Chapter 4
blind spot
A visual peculiarity occurs where the optic nerve exits the eye. Because there are no receptor cells for visual stimuli in that area, we have a tiny hole, or blind spot, in our field of vision.
place theory for hearing
According to the ____, we hear different pitches because different sound waves stimulate different sections (or places) on our cochlea's basilar membrane (see again Process Diagram 4.2). Our brains figure out the pitch of a sound by detecting the position of the hair cells that sent the neural message. High frequencies produce large vibrations near the start of the basilar membrane—next to the oval window. However, this theory does not predict well for low frequencies, which tend to excite the entire basilar membrane.
cochlear implant
Although most hearing loss is temporary, damage to the auditory nerve or receptor cells is generally considered irreversible. The only treatment for auditory nerve damage is a small electronic device called a cochlear implant. If the auditory nerve is intact, the implant bypasses hair cells to stimulate the nerve. Currently, cochlear implants produce only a crude approximation of hearing, but the technology is improving.
trichromatic theory of color
Although we know color is produced by different wavelengths of light, the actual way in which we perceive color is a matter of scientific debate. Traditionally, there have been two theories of color vision: the trichromatic (three‐color) theory and the opponent‐process theory. The trichromatic theory of color(from the Greek word tri, meaning "three," and chroma, meaning "color") suggests that we have three "color systems," each of which is maximally sensitive to red, green, or blue (Young, 1802). The proponents of this theory demonstrated that mixing lights of these three colors could yield the full spectrum of colors we perceive (Figure 4.10).
absolute threshold
Another scientist, Gustav Fechner (1801-1887), expanded on Weber's law to determine what is called the absolute threshold, the minimum stimulation necessary to consciously detect a stimulus 50% of the time. See Table 4.2 for a list of absolute thresholds for our various senses.
Processing
As you can see, the processes of sensation and perception are complex, but also very interesting. Now that you understand and appreciate the overall purpose of these two processes, let's dig deeper, starting with the first step of sensation
One additional way to understand the difference between bottom‐up and top‐down processing is to think about what happens when we "see" a helicopter flying overhead in the sky. According to the bottom‐up processing perspective, receptors in our eyes and ears record the sight and sound of this large, loud object, and send these sensory messages on to our brains for interpretation. The other, top‐down processing, approach suggests that our brains quickly make a "best guess," and interpret the large, loud object as a "helicopter," based on our previous knowledge and expectations. Given that most of our students have difficulty with this distinction
Bottom‐Up versus Top‐Down Processing When first learning to read, you used bottom‐up processing. You initially learned that certain arrangements of lines and "squiggles" represented specific letters. You later realized that these letters make up words that have meaning—an example of topdown processing. Now, yuor aiblity to raed uisng top‐dwon prcessoing mkaes it possible to unedrstnad this sntenece desipte its mnay mssipllengis.
subliminal perception
Can unconscious stimuli really affect our behavior? Experimental studies on ____have clearly shown that we can detect stimuli and information below our level of conscious awareness (Farooqui & Manly, 2015; Rabellino et al., 2016; Urriza et al., 2016). These studies commonly use an instrument, called a tachistoscope, to flash images too quickly for conscious recognition, but slowly enough to be registered by the brain. How does this happen? As we've just seen, our "absolute threshold" is the point at which we can detect a stimulus half the time. Subliminal stimuli are just stimuli that fall below our 50% absolute threshold, and they can be detected without our awareness
transduction
For each sense, these specialized cells respond to a distinct stimulus, such as sound waves or odor molecules. Next, during the process of transduction, the receptors convert the energy from the specific sensory stimulus into neural impulses, which are then sent on to the brain. For example, in hearing, tiny receptor cells in the inner ear convert mechanical vibrations from sound waves into electrochemical signals. Neurons then carry these signals to the brain, where specific sensory receptors detect and interpret the information.
priming
Furthermore, research on __finds that certain unconscious or unnoticed stimuli can reach our brains and predispose (prime) us to make it easier or more difficult to recall related information already in storage (Loebnitz & Aschemann‐Witzel, 2016; Xiao & Yamauchi, 2016). If a researcher shows you the words "red" and "fire engine," you'll be slightly faster to recognize the word "apple" because all of these words have been previously stored and closely associated in your memory. Despite the fact that subliminal perception and priming do occur, it doesn't mean that such processes lead to significant behavioral changes. Subliminal stimuli are basically weak stimuli. However, they sometimes have an effect on indirect, more subtle reactions, such as our more casual attitudes
Preventing Hearing Loss
Given the limited benefits of medicine or technology to help improve hearing following damage, it's even more important to protect our sense of hearing. We can do this by avoiding exceptionally loud noises, wearing earplugs when we cannot avoid such stimuli (see photo), and paying attention to bodily warnings of possible hearing loss, including a change in our normal hearing threshold and tinnitus, a whistling or ringing sensation in the ears. These relatively small changes can have lifelong benefits!
