1982; Harris Interactive, 2008).

Behaviorism-Learning Behaviorists argue that if you want to understand behavior then focus only on behavior, not hypothetical and unobservable internals states such as thoughts, feelings, drives, or motives. All behaviors are learned through association and/or their consequences (whether it is reinforced or punished). To shape desired behavior, we have to understand and then establish the conditions that bring about those particular behaviors.

Humanistic-Positive Humanistic and positive psychologists assume that people strive toward mean- ing, growth, well-being, happiness, and psychological health; positive emotions and happiness foster psychological health and pro-social behavior. Understanding these evolved positive aspects of human behavior provides just as much insight into human nature as does understanding the pathological aspects (Seligman, 2003).

We seldom have trouble accepting the idea that heredity is responsible for out- ward family resemblances, such as the shape of the nose and face, height, and the color of hair and skin. But when it comes to behavior, many of us are uncomfor- table with the idea that heredity might strongly influence what we think and do. Research has revealed that heredity strongly shapes our behavior and experi- ence, although it does not operate in a simple, deterministic way. Before we can explore how our hereditary material and behavior are linked, we must first determine the structures and mechanisms involved in heredity. Your genetic material is composed mainly of DNA (deoxyribonucleic acid) and is passed down in the form of chromosomes from both your mother and your father. A chromosome is a very long thread of DNA wrapped around proteins to hold it all together. You inherit 23 chromosomes from one parent and 23 chro- mosomes from the other parent such that you end up with 23 pairs of chromo- somes (46 individual chromosomes) in every cell of your body. Together, the total amount of your unique DNA is referred to as your genome. Each person's unique and incomparable genome is called his or her genotype. In our genome we carry our entire ancestral history (Pickrell & Reich, 2014; Tucci & Akey, 2016). Recently companies have developed the technology to com- mercially analyze anyone's genome and tell them which geographical regions of world their ancestors came from. For instance, a report might show that some- one has an ancestry makeup that is 29% Asian Native American, 22% European, and 3% sub-Saharan African, when in fact, all the person ever knew about was her Asian Native American ancestry. Our genetic makeup is more complex than we often believe, and is yet another example of the interaction between nature (genes) and nurture (geography and place). But our unique genotype that each of us is born with is not the end point but the starting point of gene expression. What form a gene takes and how it gets expressed in observable characteristics is known as the phenotype. As we see at the end of this section, there are many ways in which our genes get turned on or off from our experience, many after the genome is established. Within your genome, some information that codes for the production of proteins. That is what genes do—they are the segments of DNA that code for protein synthesis, and are therefore the functional segment of DNA. In fact, the vast majority of DNA (98%) is not genetic because it does not code for proteins (Zimmer, 2015). It's not "junk" as some biologists used to say because it does other things, but it does not code for proteins. The proteins that are coded from genes in turn make up most chemicals and structures in the body (see Figure 2). As a re- sult, genes have a profound control over physical characteristics, such as height or hair color, by directing the synthesis of proteins. In addition, there are genes that code for proteins responsible for making up your brain and the chemicals it needs to make you feel happy or sad. Thus, genes play an important role in shap- ing how you think and feel. Most traits, such as height, weight, intelligence, and personality, are the result of many dozens or even hundreds of genes and these are known as polygenic traits. Any characteristic that cannot be placed in a small number of categories and ranges from a little to a lot is polygenic (Clark & Grunstein, 2000; Plomin, DeFries, Knopik, & Neiderhiser, 2013). All psychological and almost all physical traits in humans are polygenic (Ebstein, 2006; Plomin et al., 2013). By contrast, traits that have a one-to-one connection to a gene are known as monogenic traits. Humans have very few traits that result from a single gene. Lactose tolerance/intolerance is one of the few examples of a monogenic trait in humans. Everyone can metabolize lactose (digest milk) as an infant, DNA (deoxyribonucleic acid) A large molecule that contains genes. chromosome A coiled-up thread of DNA. genome All the genetic information in DNA. genotype The entire genetic makeup of an organism. phenotype An organism's observed characteristics. genes Small segments of DNA that contain information for producing proteins. polygenic The process by which many genes interact to create a single characteristic. monogenic The hereditary passing on of traits determined by a single gene. Genes and Behavior 77 FIGURE 2 DNA, CHROMOSOMES, AND THE HUMAN CELL. Every cell in the human body contains the same genetic material distributed in 23 pairs of chromosomes. Each human cell (except red blood cells) contains a nucleus. Each body cell nucleus contains 46 chromosomes arranged in 23 pairs. Each parent contributes one chromosome to every pair. an body contains The huma 100 trillion cells. Each chromosome contains numerous genes, segments of DNA that contain instructions to make proteins—the building blocks of life. mutation A random change in genetic sequence. alleles Different forms of a gene. dominant alleles Alleles that show their effect even if there is only one allele for that trait in the pair. recessive alleles Alleles that show their effects only when both alleles are the same. (cells): ©phil morley/Getty Images RF; (torso): ©Juice Images/Alamy RF but most people lose this ability with age, because the activity of lactase (the protein that breaks down lactose) decreases. Some humans, however, have a change, or mutation, in their genetic sequence that allows lactase activity to persist into adulthood, so they can eat and drink dairy products without getting an upset stomach. This means that some people have one form of the gene, which allows lactase persistence (they are lactose tolerant), and some people have an- other form, which results in lactase nonpersistence (they are lactose intolerant). These different forms of a gene are known as alleles (Clark & Grunstein, 2000; Starr & Taggart, 2004), one of which you inherit from ©2005 Kathy Hutchins/Hutchins Ph/Newscom Actors (and siblings) Maggie and Jake Gyllenhaal inherited their blue eyes from their parents. Blue eyes are a recessive trait, which means that each parent must possess at least one allele for blue eyes. your mother and the other from your father. If you receive alleles for lactose tolerance from both your mother and your father, then you will digest dairy products easily into adulthood. However, what happens if you inherit one lactose tolerant gene and one lactose intolerant gene from your parents? The lactase persistent or tolerant allele is dom- inant over the intolerant one. Dominant alleles show their effect even if there is only one copy of that allele in the pair. So if you have one of each kind of allele (tol- erant and intolerant) chances are you will still be able to digest some dairy products. Alternatively, recessive alleles show their effects only when both alleles are the same. Consequently, a person will be lactose intolerant only if he or she receives a lactase persistent allele from each parent.

