Chapter 5: Physical and Cognitive Development in Infancy

The Growth of Attention and Memory

Although we have not yet discussed it specifically, a baby's ability to pay attention to and remember specific aspects of the environment clearly plays an important role in many of the developments described above. Obviously, before babies can figure out whether an object with wings has feathers or a different surface, they first need to attend to the object. And it would be impossible for babies to understand cause-effect relationships if, as they were watching some effect, they could not remember the earlier event that caused it. Developing Attention The process of attention appears to involve four distinct phases that can be distinguished by changes in infants' heart rates (Figure 5.21) (Courage, Reynolds, & Richards, 2006): Phase I: Stimulus-detection reflex. The stimulus-detection reflex signals the baby's initial awareness of some change in the environment. In this phase (not labeled in the figure), there is a very brief slowing and then quickening of the heart rate. Phase II: Stimulus orienting. During the second phase, the baby's attention becomes fixed on the stimulus. As you can see in the figure, the heart rate slows considerably during this period. Phase III: Sustained attention. In the third phase, the heart rate remains slow as the baby cognitively processes the stimulus. The baby's entire body may become still, and it is relatively more difficult to distract the baby with a new stimulus (Reynolds & Richards, 2007). Sustained attention is believed to be a voluntary state; that is, the baby purposefully controls and focuses his or her attention on the stimulus (Johansson et al., 2016). At this point, the baby is truly paying attention. Phase IV: Attention termination. In this phase, the baby is still looking at the object but is no longer processing its information. (It takes a moment to break contact with the stimulus.) The heart rate begins to return to prestimulus levels. FIGURE5.21 Attention is a process involving four phases that can be distinguished by changes in the infant's heart rate. As shown here, the heart rate drops considerably when the infant is engaged in sustained attention. The horizontal axis represents the number of seconds following stimulus onset and ranges from negative 5 to 25 in increments of 5. The vertical axis represents the heart rate change (in beats per minute) and ranges from negative 10 to 2 in increments of 2. The baseline of the heartbeat ranges from negative one to 0.5 beats per minute in negative 5 to 0 seconds. The stimulus orienting phase ranges from 0 to 5 seconds. The heart rate in this phase ranges from 0.5 beats per second to negative 8 beats per minute. The sustained attention ranges from 5 to 10 seconds. The heart rate ranges from negative 8 to negative 7 beats per second. The heart rate returns to the baseline at 18 seconds. The heart rate during the attention termination phase ranges from 0 to negative 2 beats per minute. All data in the graph are approximate. The horizontal axis represents the number of seconds following stimulus onset and ranges from negative 5 to 25 in increments of 5. The vertical axis represents the heart rate change (in beats per minute) and ranges from negative 10 to 2 in increments of 2. The baseline of the heartbeat ranges from negative one to 0.5 beats per minute in negative 5 to 0 seconds. The stimulus orienting phase ranges from 0 to 5 seconds. The heart rate in this phase ranges from 0.5 beats per second to negative 8 beats per minute. The sustained attention ranges from 5 to 10 seconds. The heart rate ranges from negative 8 to negative 7 beats per second. The heart rate returns to the baseline at 18 seconds. The heart rate during the attention termination phase ranges from 0 to negative 2 beats per minute. All data in the graph are approximate. From the descriptions of these phases, you can imagine why developmentalists are particularly interested in the development of sustained attention. It is during the attention phase that babies actively learn about and remember their experiences. At 3 months of age, babies can sustain their attention only for periods of 5 to 10 seconds. Certainly, one of the most significant developments in the first 2 years is infants' increasing ability to focus their attention in a sustained way. In addition to getting better at focusing their attention over the course of the first 2 years, babies get faster at processing information about the targets of their attention. Show 1-year-olds a picture of a bunny, and they are likely to stare with rapt attention for a long period of time. Show the same picture to 2-year-olds, and they may look at it for a few seconds and be done with it. They have processed it and recognized it, and they are ready to turn their attention elsewhere. Clearly, it is not the case that 1-year-olds have better sustained attention than 2-year-olds. Rather, 1-year-olds need more time to process the information. Indeed, research indicates that with increasing age, there is a decrease in the amount of time that babies spend looking at simple patterns or figures. It has even been found that 6-month-olds who spend relatively long periods of time looking at simple patterns tend to have lower intelligence quotients (IQs) when they are tested at the age of 11 (Rose, Feldman, & Jankowski, 2004, 2009; Figure 5.22a). Among other things, all this means that care must be taken not to confuse visual attention (how the baby processes information) with visual fixation (the amount of time the baby looks at an object). FIGURE5.22 (a) Between 6 and 22 weeks of age, there is a significant decline in the amount of time that infants looks at simple geometric figures. (b) Between 6 and 24 months