Subliminal Stimuli
Have you heard some of the wild rumors about subliminal messages? During the 1970s, it was said that rock songs contained demonic messages, which could only be heard when the songs were played backwards! Similarly, in the 1990s, many suggested that some Disney films contained obscene subliminal messages. For example, in the film Aladdin, the lead character supposedly whispers, "all good teenagers take off your clothes," and The Lion King reportedly showed closeup shots of the dust with a secret spelling out of the word "sex." In addition, at one time movie theaters were reportedly flashing messages like "Eat popcorn" and "Drink Cola‐Cola" on the screen. Even though the messages were so brief that viewers weren't aware of seeing them, it was believed they increased consumption of these products (Bargh, 2014; Blecha, 2004; Vokey & Read, 1985).
Pitch Perception
How do we determine that certain sounds are from a child's voice, and not from an adult's? We distinguish between high‐ and low‐pitched sounds by the frequency of the sound waves. The higher the frequency, the higher the pitch. There are three main explanations for how we perceive pitch
coding
How does your brain differentiate between sensations, such as sounds and smells? Through a process known as __1, the brain interprets different physical stimuli as distinct sensations because their neural impulses travel by different routes and arrive at different parts of the brain
opponent‐process theory of color
However, trichromatic theory doesn't fully explain color vision, and other researchers have proposed alternative theories. For example, the opponent‐process theory of color agrees that we have three color systems, but it says that each system is sensitive to two opposing colors—blue and yellow, red and green, black and white—in an "on/off" fashion. In other words, each color receptor responds either to blue or yellow, or to red or green, with the black‐or‐white system responding to differences in brightness levels. This theory makes a lot of sense because when different‐colored lights are combined, people are unable to see reddish greens and bluish yellow. In fact, when red and green lights or blue and yellow lights are mixed in equal amounts, we see white. This opponent‐process theory also explains color afterimages, a fun type of optical illusion in which an image briefly remains after the original image has faded (Psychology and You). Today we know that both trichromatic and opponent‐process theories are correct—they just operate at different levels in visual processing. Color vision is processed in a trichromatic fashion in the retina. In contrast, color vision during opponent processing involves the retina, optic nerve, and brain.
sensory adaptation
Imagine that friends have invited you to come visit their beautiful new baby kitten. As they greet you at the door, you are overwhelmed by the odor of the kitten's overflowing litter box. Why don't your friends do something about that smell? The answer lies in the previously mentioned sensory reduction, as well as . When a constant stimulus is presented for a length of time, sensation often fades or disappears. Receptors in our sensory system become less sensitive. They get "tired" and actually fire less frequently. Sensory adaptation can be understood from an evolutionary perspective. We can't afford to waste attention and time on unchanging, normally unimportant stimuli. "Turning down the volume" on repetitive information helps the brain cope with an overwhelming amount of sensory stimuli and enables us to pay attention to change. Sometimes, however, adaptation can be dangerous, as when people stop paying attention to a small gas leak in the kitchen. Although some senses, like smell and touch, adapt quickly, we never completely adapt to visual stimuli or to extremely intense stimuli, such as the odor of ammonia or the pain of a bad burn. From an evolutionary perspective, these limitations on sensory adaptation aid survival by reminding us, for example, to keep a watch out for dangerous predators, avoid strong odors and heat, and take care of that burn.