To understand how heredity affects behavior, psychologists turn to the science of behavioral genetics (Fuller & Thompson, 1960; Plomin et al., 2013). There are three principles of behavioral genetics that are especially relevant to psychology: 1. The relationship between specific genes and behavior is complex, usually with many genes involved in each trait. 2. By studying twins and adoptees, as well as genetic markers, behavioral geneticists may disentangle the contributions of heredity (nature) and environment (nurture) that influence behavior. 3. The environment influences how and when genes affect behavior. The Connection between Genes and Behavior Is Complex The connec- tion between genes and behavior is complex. To understand how genes influence behavior, we must abandon the notion of simple causation (Rutter, 2006). Genes seldom make behaviors a certainty. For example, no single gene causes anxi- ety. Both genetic and environmental factors make anxiety more likely to trouble some people than others. Connection In a few cases, having a specific gene guarantees an outcome—such as the incurable neuromuscular disease called Huntington's—but these outcomes are primarily physical, not behavioral. Typically, a specific gene plays only a small part in creating a given behavior, which is precisely what happens in polygenic traits. For example, there is wide variation in intelligence because numerous genes contribute to it. Other examples of polygenic traits are skin color, mental disorders, personality traits (such as whether a person is likely to be adventur- ous), height, and weight (Clark & Grunstein, 2000; Ebstein, 2006; Evans et al., 2007). Environmental events such as smoking during pregnancy, early childhood experiences, stress or trauma, and enriched environments all interact with genes to make specific behaviors more or less likely. The Relative Effects of Genes and Environment Can Be Teased Apart The extent to which a characteristic is influenced by genetics is known as heritability. The second principle of behavioral genetics is that teasing apart and identifying genetic and environmental influences on behavior can be done but requires special techniques. Recall from the chapter "Conducting Research in Psychology" that researchers use two different research methods to study the relative effects of nature and nurture (heritability), namely twin-adoption studies and gene-by-environment studies. Twin-adoption studies take advantage of the fact that genetic similarity ranges from 0% (strangers) to 100% (identical twins) and environmental similarity ranges from a little (different families) to a lot (same families). Genetic influence or heri- tability is strongest when twins—who have high genetic similarity—are still very much alike on traits even when they are raised by different families. Environmental influence is strongest when adopted siblings—who have no genetic similarity—are still very much alike on traits when they are raised by the same family. Gene-by-environment studies do not use twins but rather examine whether genes that vary in people are correlated with particular trait. An example of this kind of research is seen from the findings that people with certain genetic mark- ers are more likely to be depressed, anxious, or hyperactive than people without those markers (Moffitt, Caspi, & Rutter, 2005; Thapar, Langley, & Asherson, 2007). The Environment Can Change Gene Expression: Epigenetics The third—and, in many ways, the most important—principle of behavioral genet- ics is a relatively new one, epigenetics. Epigenetics is the study of changes in the way genes are expressed—that is, are activated (turned "on") or deactivated heritability The extent to which a characteristic is influenced by genetics. behavioral genetics The scientific study of the role of heredity in behavior. Genetic influence accounts for about 50% of the differences in performance on intelligence tests, leaving about the same amount to be explained by nongenetic influences. See "The Nature and Nurture of Human Intelligence," in the chapter "Intelligence, Problem Solving, and Creativity," p. 383 epigenetics The study of changes in the way genes are turned on or off without a change in the sequence of DNA. Genes and Behavior 79 ©Sam Edwards/Glow Images RF The field of study known as epigenetics examines how experience can turn genes on or off. What implications does this have for what we eat, drink, and are exposed to? (turned "off")—without changing the sequence of DNA (Meaney, 2010; Plomin et al., 2013). Some substances that we eat, drink, or get exposed to result in molecules attaching to certain base pairs of genes. By doing so these tags turn off or on the gene expression process. Put differently, epigenetics involves heritable changes to DNA that are independent of the genetic sequence yet influence its expression. This means that experience (nurture) shapes our nature. The food we eat, the drugs we take, and our expo- sure to certain chemicals in the environment, among other things, can have epigenetic consequences. Contrary to what many people think, genes are not destiny. They are simply the starting point for biological structures. Many things—including experience—can turn genes on or off. Epigenetic effects have been demonstrated in a host of psychological traits—including attention deficit hyper- activity disorder (ADHD), aggression, dementia, obesity, and anxiety, just to name a few (Curley et al., 2011; Crop- ley et al., 2016; Mill & Petronis, 2008; Sweatt, 2010). Challenge Your Assumptions True or False? Genetically influ- enced traits are set and unchanging after conception. False: Genes continue to get turned on or off throughout our lives by what we eat, drink, or are exposed to. Connection What is even more amazing is that these environ- mentally produced tags can be inherited—passed on from parent to offspring. In other words, genetics is not the only way inheritance works. It also works via epigenetics (Meaney, 2010; Zimmer-Gembeck & Collins, 2008). An activated gene in your grandparent that gets turned off environmentally in one of your parents can be inherited by you as a deactivated gene. This secondary form of inheri- tance via epigenetics is sometimes referred to as soft inheritance to contrast it with traditional genetically based inheritance (Graff & Mansury, 2008). The term soft inheritance is another example of how nature and nurture work side-by-side. Epigenetics offers one explanation for why identical twins—whose ge- nomes are 100% alike—end up being not completely identical on numerous traits. For instance, they do not have identical fingerprints and sometimes not even the same gender identity (see the chapter "Human Development"). Recent longitudi- nal research shows that differences in epigenetic tags in identical twins already exist in early to middle childhood and that these differences can be related to per- sonality differences in twins (Kaminsky et al., 2008; Wong et al., 2010). In short, although identical twins share 100% of their genotype, their phenotype—or their observed characteristics—may be subtly (even strikingly) different because dif- ferent epigenetic tags are turning different genes on or off. Genes are not destiny. Identical twins are often nearly identical in thought and behavior, but for epigenetic reasons this is not always so, as is clear in a case of identical twins, born male, but one of whom identified as female. See the chapter opening for the chapter "Human Development." (p. 164) Quick Quiz 1: Genes and Behavior 1. Genes occur in pairs, or alternate forms of each other, called a. chromosomes. b. alleles. c. basepairs. d. ribosomes. 2. Why are twin-adoption studies powerful ways to untan- gle the effects of genes and the environment on thought andbehavior? a. They allow both genetic and environmental similarity to be compared and contrasted. b. Twins share genes. 3. c. They allow for understanding epigenetic influences. d. They allow researchers to experimentally manipulate genetic and environmental similarity. Nurturing behavior in rats can produce calmer, less stressed offspring because genes that are involved in stress reactions are turned off. This is an example of a. epigenetics. b. genetic engineering. c. recessivegenes. d. dominant genes. 80 CHAPTER 3 The Biology of Behavior Answers can be found at the end of the chapter. THE NERVOUS SYSTEM The human genome contains an estimated up to 30,000 genes (National Human Genome Research Institute, 2010). At least half of these genes code for proteins in the brain, where they play a central role in seeing, hearing, thinking, memory, learning, movement, and all other behavior. The brain mediates all of our experi- ences and orchestrates our responses to those experiences. The nervous system controls all the actions and automatic processes of the body. Ultimately, everything we experience and do results from the activity of nerve cells, which are organized in a net of circuits far more complex than any electrical system you could imagine. Organization of the Nervous System The human nervous system has two main parts and several components, as de- picted in Figure 3. It is divided into the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system, which consists of all the other nerve cells in the body. The peripheral nervous sys- tem includes the somatic nervous system and the autonomic nervous system. The somatic nervous system serves the skeletal muscles of the body: It sends messages out to the skeletal muscles from the CNS and transmits sensory in- formation back to the CNS from the skeletal muscles. The autonomic nervous system (ANS) serves the involuntary systems of the body, such as the internal organs and glands. Autonomic means "self-governing," and to a large extent the structures served by the autonomic nervous system control bodily processes over which we have little conscious control, such as changes in heart rate and blood pres- sure. The ANS has two main branches: the sympathetic nervous system and the central nervous system (CNS) The part of the nervous system that comprises the brain and spinal cord. peripheral nervous system The part of the nervous system that comprises all the nerve cells in the body outside the central nervous system. somatic nervous system Nerve cells of the peripheral ner- vous system that serve the skeletal muscles. Somatic nerves transmit from the central nervous system (CNS) to the skeletal muscles and sensory information from the skel- etal muscles back to the CNS. autonomic nervous system (ANS) All the nerves of the peripheral ner- vous system that serve involuntary systems of the body, such as the internal organs and glands. sympathetic nervous system The branch of the autonomic ner- vous system that activates bodily systems in times of emergency. Central nervous system (CNS) Peripheral nervous system (PNS) NERVOUS SYSTEM Brain Spinal cord Somatic nervous system (voluntary) Autonomic nervous system (involuntary) Sympathetic nervous system (arousing) Parasympathetic nervous system (calming) FIGURE 3 THE NERVOUS SYSTEM. The central nervous system processes incoming information and crafts a response, if one is needed. The peripheral nervous system transmits information between the external environment and internal systems of the body and the central nervous system. The Nervous System 81 parasympathetic nervous system The branch of the autonomic ner- vous system that usually relaxes or returns the body to a less active, restful state. parasympathetic nervous system. The nerves of both of these systems control muscles in organs such as the stomach, small intestine, and bladder and in glands such as the sweat glands. The sympathetic nervous system activates bodily sys- tems in times of emergency by increasing the heart rate, dilating the pupils of the eyes, or inhibiting digestion. It is responsible for what the physiologist Walter Cannon (1939) labeled the fight-or-flight response. The function of the parasym- pathetic nervous system is largely one of relaxation, returning the body to a less active, restful state. All of the systems that are aroused by the sympathetic ner- vous system are relaxed by the parasympathetic nervous system (see Figure 4). FIGURE 4 THE SYMPATHETIC AND PARASYMPATHETIC NERVOUS SYSTEMS. The sympathetic nervous system prepares the body for action, whereas the parasympathetic nervous system returns it to a relaxed and resting state. Constricts bronchi Slows heartbeat Stimulates activity Dilates vessels Parasympathetic and sympathetic nervous systems Spinal cord Parasympathetic Constricts pupil Sympathetic Dilates pupil (enhanced vision) Relaxes bronchi (increased air to lungs) Brain 82 CHAPTER 3 The Biology of Behavior Contracts bladder Stimulates ejaculation in male ©James Woodson/Getty Images RF Accelerates, strengthens heartbeat (increased oxygen) Inhibits activity (blood sent to muscles instead) Contracts vessels (increased blood pressure) Inhibits bladder contraction Allows blood flow to sex organs Because of its effects on these various bodily systems, the ANS produces many of the physical sensations we experience during emotional arousal, such as a racing heart or sweaty palms. The Cells of the Nervous System: Glial Cells and Neurons Without a nervous system, we would have no sensory experiences—no seeing, hearing, touching, tasting, smelling, or feeling. We would also have no thoughts, memories, or emotions. Everything we sense or do is accomplished by means of nerve cells. The central nervous system is made up of two types of cells: glial cells and neurons. Glia is the Greek word for "glue." Indeed glial cells serve the primary func- tion of holding the CNS together. For years their primary functions were thought to be structural support for the CNS and the removal of cellular debris (Kandel, 2000b). We now know that glial cells also play an important role in communica- tion between neurons, produce the material that insulates neurons (myelin), aid cell metabolism, help form the blood-brain barrier, play a key role in the control of breathing, regulate neuronal transmission, and may play an important role in neu- ral regeneration repair after brain injury (Ballanyi, Panaitescu, & Ruangkittisakul, 2010; Benner et al., 2013; Charsar, Urban, & Lepore, 2016; Eroglu & Barres, 2010; Li & Chen, 2016; Verkhratsky, Rodrıguez, & Parpura, 2012). Glial cell abnormalities may also play a role in the development of schizophrenia (Bernstein et al., 2015). Neurons are the cells that process and transmit information throughout the nervous system. Within the brain, neurons receive, integrate, and generate mes- sages. By most estimates, there are more than 10 billion neurons in the human brain. Each neuron has approximately 10,000 connections to other neurons, mak- ing for trillions of neural connections in the human brain (Hyman, 2005; Nauta & Feirtag, 1979). Thus, it is understandable why some scientists consider the human brain to be one of the most complex structures in the known universe. Over the last 125 years, three major principles of neuroscience have emerged concerning the neuron and how it communicates with other neurons (Kandel, 2006): 1. Neurons are the building blocks of the nervous system. All the major structures of the brain are composed of neurons. 2. Information travels within a neuron in the form of an electrical signal by action potentials. 3. Information is transmitted between neurons by means of chemicals called neurotransmitters. Let's explore each of these principles to better understand the mechanisms of brain function and behavior. The Structure and Types of Neurons Whereas most cells in the body have a round shape, neurons are spidery, with long branches and projections. Neurons are so small that they cannot be seen with the naked eye; only a strong micro- scope can magnify them enough to be viewed and described. In the late 1800s, the Spanish anatomist Santiago Ramón y Cajal deciphered the precise nature and structure of nerve cells, which he named neurons. It was Ramón y Cajal who iden- tified the three major parts of the neuron: cell body, dendrites, and axon. As in other cells, the cell body, or soma, of the neuron contains a nucleus and other components needed for cell maintenance and function (see Figure 5 ). The genes that direct neural change and growth lie within the nucleus itself. Extending from one side of the soma is a long projection called an axon, which transmits electrical impulses toward the adjacent neuron. On the other side of the soma are dendrites, fingerlike projections that receive incoming messages from other neurons. glial cells Central nervous system cells that provide structural support, promote efficient communication between neurons, and serve as scavengers, removing cellular debris. neurons The cells that process and transmit information in the nervous system. neurotransmitters Chemicals that transmit information between neurons. soma The cell body of the neuron. axon A long projection that extends from a neuron's soma; it transmits electri- cal impulses toward the adjacent neuron and stimulates the release of neurotransmitters. dendrites Fingerlike projections from a neu- ron's soma that receive incoming messages from other neurons. The Nervous System 83 Soma Dendrites Nucleus Axon FIGURE 5 STRUCTURE OF THE NEURON. When an electrical impulse is received at the dendrites, it moves through the axon to the terminal buttons. There it triggers the release of neurotransmitters, which carry the impulse across the synapse to the dendrites of the receiving neuron. Myelin sheath surrounding the axon Axon Terminal button Sending Neuron Presynaptic Neuron myelin sheath The fatty substance wrapped around some axons, which insulates the axon, making the nerve impulse travel more efficiently. synapse The junction between an axon and the adjacent neuron, where informa- tion is transmitted from one neuron to another. terminal button A little knob at the end of the axon that contains tiny sacs of neurotransmitters. sensory neurons Nerve cells that receive incoming sensory information from the sense organs (eye, ear, skin, tongue, nose). motor neurons Nerve cells that carry commands for movement from the brain to the muscles of the body. mirror neurons Nerve cells that are active when we observe others performing an action as well as when we are performing the same action. The axons of some neurons are wrapped in a fatty myelin sheath. Just like rubber around an electrical wire, the myelin sheath insulates the axon, so that the impulse travels more efficiently, strengthening the connection to adjacent neurons. The process of myelination is a gradual one that starts before birth, is facilitated in breast-fed babies, and continues into early adulthood (Deoni et al., 2013; Fields, 2008). The glial cells are responsible for creating the myelin that insulates axons throughout the nervous system (Simons & Nave, 2016). The junction between the axon and the adjacent neuron is known as the synapse. At the end of the axon, at each synapse, is a terminal button containing tiny sacs of neurotransmitters. When an electrical impulse reaches the terminal button, it triggers the release of neu- rotransmitter molecules into the gap between neurons, known as the synaptic cleft. The neurotransmitter carries the signal across the synaptic cleft to the next neuron. There are three kinds of neurons: sensory neurons, motor neurons, and in- terneurons. Sensory neurons receive incoming sensory information from the sense organs (eyes, ears, skin, tongue, and nose). Any sensation you receive— anything you see, hear, touch, taste, or smell—activates sensory neurons, which take the message to the brain for processing. Motor neurons take commands from the brain and carry them to the mus- cles of the body. Each time you move any muscle in your body, intentionally or not, motor neurons are at work. Researchers have identified motor neurons that are active when monkeys observe others performing an action, as well as when the monkeys undertake the same action (Rizzolatti et al., 1996). Neurons that be- have this way, called mirror neurons, appear to play an important role in learn- ing by observation (Lametti & Watkins, 2016). The most definitive work on mirror neurons has been conducted on monkeys because it has been possible to record directly from single neurons deep in their brains. So far, this has not been done with humans, but there is indirect evidence 84 CHAPTER 3 The Biology of Behavior Axon Receiving Neuron Postsynaptic Neuron ©John Lund/Blend Images LLC RF Sensory and motor neurons working in concert with the brain make this sprinter's elegant strides possible. of systems of neurons acting as mirrors in humans (Debes, 2010). One piece of evi- dence is from studies that measure brain activity while people engage in various tasks that involve imitation or observation. Such evidence suggests that human mir- ror neuron systems are activated when we process social cues from others (Coudé et al., 2016; Mainieri et al., 2013). Certain patterns of electrical activity measured from the cerebral cortex may be a sign of human mirror neuron system, though this re- mains a matter of debate in neuroscience (Hobson & Bishop, 2016). The discovery of mirror neurons has changed the way we make sense of a wide range of human expe- riences, including how we interpret the emotions of and feel empathy toward others. Interneurons communicate only with other neurons. Most interneurons connect neurons in one part of the brain with neurons in another part. Others receive information from sensory neurons and transmit it to motor neurons for action. If you touched a sharp object, interneurons in your spinal cord would receive pain information from sensory neurons in your fingers and communicate it to motor neurons in the muscles of your arm, so that you could pull away. Inter- neurons are the most common kind of neuron in the brain, outnumbering sensory and motor neurons by at least 10 to 1 (Nauta & Feirtag, 1979). They play a crucial role in the inhibition of impulses between one brain region and another (Crandall & Connors, 2016). Dysfunction in these important inhibitory circuits has been im- plicated in disorders associated with overexcitation in the brain, such as epilepsy and schizophrenia (Marin, 2012) and may play a role in the memory deficits of Alzheimer's disease (Schmid et al., 2016). Neural Communication Neural communication is a two-step process: action potential and neurotransmission. The Action Potential The action potential, an electrical and chemical process, is the positively charged impulse that moves one way down an axon. Connection Mirror neurons support learning by imitation as well as empathy. See "The Developing Infant and Child," in the chapter "Human Development," p. 171; "Imitation, Mirror Neurons, and Learning," in the chapter "Learning," p. 324; and "Prosocial Behavior," in the chapter "Social Behavior," p. 552. interneurons Neurons that communicate only with other neurons. action potential The impulse of positive charge that runs down an axon. The Nervous System 85 ions Chemically charged particles that predominate in bodily fluids; found both inside and outside cells. resting potential The difference in electrical charge between the inside and outside of the axon when the neuron is at rest. This happens by virtue of changes in the neuron itself. The neuron, like all cells in the body, is surrounded by a membrane that is somewhat permeable, letting only certain particles move through it. The fluid inside and outside the cell contains electrically charged particles called ions. Positively charged sodium and potas- sium ions and negatively charged chloride ions are the most common. Channels in the membrane of the neuron allow ions to flow between the inside and out- side of the cell. Some of these channels are always open. Others, called voltage- dependent channels, open only when certain electrical conditions are met. Due to the flow of ions into and out of the neuron, there is a difference in charge inside the cell compared to outside at all times. In the resting state, there is an excess of negatively charged particles inside the axon, whereas the fluid outside the axon has a positive charge. When a neuron is at rest, the charge dif- ference, known as a potential, between the inside and the outside of the axon is −70 millivolts (mV). This value is the resting potential of the neuronal mem- brane (see Figure 6a). Neurons do not stay at rest, however. An incoming impulse—which may have been stimulated by events as different as pressure to the skin and the thought of a loved one—can temporarily change the potential. Here is how touch can stimulate a neural impulse: A message received from sense recep- tors in the skin or from other neurons changes the axonal membrane's perme- ability, especially to positively charged sodium ions. If an incoming impulse increases the positive charge inside the neuron to a certain threshold, the neuron becomes depolarized and fires an action potential, a surge in posi- tive charge (see Figure 6b). The sodium channels at the top of the axon fly open, and positively charged sodium ions pour into the cell. The influx of sodium leads to a brief spike in positive charge, raising the membrane poten- tial from −70 mV to +40 mV. Once initiated, the action potential causes sodium channels to close and potassium voltage-dependent channels to open (see Figure 6c). As positively charged potassium ions flow out of the cell, the membrane potential returns to its resting state of −70 mV. While the neuron is returning to its resting state, it temporarily becomes supernegatively charged. During this brief period, known as the refractory period, the neuron cannot generate another action potential. We can summarize the electrical changes in the neuron from resting to ac- tion potential to refractory period and back to the resting state as follows (see Figure 6d): 1. Resting potential is −70 mV. 2. If an incoming impulse causes sufficient depolarization, voltage-dependent sodium channels open and sodium ions flood into the neuron. 3. The influx of positively charged sodium ions quickly raises the membrane potential to +40 mV. This surge in positive charge inside the cell is the action potential. 4. When the membrane potential reaches +40 mV, the sodium channels close and potassium channels open. The outward flow of positively charged potassium ions restores the negative charge inside the cell. This process repeats all along the axon, as the impulse moves toward the syn- apse. As the action potential subsides in one area, it immediately depolarizes the next portion of membrane, causing sodium channels to open there, continu- ing the action potential. This process of how an impulse move down the axon is known as propogation. Like a wave, the action potential travels along the axon, until it reaches the terminal buttons. In myelinated neurons, the action potential travels faster still, as depolarization occurs only at gaps in the myelin sheath and the action potential jumps from gap to gap (see Figure 5). The gaps refractory period The span of time, after an action potential has been generated, when the neuron is returning to its resting state and the neuron cannot gener- ate an action potential. 86 CHAPTER 3 The Biology of Behavior FIGURE 6 HOW NEURONS FIRE: MEMBRANES AND VOLTAGE CHANGES IN ACTION POTENTIALS Axon Membrane Sodium Potassium More sodium channels open Sodium channels close; potassium channels open. Na+ channel channel K+ A- Na+ A- A- Na+ Sodium channels open +40 -55 -70 Potassium ions flow out 3 Repolarization Refractory period Return to resting potential +40 mV 0 mV -70 mV Na+ 2 Depolarization +40 mV 0mV + -70mV Na 4 Refractory period (a) Resting potential: Time 1. In the resting neuron, the fluid outside the axon contains a higher concentration of positive ions than the inside of the axon, which contains many negatively charged anions (A-). Na+ Na+ (b) Action potential: Time 2. An action potential occurs in response to stimulation of the neuron. Sodium channels in the axonal membrane open, and positively charged sodium ions (NA+) pour into the axon, temporarily raising the charge inside the axon up to +40 mV. K+ Na+ 1 Depolarization 1 Resting Na+ potential 2 4 Time 0 mV -70 mV Voltage Na+ K+ K+ 1 Resting +40 mV K+ + 0mV Na + -70mV Na K+ K+ K+ Na+ (c) Resting potential restored: Time 3. As the impulse moves on down the axon, potassium (K ) channels open, allowing more K+ to flood out of the cell, 3 Repolarization restoring the negative resting potential (-70 mV). + How does a neural firing (action potential) happen? in the myelin sheath across which the action potential jumps are known as the nodes of Ranvier. How fast are action potentials? In the 1920s, Edgar Douglas Adrian recorded individual action potentials of sensory neurons and confirmed a speed of about 100 feet per second (Kandel, 2006). Adrian's work also confirmed the existence of a threshold—a point of no return. Once the charge inside the neuron exceeds threshold (and only if it exceeds threshold), the action potential fires. This is (d) This graph depicts the electrical changes that occur during each stage of an action potential (resting, depolarization, repolarization, refractory period). The top portion shows changes in voltage over time as measured by direct recording from single neurons in animal research. The lower four pictures show the membrane changes that correspond to each stage. The electrical changes of an action potential occur in a few thousandths of a second. During the refractory period, no new action potential can be generated. node of Ranvier The gap(s) in the myelin sheath across which the action potential jumps. The Nervous System 87 Voltage (millivolts) Source: Tina Carvalho/NIH-NIGMS In this image taken by a scanning electron microscope, we see a terminal button that has been broken to show vesicles (colored balls). Neurotransmitters reside in the vesicles. known as the all-or-none principle; that is, either an ac- tion potential fires or it does not. Neurotransmission The arrival of an action po- tential at the terminal buttons of a neuron triggers the second phase in neural communication—the release of neurotransmitters into the synaptic cleft to pass on the impulse to other neurons. Neurotransmitters are packaged in sacs called synaptic vesicles in the ter- minal button. When an action potential reaches the terminal button, the vesicles fuse with the cell mem- brane of the terminal and release neurotransmitter mol- ecules into the synaptic cleft, where they may be taken up by receptors in the dendrites of adjacent neurons (Schwartz, 2000). In a synapse, the neuron on the receiving end is known as the postsynaptic neuron. Neurotransmitters bind with receptors in the postsynaptic neuron in a lock- and-key type of arrangement (see Figure 7). There are many different types of neurotransmitters, each of which binds only with a specific receptor. For example, some receptors bind only with the neurotransmitter acetylcho- all-or-none principle The idea that, once the threshold has been crossed, either an action potential fires or it does not. synaptic vesicles Tiny sacs in the terminal buttons that contain neurotransmitters. enzymatic degradation A way of removing excess neu- rotransmitter from the synapse in which enzymes specific for that neurotransmitter bind with the neurotransmitter and destroy it. reuptake A way of removing excess neurotrans- mitter from the synapse, in which excess neurotransmitter is returned to the sending, or presynaptic, neuron for storage in vesicles and future use. graded potentials Small changes in membrane poten- tial that by themselves are insuffi- cient to trigger an action potential. glutamate A major excitatory neurotransmitter in the brain that increases the likeli- hood that a postsynaptic neuron will fire; important in learning, memory, neural processing, and brain development. line. If other neurotransmitters come in contact with acetylcholine receptors, they will not bind and no signal will be transmitted. Not all of the neurotransmitter molecules that are released into the synaptic cleft bind with receptors. Usually, excess neurotransmitter remains in the synap- tic cleft and needs to be removed. There are two removal methods: (1) enzymatic degradation, in which enzymes specific to that neurotransmitter bind with the neu- rotransmitter and destroy it, and (2) reuptake, which returns excess neurotransmit- ter to the sending, or presynaptic, neuron for storage in vesicles and future use. Even the neurotransmitter that binds to the dendrites of the receiving or postsynaptic neu- ron does not stay there. Eventually, it disengages from the receptor and floats away. After a neurotransmitter binds to a receptor on the postsynaptic neuron, a series of changes occurs in that neuron's cell membrane. These small changes in membrane potential are called graded potentials. Unlike action potentials, these are not "all-or-none." Rather, they affect the likelihood that an action po- tential will occur in the receiving neuron. Some neurotransmitters, called inhibi- tory neurotransmitters, create graded potentials that decrease the likelihood of a neuron firing. One such neurotransmitter is GABA (gamma-aminobutyric acid). In contrast, excitatory neurotransmitters create graded potentials that increase the likelihood of an action potential. Glutamate is the most common excitatory neurotransmitter in the brain. The excitatory potentials bring the neuron closer to threshold, while the in- hibitory potentials bring it further away from threshold. The soma in the postsyn- aptic neuron integrates the various graded potentials. If the integrated message from these graded potentials depolarizes the axon enough to cross the threshold, then an action potential will occur. Common Neurotransmitters Within the past century, researchers have discovered at least 100 distinct neu- rotransmitters and related chemical messengers and have learned what most of them do, though the exact number of neurotransmitters is unknown. Of the known neurotransmitters, those most relevant for the study of human thought and behavior are acetylcholine, dopamine, epinephrine, norepinephrine, 88 CHAPTER 3 The Biology of Behavior (a) The neural impulse from the presynaptic neuron travels down the axon toward dendrites of the next neuron. Direction of nerve impulse Soma Dendrites Axon Presynaptic Neuron Terminal button (b) In the terminal button, the impulse triggers the release of neurotransmitters into the synaptic cleft. Terminal button Postsynaptic Neuron (c) At a receptor site on the dendrite of the receiving (postsynaptic) neuron, the neurotransmitter causes channels to open and changes the membrane potential. (d) Receptors will bind only with specific neurotransmitters. If no binding occurs, no action potential is generated in the postsynaptic neuron. Transmitter will not fit receptor; channel remains closed Transmitter will fit receptor; channel opens and ion can pass + Receptor molecules in postsynaptic membrane Neurotransmitters + + Channel (open) Axon of sending neuron Synaptic vesicle containing neurotransmitters Synaptic cleft Receptor site Dendrite of receiving neuron + + FIGURE 7 HOW SYNAPSES AND NEUROTRANMSITTERS WORK. In (a), two neurons connect, a presynaptic neuron and a postsynaptic neuron. They do not touch, but terminal buttons in the presynaptic neuron form a synaptic cleft with the postsynaptic neuron. In (b), the synaptic cleft has been enlarged to show the synaptic vesicles that carry neurotransmitters. They release neurotransmitters into the cleft where they bind to receptor sites on the postsynaptic neuron. In (c), we see a further enlargement of the neurotransmitters being released into the synaptic cleft and binding to receptor sites in the postsynaptic neuron. In (d), each receptor site binds to only one specific kind of neurotransmitter. Below is a three-dimensional artistic interpretation of neurons in the brain. Synaptic vesicle releases neurotransmitters. Neurotransmitters attach at receptor site; channel opens. ©Jim Dowdalls/Science Source The Nervous System 89 Neurotransmitter Major Function Acetylcholine Slows ANS activity; eating, drinking, neuromuscular junction; involved in learning, memory, sleeping, and dreaming Dopamine Plays an important role in arousal, mood (especially positive mood); oversupply correlates with schizophrenia; voluntary muscle control Epinephrine Increases ANS activity; fight-or-flight response Norepinephrine Affects CNS activity; plays role in increasing alertness, attention Serotonin Plays role in mood, sleep, eating, temperature regulation; undersupply correlates with anxiety and depression GABA Is the major inhibitory neurotransmitter in the brain; slows CNS function; correlates with anxiety and intoxication Glutamate Is the most common excitatory neurotransmitter in the brain; involved in learning and memory; may be involved in schizophrenia acetylcholine (ACh) A neurotransmitter that controls muscle movement and plays a role in mental processes such as learn- ing, memory, attention, sleeping, and dreaming. dopamine A neurotransmitter released in re- sponse to behaviors that feel good or are rewarding to the person or animal; also involved in voluntary motor control. epinephrine Also known as adrenaline, a neu- rotransmitter that arouses bodily sys- tems (such as increasing heart rate). norepinephrine A neurotransmitter that activates the sympathetic response to stress, increasing heart rate, rate of respi- ration, and blood pressure in sup- port of rapid action. FIGURE 8 MAJOR NEUROTRANSMITTERS AND THEIR FUNCTIONS. Neurotransmitters can be excitatory, increasing the likelihood of an action potential, or inhibitory, decreasing the likelihood of an action potential. serotonin, GABA, and glutamate (see Figure 8). Neurotransmitters are found only in the brain. They are synthesized inside the neuron for the purpose of neurotransmission. The neurotransmitter acetylcholine (ACh) is released at synapses that control muscle movement (these are known as neuromuscular junctions), and it also released at synapses involved in learning, memory, attention, sleeping, and dreaming. Whether ACh excites muscles or slows them down depends on what kind of receptor receives it. Furthermore, researchers have discovered that the degenerative memory disorder called Alzheimer's disease results at least partly from a decrease in ACh activity and that ACh drug enhancers aid memory. ACh enhancers are now used to treat memory disorders, such as Alzheimer's disease, and they seem to slow the progression of memory loss (Czech & Adessi, 2004; Selkoe, 2002). Dopamine is involved in voluntarily controlling your muscles and is re- leased during feelings of pleasure or reward. Eating a good meal, doing well on an exam, having an orgasm, or drinking a glass of water when really thirsty—each of these behaviors stimulates dopamine activity in the brain (Hamer & Copeland, 1998; Kringelbach & Berridge, 2015). Because dopamine activity makes us feel good, many drug addictions involve increased dopamine activity. For instance, cocaine blocks the reuptake of dopamine into the presynaptic neuron, leaving it in the synaptic cleft for a longer period of time before it binds to receptors in the postsynaptic neuron (Bradberry, 2007). The result is a feeling of euphoria and pleasure. Epinephrine and norepinephrine primarily have energizing and arous- ing properties. (Epinephrine was formerly called adrenaline, a term that is still widely used in everyday speech—"Wow! What an adrenaline rush!") Both are produced in the brain and by the adrenal glands that rest atop the kidneys. Epi- nephrine tends not to affect mental states, whereas norepinephrine increases mental arousal and alertness. Norepinephrine activity also leads to physical 90 CHAPTER 3 The Biology of Behavior arousal—increased heart rate and blood pressure. People who suffer from ADHD have unusually low norepinephrine levels, and treatment sometimes includes drugs to increase norepinephrine levels (Barr et al., 2002). Serotonin plays a role in a wide range of behaviors, including dreaming and controlling emotional states such as anger, anxiety, and depression. People who are generally anxious and/or depressed often have low levels of serotonin (Caspi, Sugden, et al., 2003; Frokjaer et al., 2009; Kendler et al., 2005). Drugs that block the reuptake of serotonin in the synapse are used to treat anxiety and de- pression. It is well known that depression runs in families (Weissman et al., 2016). Serotonin related genes appear to modulate family risk for depression (Bansal et al., 2016). People who are consistently angry and/or aggressive (especially males) often have abnormally low levels of serotonin as well. The administration of se- rotonin reduces aggressive behavior in monkeys (Suomi, 2005). The street drug ecstasy or molly (MDMA), which makes people feel social, affectionate, and eu- phoric, stimulates extremely high levels of serotonin. Ironically, however, ecstasy ultimately interferes with the brain's ability to produce serotonin, and so depres- sion can be an unpleasant side effect of the drug (de Win et al., 2004). The psy- chedelic state created by hallucinogenic drugs, such as psilocybin mushrooms, appears to involve the activation of serotonergic systems (Muthukumaraswamy et al., 2013). Gamma-aminobutyric acid, or GABA, is a major inhibitory neurotrans- mitter in the brain. Remember that inhibitory neurotransmitters tell the post- synaptic neurons not to fire. GABA slows CNS activity and is necessary for the regulation and control of neural activity. Without it, the central nervous system would have no "brakes" and could run out of control. One theory about epilepsy is that GABA does not function properly in people who suffer from the disorder (Laschet et al., 2007). Many drugs classified as depressants, such as alcohol, increase GABA activity in the brain and lead to relaxing yet ultimately uncoordinated states. Because GABA inhibits much of the CNS activity that keeps us conscious, alert, and able to form memories, large amounts of alcohol consumption can lead to memory lapses, blackouts, loss of consciousness, and even death (White, 2003). Stress can increase GABA and thereby increase its inhibitory effects on organs such as the large intestine, which might be one reason why some people experience diarrhea when under extreme stress (Reed et al., 2016). serotonin A neurotransmitter with wide-rang- ing effects; involved in dreaming and in controlling emotional states, espe- cially anger, anxiety, and depression. Glutamate, the brain's major excitatory neu- rotransmitter, is important in learning, memory, neural processing, and brain development. More specifically, glutamate facilitates growth and change in neurons and the migration of neurons to different sites in the brain, all of which are basic processes of early brain develop- ment (Nadarajah & Parnavelas, 2002). It also amplifies some neural transmissions, so that a person can tell the difference between important and less important infor- mation. For example, is it more important to notice that a car is skidding out of control in front of you or that your shoes are still the same color they were when you put them on this morning? Glutamate boosts the signals about the car. The physiologically stimulating effects of nicotine in tobacco stem from glutamate synapses (Guillem & Peoples, 2010). The balance between the ex- citatory effects of glutamate and the inhibitory effects of GABA may be involved in supporting the repetitive motor behaviors seen in autistic spectrum disorder (Dickinson, Jones, & Milne, 2016). ©Rommel Canlas/Shutterstock.com GABA (gamma-aminobutyric acid) A major inhibitory neurotransmitter in the brain that tells postsynaptic neurons not to fire; it slows CNS activity and is necessary to regulate and control neural activity. The street drug known as ecstasy or molly stimulates the release of high levels of the neurotransmitter serotonin, which makes people temporarily feel euphoric and affectionate. By interfering with the body's ability to produce serotonin, however, ecstasy eventually may cause depression in some people. The Nervous System 91 Quick Quiz 2: The Nervous System 1. Which branch of the nervous system is responsible for the fight-or-flight response? a. the parasympathetic nervous system b. the somatic nervous system c. thesympatheticnervoussystem d. the central nervous system 2. The fingerlike projections on neurons that receive input from other neurons are called a. dendrites. b. nuclei. c. axons. d. terminal buttons. Answers can be found at the end of the chapter. 3. What property of the neuron is most directly responsible for the changes that lead up to an action potential? a. sodium ions outside the cell b. its permeable membrane c. chloride ions inside the cell d. the flux of potassium ions 4. What is the most common excitatory neurotransmitter in the brain? a. GABA b. serotonin1 c. glutamate d. acetylcholine Summary of the Steps in Neural Transmission We have considered the complex phenomena of action potentials and neurotrans- mission and described the neurotransmitters involved in human thought and be- havior. Before we discuss the major structures of the brain, let's take time to summarize the process of neural communication. • The information in neural transmission always travels in one direction in the neuron—from the dendrites to the soma to the axon to the synapses. This process begins with information received from the sense organs or other neurons, which generate a nerve impulse. • The dendrites receive a message from other neurons. That message, in the form of an electrical and chemical impulse, is then integrated in the soma. • If the excitatory messages pass the threshold intensity, an action potential will occur, sending the nerve impulse down the axon. If the inhibitory messages win out, the likelihood that the postsynaptic neuron will fire goes down. • The nerve impulse, known as the action potential, travels down the axon, jumping from one space in the axon's myelin sheath to the next, because channels are opening and closing in the axon's membrane. Ions, mostly sodium and potassium, pass in and out of the membrane. • This impulse of opening and closing channels travels like a wave down the length of the axon, where the electrical charge stimulates the release of neurotransmitter molecules in the cell's synapses and terminal buttons. • The neurotransmitters are released into the space between neurons, known as the synaptic cleft. Neurotransmitters released by the presynaptic neuron then bind with receptors in the membrane of the postsynaptic neuron. • This binding of neurotransmitter to receptor creates electrical changes in the postsynaptic neuron's cell membrane, at its dendrites. Some neurotransmitters tend to be excitatory and increase the likelihood of an action potential. Others tend to be inhibitory and decrease the likelihood of an action potential. • The transmission process is repeated in postsynaptic neurons, which now become presynaptic neurons. 92 CHAPTER 3 The Biology of Behavior THE BRAIN The brain is a collection of neurons and glial cells that controls all the major functions of the body; produces thoughts, emotions, and behavior; and makes us human. This jellylike mass at the top of the spine has been mapped and de- scribed in astonishing detail. Here we consider the evolution of the brain, look at key brain regions, and explore what is currently known about their specialized functions. At this point, the picture is still far from complete, and neuroscientists continue to piece it together. Evolution of the Human Brain Evolution provides a fundamental example of how biology and environment in- teract. As we discussed in the chapter "Introduction to Psychology," over long periods of time, nature selects traits and behaviors that work well in a given envi- ronment. Recall the example of the beetle population becoming more brown than green as brown beetles blended into their surroundings better and were more likely to survive and reproduce. This natural selection process gradually leads to big changes in living forms and structures—from cells to muscles to brains to new species. The human brain has been shaped, via natural selection, by the world in which humans have lived. It is worth noting that brains do not fossilize to allow a present-day analysis, but the skulls that hold them do. By looking at the size and shape of skulls from all animals and over very long time periods, scientists can glean something about how and when human brains evolved. The evolution of the human brain is a fascinating story. Although the details lie well beyond the scope of this book, we can consider a general outline of brain evolution (Dunbar, 2001; Jerison, 2000; Klein, 1999; Striedter, 2005). When did the very first brain show up on the planet? Ey Arthropods, which have no backbone and external skeleton, were probably the first organisms with a central nervous system (brain) about 520 million years ago (Ma et al., 2015). Within a few million years, the first primitive vertebrates (ani- mals with backbones) appeared. They were jawless fish, and they had a bigger mass of nerve cells than flatworms (Jeri- son, 2000). The first land animals came into existence around 450 million years ago and the first mammals around 200 million years ago. Land animals had more than a bundle of neurons above the spinal cord; they had complex brains with numerous structures. The first primates lived around 55 million years ago— 10 million years after the dinosaurs went extinct (Jerison, 2000; Zhang et al., 2008). Compared to other mammals, birds, reptiles, and fish, primates have relatively large amounts of brain cortex, allowing more complex thinking and problem solving. The earliest ancestors of humans appeared in Africa about 6 million years ago. One of our closest evolutionary relatives, the Neanderthals (Homo neanderthalensis), lived from about 350,000 to 28,000 years ago, when they were re- placed by our species (Homo sapiens). Neanderthals had brains slightly larger, on average, than those of modern hu- mans (see Figure 9). Es Oc Hs A1 Th Ab Photo ©Xiaoya Ma http://nhm.academia.edu/XiaoyaMa The very first brain on earth probably belonged to this 520 million year old arthropod.