of age, however, there is a significant increase in the amount of time that infants look at complex stimuli, such as Sesame Street videotapes, while the amount of time they spend looking at simple figures remains stable. The horizontal axis in the first graph represents the age in weeks ranging from 2 to 50 weeks in increments of 4 and the vertical axis represents the look duration ranging between negative 1.5 to 1.5 seconds in increments of 0.5 seconds. At birth, the look duration starts at negative 0.5 seconds and increases substantially to 1 second at 6 weeks after birth. There is a significant decline in the time duration it decreases to negative 0.75 seconds at 22 weeks after birth. The look duration gradually increases up to negative 0.5 seconds by the fiftieth week. The second graph shows the look duration of infants at complex stimuli. The horizontal axis ranges from 0 to 24 months in increments of six months and the vertical axis ranges from 0 to 30 seconds in increments of 5. Two graph lines depicting children watching Sesame Street and Computer-generated simple figures are shown. Children aged 6 months who watched the Sesame Street videotapes looked at the complex stimuli for around 13 seconds. The look duration increased gradually to 25 seconds for the children aged 2 years. Children aged 6 months who watched computer-generated simple figures looked at complex stimuli for about 8 seconds. The graph remains stable as the look duration slightly increased to 10 seconds for children aged 24 months. All data in the graph are approximate. While infants' attention to simple visual displays decreases after the first few months of life, attention to complex stimuli increases (Rose et al., 2009). Figure 5.22b illustrates the amount of time babies of different ages, ranging from 6 to 24 months, looked at two different videotapes. One videotape showed a computer-generated display of simple geometric patterns. The other showed a segment from Sesame Street. The time spent watching the computer-generated film was about the same for all babies, whereas the time spent watching the Sesame Street segment increased with age. As we mentioned earlier, the development of attention, especially focused, sustained attention, is of enormous significance to the infant's emerging ability to remember past events and learn about the environment, a topic we address next. Developing Memory Carolyn Rovee-Collier and her colleagues explored the complexities of infants' memory development throughout the 1st year of life (Cuevas, Learmonth, & Rovee-Collier, 2016; Rovee-Collier, Mitchell, & Hsu-Yang, 2013). Using the operant-conditioning procedure described in Chapter 4 (pp. 148-149), the researchers trained babies between ages 2 and 6 months of age to kick in order to make an overhead mobile move. (One of the infants' ankles, you will recall, was connected to the mobile by a ribbon; Figure 5.23.) Following the training, the babies were returned to the lab after delays of various durations to see if they remembered how to make the mobile move. The researchers found that 2-month-olds started kicking immediately following a 24-hour delay but seemed to forget the procedure if the delay lasted 3 days. Memory for the task was better in 3-month-olds and better yet in 6-month-olds, who remembered their training 2 weeks later but not 3 weeks later. Interestingly, if infants are permitted to observe the experimenter pulling the string to shake the mobile, their apparently forgotten memories can be "reactivated" (Joh, Sweeney, & Rovee-Collier, 2002). FIGURE5.23 Because of the ribbon tied between her ankle and the mobile overhead, this infant will learn that kicking causes the mobile to move. Research indicates that she is likely to remember what she learned about the mobile for several days. However, she will probably be at least 6 months old before she can remember the task for 2 or more weeks. Infants' memories can also be strengthened by other memories. In one study, for example, 6-month-olds were trained to push a button to activate an electronic train and then returned to the lab days and weeks later to see how long they remembered the task (Rovee-Collier et al., 2013). But before learning how to operate the train, some of the babies spent time in two free-play sessions with a number of objects, including two puppets. Other babies spent time in the free-play sessions, but the two puppets were not present together — one was present in the first session; the other in the second. The two puppets were present together when the babies learned how to operate the train. Babies who had associated the two puppets together during the free-play sessions remembered how to work the train five times longer than those who saw the puppets separately. According to the researchers, these results tell a fascinating story about how young infants learn and remember. As they undergo dramatic development, young infants are especially quick to form associations between objects and events that occur in their continually and rapidly changing environments — a tendency that Rovee-Collier and her colleagues referred to as a "period of exuberant learning," which ends around 9 months of age. Exuberant learning may account for the infants' association of the two puppets and how that earlier association strengthened the memory of the association between pushing the button and the movement of the train. Memory is considered an especially important cognitive achievement because it seems to require the generation of a mental representation for something that is not present to the senses. As we discuss in later chapters, developments in memory and attention are intertwined with the other cognitive achievements, and, over time, come under increasingly purposeful control.