gate‐control theory of pain
In addition to endorphin release and distraction, one of the most widely accepted explanations of pain perception is the ____, first proposed by Ronald Melzack and Patrick Wall (1965). According to this theory, the experience of pain depends partly on whether the neural message gets past a "gatekeeper" in the spinal cord. Normally, the gate is kept shut, either by impulses coming down from the brain or by messages being sent from large‐diameter nerve fibers that conduct most sensory signals, such as touch and pressure. However, when body tissue is damaged, impulses from smaller pain fibers open the gate (Price & Prescott, 2015; Rhudy, 2016; Zhao & Wood, 2015). Can you see how this gate‐control theory helps explain why massaging an injury or scratching an itch can temporarily relieve discomfort? It's because pressure on large‐diameter neurons interferes with pain signals. In addition, studies suggest that the pain gate may be chemically controlled. A neurotransmitter called substance P opens the pain gate, and endorphins close it (Fan et al., 2016; Krug et al., 2015; Wu et al., 2015). In sum, endorphins, distraction, listening to music, holding a loved one's hand, pain gates, and substance P may all provide soothing comfort and pain reduction, especially for those who are very anxious (Bradshaw et al., 2012; Fan et al., 2016; Gardstrom & Sorel, 2015). Did you know that when normal sensory input is disrupted, the brain can also generate pain and other sensations entirely on its own, as is the case with phantom limb pain (PLP) (Deer et al., 2015; Melzack, 1999; Raffin et al., 2016)? After an amputation, people commonly report detecting their missing limb as if it were still there with no differences at all. In fact, up to 80 percent of people who have had amputations sometimes "feel" pain (and itching, burning, or tickling sensations) in the missing limb, long after the amputation. Numerous theories attempt to explain this type of PLP, but one of the best suggests that there is a mismatch between the sensory messages sent and received in the brain. Can you explain how this may be an example of our earlier description of how bottom‐up processes (such as the sensory messages sent from our limbs to our brains) combine with our top‐down processes (our brain's interpretation of these messages)? Messages are no longer being transmitted from the missing limb to the brain (bottom up), but areas of the brain responsible for receiving messages are still intact (top down). The brain's attempt to interpret the confusing messages may result in pain and other sensations. In line with this idea of mismatched signals, when amputees wear prosthetic limbs, or when mirror visual therapy is used, phantom pain often disappears. In mirror therapy (Figure 4.6), pain relief apparently occurs because the brain is somehow tricked into believing there is no longer a missing limb (Deconinck et al., 2015; Foell et al., 2014; Hagenberg & Carter, 2014). Others believe that mirror therapy works because it helps the brain reorganize and incorporate this phantom limb into a new nervous system configuration.
amplitude
In addition to wavelength/frequency, waves also vary in height (technically called amplitude). This wave height/amplitude determines the intensity of sights and sounds. Finally, waves also vary in range, or complexity, which mixes together waves of various wavelength/frequency and height/amplitude
light adaptation
In contrast, light adaptation, the adjustment that takes place when you go from darkness to a bright setting, takes about 7 to 10 minutes and is the work of the cones.
fovea
Interestingly, a region in the center of the retina, called the fovea, has the greatest density of cones, which are most sensitive in brightly lit conditions. They're also responsible for color vision and fine detail.
Color‐Deficient Vision
Most people perceive three different colors—red, green, and blue—and are called trichromats. However, a small percentage of the population has a genetic deficiency in the red-green system, the blue-yellow system, or both. Those who perceive only two colors are called dichromats. People who are sensitive to only the black-white system are called monochromats, and they are totally color blind. If you'd like to test yourself for red-green color blindness,
Sensory processing within the brain
Neural messages from the various sense organs must travel to specific areas of the brain in order for us to see, hear, smell, and so on. Shown here in the red‐colored labels are the primary locations in the cerebral cortex for vision, hearing, taste, smell, and somatosensation (which includes touch, pain, and temperature sensitivity).
Olfaction(smell) Molecules dissolved on nose's mucous membranes
Neurons in the nose's olfactory epithelium Temporal lobe and limbic system
Waves of light and sound
Ocean waves have a certain distance between them (the wavelength), and they pass by you at intervals. If you counted the number of passing waves in a set amount of time (for example, 5 waves in 60 seconds), you could calculate the frequency (the number of complete wavelengths that pass a point in a given time). Longer wavelength means lower frequency and vice versa.