Behaviorism In 1913, a little-known 34-year-old psychologist, John Watson, directly challenged the use of introspection. He founded behaviorism, which asserts that psychology can be a true science only if it examines observable 16 CHAPTER 1 Introduction to Psychology behavior, not ideas, thoughts, feelings, or motives. In Watson's view, mental experiences are hypothetical con- cepts, for they cannot be directly measured. As long as psychology focused on such internal states, it would for- ever be a false science. Behaviorism is an extreme form of environmentalism, the view that all behavior comes from experience interacting with the world. It is the school of psychology that most clearly expresses John Locke's ideas about our minds being a blank slate at birth.

A decade or so after behaviorism emerged, it became the dominant force in experimental psychology. Its most famous figure, B. F. Skinner (1904-1990), was largely re- sponsible for making behaviorism the major approach in experimental psychology, a position it held for nearly 50 years. Skinner modified Watson's ideas and argued that consequences shape behavior. Humanistic and Positive Psychology During the first half of the 20th century, the two major schools of thought in psychology were split along the divide be- tween practice and science. On the therapeutic side were psychoanalysis and Freud, and on the scientific side were behaviorism and Skinner. In the 1940s and 1950s, Abra- ham Maslow and Carl Rogers presented an alternative to both of these perspectives. They argued that both psycho- analysis and behaviorism ignored people at their best, and neither approach considered what it meant to be psycho- logically healthy. Maslow and Rogers proposed an alter- native called humanistic psychology, which promoted personal growth and meaning as a way of reaching one's highest potential.

Not all products of evolution are adaptations. Sometimes things evolve be- cause they solve one problem and just happen to solve another one too. These structures or features that perform a function that did not arise through natural selection are often called by-products or, more technically, exaptations (Buss, 1999; Gould & Vrba, 1982). An example of a by-product is feathers. Feathers prob- ably evolved for insulation in flightless dinosaurs, but they turned out to be useful for flight in birds, the dinosaurs' descendants. Because feathers did not evolve for that purpose, they are considered by-products ("Exaptations," 2006). Evolution- ary changes in bodies and brains are prime examples of how nature and nurture interact to shape the psychology of human thought and behavior. Nothing illustrates more vividly than evolution how nature and nurture work together. Depending on how they enable organisms to respond to their en- vironment, certain characteristics of animals predominate or not—such as the brown color of a beetle and the fear response in humans. Nature and nurture work together to create our bodies (including our brains) and behavior. They are interdependent—they depend on and interact with each other.

As we have seen in this chapter, in order to fully appreciate the complexity of human thought and behavior, one must consider a wide variety of perspectives— no one perspective tells the whole story. Throughout this text we highlight diverse explanations of human thought and behavior. This variety of perspectives raises the question, How does one resolve the various views? There are two strategies for answering this question: by using science and critical thinking and by making connections. Whether we are evaluating the ideas of a Facebook feed or the merits of a scien- tific perspective, we need to use our skills as critical thinkers to distinguish fact from fiction. You've probably heard about "critical thinking" quite often. Teachers are always talking about getting their students to think critically. To apply critical thinking skills, we should ask ourselves, What is the evi- dence for this conclusion, and is it valid? Suppose you are on a jury in a murder trial. The primary evidence on which the case is based is eyewitness testimony: Two people picked out the defendant from a lineup. The prosecutor offers no other concrete evidence, such as DNA findings, fingerprints, bloodstains, or bal- listic (bullet) matching. Your job is to decide whether the defendant committed the murder. You will want to draw on your critical thinking skills, because in this situation ignoring evidence and basing judgments on bias can have costly, even deadly, consequences. So what exactly is critical thinking? We can answer this question in part by examining the origin of the word critical. It comes from the ancient Greek word kritikos and means "to question, to make sense of, and to be able to analyze; or to be skilled at judging" (Chaffee, 1999, p. 32). Educator Paul Chance has provided a more complete definition of critical thinking: "The ability to analyze facts, gen- erate and organize ideas, defend opinions, make comparisons, draw inferences, evaluate arguments, and solve problems" (Chance, 1986, p. 6). The core traits of critical thinking are sound analysis, evaluation, and the formation of ideas based on the evidence at hand. In the late 1980s a group of educators, philosophers, psychologists, and bio- logical and physical scientists organized a conference around the topic of critical thinking in education, and there they arrived at a consensus on what it means to be a good critical thinker. They were nearly unanimous in identifying six activi- ties or qualities that define critical thinking (Facione, 1990).