Cognitive Development: The Great Debate

As the physical body, and the ability to control it, continue to mature across the first 2 years after birth, so too does the mind. As we shall see in the following sections, developmentalists are engaged in a great debate about how thinking progresses during the first 2 years. [Piaget: do young children have the same kind of thinking that adults do?/ does thinking develop in a linear way? is it finished at a certain point?] For some developmentalists, such as Piaget, the mind undergoes a radical, discontinuous shift at the end of infancy (Müller, 2009). According to Piaget's stage theory, young infants are limited to sensorimotor intelligence; that is, they understand the world only through their own actions and perceptions. They, therefore, cannot think about people and objects that are not immediately present to be seen, heard, or felt, and acted upon. All this changes fundamentally at 18 or so months of age, when infants become capable of representational thinking, forming mental pictures or images of the world. The ability to form such mental images, and to reason about them, is a significant turning point in cognitive development. Knowledge is no longer tied to the immediate here and now. Instead, infants can hold in mind past experiences, compare and contrast them with each other and with present circumstances, and use them to anticipate the future and guide their actions. Developmentalists who take this view claim that the emergence of the ability to represent the world mentally results in a mind that is truly conceptual rather than simply "sensorimotor." On the other side of the debate are developmentalists who maintain that mental development is more continuous than Piaget supposed — that the ability to represent and understand the world conceptually is present very early in development, if not from birth. According to this view, conceptual understanding does not emerge out of sensorimotor knowledge, as Piaget claimed. Instead, young babies are believed to possess at least a rudimentary conceptual system. This system is thought to develop separately from, although in close association with, the sensorimotor system (Mandler, 2012; Marshall & Meltzoff, 2014). As you will see, there is much at stake in the debate about the nature and development of the human mind. [school model based on piaget's stages of cognitive development] Sensorimotor Development (First Stage) Piaget referred to infancy as the stage of sensorimotor development because of his belief that at this early age, infants acquire knowledge exclusively through motor actions that are directed at their immediate environment and guided by their sensory organs. He combined the terms sensory and motor to emphasize the intimate relationship between sensing the world and acting upon it. Each influences the other: What infants perceive depends on what they are doing, and what they do depends on what they are perceiving at the moment (Piaget, 1973). As noted above, Piaget maintained that infants are bound to this moment-to-moment, here-and-now form of understanding until the final stage of sensorimotor development, when they begin to think representational. [in terms of cognition; pre-operational; between age 2 and 6; can be deceived easily;for Piaget operational thinking means the capacity to use logic and reason] As we explained in our previous discussions (Chapter 1, p. 20; Chapter 4, pp. 146-147), Piaget divided the sensorimotor period into six substages (see Table 5.1). During the first substage, the newborn learns to control and coordinate reflexes, and during the second, the newborn begins to modify and repeat behaviors, such as thumb-sucking, simply because they are pleasurable (primary circular reactions). The following sections provide an overview of the four remaining substages of sensorimotor development. As you read through the sections, notice how infants become increasingly flexible, purposeful, and inventive. TABLE 5.1 Piaget's Sensorimotor Substages [image on slide] Substage Age (months) Characteristics of Sensorimotor Substage 1 0-1½ Exercising reflexive schemas: involuntary rooting, sucking, grasping, looking 2 1½-4 Primary circular reactions: repetition of actions that are pleasurable in themselves 3 4-8 Secondary circular reactions: dawning awareness of the relationship of own actions to the environment; extended actions that produce interesting changes in the environment 4 8-12 Coordination of secondary circular reactions: combining schemas to achieve a desired effect; earliest form of problem solving 5 12-18 Tertiary circular reactions: deliberate variation of problem-solving means; experimentation to see what the consequences will be 6 18-24 Beginning of symbolic representation: images and words come to stand for familiar objects; invention of new means of problem solving through symbolic combinations [piaget's theory of cognitive development : youtube] Reproducing Interesting Events (Substage 3) In contrast to the