Color Vision
Our ability to perceive color is almost as remarkable and useful as vision itself. Humans may be able to discriminate among 7 million different hues, and research conducted in many cultures suggests that we all seem to see essentially the same colored world (Maule et al., 2014; Ozturk et al., 2013). Furthermore, studies of infants old enough to focus and move their eyes show that they are able to see color nearly as well as adults and have color preferences similar to those of adults (Bornstein et al., 2014; Yang et al., 2015).
olfaction
Our sense of smell,, which results from stimulation of receptor cells in the nose, is remarkably useful and sensitive. We possess more than 1,000 types of olfactory receptors, which allow us to detect more than 10,000 distinct smells. The nose is more sensitive to smoke than any electronic detector, and—through practice—blind people can quickly recognize others by their unique odors.
Skin Senses
Our skin is uniquely designed for the detection of touch (or pressure), temperature, and pain (Figure 4.14a). The concentration and depth of the receptors for each of these stimuli vary (Hsiao & Gomez‐Ramirez, 2013; Ruzzoli & Soto‐Faraco, 2014). For example, touch receptors are most concentrated on the face and fingers and least concentrated in the back and legs. Getting a paper cut can feel so painful because we have many receptors on our fingertips. Some receptors respond to more than one type of stimulation. For example, itching, tickling, and vibrating sensations seem to be produced by light stimulation of both pressure and pain receptors. The benefits of touch are so significant for human growth and development that the American Academy of Pediatrics recommends that all mothers and babies have skin‐to‐skin contact in the first hours after birth. This type of contact, which is called kangaroo care, is especially beneficial for preterm and low‐birth‐weight infants, who then experience greater weight gain, fewer infections, and improved cognitive and motor development. How does kangaroo care lead to these improvements in infant health?
Are You Color Blind?
People who suffer red-green color deficiency have trouble perceiving the number in this design. Although we commonly use the term color blindness, most problems are color confusion rather than color blindness. Furthermore, most people who have some color blindness are not even aware of it.
Audition(hearing) Sound waves
Pressure-sensitive hair cells in ear's cochlea Auditory cortex in the temporal lobe
Sense Stiumulus Vision Light waves
RECEPTORS Light-sensitive rods and cones in eye's retina BRAIN Visual cortex in the occipital lobe
Before going on, we need to update you on research findings on taste perception. It was long believed that we had only four distinct tastes: sweet, sour, salty, and bitter. However, we now know that we also have a fifth taste sense, umami, a word that means "delicious" or "savory" and refers to sensitivity to an amino acid called glutamate (Bredie et al., 2014; Lease et al., 2016). Glutamate is found in meats, meat broths, and monosodium glutamate (MSG).
Scientists also once believed that specific areas of the tongue were dedicated to detecting bitter, sweet, salty, and other tastes. Today we know that taste receptors, like smell receptors, respond differentially to the varying shapes of food and liquid molecules. The major taste receptors—taste buds—are distributed all over our tongues within little bumps called papillae
Gustation(taste) Molecules dissolved on tongue
Taste buds on tongue's surface Limbic system, somatosensory cortex, and frontal lobe
How Our Ears Hear
The outer ear captures and funnels sound waves into the eardrum. Next, three tiny bones in the middle ear pick up the eardrum's vibrations, and transmit them to the inner ear. Finally, the snail‐shaped cochlea in the inner ear transforms (transduces) the sound waves into neural messages (action potentials) that our brains process into what we consciously hear
audition
The sense or act of hearing, known as ____, has a number of important functions, ranging from alerting us to dangers to helping us communicate with others. In this section we talk first about sound waves, then about the ear's anatomy and function, and finally about problems with hearing. Like the visual process, which transforms light waves into vision, the auditory system is designed to convert sound waves into hearing. Sound waves are produced by air molecules moving in a particular wave pattern. For example, vibrating objects like vocal cords or guitar strings create waves of compressed and expanded air resembling ripples on a lake that circle out from a tossed stone. Our ears detect and respond to these waves of small air pressure changes, our brains then interpret the neural messages resulting from these waves, and we hear!
Why is our difference threshold important?
This radiologist is responsible for detecting the slightest indication of a tumor in this mammogram of a female breast. The ability to detect differences between stimuli (like the visual difference between normal and abnormal breast tissue) can be improved by special training, practice, and instruments. However, it's still limited by our basic sensory difference thresholds.