The humanistic movement had waned by the late 1970s, mostly because it had moved away from its research and scientific base. It surfaced again in the late 1990s, however, when Martin Seligman and Mihaly Csikszentmihalyi started the positive psychology movement (Seligman & Csikszentmihalyi, 2000). Positive psychology shares with humanism a belief that psychology should focus on studying, understanding, and promoting healthy and positive psychological func- tioning. It does so with a better appreciation than humanistic psychology for the importance of studying well-being from a scientific perspective. As you will see in this text, much of contemporary psychology embraces the positive psychologi- cal view.

Cognitivism After Watson banished thoughts, feelings, and motives as the focal point of the modern science of psychology in the 1910s, research into these topics nearly disappeared from the field for almost 50 years. Two events kept them in the minds of psychologists, however. First, in the 1920s and 1930s, a move- ment in Germany called Gestalt psychology attracted worldwide attention. Led by Max Wertheimer (1880-1943), Gestalt psychology—after the German word for "whole form"—proposed that perception occurs in unified wholes, where the whole is more than the sum of its parts. As the Gestaltists suspected, our brains actively shape sensory information into perceptions. For an example of this phe- nomenon, look at Figure 2. You see a triangle within three circles, but no triangle actually exists. The brain, however, organizes your perception of the markings on the page into the shape of a triangle.

We do not draw any conclusions from descriptive results. We just describe the scores with them. Inferential statistics, however, allow us to test hypotheses and draw a conclusion (that is, make an inference) as to how likely a sample score is to occur in a population. They also allow us to determine how likely it is that two or more samples came from the same population. In other words, inferential statistics use probability and the normal distribution to rule out chance as an explanation for why group scores are different. What is an acceptable level of chance before we say that a score is not likely to occur by chance? Five in 100 (5%) is the most frequent choice made by psycho- logical researchers and is referred to as the probability level. So if we obtain two means and our statistical analysis tells us there is only a 5% or less chance that these means come from the same population, we conclude that the numbers are not just different but statistically different and therefore not likely to be due to chance. Researchers use many kinds of statistical analyses to rule out chance, but the most basic ones involve the comparison of two or more means. To compare just two means, we use a statistic known as the t-test. The basic logic of t-tests is to deter- mine whether the means for your two groups are so different that they are not likely to come from the same population. If our two groups are part of an experiment and one is the experimental group and the other the control group, then we are determin- ing whether our treatment caused a significant effect, seen in different means. In short, t-tests allow us to test our hypotheses and rule out chance as an explanation. Let's look at an example, by returning to a question we considered earlier: Does sugar cause hyperactive behavior in children? We will make the common- sense prediction that sugar does cause hyperactive behavior. We randomly assign 100 children to consume sugar (experimental group); another 100 children do not consume sugar (control group). We then wait 30 minutes—to let the sugar effect kick in—and observe their behavior for an additional 30 minutes. We video record each child's behavior and code it on number of "high activity acts." If sugar causes activity levels to increase, then the sugar groups number of high activity acts should be higher than those of the no-sugar group. Our data show that the experi- mental (sugar) group exhibited an average of 9.23 high activity behaviors in the 30 minutes after eating the sugar; the control (no-sugar) group exhibited an aver- age of 7.61 such behaviors. On the face of it, our hypothesis seems to be supported. After all, 9.23 is higher than 7.61. However, we need to conduct a statistical test to determine whether the difference in the number of hyperactive behaviors between our groups of kids who ate sugar versus those who did not really represents a true difference between these two different populations of kids in the real world.

Due to current ethical guidelines, some of the most important and classic studies in psychology could not be performed today. One of them is the Stanford Prison Experiment, which you read about at the beginning of this chapter. This experi- ment subjected participants to conditions that so altered their behavior the re- searchers had to intervene and end the study early. In 1971, there were few ethical limitations on psychological research. Since then, and partly as a consequence of studies like the Stanford Prison Experiment, professional organizations and universities have put in place strict ethical guidelines to protect research partici- pants from physical and psychological harm. Ethics are the rules governing the conduct of a person or group in general or in a specific situation; stated more simply, ethics are standards of right and wrong. What are the ethical boundaries of the treatment of humans and animals in psychological research? In psychology today, nearly every study conducted with humans and animals must pass through a rigorous review of its methods by a panel of experts. If the proposed study does not meet the standards, it cannot be approved. Ethics involve rules against scientific misconduct and rules for treat- ment of human participants and animals. Ethical violations and scientific misconduct in science range from honest errors or mistakes to fraud. Errors can be the result of carelessness, bias, or mistakes, but tend not to be intentional. Scientific misconduct, however, is intentional and therefore the most serious ethical violation. According to both the National Science Foundation and the American Psychological Association, scientific fraud or misconduct comes in three forms: plagiarism, falsification, and fabrication (Code of Federal Regulations-689, 2002; Research Misconduct, n.d.). Plagiarism is when someone presents the words or ideas of other people as their own. Falsification is changing, altering, or deleting data. The most serious and blatant form of scientific misconduct and fraud is when a researcher commits scientific fabrication, that is, presenting or publishing scien- tific results that are made up. Fortunately, fraud and misconduct are relatively rare in science— estimates are about 1 in 5,000 to 1 in 23,000 papers need to be taken back or retracted for serious errors or misconduct (Steen, 2010; Steen et al., 2013). One of the worst recent cases of scientific fraud recently involved a social psychologist by the name of Diederik Stapel, who was an up- and-coming psychologist, publishing in the top journals. But one of his studies did not provide the results he predicted. In his words: "I said, you know what, I am going to create the dataset" (Bhattacharrjee, 2013). So he sat down at his kitchen table and literally fabricated an entire dataset. It worked. The paper was published in a top psychological journal. Over the next dozen years or so, a total of 55 scientific articles and 10 PhD theses were based on fabricated data. When it was all over, Stapel was fired, lost his career, and admit- ted "I have failed as a scientist" (Bhattacharrjee, 2013).

In medieval Europe from approximately 400 to 1400 CE (Common Era), psychological disorders were again attributed to supernatural causes. In the worldview that dominated this era and the Renaissance (from about 1400 to the early 1600s), people were thought to be possessed by de- mons, spirits, and the devil—not by physical disorders. These views were taken to an extreme during the Inquisition, when the Catholic Church investigated witch- craft and heresy as part of a broad campaign to eliminate dissent from established Church dogma. Some witchcraft practices were viewed as harmless and even beneficial, but others were branded as the work of the devil. In order to distinguish good witchcraft from bad, Church officials held inquisitions and trials, using several techniques to determine whether a person was a witch (D. N. Robinson, 1995). Sometimes the accused was prodded with a metal pole and spears; if she felt no pain, she was protected by the devil and therefore was a witch. In another common method, the float test, the woman's hands and feet were tied, and she was thrown into a lake or river. If she floated, she had to be guilty, because only the devil could make someone float; if she sank, she was innocent—but had drowned (Robinson, 1995). The most common punishment for the infrequent survivor of the float test— deemed to be a witch—was being burned at the stake. To be fair, numerous writers during the 14th to 16th centuries argued that witchery was caused not by spirits and supernatural elements but rather by natural ones, such as hallucinations or "melancholia"—what we would now call depression.

During the witch hunts of the 16th and 17th centuries, the first facilities for the mentally ill—called asylums—were built throughout Europe. The most famous, or infamous, of these was located at St. Mary of Bethlehem in London, England. Although it had served as a hospital for the mentally ill and others since the 1300s, Henry VIII designated it as a hospital for the insane in 1547. It was really no more than a storage house for the mentally ill and other social castaways. For the most part, early efforts to "treat" mental illness focused on removing afflicted people from society rather than helping them adjust to society. The conditions were deplorable and chaotic—patients were put in windowless and filthy rooms and were chained and shackled to the walls. The local population, including William Shakespeare, called the place Bedlam, a shortened version of Bethlehem, and that is how the term came to be associated with chaotic and noisy conditions. In response to these inhumane conditions, reform movements in support of moral treatment emerged in Europe and the United States. The main idea was to provide a relaxing place where patients would be treated with dignity and care. The first major proponent of humane therapies was the Frenchman Philippe Pinel in 1783. Dorothea Dix pioneered moral treatment in the United States. After visiting a prison in 1841 and witnessing the abhorrent and inhumane treatment of the inmates, some of them suffering from psychological disorders, Dix vowed to change these conditions. Over the next 40 years, she helped open 30 homes throughout North America (Nolen-Hoeksema, 2007). Moral therapies were among the first forms of treatment that regularly helped people get better. Modern Views The last decades of the 1800s also saw the emergence of the first truly modern view of psychological disorders—the idea that they are simply one form of illness and should be treated as medical conditions, with appropriate diagnosis and therapy. This view is now known as the "medical model" perspec- tive in clinical psychology. In the 1880s and 1890s, the German psychiatrist Emil Kraepelin collected data on the various kinds of psychological disorders and began systematically classifying and diagnosing them (Shepard, 1995). He popu- larized the term dementia praecox (premature dementia), which he later changed to schizophrenia, to refer to the major thought disorder known previously as "split mind." He was also the first to distinguish thought disorders (schizophre- nia) from the mood disorders of melancholia (depression) and manic depression (bipolar disorder; Jablensky & Woodbury, 1995). In short, his views were a major influence on diagnostic categories formulated during the 20th century. Around the turn of the 20th century in Austria, Sigmund Freud developed a form of therapy called psychoanalysis. A clinical approach to understanding and treating psychological disorders, psychoanalysis assumes that the unconscious mind is the most powerful force behind thought and behavior and that dreams have meaning and are the most direct route to the unconscious mind (Freud, 1900/1953). It also assumes that our experiences during childhood are a power- ful force in the development of our adult personality. Psychoanalysis assumes that people use psychological defenses to protect themselves against threatening impulses, thoughts, feelings, and fantasies. Last, it assumes that the unconscious blocking, or repression, of disturbing thoughts and impulses—especially sexual and aggressive impulses—is at the heart of all maladaptive adult behavior. By the mid-20th century, three of the major modern developments in clini- cal psychology had emerged: psychotherapy, drug therapy, and modern crite- ria for diagnosing mental disorders. For example, one common form of modern therapy—cognitive-behavioral—focuses on changing a person's maladaptive thought and behavior patterns by discussing and rewarding more appropriate ways of thinking and behaving. Although we will consider the modern diagnos- tic criteria in detail in the chapter "Psychological Disorders" and psychotherapy (psychological assessment and treatment by a trained therapist) and drug therapy in detail in the chapter "Treatment of Psychological Disorders", it is appropriate asylums Facilities for treating the mentally ill in Europe during the Middle Ages and into the 19th century. moral treatment A 19th-century approach to treat- ing the mentally ill with dignity in a caring environment. Connection Disturbance, dysfunction, distress, and deviance must be present for the diagnosis of psychological disorders. The DSM-5 describes specific symptoms of more than 250 different disorders. See "Defining Psychological Disorders," in the chapter "Psychological Disorders". (p. 569) psychoanalysis A clinically based approach to under- standing and treating psychological disorders; assumes that the uncon- scious mind is the most powerful force behind thought and behavior. Source: Library of Congress, Prints & Photographs Division, Sigmund Freud Collection [LC-USZ62-72266] Sigmund Freud The Origins of Psychology 13 empiricism The view that all knowledge and thoughts come from experience. to conclude our discussion of the history of psychology as a clinical practice with a brief introduction to the classification system that guides the diagnosis of psychological disorders today. When diagnosing psychological disorders, psychologists use the Diagnostic and Statistical Manual. Currently in its fifth edition, this standardized reference is referred to as the Diagnostic and Statistical Manual-5, or DSM-5 (American Psychiatric Association, 2013). Originally published in 1952, the DSM includes di- agnoses for more than 250 psychological disorders. The various editions of the DSM have incorporated new findings and added new disorders, objectively de- scribing the behaviors and symptoms of each disorder, so that psychologists from all perspectives can agree on a single diagnosis for an individual with a given set of symptoms. You might find it surprising to know, however, that this goal of universal agreement often is not achieved, so different clinicians hold different views about what constitutes a mental disorder. Occasionally, the DSM authors have removed behavior patterns (such as homosexuality, which was deleted from the list of disorders recognized by the American Psychiatric Association in 1973) that do not meet updated diagnostic criteria. Further, practitioners from the various subfields do not always agree with each other about the definitions of a given disorder. Cognitive-behavioral practitioners view depression, for example, as the patient's distorted thinking ("I am worthless"), whereas psychodynamic practitioners might consider the same person's depression (and expressed thoughts) to be the result of unconscious disturbing family relationship patterns that need to be made conscious. Clearly, perspective matters when it comes to psychological treatment, and we must continually question what we know from the perspective we are adopting.

Neuropsychological-Behavioral Genetic Behavior, thought, feelings, and personality are influenced by differences in basic genetic, epigenetic, and neurological systems between individuals. The reason some people have different traits, dispositions, and ways of thinking stem from differences in their genotype and central nervous system (brain structures and neurochemistry).

Evolutionary Because they are based on evolved brain systems, human thought, behavior, and personality have been shaped by forces of evolution (natural and sexual selec- tion) over millions of years. The body, brain, and environment coexist and co- evolved and so more than any other psychological perspective the evolutionary perspective emphasizes that what we think, feel, and do is always an interaction between nature (biological) and nurture (environment). In addition to these seven psychological perspectives, there are two other overarching issues that have colored much of psychology over the previous few decades: the nature-nurture debate and an increased appreciation for the evolution of human behavior.

Another form of selection happens not through mutation and chance but rather by being attractive to members of the opposite sex. Darwin in fact pro- posed a second form of selection, namely sexual selection, which operates when members of the opposite sex find certain traits attractive or appealing and there- fore over long periods of times these traits become more common in the population (Darwin, 1859; Miller, 2000). Natural and sexual selection create structures, behaviors, and traits that solve adaptive problems. Among the adaptive problems that our early human ancestors faced were avoiding predators, choosing nutritious foods, finding a mate, and communicating effectively with others. Adaptations are inherited solutions to ancestral problems that have been naturally and sexually selected because they directly contribute in some way to reproductive success (Tooby & Cosmides, 1992). Adaptations evolved to solve problems in past generations, not current ones. In other words, we are living with traits and tendencies that benefited our ancestors. Even though these tendencies might not seem to enhance our fitness in today's world, eons spent in harsher environments have left us predisposed to perform certain social behaviors when a situation calls forth ancient pat- terns. Consider our preference for fatty foods. In our evolutionary past, eating fat was a good strategy. Early humans, as hunter-gatherers, did not know when they would find food. If they found fat, they ate it, because fat could be stored in the body and used later when food might be scarce. For this reason, humans evolved to like fat. Modern society, however, offers easy access to food. Now eating fat is not the best strategy, because we don't need to store it for future use. More food will be available when we need it. So we eat fat, store it up, and carry it around as extra weight. Human cravings have not changed much, even though our environments have.

Evolutionary psychology is the branch of psychology that aims to un- cover the adaptive problems the human mind may have solved in the distant past and the effect of evolution on behavior today. Rather than just describing what the mind does, evolutionary psychologists are interested in the functions of the human mind (Tooby & Cosmides, 1992). Evolutionary changes in organs and bodily structures—or color, as in our beetle example—are not difficult to under- stand, but how do human behaviors evolve? Let's consider the emotions as an example of a behavioral adaptation. In the chapter "Motivation and Emotion", we discuss emotions in detail and explore the feelings that move us powerfully. For now, imagine that you are driving on the high- way and the car in the lane next to you has just cut you off. You have to slam on your brakes to keep from smashing into it, and you are shaking with fright. The possible car accident is an immediate cause of your fear. Why do you experience this intense bodily reaction called fear in the first place? The answer, from an evolutionary perspective, is that fear was naturally selected to solve an adaptive problem. What we call fear—including the way it moves our bodies, impels us to act, and makes our hearts race—evolved because it helps us deal quickly and efficiently with danger (Ekman, 2003). Eons ago, a genetic variation occurred in a human that somehow led to a specific way of re- sponding to threatening circumstances—quick action to avoid being killed—and the human was able to avoid harm and reproduce more readily; that is, it had an advantage. Without thinking about it, the ancestor who recognized a beast that could kill her while she was picking berries just wanted to get out of harm's way. Experiencing fear, she was more likely to escape death. This woman survived, reproduced, and passed on a genetic tendency to experience fear to the next gen- eration. Thus, emotions are behavioral adaptations. They are quick and ready response patterns that tell us whether something is good or bad for our well-being (Ekman, 2003; Lazarus, 1991).

The Evolution of Human Behavior One principle that plays an important role in understanding human behavior is evolution. The basics of this theory are more complex than most of us realize. Here we briefly explain the fundamental processes of evolution. Evolution means "change." With respect to biological species, evolution is the change over time in the frequency with which specific genes occur within a breeding species (Buss, 1999). What does the frequency of gene transmission have to do with behavior? Our genes contain instructions for making all the proteins in our bodies. Proteins in turn make up a lot of what we are: cell membranes, hor- mones, enzymes, and muscle tissue, for instance. These constituents carry out our intentions, in our brains and in our bodies. Thus, behaviors have genetic bases that are affected by many environmental factors. Human interaction with the world in- fluences which genes are passed on to future generations, and these in turn shape human behavior. These changes take place by natural and sexual selection.