first two substages, in which infants' actions primarily involve their own body, in the third substage, 4- to 8-month-olds begin to direct their attention and their actions to the external world — to objects and outcomes. This new interest in external things gives rise to a characteristic behavior observed in infants during this substage — the repetition of actions that produce interesting changes in the environment. For example, when babies in this substage accidentally discover that a particular action, like squeezing a rubber toy, produces an interesting effect, such as squeaking, they repeat the action again and again to produce the effect. Similarly, when babies vocalize by cooing or gurgling and a caregiver responds, they repeat the sound they made. Piaget termed these new, object-oriented actions secondary circular reactions. They are "secondary" because they apply to something outside the infant, in contrast to primary circular reactions, which apply to the infant's own body (see Chapter 4, p. 146). The change from primary circular reactions to secondary circular reactions indicated to Piaget that infants are beginning to realize that objects are more than an extension of their own actions — that objects have their own, separate identities. In this substage, however, babies still have only a rudimentary understanding of objects and space, and their discoveries about the world seem to have an accidental quality. The Emergence of Intentionality (Substage 4) The hallmark of the fourth sensorimotor substage, which occurs between 8 and 12 months of age, is the emergence of the ability to engage in behaviors directed toward achieving a goal. Piaget called this ability intentionality. He believed goal-directed behavior to be the earliest form of true problem solving. Piaget's son, Laurent, provided a demonstration of intentional problem solving of this kind when he was 10 months old. Piaget had given him a small tin container, which Laurent dropped and picked up repeatedly (a secondary circular reaction characteristic of behavior in substage 3). Piaget then placed a washbasin a short distance from Laurent and struck it with the tin box, producing an interesting sound. From earlier observations, Piaget knew that Laurent would repeatedly bang on the basin to make the interesting sound occur (another typical secondary circular reaction). This time Piaget wanted to see if Laurent would combine the newly acquired "dropping the tin box" schema with the previously acquired "make an interesting sound" schema. Here is his report of Laurent's behavior: Now, at once, Laurent takes possession of the tin, holds out his arm and drops it over the basin. I moved the latter as a check. He nevertheless succeeded, several times in succession, in making the object fall on the basin. Hence this is a fine example of the coordination of two schemas of which the first serves as a "means" whereas the second assigns an end to the action. (Piaget, 1952b, p. 255.) In Piaget's view, then, over the course of substages 3 and 4 of sensorimotor intelligence, infants become capable of intentional action directed at objects and people around them, but these abilities come fully into play only when infants can directly perceive the objects and people in question. Piaget maintained that this is because infants lack object permanence — that is, the understanding that objects exist even when they are out of view. Until substage 4 of sensorimotor development, according to Piaget, infants live in a world in which objects come and go from their line of sight, each "a mere image which reenters the void as soon as it vanishes, and emerges from it for no apparent reason" (1954, p. 11). Piaget's classic test of object permanence was to put a cloth over a young infant's favorite toy as the infant watched and then observe whether the infant searched for the hidden toy. Unfailingly, infants under 8 months of age not only did not search for the vanished toy, they also showed no interest or surprise in its vanishing — as though it had never existed. Thus, Piaget believed that for young babies, out of sight is literally out of mind. In stage 4, infants begin to demonstrate some degree of object permanence (they lift the cloth off the hidden toy), but until substage 6, it is rudimentary and fragile. Exploring by Experimenting (Substage 5) The fifth substage of the sensorimotor period, tertiary circular reactions, emerges between 12 and 18 months of age and is characterized by an ability to vary the actions of substage 4 systematically and flexibly. This ability makes explorations of the world more complex. Indeed, Piaget (1952b) referred to tertiary circular reactions as "experiments in order to see" because children seem to be experimenting in order to find out about the nature of objects and events (p. 272). Here is Piaget's description of this kind of behavior in Laurent, at 10 months and 11 days, lying in his crib: He grasps in succession a celluloid swan, a box, etc., stretches out his arm