Infant benefits from kangaroo care
This type of skin‐to‐skin touch helps babies in several ways, including providing warmth, reducing pain (lower levels of arousal and stress increases pain tolerance and immune functioning), and better sleep quality. Other research, including a meta‐analysis (which combines results from multiple studies), also found that babies who receive kangaroo care have a 36% lower likelihood of death—as well as a lower risk of blood infection and similar positive long‐term effects beyond infancy (Boundy et al., 2016; Burke‐Aaronson, 2015; Castral et al., 2015; Feldman et al., 2014). As we discovered earlier in this and other chapters of this text, skin‐to‐skin contact, including holding hands and hugs, provides numerous physical and mental benefits for people of all ages.
perception
Through the process of , the brain then assigns meaning to this sensory information (Table 4.1). Another clever way to differentiate sensation and perception is shown in
Vision Did you know that professional baseball batters can hit a 90‐miles‐per‐hour fastball four‐tenths of a second after it leaves the pitcher's hand? How can the human eye receive and process information that fast? To understand the marvels of vision, we need to start with the basics—that light waves are a form of electromagnetic energy and only a small part of the full electromagnetic spectrum
To fully appreciate how our eyes turn these light waves into the experience we call vision, we need to first examine the various structures in our eyes that capture and focus the light waves. Then, we need to understand how these waves are transformed (transduced) into neural messages (action potentials) that our brains can process into images we consciously see
SENSEABSOLUTE THRESHOLD VisionA candle flame seen from 30 miles away on a clear, dark night Audition (hearing)The tick of an old‐fashioned watch at 20 feet Olfaction (smell)One drop of perfume spread throughout a six‐room apartment Gustation (taste)One teaspoon of sugar in 2 gallons of water Body sensesA bee's wing falling on your cheek from a height of about half an inch
To measure your senses, an examiner presents a series of signals that vary in intensity and asks you to report which signals you can detect. In a hearing test, the softest level at which you can consistently hear a tone is your absolute threshold. The examiner then compares your threshold with those of people with normal hearing to determine whether or not you have hearing loss
gustation
Today, the sense of taste, , which results from stimulation of receptor cells in the tongue's taste buds, may be the least critical of our senses. In the past, however, it probably contributed significantly to our survival. For example, humans and other animals have a preference for sweet foods, which are generally nonpoisonous and are good sources of energy. However, the major function of taste, aided by smell, is to help us avoid eating or drinking harmful substances. Because many plants that taste bitter contain toxic chemicals, an animal is more likely to survive if it avoids bitter‐tasting plants (French et al., 2015; Sagong et al., 2014; Schwartz & Krantz, 2016).. Did you know that our taste and smell receptors normally die and are replaced every few days? This probably reflects the fact that these receptors are directly exposed to the environment, whereas our vision receptors are protected by our eyeball and hearing receptors are protected by the eardrum. However, as we grow older, the number of taste cells diminishes, which helps explain why adults enjoy spicier foods than do infants. Scientists are particularly excited about the regenerative capabilities of the taste and olfactory cells because they hope to learn how to transfer this regeneration to other types of cells that are currently unable to self‐replace when damaged.
Primary colors
Trichromatic theory found that the three primary colors (red, green, and blue) can be combined to form all colors. For example, a combination of green and red creates yellow.
Color Afterimages
Try staring at the dot in the middle of this color‐distorted U.S. flag for 60 seconds. Then stare at a plain sheet of white paper. You should get interesting color aftereffects—red in place of green, blue in place of yellow, and white in place of black: a "genuine" U.S. flag. (If you don't see the afterimage, blink once or twice and try again.) What happened? As you stared at the green, black, and yellow colors, the neural systems that process those colors became fatigued. Then when you looked at the plain white paper, which reflects all wavelengths, a reverse opponent process occurred: Each fatigued receptor responded with its opposing red, white, and blue colors! This is a good example of color afterimages—and further support for the opponent‐process theory.
dark adaptation
Two additional peculiarities happen when we go from a bright to dark setting and vice versa. Have you noticed that when you walk into a dark movie theater on a sunny afternoon, you're almost blind for a few seconds? The reason is that in bright light, the pigment inside the rods (refer to Process Diagram 4.1) is bleached, making them temporarily nonfunctional. It takes a second or two for the rods to become functional enough again for you to see. This process of dark adaptation continues for 20 to 30 minutes.