First described by the 19th-century English naturalist Charles Darwin (1809-1882), natural selection is formally defined as a feedback process whereby nature favors one design over another, depending on whether it has an impact on reproduction. This process takes a long time to work, but it ultimately shapes who we are and how species evolve. Charles Darwin's great contribution was not the theory of evolution itself but rather his explanation of how evolution works—that is, by natural selection. Natural selection occurs by chance. Every once in a while, genes change for no apparent reason. Spontaneous changes in genes, called chance mutations, can alter the design of a structure or a set of behaviors. Let's suppose that a chance mutation in a population of green beetles results in a brown beetle. If the brown beetle is less visible to predators, it might have more success in surviving and reproducing, as Figure 5 shows. When it reproduces, the brown beetle passes on its "brown" genes to its offspring. The brown offspring have a better survival rate, which means they are more likely to reproduce. Eventually, this physiological trait becomes common among members of the species. The complete change takes many generations, but even- tually the entire beetle species will be brown (Tooby & Cosmides, 1992). The key in natural selection is that the behaviors have to increase reproductive success, because reproduction and gene transmission drive the whole process. The accu- mulation of chance mutations underlies evolutionary change. Each generation is a product of beneficial modifications from its evolutionary past.

Personality Psychology A personality psychologist could ask many questions about electronic interaction and presentation—such as "Are people who interact extensively with other people via Facebook more or less outgoing than those who do not?" Moreover, how much of people's personality is reflected in their Facebook profiles? Scientific literature consistently finds that people who are extraverted are more likely than introverts to use Facebook and have a wider network of social relationships (Amichai- Hamburger & Vinitzky, 2010; Nadkarni & Hofmann, 2012). Yet introverts are more likely than extraverts to spend more time on Facebook and have a more favorable attitude toward it (Orr et al., 2009).

Health Psychology A very innovative and at least partially successful application of electronic media is using a mobile device to access health information and symptoms of various diseases. A program in San Francisco, California, has phone numbers for people to call if they suspect they have a particular disease, often a sexual disease. The embarrassment of having to ask questions face-to-face is taken away when one can call or text to obtain a health diagnosis anonymously. Clinical Psychology Clinical psychologists can diagnose disorders of technology use but also use the same technologies to help treat people with various kinds of disorders. When do SNSs and other electronic interactions become a problem? Can one become "addicted" to such behavior, and can such interactions become dangerous to those involved? One of the main criteria for a mental illness is that it interferes with everyday life and functioning. If one is online for 10-12 hours a day, is that healthy? What about the danger involved in meeting someone in person whom you know only from online interaction? Sexual predators use these connections to meet victims. They contact potential victims through chat rooms, instant messages, and email. According to one study, one in seven teens (ages 10-17) have been sexually solicited online (Ybarra & Mitchell, 2008).

According to structuralism, breaking down experience into its elemen- tal parts offered the best way to understand thought and behavior. Structural- ists believed that a detailed analysis of experience as it happened provided the most accurate glimpse into the workings of the human mind. Their method was introspection, looking into one's own mind for information about the nature of conscious experience. Structuralists divided each experience into its small- est elements. Wundt, the chief proponent of structuralism, wanted to describe human experience in terms of the elements that combined to produce it (Benja- min, 2007). For example, structuralists, like chemists describing elements, would not describe a peach as "a good peach" but rather would describe their experience with the peach as sweet, round, slightly orange, fuzzy, wet, and juicy.

Influenced by Charles Darwin's theory of natural selection, psychologists who supported functionalism thought it was better to look at why the mind worked the way it did rather than to describe its parts. The functionalists asked, "Why do people think, feel, or perceive, and how did these abilities come to be?" Functionalists used introspection as well. William James, the most famous func- tionalist, relied on introspection as a primary method of understanding how the mind worked. James's and Wundt's methods of introspection were impressive attempts to describe the conscious mind. Eventually, however, introspection failed as a method of science because of difficulties in reaching a consensus as to the nature of certain experiences. Moreover, the rise of psychology as the science of observ- able behavior led to complete rejection of the study of the mind. It also gave way to the rise of behaviorism.

If you become skilled in these activities, or at least in most of them, you will be able to think critically. In particular, you will be able to counter assertions that have little basis in reality, and you will know the difference between sound and faulty reasoning. For instance, the following argument was made by Charles Johnson, a former president of the International Flat Earth Research Society: "Nobody knows anything about the true shape of the world. The known, inhabited world is flat. Just as a guess, I'd say that the dome of heaven is about 4,000 miles away, and the stars are about as far as San Francisco is from Boston."

Instead of simply saying "That's silly," "That's stupid," or "That's just wrong," a critical thinker would examine the claim by analyzing it, evaluating it, and Challenge Your Assumptions True or False? Psychologists agree that most of human thought and behavior cannot be explained by one perspective. True: Human thought and behavior are so complex and determined by so many different factors that no one perspective can fully capture the richness of human psychology. drawing conclusions based on the facts and evidence at hand. A great deal of evidence directly and clearly contradicts the belief that Earth is flat. Just consider these two pieces of evidence: (1) The top of a ship is the last thing we see as it sails out to sea because it is sailing on a sphere rather than on a flat surface (see Figure 6), and (2) images and pho- tographs taken from spaceships and satellites show Earth as a round sphere with half of it shining in the light of the sun.

Behavioral Genetics, Behavioral Neuroscience, and Evolutionary Psychology By the 1980s, more and more psychologists had become receptive to the ideas that who we are and what we do and think are very much influenced by genetic factors (behavioral genetics) and brain activity (behavioral neuroscience), with a long evolutionary past (evolutionary psychology). The roots of this approach lie in many related fields. Recent behavioral genetic research has overturned a long-held notion that genetic influence is set at birth and is unchanging. We now know that genes get turned on and off by experience—that is, genetic influence changes how we think and behave over the course of our lives. Similarly, evolutionary psychology was jump-started in 1992 when John Tooby and Leda Cosmides (1992) published "The Psychological Foundations of Culture" in a seminal book on evolutionary psychology. These developments all began to shift psychology toward a more complex view of the origins of human thought and behavior as products of nature and nurture, enhanced by new brain imaging techniques and the sequencing of the human genome.

Our review of the history of psychological science, summarized in Figure 3, has only scratched the surface of how psychologists think about human thought and behavior, about mind, body, and experience. Debates and theories about how and why we think and act the way we do go back thousands of years. Some of the key debates remain unresolved to this day, primarily because in many cases no one perspective explains the whole story of how things work. These systems of thought have profoundly influenced the development of psychology. Let's now consider the major ways of thinking about mind, body, and experience that have shaped modern psychological science.

The Nature-Nurture Debate For millennia, thinkers have argued over what determines our personality and behavior—innate biology or life experience (Pinker, 2004)—a conflict known as the nature-nurture debate. The nature-only view is that who we are comes from inborn tendencies and genetically based traits. On the one hand, the nature-only position argues that inborn and innate (that is, genetic and biological) qualities are the strongest determinants of thought and behavior. We are born predisposed toward particular personality traits and styles of thinking and behaving. On the other hand, the nurture-only side states that we are all essentially the same at birth and that we are the product of our experiences. As we have already considered, John Locke (1690/1959) popularized the idea that the newborn human mind is a blank slate on which the experiences of life are written. This accumulation of experiences makes us who we are. This view means that anything is possible. You can be anything you want to be. This notion is a very Western, very North American idea. It stands as the cornerstone of democracy, free will, and equality (Pinker, 2002).

Pitting nature against nurture, however, gets us nowhere. It creates a false split, or false dichotomy, that hinders our understanding of the mind and behavior. Almost nothing in psychology can be categorized as either nature or nurture— not learning, not memory, not cognition, not emotion, not even social behavior! These forces work together almost all the time; they are interdependent. Throughout this text, we will point out many cases in which environmental and genetic forces work together to shape who we are (Rutter, 2002). For ex- ample, in the processes of learning and remembering, certain genes in the brain are turned on or off by what happens to us (Kandel, 2006). New connections be- tween brain cells result from these changes in the genes. Consequently, the brains of people and animals reared in richly stimulating environments differ from the brains of people reared in understimulating, neglectful, or abusive environments. What we are born with and what we are exposed to interact to create thought and behavior. For decades, many psychologists have shied away from the idea of an interrelationship, clinging to the nature-nurture debate. Old habits die hard. To fully appreciate human behavior, we must take a broader view. All creatures are born with genetic instructions, but even before birth environmental factors alter the ways in which genes are expressed. Throughout life, genetic factors, such as a familial predisposition toward anxiety, assert themselves. Rather than pitting nature against nurture, we prefer the phrase nature through nurture, whereby the environment—be it the womb or the world outside—interacts continuously with biology to shape who we are and what we do (Begley, 2007; Pinker, 2004; Ridley, 2003).

Critical thinking and its cousin, scientific thinking, both involve being able to think metacognitively. Metacognitive thinking requires the ability first to think and then to reflect on one's own thinking (Feist, 2006b; Kuhn & Pearsall, 2000). People who can think metacognitively are able to question their own thinking (see Figure 7). This ability is not universal, however. Without specific training, many people find it difficult to question their own thinking. If one were able to do so as a matter of course, one could more readily dismiss a line of thinking as wrong when it was not supported by evidence.

Science tests our assumptions against observation from the real world. Think about it: People thought the world was flat until explorers began to map out the surface of the Earth. Because it is based on skepti- cism, the scientific view encourages critical thinking—that is, not believing every- thing we think. By comparing our assumptions with real-world observation, science helps us choose among competing explanations of behavior. For example, one re- cent popular theory has been that something in childhood vaccines causes autism. Over the last 10 years, scientists have conducted many studies of the vaccine-autism explanation and have found no support for it. As we discuss in the research ethics section of "Conducting Research in Psychology," the original study on which the argument had been based turned out to be fraudulent, consisting of false data.

Second, mental processes returned to psychology full force in the 1950s and 1960s—just when the influence of behaviorism was at its peak. The new emphasis was really a forgotten focus on the processes that fascinated Fechner, Wundt, and Helmholtz in the 19th century: sensation, perception, and mental processes. The term mental, however, had lost its appeal. Instead, a new word for thought and mental processes appeared: cognition (Benjamin, 2007; Gardner, 1987). By the 1960s, the field of cognitive science had been born, with a focus on the scientific study of thought (Gardner, 1987). In addition to freeing itself from the label mental, cognitive science made use of a new modern metaphor for the human mind—the computer. A fairly recent innovation at the time, the computer seemed to have a lot in common with the human mind. Computers store, retrieve, and process information, just as the brain stores, retrieves, and processes sensations, memories, and ideas. Sensation was the input; perception was the interpretation and processing of the input; and behavior and thoughts were the output. By the 1980s, cognitive science had combined many disciplines in addition to psychology—namely, linguistics, philosophy, anthropology, artificial intelligence, and neuroscience (Gardner, 1987).

Some of the thinking in this new cognitive movement was based on a book by the British psychologist Frederick Bartlett (1886-1969). Bartlett wrote that memory is not an objective and accurate representation of events but rather a highly personal reconstruction based on one's own beliefs, ideas, and point of view. For example, racial-ethnic stereotypes are frameworks that can alter memory (Graham & Lowery, 2004). If a witness to a crime holds a bias about how likely a crime is to be perpetrated by a person of a certain racial-ethnic background, the witness may misremember the appearance of the accused. This example illustrates that, as Bartlett argued, when people remember, they recon- struct experience in terms of what is most relevant to them rather than providing an unbiased account of events. Bartlett showed that our cognitive frameworks organize how we experience the world. This view is now well accepted in psychology, though Bartlett's insights were unappreciated in the United States for decades (Benjamin, 2007).

One important principle of psychophysics is that the perception of physical properties is not the same as the physical properties themselves. To demonstrate, let's consider the classic question, What weighs more, a pound of feathers or a pound of bricks? You might be thinking, How dumb do they think I am? I've heard that so many times. They weigh the same! A pound is a pound. Maybe, for that answer is true only for the objective, physical property of weight. The perceived weight of the two—a psychological property—would be very different. Research- ers found that, when people's estimates of the weights of both items are empiri- cally tested, contrary to common sense, people think a pound of bricks weighs two to three times as much as a pound of feathers (Benjamin, 2007). If you don't believe us, try it for yourself.

Structuralism and Functionalism What is the best way to understand the human mind, by examining its parts or its function? In the last decades of the 1800s, psychology weathered its first major scientific debate, with two different perspectives on how to study thought and behavior. The field was divided over whether it was more important to study the elements or the func- tions behind human thought and behavior. Focus on the elements of mind led to the school of thought known as structuralism, whereas focus on the func- tions of mind led to the school of thought known as functionalism. Edward Titchener (1867-1927), a British American psychologist trained by Wilhelm Wundt, coined both terms.

Behavioral measures involve the systematic observation of people's actions either in their normal environment (that is, naturalistic observation) or in a laboratory setting. A psychologist interested in aggression might bring people into a laboratory, place them in a situation that elicits aggressive behavior, and video- tape the responses. Afterward, trained coders observe the videos and, using a prescribed method, code the level of aggressive behavior exhibited by each per- son. Training is essential for the coders, so that they can evaluate the video and apply the codes in a reliable, consistent manner. Behavioral measures are less susceptible to social desirability bias than are self-report measures. They also provide more objective measurements, because they come from a trained outside observer, rather than from the participants them- selves. This is a concern for researchers on topics for which people are not likely to provide accurate information in self-report instruments. In the study of emotion, for example, measuring facial expressions from video reveals things about how people are feeling that they might not reveal on questionnaires (Rosenberg & Ekman, 2000). One drawback of behavioral measures is that people may modify their behavior if they know they are being observed and/or measured. The major drawback of behavioral measurement, however, is that it can be time-intensive; it takes time to train coders to use the coding schemes, to collect behavioral data, and to prepare the coded data for analysis. As a case in point, one of the most widely used methods for coding facial expressions of emotion requires intensive training, on the order of 100 hours, for people to be able to use it correctly (Ekman, Friesen, & Hager, 2002)! Moreover, researchers can collect data on only a few participants at once, and therefore behavioral measures are often impractical for large-scale studies. Physiological Measures Physiological measures provide data on bodily responses. For years, researchers relied on physiological information to index possible changes in psychological states—for example, to determine the magnitude of a stress reaction. Research on stress and anxiety often measures electrical changes in involuntary bodily responses, such as heart rate, sweating, and respiration, as well as hormonal changes in the blood that are sensitive to changes in psychological states. Some researchers measure brain activity while people perform certain tasks to deter- mine the speed and general location of cognitive processes in the brain. We will look at specific brain imaging technologies in the chapter "The Biol- ogy of Behavior". Here we note simply that they have enhanced our understanding of the brain's structure and function tremendously. However, these technologies, and even more simple ones, such as the measurement of heart rate, often require specialized training in the use of equipment, collection of measurements, and in- terpretation of data. Further, some of the equipment is expensive to buy and main- tain. Outside the health care delivery system, only major research universities with medical schools tend to have them. In addition, researchers need years of training and experience in order to use these machines and interpret the data they generate. Once researchers collect data, they must make sense of them. Raw data are difficult to interpret. They are, after all, just a bunch of numbers. It helps to have some way to organize the information and give it meaning. To make sense of in- formation, scientists use statistics, mathematical procedures for collecting, analyzing, interpreting, and presenting numeric data. For example, researchers use statistics to describe and simplify data and to understand how variables relate to one another. There are two classes of statistics: descriptive and inferential.

The first step in understanding research results involves calculating descriptive statistics, which simply tell researchers the range, average, and variability of the scores. For instance, one useful way to describe data is by calculating the center, or average, of the scores. There are three ways to calculate an average— the mean, median, and mode. The mean is the arithmetic average of a series of numbers. It is calculated by adding all the numbers together and dividing by the number of scores in the series. An example of a mean is your GPA, which aver- ages the numeric grade points for all of the courses you have taken. The median is the middle score, which separates the lower half of scores from the upper half. The mode is the most frequently occurring score. Sometimes scores vary widely among participants, but the mean, median, and mode do not reveal anything about how spread out—or how varied—scores are. For example, one person's 3.0 GPA could come from getting B's in all his courses, while another person's 3.0 could result from getting A's in half her classes and C's in the other half. The second student has much more variable grades than the first. The most common way to represent variability in data is to calculate the standard deviation, a statistical measure of how much scores in a sample vary around the mean. A higher standard deviation indicates more variability (more spread); a lower one indicates less variability (less spread). In the example, the student with all B's would have a lower standard deviation than the student with A's and C's. Another useful way of describing data is by plotting, or graphing, their fre- quency. Frequency is the number of times a particular score occurs in a set of data. A graph of frequency scores is known as a distribution. To graph a distribu- tion, we place the scores on the horizontal axis, or X-axis, and their frequencies on the vertical axis, or Y-axis. When we do this for many psychological variables, such as intelligence or personality, we end up with a very symmetrical shape to our distribution, which is commonly referred to as either a normal distribution or a "bell curve"—because it looks like a bell (see Figure 14). Let's look at a concrete example of a normal distribution with the well- known intelligence quotient (IQ). If we gave 1,000 children an IQ test and plotted all 1,000 scores, we would end up with something very close to a symmetrical, bell-shaped distribution. Very few children would score 70 or below, and very few children would score 130 or above. These are infrequent or rare scores. The ma- jority of children would be right around the average, or mean, of 100. In fact, two-thirds (68%, to be exact) would be within 1 standard deviation (15 points) of the mean. These are frequent or common scores. Moreover, about 95% would be within 2 standard deviations, or between 70 and 130. How do we know this? We know it because we know the exact shape of a normal distribution in the general population of people being studied. Know- ing the shape of the distribution allows us to make inferences from our specific sample to the general population. For example, because a normal distribution has a precise shape, we know exactly what percentage of scores is within 1 standard deviation of the mean (68%) and how many are within 2 standard deviations of the mean (95%). This is why we know that a mean IQ score of 70 or lower or 130 or higher occurs only 5 times in 100—both are very unlikely to occur by chance. This quality of allowing conclusions or inferences to be drawn about populations is the starting point for the second class of statistics, inferential statistics.