Treating phantom limb pain
Using mirror therapy, an amputee patient places his or her intact limb on one side of the mirror, and the amputated limb on the other. He or she then concentrates on looking into the mirror on the side that reflects the intact limb, creating the visual impression of two complete undamaged limbs. The patient then attempts to move both limbs. Thanks to the artificial feedback provided by the mirror, the patient sees the complete limb, and the reflected image of the complete limb, moving. He or she then interprets this as the phantom limb moving. Now that we've studied how we perceive pain, how we might ignore or "play through" it, and how we might misperceive it with phantom limb pain, it's important to point out that when we get anxious or dwell on our pain, we can intensify it (Lin et al., 2013; Ray et al., 2015; Wertli et al., 2014). Surprisingly, social and cultural factors, such as well‐meaning friends or anxious parents who ask pain sufferers about their pain, may unintentionally reinforce and increase it
Body senses Variety of stimuli
Variety of receptors (the drawing on the right is a model of our sensory receptor cells for touch) Motor cortex in the frontal lobe and the somatosensory cortex in the parietal lobe
sensory reduction
We also have structures that purposefully reduce the amount of sensory information we receive. In this process of sensory reduction, we analyze and then filter incoming sensations before sending neural impulses on for further processing in other parts of our brains. Without this natural filtering of stimuli, we would constantly hear blood rushing through our veins and feel our clothes brushing against our skin. Some level of filtering is needed to prevent our brains from being overwhelmed with unnecessary information. All species have evolved selective receptors that suppress or amplify information for survival. Humans, for example, cannot sense ultraviolet light, electric or magnetic fields, the ultrasonic sound of a dog whistle, or infrared heat patterns from warm‐blooded animals, as some other animals can.
Conduction hearing loss
What are the types, causes, and treatments of hearing loss? Conduction hearing loss, also called conduction deafness, results from problems with the mechanical system that conducts sound waves to the cochlea. Hearing aids that amplify the incoming sound waves, and some forms of surgery, can help with this type of hearing loss.
Why we enjoy eating pizza: olfaction plus gustation
When we eat pizza, the crust, cheese, sauce, and other food molecules activate taste receptor cells on our tongue, while the pizza's odors activate smell receptor cells in our nose. This combined sensory information is then sent on to our brain where it is processed in various association regions of the cortex. Interestingly, taste and smell also combine with sensory cells that respond to touch and temperature, which explains why cold, hard pizza "tastes" and "smells" different than hot, soft pizza.
difference threshold
also known as Weber's Law of just noticeable differences (JND), is the minimum difference that is consciously detectable 50% of the time
sensorineural hearing loss
also known as nerve deafness, results from damage to the cochlea's receptor (hair) cells or to the auditory nerve. Disease and biological changes associated with aging can result in sensorineural hearing loss. But its most common (and preventable) cause is continuous exposure to loud noise, which can damage hair cells and lead to permanent hearing loss. Even brief exposure to really loud sounds, like a stereo or headphones at full blast, a jackhammer, or a jet airplane engine, can cause permanent nerve deafness (see again Figure 4.12). In fact, a high volume on earphones can reach the same noise level as a jet engine! All forms of high volume noise can damage the coating on nerve cells, making it harder for the nerve cells to send information from the ears to the brain (Eggermont, 2015; Fagelson et al., 2016; Jiang et al., 2016).
Learning and Culture
any food and taste preferences are learned from an early age and from personal experiences (Fildes et al., 2014; Nicklaus, 2016; Tan et al., 2015). For example, adults who are told a bottle of wine costs $90 (rather than its real price of $10) report that it tastes better than the supposedly cheaper brand. Ironically, these false expectations actually trigger areas of the brain that respond to pleasant experiences (Plassmann et al., 2008). This means that in a neurochemical sense, the wine we believe is better does, in fact, taste better! The culture we live in also affects our taste preferences. Many Japanese children eat raw fish, and some Chinese children eat chicken feet as part of their normal diet. Although most U.S. children might consider these foods "yucky," they tend to love cheese, which children in many other cultures find repulsive.