Is physics a science? Few would argue that it is not. What about biology? Psychology? Astrology? How does one decide? Now that we have looked at some of the components of science and explored their limitations, let's consider the larger question: What is science? People often think only of the physical sciences as "science," but science comes in at least three distinct flavors (Feist, 2006b): physical science, biological science, and social science. As we mentioned in the chapter "Introduction to Psychology", psychology is a social science (see Figure 1).

The physical sciences study the world of things—the inanimate world of stars, light, waves, atoms, the Earth, compounds, and molecules. These sciences include physics, astronomy, chemistry, and geology. The biological sciences study plants and animals in the broadest sense. These sciences include biology, zoology, genetics, and botany. Finally, the social sciences study humans, both as individuals and as groups. These sciences include anthropology, sociology, economics, and psychology. Science is as much a way of thinking or a set of attitudes as it is a set of procedures. Scientific thinking involves the reasoning skills required to generate, test, and revise theories (Koslowski, 1996; Kuhn, Amsel, & O'Loughlin, 1988; Zimmerman, 2007). What we believe or theorize about the world and what the world is actually like, in the form of evidence, are two different things. Scientific thinking keeps these two things separate. In other words, scientists remember that belief is not the same as reality.

There are three attitudes central to scientific thinking. The first is to ques- tion authority—including scientific authority. Be skeptical (see Figure 2). Don't just take the word of an expert; test ideas yourself. The expert might be right, or not. That advice extends to textbooks—including this one. Wonder. Question. Ask for the evidence. Be a critical thinker. Also question your own ideas. Make your own observations—be empirical. Our natural inclination is to really like our own ideas, especially if they occur to us in a flash of insight. As one bumper sticker extols, "Don't believe everything you think." Believing something does not make it true.

The second attitude of science is open skepticism (Sagan, 1987). Doubt and skepticism are hallmarks of critical and scientific reasoning. The French philosopher Voltaire put scientific skepticism most bluntly: "Doubt is uncomfortable, certainty is ridiculous"; however, skepticism for skepticism's sake is also not scientific, but stub- born. Scientists are ultimately open to accepting whatever the evidence reveals, how- ever bizarre it may be and however much they may not like it or want it to be the case. For example, could placing an electrical stimulator deep in the brain, as if it were a switch, turn off depression? That sounds like a far-fetched treatment, worthy of skep- ticism, but it does work for some people (Mayberg et al., 2005). Confirming Voltaire's assertion that doubt is uncomfortable, brain imaging evidence suggests that doubt and skepticism are associated with areas of the brain involved in the sensation of taste and disgust (and belief with reward and pleasure), so doubt is a less pleasant state than belief (Harris, Sheth, & Cohen, 2008; Harris et al., 2009; Shermer, 2011).

Research can also lead us to surprising findings, sometimes challenging our most basic assumptions. For example, a young neuroscientist named Helen May- berg parted paths with most of her colleagues and did not focus on drug therapies to treat depression. She focused instead directly on the brain. In so doing she stum- bled on a surprising and counterintuitive discovery: A particular part of the brain is overactive in depressed people (Mayberg, 1997, 2003). She went on to pioneer treatment for depression by stimulating the part of the brain that was overactive. There is a psychology behind the science of psychology, and there are per- sonal stories for every discovery (Feist, 2006b). Seeing the dynamic and often personal side of psychological science leads to a better appreciation of how psy- chological science came about and may help you challenge assumptions to break new ground.

To bring together the various perspectives, we also explicitly connect theories and findings throughout the text. Seeing connections is a creative act, and psy- chological ideas and research findings are connected sometimes in obvious ways and sometimes in surprising ways. Learning to bring together ideas is an im- portant part of learning to think critically. To facilitate this skill, we connect concepts both within and between chapters, as we just did with deep brain stimu- lation and depression. We do so by means of a "Connection" note alongside the primary narrative, in which we provide section, chapter, and page number to fa- cilitate easy access to these related ideas. By regularly returning to ideas from the same or different chapters, we can put them in a different context. As a way of reviewing and connecting all of the important topics in each chapter, but in an applied way, we end each chapter with a section titled "Bringing It All Together". In this section, we explore one topic that brings together most of the main concepts and ideas in the chapter. For example, in this chapter, we con- sider how psychologists in different subfields of psychology have begun to study the effects of electronic social interactions on human behavior.

Science involves more than common sense, logic, and pure observation. Although reason and sharp powers of observation can lead to knowledge, they have limi- tations. Consider common sense, the intuitive ability to understand the world. Often common sense is quite useful: Don't go too close to that cliff. Don't rouse that sleeping bear. Don't eat food that smells rotten. Sometimes, though, common sense leads us astray. In psychology, our intuitive ideas about people's behavior are often contradictory or flat-out wrong. For example, most of us intuitively believe that who we are is influenced by our parents, family, friends, and society. It is equally obvious, especially to parents, that children come into the world as unique people, with their own temperaments, and people who grow up in similar environments do not have identical personalities. To what extent are we the prod- ucts of our environment, and how much do we owe to heredity? Common sense cannot answer that question, but science can. Rationalism is the view that using logic and reason is the way to under- stand how the world works. Logic is also a powerful tool in the scientist's arsenal, but it can tell us only how the world should work, not how the world actually works. Sometimes the world is not logical. A classic example of the shortcoming of logic is seen in the work of the ancient Greek philosopher Aristotle. He argued that heavier objects should fall to the ground at a faster rate than lighter objects. Sounds reasonable, right? Unfortunately, it's wrong. For 2,000 years, however, the argument was accepted simply because the great philosopher Aristotle wrote it and it made intuitive sense. It took the genius of Galileo to say, "Wait a minute. Is that really true? Let me do some tests to see whether it is true." He did and dis- covered that Aristotle was wrong (Crump, 2001); the weight of an object does not affect its rate of speed when falling. Science combines logic with research and experimentation.

Recall from The Origins of Psychology (in chapter "Introduction to Psychology") that empiricism is the view that our observations and experience, not pure rea- son and logic, are another path to knowledge. Science is empirical in that it is based on observations and experience. Science relies on observation, but even observation can lead us astray. Our knowledge of the world comes through our five senses, but they can be fairly easily fooled, as any good magician or artist can demonstrate—and as we explore in some detail in the chapter "Sensing and Perceiving Our World". Even when we are not being intentionally fooled, the way in which our brains organize and interpret sensory experiences may vary from person to person. Another problem with observation is that people tend to generalize from their observations and assume that what they witness in one situation applies to all similar situations. Imagine you are visiting another country for the first time. Let's say the first person you have any extended inter- action with is rude, and a second, briefer interaction goes along the same lines. Granted, you have lots of language difficulties; nevertheless, you might conclude that all people from that country are rude. After all, that has been your ex- perience. Those, however, were only two interactions, and after a couple of days you might meet other people who are quite nice. The point is that one or two cases are not a solid basis for a generalization. Scientists must collect numerous observations and conduct several studies on a topic before generalizing their conclusions.

Although collecting observations and conducting research help us choose one viewpoint over another, sometimes more than one perspective can be correct. Con- sider the psychological disorder of schizophrenia. For years people attributed the development of this disorder mostly to upbringing, arguing for a pure "nurture" expla- nation. Then biological explanations, such as an imbalance of particular neurotrans- mitters, became fashionable. The most recent research suggests that schizophrenia emerges from an interaction of biological and environmental influences—in a very real sense, elements of both explanations are correct (Moffitt, Caspi, & Rutter, 2005). The more open we are to diverse perspectives, the better able we will be to explain the whole and often surprising picture of human behavior.

We believe strongly that modern psychological science tells us that we must combine multiple perspectives in order to come to a complete understanding of human thought and behavior. One of the overarching themes of multiple per- spectives is the proverbial nature-nurture question. Psychological science shows that almost every fundamental aspect of human behavior—whether it is brain development, learning, intelligence, perception, personality, social behavior, or psychological disorders—develops from a complex interplay of biological and environmental forces, of nature and nurture.

PSYCHOLOGICAL PERSPECTIVES: EXPLAINING HUMAN BEHAVIOR One of the primary functions of science is to describe and explain how the world works. Psychologists attempt to explain how human thought, emotion, motivation, and behavior work. Yet, people are so complex that many different perspectives have developed on how to best explain human thought and behavior. These perspectives make different assumptions and focus on different aspects of behavior. In psychology, there are at least seven major perspectives that explain human behavior. These perspectives are distinct but can be and sometimes are integrated. After all, it's not all black and white.

Psychoanalytic-Psychodynamic Beginning with Freud, psychoanalytic and then later the psychodynamic approaches focus on the importance of early childhood experience and relationships with parents as guiding forces that shape personality development. Additionally, this view sees the unconscious mind and motives as much more powerful than the conscious awareness. Psychoanalysis traditionally used dream interpretation and uncovering the unconscious thoughts, feelings, and impulses as a main form of treatment of neurosis and mental illness.

The third scientific attitude is intellectual honesty. When the central tenet of knowing is not what people think and believe, but rather how nature behaves, then we must accept the data and follow them wherever they take us. If a re- searcher falsifies results or interprets them in a biased way, then other scientists will not arrive at the same results if they repeat the study. Every so often we hear of a scientist who faked data in order to gain fame or funding. For the most part, however, the fact that scientists must submit their work to the scrutiny of other scientists helps ensure the honest and accurate presentation of results. All sciences—whether physics, chemistry, biology, or psychology—share the general properties of open inquiry that we have discussed. Let's now turn to the spe- cific methods scientists use to acquire new and accurate knowledge of the world. Science depends on the use of sound methods to produce trustworthy results that can be confirmed independently by other researchers. The scientific method by which scientists conduct research consists of five processes: Observe, Predict, Test, Interpret, and Communicate (O-P-T-I-C; see the Research Process for this chapter, Figure 3). In the observation and prediction stages of a study, researchers develop expectations about an observed phenomenon. They express their expectations as a theory, defined as a set of related assumptions from which testable predictions can be made. Theories organize and explain what we have observed and guide what we will observe (Popper, 1965). To put it simply, theories are not facts—they explain facts. Our observations of the world are always either unconsciously or consciously theory-driven, if you understand that theory in this broader sense means little more than "having an expectation." In science, however, a theory is more than a guess. Scientific theories must be tied to real evidence, they must organize observations, and they must generate expectations that can be tested systematically. A hypothesis is a specific, informed, and testable prediction of what kind of outcome should occur under a particular condition. For example, consider the real- life study that suggests that caffeine increases sex drive in female rats (Guarraci & Benson, 2005). The hypothesis may have been phrased this way: "Female rats that consume caffeine will have more couplings with male rats than female rats that do not consume caffeine." This hypothesis predicts that a particular form of behavior (coupling with male rats) will occur in a specific group (female rats) under particular conditions (the influence of caffeine). The more specific a hypothesis is, the more eas- ily each component can be changed to determine what effect it has on the outcome. To test their hypotheses (the third stage of the scientific method), scientists select one of a number of established research methods, along with the appropri- ate measurement techniques. Selecting the methods involves choosing a design for the study, the tools that will create the conditions of the study, and the tools for measuring responses (such as how often each female rat allows a male to mount her). One basic principle of all scientific research is that measures and tools need to be both reliable and valid. Reliability means the test or measure gives us a consistent result over time or between different raters. Validity means when a scientist claims to measure a particular concept, such as sex drive for example, she really is measuring that concept and not something else. We will examine each of these elements in the next section "Research Designs in Psychology". In the fourth step of the scientific method, scientists use mathematical tech- niques to interpret the results and determine whether they are significant (not just a matter of chance) and whether they closely fit the prediction. Do psycholo- gists' ideas of how people behave hold up, or must they be revised? Let's say that the caffeine-consuming female rats coupled more frequently with males than did nonconsuming females. Might this enhanced sexual interest hold for all rats or just those few we studied? Statistics, a branch of mathematics we will discuss shortly, helps answer that question. The fifth stage of the scientific method is to communicate the results. Gener- ally, scientists publish their findings in a peer-reviewed professional journal. Follow- ing a standardized format, the researchers report their hypotheses, describe their research design and the conditions of the study, summarize the results, and share their conclusions. In their reports, researchers also consider the broader implica- tions of their results. What might the effects of caffeine on sexuality in female rats mean for our understanding of caffeine, arousal, and sex in female humans? Publi- cation also serves an important role in making research findings part of the public domain. Such exposure not only indicates that colleagues who reviewed the study found it to be credible but also allows other researchers to repeat and/or build on the research. It is important to point out, however, that not all published scientific papers are of equal quality (that is, use equally reliable and valid measures and techniques).

As when reading any kind of information, one should always ask "how did they come to that conclusion?" and "on what evidence did they draw that conclusion?" Replication is the repetition of a study to confirm the results. The advance- ment of science hinges on replication. No matter how interesting and exciting results are, if they cannot be duplicated, the original findings may have been ac- cidental. Whether a result holds or not, new predictions can be generated from the data, leading in turn to new studies. For example, recently, a team of more than 50 social psychologists from around the world replicated 13 classic findings in so- cial psychology and found that although 10 of the 13 findings were replicated, the strength of the findings decreased (Klein et al., 2014). Three did not replicate and the field now knows that they were by chance and cannot be trusted. The other 10 findings are real (if a bit smaller in size) and can be built upon. This finding confirms the cumulative nature of scientific progress. What Science Is Not: Pseudoscience Do you believe that the planets and stars determine our destiny, that aliens have visited Earth, or that the human mind is capable of moving or altering physical objects? Astrology, unidentified flying objects (UFOs), and extrasensory percep- tion (ESP) are certainly fascinating topics to ponder. As thinking beings, we try to understand things that science may not explain to our satisfaction. Many of us are willing to believe things that science and skeptics easily dismiss. For ex- ample, in 2015 a Chapman University poll of 1,500 representative American adults found the following (Ledbetter, 2015): Fifty percent endorsed at least one paranormal belief (e.g., ghosts, ESP, astrology, etc.). Forty-one percent believed that spirits inhabit haunted places. Twenty-sevenpercentbelievethedeadcancommunicate with the living. Twenty-one percent believe aliens have visited Earth. Similarly, a 2015 survey of of more than 1,000 American adults reported that 72% believed in angels, 42% in demonic possession, and 62% believed the Earth was made 6,000 years ago (creationism), only 45% believed in the theory of evolution, and 56% believed in UFOs (What People, 2009). People often claim there is "scientific evidence" for cer- tain unusual phenomena, but that does not mean the evidence is truly scientific. There is also false science, or pseudosci- ence. Pseudoscience refers to practices that appear to be and claim to be science but, in fact, do not use the scientific method to come to their conclusions. What makes something pseudoscientific comes more from the way it is studied than from the content area. According to Derry (1999) pseudosci- ence practitioners 1. make no real advances in knowledge, 2. disregardwell-knownandestablishedfactsthat contradict their claims, 3. do not challenge or question their own assumptions, 4. tend to offer vague or incomplete explanations of how they came to their conclusions, and 5. tend to use unsound logic in making their arguments (see Figure 4). Philosophy, art, music, and religion, for instance, are not pseudosciences be- cause they do not claim to be science. Pseudoscientific claims have been made for alchemy, creation science, intelligent design, attempts to create perpetual motion ma- chines, astrology, alien abduction, psychokinesis, and some forms of mental telepathy. Perhaps the most pervasive pseudoscience is astrology, which uses the posi- tions of the sun, moon, and planets to explain an individual's personality traits and to predict the future. There simply is no credible scientific evidence that the posi- tions of the moon, planets, and stars and one's time and place of birth have any in- fluence on personality or life course (Hartmann, Reuter, & Nyborga, 2006; Shermer, 1997; Zarka, 2011), yet about one in four American adults believe in astrology. Overall, telekinesis, astrology, alien abduction explanations of UFOs, and cre- ation science, to name a few, meet the criteria for pseudoscience. For instance, as- trology or ESP as fields of study are very much the same in their knowledge and ideas as they were 50 years ago, neither doubts and questions their own assumptions, methods, or results, and the conclusions are often vague and non-testable. In all fair- ness, there have been some peer-reviewed reliable observations of UFOs and some scientifically sound evidence for precognition (anticipating the future) and telepa- thy (Bem, 2011; Bem & Horonton, 1994; Bem, Palmer, & Broughton, 2001; Rosenthal, 1986). However, other attempts to replicate these findings have not been successful (Galak, LeBeouf, Nelson, & Simmons, 2012; Rouder & Morey, 2011). Had they been replicated, we would be forced to accept them, at least tentatively. Remember, open skepticism is the hallmark of science. If there is scientifically sound evidence for something—even if it is difficult to explain—and it has been replicated, then we have to accept it. The key is to know how to distinguish sound from unsound evidence.