rods
are highly sensitive in dim light, but are less sensitive to detail and color
Sensation
begins with specialized receptor cells located in our sense organs (eyes, ears, nose, tongue, skin, and internal body tissues). When sense organs detect an appropriate stimulus (light, mechanical pressure, chemical molecules), they convert it into neural impulses (action potentials) that are transmitted to our brains
pheromones
chemicals released by organisms that trigger certain responses, such as aggression or sexual mating, in other members of the same species—also affect human sexual responses (Baum & Cherry, 2015; Jouhanneau et al., 2014; Ottaviano et al., 2015). However, others suggest that human sexuality is far more complex than that of other animals
The frequency theory for hearing
differs from place theory because it states that we hear pitch by the frequency of the sound waves traveling up the auditory nerve. High-frequency sounds trigger the auditory nerve to fire more often than do low‐frequency sounds. The problem with this theory is that an individual neuron cannot fire faster than 1,000 times per second, which means that we could not hear many of the notes of a soprano singer
cones
he reverse is true for the cones, which are highly sensitive to color and detail, and less sensitive in dim light. Can you see how this explains why you're cautioned to look away from bright headlights when driving or biking at night? Staring into the bright lights will activate your cones, which are less effective in dim light, whereas looking away activates the rods in your peripheral vision, which are more sensitive at night.
Softness versus Loudness
how we detect a sound as being soft or loud depends on its amplitude (or wave height). Waves with high peaks and low valleys produce loud sounds; waves with relatively low peaks and shallow valleys produce soft sounds. The relative loudness or softness of sounds is measured on a scale of decibels (dBs) Beware of loud sounds The higher a sound's decibel (dB) reading, the more damaging it is to the ear.
bottom‐up processing
information processing starts at the "bottom" with an analysis of smaller features, and then builds on them to create complete perceptions. In other words, processing begins at the sensory level and works "up."
top‐down processing,
our brains create useable perceptions from the sensory messages based on prior knowledge and expectations. In this case, processing begins at the "top," our brain's higher‐level cognitive processes, and works "down."
chemical senses
smell and taste are sometimes called the chemical senses because they both rely on chemoreceptors that are sensitive to certain chemical molecules. Have you wondered why we have trouble separating the two sensations? Smell and taste receptors are located near each other and closely interact
volley principle for hearing
solves the problem of frequency theory, which can't account for the highest pitched sounds. It states that clusters of neurons take turns firing in a sequence of rhythmic volleys. Pitch perception depends upon the frequency of volleys, rather than the frequency carried by individual neurons. ow that we've explored the mechanics of pitch and pitch perception, would you like a real‐world example that you can apply to your everyday life? A recent experiment revealed that research participants who lowered the pitch of their voices were seen as being more influential, powerful, and intimidating (Cheng et al., 2016). This finding also held true in a second experiment in which the people only listened to audio recordings of various voices. Can you see why the famous deep‐voiced actor James Earl Jones was chosen as the voice of Darth Vader in the Star Wars films (see photo)? Given that women generally tend to have higher‐pitched voices, can you also see how this research might help explain why women often find it harder to gain leadership positions? Interestingly, as we age, we tend to lose our ability to hear high‐pitched sounds but are still able to hear low‐pitched sounds. Given that young students can hear a cell phone ringtone that sounds at 17 kilohertz—too high for most adult ears to detect—they can take advantage of this age‐related hearing difference and call or text one another during class (Figure 4.11). Ironically, the cell phone's ringtone that most adults can't hear is an offshoot of another device, called the Mosquito, which was originally designed to help shopkeepers annoy and drive away loitering teens!
If we don't adapt to pain, how do athletes keep playing despite painful injuries? In certain situations, including times of physical exertion, the body releases natural, pain‐killing neurotransmitters, called endorphins
which inhibit pain perception. This is the so‐called "runner's high," which may help explain why athletes have been found to have a higher pain tolerance than nonathletes (Tesarz et al., 2012). (As a critical thinker, is it possible that individuals with a naturally high pain tolerance are just more attracted to athletics? Or might the experience of playing sports change your pain tolerance?)
psychophysics
which studies and measures the link between the physical characteristics of stimuli and the psychological experience of them One of the most interesting insights from psychophysics is that what is out there is not directly reproduced inside our bodies. At this moment, there are light waves, sound waves, odors, tastes, and microscopic particles touching us that we cannot see, hear, smell, taste, or feel. We are consciously aware of only a narrow range of stimuli in our environment. German scientist Ernst Weber (1795-1878) was one of the first to study the smallest difference between two weights that could be detected (Goldstein, 2014; Schwartz & Krantz, 2016).