Social Psychology More than just about any other area of psychology, social psychology lends itself to a rich set of research questions regarding electronic interactions. Texting in particular and mobile device use in general are the primary tools for staying connected to friends and peers (Harris Interactive, 2008; Walsh et al., 2009). One of the first Internet applications for social purposes was online dating services. Such forms of electronic interaction may be a preferred method of contact for people with high social anxiety (Stevens & Morris, 2007). Although most people who use online dating services tend to be over 30, college-age teens and young adults are increasingly using them as well (Stevens & Morris, 2007; Valkenburg & Peter, 2007b). Contrary to what some people originally thought, however, electronic interactions cannot easily be used to hide one's "real personality" and to avoid ever having real face-to-face contact with others. Research on this phenomenon suggests that people use the Internet not simply to interact with others from afar but also to arrange real face-to-face meetings (Couch & Liamputtong, 2008).

Electronic interactions have led to new behaviors and language as the boundaries between public and pri- vate have broken down. For instance, being privately public means connecting with many other people while being relatively nonpublic about revealing who you are. Being publicly private means you disclose a lot of details of your private life and may or may not limit access to your site (Lange, 2008). Another electronic behavior is "friending," which raises ancient issues of being "popular," socially excluded, rejected, or accepted. In one tragic case of online rejection, a 13-year-old girl was so distraught over being rejected by a boy online that she committed suicide. The even greater tragedy, however, was that the boy did not exist: A neighbor's mother allegedly had made him up to get back at the girl for making disparaging remarks about her daughter.

Twin-Adoption Studies The best way to untangle the effects of genetics and twin-adoption studies environment is to study twins who are adopted or not and compare them to other siblings who are adopted or not, which is what twin-adoption studies do. We will be discussing twin-adoption research throughout the rest of the book, so it is important that you understand the logic of how these studies tease apart the ex- tent to which nature and nurture is involved in creating Research into hereditary influence on twins, both identical and frater- nal, who were raised apart (adopted) and who were raised together. differences or similarities between people. The easiest way to understand how twin-adoption research teases nature and nurture effects apart is to realize that there are three forms of similarity: genetic (nature), environmental (nurture), and trait. Genetic similarity varies based on degree of rela- tionship, for example in cases of twins, siblings, and par- ents and their children. Genetic similarity ranges from 100% with identical twins (split from a single egg) to 0% with unrelated people, such as adopted siblings. In be- tween 100% and 0% we have fraternal twins (two eggs fertilized by two sperm), siblings, and parents and their children. These all share 50% of their genes. Environments vary in many ways, the most ob- vious being raised in the same house (together) or not (apart). Researchers who make use of twin-adoption methods then look for how similar or different these dif- ferent groups are on a given trait in order to calculate how much of the variation in that trait is due to genetic influence, or its heritability. ©Monkey Business Images/Shutterstock.com Twins form a natural population for teasing apart the influences of genetics and environment on development. Researchers cannot for obvious reasons assign people to different genetic or environmental conditions to see what effect each one has on a trait. So they turn to what exists in nature to tease the two apart. The logic of all of this is laid out in Figure 12. Let's just take two of these hypothetical cases from Figure 12. First, if identical twins (100% genetically alike) are raised apart (different envi- ronments) and yet they still are very similar on certain traits such as their height, weight, intelligence, or personality, then we would know that genes play a large role in the variation of those traits. Likewise, if adopted siblings (0% genetically alike) who are raised together (same environment) share strong similarities on these traits, then we have to conclude that environment plays a large role in the variation of those traits.

Gene-by-Environment Studies The second technique in the study of herita- bility, gene-by-environment interaction research, allows researchers to as- sess how genetic differences interact with the environment to produce certain behavior in some people but not in others (Moffitt, Caspi, & Rutter, 2005; Thapar, Langley, & Asherson, 2007). Instead of using twins, family members, and adoptees to vary genetic similarity, gene-by-environment studies directly measure genetic variation in parts of the genome itself and examine how such variation interacts with different kinds of environments to produce different behaviors or traits. Meta-Analysis As powerful as results may be from an individual study, the real power of sci- entific results comes from the cumulative overall findings from all studies on a given topic. If a topic or question has been sufficiently studied, researchers may choose to stand back and analyze all the results of the numerous studies on a given topic. For example, a researcher interested in the effects of media violence on children's aggressive behavior might want to know what all of the research— not just one or two studies—suggests. Meta-analysis is a quantitative method for combining the results of all the published and even unpublished results on one question and drawing a conclusion based on the entire set of studies on the topic. To do a meta-analysis, the researcher converts the findings of each study into a standardized statistic known as effect size. Effect size is a measure of the strength of the relationship between two vari- ables. The average effect size across all studies reflects what the literature overall says on a topic or question. For example, a meta-analysis of 28 different studies from the United States, Europe, and Asia compared technology-based learning (e.g., tablets, laptops, and smart phones) to traditional non-technology-based instruction and found that students using tablets learned better than those without. The aver- age effect size for these 28 studies was 0.23, meaning that students using tablets scored 0.23 of a standard deviation (the average variation around the mean) higher on learning outcomes compared to students with no tablets (Tamin et al., 2015). (See "Making Sense of Data with Statistics" later in this chapter.) In short, meta-analysis tells us whether all of the research on a topic has or has not led to consistent findings and what the effect size is. It is more reliable than the results of any single study. Big Data More than 1 billion of the world's 7 billion people use some form of social media (Facebook, Twitter, Instagram, and others). With the increase in storage and speed of the Internet and the proliferation of mobile apps, a whole new way of col- lecting data on human behavior has arisen—so-called "big data." Big Data con- sists of the extremely vast amounts of information from websites and apps that is collected and analyzed by unusually large and sophisticated computer programs. Big Data come mostly from social media, smartphones, and wearable devices, but sometimes from the scientific literature itself (Augur, 2016). In psychology, compared to the traditional survey, questionnaire, and even experimental techniques, Big Data afford a much more extensive and reliable means of measuring interests, social relationships, personality, emo- tion, political attitudes, exercise behaviors, brain activity and structure, and language just to name a few (Schwartz & Ungar, 2015). For example, Tan and colleagues (2016) used Big Data to find and narrow down all brain studies on hippocampus size (a brain structure most notably associated with learning and memory) and gender. By doing so, they narrowed the field down to 76 studies with more than 6,000 participants. Further, using meta-analysis, once they con- trolled for overall brain size (because men are larger and have larger overall big data Extremely large amount of data captured from online behaviors (especially social media), which are then collected and analyzed for patterns by sophisticated analytic programs. 56 CHAPTER 2 Conducting Research in Psychology brains), the researchers found there was no size difference in the hippocampi of men and women, further eroding the assumption that men and women have dif- ferent brains. This study took advantage of both Big Data and meta-analysis. Quick Quiz 2: Research Methods in Psychology 1. Dr. Lovejoy wanted to do research on real-world conditions that lead to aggression in 10-year-old children, defining aggression as "intent to harm another person." She went to a local elementary school and videotaped a 10-minute recess period. She and her trained coders then coded the behavior of every child and counted the number of times each child acted aggressively. This is an example of what kind of research design? a. descriptive c. case study b. correlational d. experimental 2. If Dr. Lovejoy wanted to examine whether certain person- ality traits make aggression more likely, she would prob- ably use what kind of research design? a. descriptive b. correlational c. interview d. experimental 3. Researchers have consistently found that married men live longer than single men. From this finding, we can conclude that a. if a man gets married, he adds years to his life. b. marriage causes men to live longer. c. being single causes men to die earlier. d. marriage correlates with longer life in men. 4. In research on whether sugar causes hyperactivity, re- searchers randomly assign children to receive no sugar, small amounts of sugar, or large amounts of sugar. They then observe and code activity levels. In this case, the sugar level is the a. outcome variable. b. dependent variable. c. independentvariable. d. control condition. 5. In contrast to other kinds of research designs, a true ex- perimental design must have two things: a. random assignment of participants to conditions and statistical analysis. b. random assignment of participants to conditions and manipulation of an independent variable. c. manipulation of an independent variable and a dependent variable. d. hypothesis testing and observation. Answers can be found at the end of the chapter. CHALLENGING ASSUMPTIONS IN THE OBJECTIVITY OF EXPERIMENTAL RESEARCH You don't have to be a scientist to understand that it would be wrong and unethi- cal for an experimenter to tell participants how to behave and what to do. Even for the participants to know what group they are in or what the hypotheses of the study are is bad science and biases behavior. Can what the experimenter knows change the behavior of the participants? In a classic case of scientific serendipity, Robert Rosenthal's PhD thesis challenged the assumption that experimenters who randomly assign animals or people to conditions and manipulate an independent variable are being quite objective—that is, these procedures assure objective results. He discovered the assumption of objectivity was wrong when he set out to conduct a study on per- ceived success and intelligence. Rosenthal hypothesized that people who believed they were successful would be more likely to see success in others. To test this idea, he conducted an experiment in which he told one group of participants they had done well on an intelligence test and another group they had done poorly on an intelligence test. Rosenthal randomly assigned participants to be in one of these conditions (there was also a neutral control condition in which participants received no feedback on the intelligence test). Then he asked all groups to look at photographs of people doing various tasks and rate how successful they thought the people in the photos were. He reasoned that people who are told they did well on an intelligence test should see more success in photographs of people doing various tasks than people who are told they did not do well on the test. As a good scientist, Rosenthal compared the average test scores of the par- ticipants assigned to different conditions before giving them any feedback on their performance—that is, before the experimental treatment. The reason is simple: If the treatment causes a difference in behavior for the different groups, the researcher needs to make sure the groups started out behaving the same way before treatment. To Rosenthal's dismay, the groups did differ before receiving treatment. They were also different in exactly the way that favored his hypothesis! Given random assignment, the only difference in the groups at the outset was Rosenthal's knowledge of who was in which group. Somehow, by knowing who was in which group, he created behaviors that favored his hypothesis. He was forced to conclude that, even when trying to be "scientific" and "objective," researchers bias results unintentionally in their favor by subtle voice changes or gestures. Instead of having a wonderful "aha moment" of scientific discovery, Rosenthal had more of an "oh no" moment: "What I recall was a panic experience when I realized I'd ruined the results of my doctoral dissertation by unintention- ally influencing my research participants to respond in a biased manner because of my expectations" (Rosenthal, personal communication, April 18, 2010). Rosenthal decided to systematically study what he came to call experimenter expectancy effects. Through several experiments, he confirmed that experi- menter expectancies can ruin even the best-designed studies. Also, he discovered that two other surprising factors can change the outcome of the study as well. First, if the study involves direct interaction between an experimenter and par- ticipants, the experimenter's age, ethnicity, personality, and gender can influence the participants' behavior (Rosenthal, 1976). Second, Rosenthal stumbled upon a more general phenomenon known as self-fulfilling prophecy. A self-fulfilling prophecy occurs when our belief or expectation that something is going to hap- pen unknowingly makes it happen. For example, if research assistants know the study's hypothesis, they may unconsciously affect the behavior of the participants and make the predicted outcome more likely to happen. Or if a teacher does not expect a student to do very well and then ignores that student, the student may well not do well, fulfilling the expectation of the teacher. Ten years after Rosenthal's first publication on experimenter expectancy effect, more than 300 other studies confirmed his results (Rosenthal & Rubin, 1978). Such expectancies affect animal participants as well as humans (Jussim & Harber, 2005; Rosenthal & Fode, 1963). Rosenthal's demonstration of experi- menter expectancy effects and self-fulfilling prophecies also led to the develop- ment of double-blind procedures in science. Think about it: If what experimenters know about a study can affect the results, then they'd better be as blind to experi- mental conditions as the participants are. All of this came to be because Rosen- thal "messed up" his dissertation and unintentionally challenged the assumptions of the best way to conduct scientific experiments. Quick Quiz 3: Challenging Assumptions in the Objectivity of Experimental Research 1. One explanation for experimenter expectancy effect is a. double-blind studies. b. self-fulfilling prophecy. c. confoundingvariables. d. experimental manipulation. Answers can be found at the end of the chapter. 2. The best way to lessen the effects of experimenter expectancy is to design a study that uses a. single-blind methods. b. double-blind methods. c. triple-blind methods. d. quasi-experimental methods. 58 CHAPTER 2 Conducting Research in Psychology COMMONLY USED MEASURES OF PSYCHOLOGICAL RESEARCH In addition to different study methods, when psychologists conduct research, they rely on a vast array of tools to measure variables relevant to their research questions. The tools and techniques they use to assess thought and behavior are called measures. Measures in psychological science tend to fall into three cat- egories: self-report, behavioral, and physiological. To study complex behaviors, researchers may employ multiple measures (see Figure 13). Self-Report Measures Self-reports are people's written or oral accounts of their thoughts, feelings, or actions. Two kinds of self-report measures are commonly used in psychology: • Interviews • Questionnaires In an interview, a researcher asks a set of questions, and the respondent usually answers in any way he or she feels is appropriate. The answers are often open- ended and not constrained by the researcher. (See the section "Descriptive Stud- ies", for additional discussion on interviews.) In a questionnaire, responses are limited to the choices given in the ques- tionnaire. In the Stanford Prison Experiment, for example, the researchers used several questionnaires to keep track of the psychological states of the prisoners and guards. They had participants complete mood questionnaires many times during the study, so that the researchers could track any emotional changes the participants experienced. The participants also completed forms that assessed personality characteristics, such as trustworthiness and orderliness, that might be related to how they acted in a prison environment (Haney et al., 1973). Self-report questionnaires are easy to use, especially in the context of col- lecting data from a large number of people at once. They are also relatively inex- pensive. If designed carefully, questionnaires can provide important information on key psychological variables. A major problem with self-reports, however, is that people are not always the best sources of information about themselves. Why? Sometimes, as a reflection of the tendency toward social desirability, called social desirability bias, people present themselves more favorably than they really are, not wanting to reveal what they are really thinking or feeling to others for fear of looking bad. Presented with questions about social prejudice, for example, respon- dents might try to avoid giving answers that suggest they are prejudiced against a particular group. Another problem with self-reports is that we have to assume that people are accurate witnesses to their own experiences. Of course, there is no way to know exactly what a person is thinking without asking that person, but people do not always have clear insight into how they might behave (Nisbett & Wilson, 1977).

There is also the psychologically interesting phenomenon of creating an alternative personality, or avatar, in the gaming world. People sometimes take on personalities that are very different from their own in an online world that allows them to say things they would not in direct, face-to-face contact. This ability to be people we are not has allowed psychotherapists to use avatar personality games, such as Second Life®, to help people overcome their social anxieties in real life (Gottschalk, 2010; Lisetti et al., 2009). Similarly, video services such as SKYPE and GoogleChat are increasingly used to connect psychotherapist and patient, who can now be in different states if need be. We hope this chapter has helped you appreciate the richness and excitement of psychology as a clinical practice and science. More than that, we hope it encourages you to become an active and critical student of human behavior: Don't believe everything you think, and question how conclusions are drawn—even conclusions in this text. We hope that at this point, as a first step toward active learning and investigating, you are ask- ing, How do psychologists know all this? How do they do research? In the next chapter, we discuss the techniques by which psychological scientists study mental processes and behavior. Welcome to the fascinating world of psychology.

Science is about testing intuitive assumptions regarding how the world works, observing the world, and being open-minded to unexpected findings. Some of science's most important discoveries happened only because the scientists were open to surprising and unexpected results. Fundamentally, science entails collecting observations, or data, from the real world and evaluating whether the data support our ideas or not. The Stanford Prison Experiment fulfilled these criteria, and we will refer to this example several times in our discussion of research methods, measures, and ethics.

RESEARCH DESIGNS IN PSYCHOLOGY Science involves testing ideas about how the world works, but how do we design studies that test our ideas? This question confronts anyone wanting to answer a psychological question scientifically. Principles of Research Design Like other sciences, psychology makes use of several types of research designs— plans for how to conduct a study. The design chosen for a given study depends on the question being asked. Some questions can best be answered by randomly plac- ing people in different groups in a laboratory to see whether a treatment causes a change in behavior. Other questions have to be studied by questionnaires or sur- veys. Still other questions can best be answered simply by making initial observa- tions and seeing what people do in the real world. Sometimes researchers analyze the results of many studies on the same topic to look for trends. In this section, we examine variations in research designs, along with their advantages and disadvantages. We begin by defining a few key terms common to all research designs in psychology. A general goal of psychological research is to measure change in behavior, thought, or brain activity. A variable is anything that changes, or varies, within or between individuals. People differ from one another on age, gender, weight, intel- ligence, level of anxiety, and extraversion, to name a few psychological variables. Psychologists do research by predicting how and when variables influence each other. For instance, a psychologist who is interested in whether girls develop verbal skills at a different rate than boys focuses on two variables: gender and vocabulary. All researchers must pay careful attention to how they obtain participants for a study. The first step is for the researchers to decide the makeup of the entire group, or population, in which they are interested. In psychology, populations can be composed of, for example, animals, adolescents, boys or girls of any age, college students, or students at a particular school. How many are older than 50 or younger than 20? How many are European American, African American, Asian American, Pacific Islander, or Native American? How many have high school edu- cations, and how many have college educations? Can you think of a problem that would occur if a researcher tried to collect data directly on an entire population? Because most populations are too large to survey or interview directly, researchers draw on small subsets of each population, called samples. A sample of a population of college students, for instance, might consist of students enrolled in one or more universities in a particular geographic area. Research is almost always conducted on samples, not populations. If researchers want to draw valid conclusions or make accurate predictions about a population, it is important that their samples accurately represent the population in terms of age, gender, ethnicity, or any other variables of interest. When a poll is wrong in predicting who will win an elec- tion, it is often because the polled sample did not accurately represent the population. Ideas for studies often start with specific and personal experiences or events— one person being painfully shy; someone rushing onto train tracks to rescue a person who had fallen in front of an ongoing train; or, having personal experience with trauma. These experiences can be and often are the driving force behind a person's desire to study them more systematically. The point is that single events and single cases often lead to new ideas and new lines of research. When a researcher is interested in a question or topic that is relatively new to the field, often the wisest approach may be to use a descriptive design. In general, in descriptive designs the researcher makes no prediction and does not try to control any variables. She simply defines a problem of interest and describes as carefully as possible the variable of interest. The basic question in a descriptive design is, What is variable X? For example, What is love? What is genius? What is apathy? The psychologist makes careful observations, often in the real world outside the research lab. Descriptive studies usually occur during the exploratory phase of research, in which the researcher is looking for meaning- ful patterns that might lead to predictions later on; they generally do not involve testing hypotheses. Survey research is an exception since it can involve testing predictions. The researcher then notes possible relationships or patterns that may be used in other designs as the basis for testable predictions (see Figure 5). Four of the most common kinds of descriptive methods in psychology are case studies, naturalistic observations, qualitative research/interviews, and surveys. Case Study Psychotherapists have been making use of insights gained from individual cases for more than 100 years. A case study involves the observation of one person, often over a long period of time. Much wisdom and knowledge of human behavior can come from careful observation of one individual over time. Be- cause case studies are based on one-on-one relationships, often lasting years, they offer deep insights that surveys and questionnaires often miss. Sometimes study- ing the lives of extraordinary individuals, such as van Gogh, Lincoln, Marie Curie, Einstein, or even Hitler, can tell us much about creativity, greatness, genius, or evil. An area of psychology called psychobiography combines psychology with history to understand human behavior through the study of individual lives in historical context (Elms, 1993; Runyan, 1982; Schultz, 2005). Like other descrip- tive research, case studies and psychobiographies do not test hypotheses but can be a rich source for them. One has to be careful with case studies, however, be- cause not all cases are generalizable to other people. That is why case studies are often a starting point for the development of testable hypotheses. Naturalistic Observation A second kind of descriptive method is naturalistic observation, in which the researcher observes and records behavior in the real world. The researcher tries to be as unobtrusive as possible so as not to influ- ence the behavior of interest. Naturalistic observation is more often the design of choice in comparative psychology by researchers who study nonhuman behavior (especially primates) to determine what is and is not unique about our species. Developmental psychologists occasionally also conduct naturalistic observa- tions. For example, the developmental psychologist Edward Tronick of Harvard University has made detailed naturalistic observations of the infants of the Efe people in Zaire. He has tracked these children from 5 months through 3 years to un- derstand how the Efe culture's communal pattern of child rearing influences social development in children (Tronick, Morelli, & Ivey, 1992). Although the traditional Western view is that having a primary caregiver is best for the social and emotional well-being of a child, Tronick's research suggests that the use of multiple, commu- nal caregivers can also foster children's social and emotional well-being. The advantage of naturalistic observation is that it gives researchers a look at real behavior in the real world rather than in a controlled setting—such as in a laboratory, where people might not behave naturally. Few psychologists use naturalistic observation, however, because conditions cannot be controlled and cause-and-effect relationships between variables cannot be demonstrated. Qualitative Research Letting people say what they want in responding to questions is the essence of an interview. Interviews occur between two people, one asking the questions and the other answering, usually in open-ended answers. Sometimes interview questions are predetermined or structured and sometimes they are spontaneous or unstructured. Interviews are an example of qualitative research, which involves data gathered from open-ended and unstructured an- swers rather than quantitative or numeric answers. The advantage to qualitative re- search, namely the open-ended and flexible answers, is also its disadvantage. How does one interpret, summarize, and make sense of a person's interview answers? Just as importantly, how do we compare one person's answers to another's and get a general sense of what the trends are? These are difficulties of qualitative research. Survey Research Surveys do not have these difficulties because more often than not, they restrict the possible answers to some kind of numeric rating scale, such as 1 for "completely disagree," 3 for "neither disagree nor agree," and 5 for "completely agree." Research that collects information using any kind of nu- meric and quantifiable scale and often has limited response options is referred to as quantitative research. These are structured and quantitative answers and can be summarized and calculated for trends and averages. Yet, answers are re- stricted to a few categories and sometimes the response options are too limited and do not capture the person's true ideas or attitudes. A common example of a limited response option is when a respondent has to answer on a 1 to 5 scale from "completely disagree" to "completely agree." Sometimes survey research is descriptive and exploratory and other times it may propose and test hypotheses. There is another concern with survey research. Think about your own re- sponse when you are contacted via phone or email about participating in a scien- tific survey. Many of us don't want to participate and ignore the request. So how does a researcher know that people who participate are not different from people who don't participate? Maybe those who participate are older or younger, have more education or less education. In other words, we need to know that the infor- mation we collect comes from people who represent the group we are interested in, which is known as a representative sample (see Figure 6). Sampling is the procedure researchers use to obtain participants from a population.

The well-known Kinsey surveys of male and female sexual behavior pro- vide good examples of the strengths and weaknesses of survey research (Kinsey, Pomeroy, & Martin, 1948; Kinsey et al., 1953). Make no mistake—just publish- ing such research caused an uproar in both the scientific community and the general public at the time. Kinsey reported, for instance, that up to 50% of the interviewed men but only about half as many (26%) of the women had had ex- tramarital affairs. Another widely cited finding was that approximately 10% of the population could be considered homosexual. The impact of Kinsey's research has been profound. By itself it began the science of studying human sexuality and permanently changed people's views. For example, Kinsey was the first to consider sexual orientation on a continuum from 0 (completely heterosexual) to 6 (completely homosexual) rather than as an either-or state with only two options. This approach remains a lasting contribution of his studies. By today's standards, however, Kinsey's techniques for interviewing and collecting data were rather primitive. He didn't use representative sampling and oversampled people in Indiana (his home state) and in prisons—both of which led to biased results. In addition, he interviewed people face-to-face about the most personal and private details of their sex lives, also making it more likely they provided less than honest and biased answers. Correlational Studies Once an area of study has developed far enough that predictions can be made, but for various reasons people cannot be randomly assigned to groups or variables cannot be manipulated, a researcher might choose to test hypotheses by means of a correlational study. Correlational designs measure two or more variables and their relationship to one another. In this design, the basic question is, Is X related to Y? For instance, "Is sugar consumption related to increased activity levels in children?" If so, how strong is the relationship, and is increased sugar consumption associated (correlated) with increased activity levels, as we would predict, or does activity decrease as sugar consumption increases? Or is there no clear relationship? Correlational studies are useful when the experi- menter cannot manipulate or control the variables. For example, it would be unethical to raise one group of chil- dren one way and another group another way in order to study parenting behavior. We could use a good question- naire to find out whether parents' scores related to their parenting behavior are consistently associated with par- ticular behavioral outcomes in children. In fact, many questions in developmental psychology, personality psychology, and even clinical psychology are examined with correlational techniques. The major limitation of the correlational approach is that it does not establish whether one variable actually causes the other. Parental neglect in childhood might be associated with antisocial behavior in adolescence, but that does not necessarily mean that neglect causes anti- social behavior. Some other variable (e.g., high levels of testosterone, poverty, antisocial friends) might be the cause of the behavior. We must always be mindful that correlation is necessary for causation but is not suf- ficient by itself to establish causation (see Figure 7). Psychologists often use a statistic called the correlation coefficient to draw conclusions from their correlational studies. Correlation coefficients tell us whether two variables relate to each other and the direction of the re- lationship. Correlations range between −1.00 and +1.00, with coefficients near 0.00 indicating that there is no relationship between the two variables. A 0.00 correlation means that knowing about one variable tells us nothing about the other. As a correlation approaches +1.00 or −1.00, the strength of the relation- ship increases. Correlation coefficients can be positive or negative. If the relationship is positive, then as a group's score on variable X increases, its score on variable Y also increases. Height and weight are positively correlated—taller people gener- ally weigh more than shorter people. For negative correlations, as one variable increases, the other decreases. Alcohol consumption and motor skills are nega- tively correlated—the more alcohol people consume, the less physically coordi- nated they become. To further demonstrate correlation, let's consider the positive correla- tion between students' scores on midterm and final exams. By calculating a correlation, we know whether students who do well on the midterm are likely to do well on the final. Based on a sample of 76 students in one of our classes, we found a correlation of +0.57 between midterm and final exam grades. This means that, generally, students who did well on the midterm did well on the final. Likewise, those who did poorly on the midterm tended to do poorly on the final. The correlation, however, was not extremely high, so there was some inconsistency. Some people performed differently on the two exams. When we plot these scores, we see more clearly how individuals did on each exam (see Figure 8). Each dot represents one student's scores on both exams. For example, one student scored an 86 on the midterm but only a 66 on the final. When interpreting correlations, it is important to remember that a correla- tion does not mean there is a causal relationship between the two variables. Cor- relation is necessary but not sufficient for causation. When one variable causes another, it must be correlated with it, but just because variable X is correlated with variable Y, it does not mean that X causes Y. The supposed cause may be an effect, or a third variable may be the cause. What if hairiness and aggression in men were positively correlated? Would that imply that being hairy makes a man more aggressive? No. In fact, both hairi- ness and aggressiveness are related to a third variable, the male sex hormone testosterone (Simpson, 2001 see Figure 9). Experimental Studies Often people use the word experiment to refer to any research study, but in science an experiment is something quite specific. All psychological studies measure behavior, but a true experiment has two unique characteristics: 1. Experimental manipulation of a predicted cause, the independent variable 2. Random assignment of participants to control and experimental groups or conditions, meaning that each participant has an equal chance of being placed in each group The independent variable in an experiment is an attribute the experimenter manipulates under controlled conditions. The independent variable is the condition the researcher predicts will cause a particular outcome. The dependent variable is the outcome, or response to the experimental manipulation. You can think of the in- dependent variable as the "cause" and the dependent variable as the "effect," although reality is not always so simple. If there is a causal connection between the two, then the responses depend on the treatment, hence the name dependent variable. Earlier we mentioned the hypothesis that sugar consumption makes kids overly active. In this example, sugar levels consumed would be the independent variable and behavioral activity level the dependent variable. Recall the study of the effect of caffeine on sex drive in rats. Is caffeine the independent or de- pendent variable? What about sex drive? Figure 10 features other examples of independent and dependent variables. Random assignment is a method used to assign participants to different research conditions to guarantee that each person has the same chance of being in one group as another. Random assignment is achieved with either a random numbers table or some other unbiased technique. Random assignment is critical, because it ensures that on average the groups will be similar with respect to all possible variables, such as gender, intelligence, motivation, and memory, when the experiment begins. If the groups are the same on these qualities at the begin- ning of the study, then any differences between the groups at the end are likely to be the result of the independent variable. Experimenters randomly assign participants to either an experimental group or the control group. An experimental group consists of participants who receive the treatment or whatever is thought to change behavior. In the sugar con- sumption and activity study, for example, the experimental group would receive a designated amount of sugar. The control group consists of participants who are treated in exactly the same manner as the experimental group but with one crucial difference: They do not receive the independent variable, or treatment. Instead, they often receive no special treatment or, in some cases, they get a placebo, a substance or treatment that appears identical to the actual treatment but lacks the active substance. In a study on sugar consumption and activity level, an appropriate placebo could be an artificial sweetener. The experimental group would receive the treatment (sugar), and the control group would be treated exactly the same way but would not receive the actual treatment. Instead, the control group could receive a food flavored with an artificial sweetener. Experimental and control groups must be equivalent at the outset of an experimental study so as to minimize the possibility that other charac- teristics could explain any difference found after the administration of the treatment. If two groups of children are similar at the start and if one group differs from the other on activity level after receiving different amounts of sugar, then we can conclude that the treatment caused the observed effect. That is, different levels of sugar consumption caused the differences in ac- tivity level. In our hypothetical study on sugar and activity, for instance, we would want to include equal numbers of boys and girls in the experimental and control groups and match them with respect to age, ethnicity, and other characteristics, so that we could attribute differences in activity level following treatment to differences in sugar consumption only. Suppose we didn't do a good job of randomly assign- ing participants to our two conditions and the experimental group ended up with 90% boys but the control group had 90% girls. If, after administering the sugar to the experimental group and the placebo (sugar substitute) to the control group, we found a difference in activity, then we would have two possible explanations for the difference: gender and sugar. Either being male or female caused the dif- ference or consuming large amounts of sugar did. In this case, gender would be a confounding variable—an additional variable that the researcher failed to control for in the experimental design (too many males), and one that could be responsible for a change in the dependent variable (activity level). Because most of the people in the experimental group were male and consumed sugar, we do not know whether being male or consuming sugar was responsible for the dif- ference in active behavior. These two variables are confounded and cannot be teased apart. The power of the experimental design is that it allows us to say that the independent variable (treatment) caused changes in the dependent variable, as long as everything other than the independent variable was held constant (see Figure 11). Random assignment guarantees group equivalence on a number of variables and prevents ambiguity over whether effects might be due to other dif- ferences between the groups. In addition to random assignment to control and experimental groups, a true experiment requires experimental control of the independent variable. Thus, researchers must make sure that all environmental conditions (such as noise level and room size) are equivalent for the two groups. Again, the goal is to make sure that nothing affects the dependent variable besides the independent variable. In our experiment on sugar consumption and activity level, we first must randomly assign participants to either the experimental group (in which partici- pants receive some amount of sugar) or the control group (in which participants receive some sugar substitute). The outcome of interest is activity level, so each group might be videotaped for a short period 30 minutes after eating the sugar or sugar substitute. What if the room where the experimental group was given the sugar was several degrees warmer than the room where the control group received the sugar substitute, and our results showed that the participants in the warmer room were more active? Could we feel confident that sugar led to in- creased activity level? No, because the heat in that room may have caused the increase in activity level. In this case, room temperature would be the confound- ing variable. There is a design that has one quality of an experiment (the manipulation of an independent variable), but not the other (random assignment), a design known as a quasi-experimental design (Shadish, Cook, & Campbell, 2002). It is called "quasi" because it is partly or almost an experimental design. It is often used with human participants, because we cannot randomly assign them to ethically untenable conditions, such as depression or childhood abuse or even personality traits such as extroversion. In these situations, the research- ers use preexisting groups but then manipulate a variable to see how the groups respond. Any knowledge that participants and experimenters have about the ex- perimental conditions to which participants have been assigned can also af- fect the outcome of an experiment. In single-blind studies, participants do not know the experimental condition to which they have been assigned. This is a necessary precaution in all studies to avoid the possibility that partici- pants will behave in a biased way. For example, if participants know they have been assigned to a group that receives a new training technique on memory, then they might try harder to perform well. This would confound the results. Another possible problem can come from the experimenter knowing who is in which group and unintentionally treating the two groups somewhat differ- ently. This could lead to the predicted outcome simply because the experimenter has biased the results. In double-blind studies, neither the participants nor the researchers (at least the ones administering the treatment) know who has been assigned to which condition. Ideally, then, neither the participants nor those col- lecting the data should know which group is the experimental group and which is the control group. The advantage of double-blind studies is that they prevent two potential problems with experimental designs: experimenter expectancy effects and demand characteristics. Experimenter expectancy effects occur when the behavior of the participants is influenced by the experimenter's knowledge of who is in which condition (Rosenthal, 1976, 1994). Demand characteristics are subtle cues given by experimenters to the participants as to how they should behave in the role of participant. These cues may be provided unconsciously, or even consciously. The latter apparently happened, for example, in the Stanford Prison Study when before the study began, Zimbardo suggested to the assigned "guards" that although they cannot abuse or torture, they can create fear, bore- dom, frustration, lack of privacy, and control (Zimbardo, 2007). That is precisely what the guards did. Longitudinal Studies People change over time—our brains, thoughts, feelings, personality, motiva- tions. In fact, every aspect of us changes. The only way to study change over time is with longitudinal studies. Longitudinal designs make observations of the same people over time, ranging from months to decades. These kinds of stud- ies are not only useful for studying change over time, but also can be used to study how specific causes affect specific outcomes. For example, we cannot ran- domly assign young children to live in abusive or neglectful home environments. But some children do and some do not. So if we follow these groups over time, we can examine the outcomes of such living conditions on thought and behav- ior. Longitudinal studies often combine observational, correlational, and quasi- experimental techniques. Twin-Adoption Studies One of the most important questions in psychology is how much of our thought, behavior, personality, and mental health stems from built-in biological forces (nurture) and how much is from learning and the environmental (nature). The nature-nurture topic runs throughout the book and our answer is always it is "both/and" not "either/or." How do researchers conduct research to answer these questions? They primarily use two different methods: twin-adoption studies and gene-by-environment studies.