and lets them fall. He distinctly varies the positions of the fall. . . . Sometimes he stretches out his arm vertically, sometimes he holds it obliquely, in front of or behind his eyes, etc. When the object falls in a new position (for example, on his pillow), he lets it fall two or three times more on the same place, as though to study the spatial relations; then he modifies the situation. (Piaget, 1952b, p. 269.) According to Piaget's observations, infants in substage 5 seem unable to reason systematically about actions and anticipate their probable consequences. As suggested in Laurent's behavior of trying different ways of dropping the object for the sheer purpose of seeing what might happen, infants in substage 5 live in a here-and-now, trial-and-error world. The ability to mentally plan, organize, and otherwise envision their actions and foresee their possible consequences does not begin until the arrival of representational thinking. Experimenting with objects, including dropping toys from one's high chair in order to watch them fall and bounce, is typical of Piaget's sensorimotor substage 5. Representation (Substage 6) According to Piaget, the hallmark of substage 6, the final stage of the sensorimotor period, between 18 and 24 months of age, is that babies begin to base their actions on internal, mental symbols, or representations, of experience. When they can re-present the world to themselves — that is, when they can present it to themselves over again mentally — they can be said to be engaging in true mental actions. Infants' ability to represent people, objects, events, and experiences mentally has been a central focus for researchers because it has enormous ramifications in other areas of development. For example, once infants are able to represent a sequence of events, they can solve problems systematically rather than by trial and error. Similarly, once babies become capable of representation, they begin to engage in symbolic play (also known as pretend play or fantasy play), in which one object is used to stand for (represent) another, as when a child combs a baby doll's hair with a twig or gives it a drink from a small plastic block. Representation also enables deferred imitation. deferred imitation: the imitation of actions observed in the past, which is of tremendous importance to children's learning and socialization. A child who observes a parent having coffee and reading the paper and then hours or days later pretends to be drinking coffee and reading is engaged in deferred imitation. Finally, of special significance is the role of representation in language, in which words are used to stand for (represent) people, objects, and events. This little boy engages in deferred imitation, giving his bear a cookie in imitation of how he himself is given treats. There is little disagreement about the importance Piaget attached to representation as a foundation for the development of problem solving, symbolic play, deferred imitation, and language. Nor do developmentalists disagree with Piaget's descriptions of the sequence of behavioral changes that occurs as children progress through the early stages of dealing with objects. Indeed, his observations have been widely replicated, not only in Europe and the United States but in traditional societies as well. For example, Baule infants living in rural areas of the West African country of Côte d'Ivoire have been found to proceed through the same sequence of object-related behaviors on almost exactly the same timetable as European children, despite vast differences in their cultural environments (Dasen, 1973). In fact, research conducted with infant great apes reveals the same pattern of sensorimotor development (Parker & McKinney, 1999). The sequence and timing of sensorimotor stages are so reliable that Piaget's procedures were long ago standardized for assessing the development of children who are at risk because of disease, physical impairment, or extreme environmental deprivation (Uzgiris & Hunt, 1975). Studies by Andrew Meltzoff (1988) have shown that young infants imitate live models and also imitate actions they have seen on television. This child observes a televised adult model manipulate blocks, and then immediately the child imitates the adult's actions. Meltzoff also demonstrated that infants who watch a televised model on one day are able to reproduce the model's behavior 24 hours later. The past two decades have brought challenges both to Piaget's theory and to his methods. In general, these challenges attack the idea that infants are unable to represent objects they cannot see, arguing instead that infants are born with, or quickly develop, a conceptual system with representational powers. As we discuss below, critics argue that young infants have the competence to form representations of objects but lack various skills needed to demonstrate that ability on traditional Piagetian tests. Using a variety of ingenious methods, the critiques suggest that infants' mental lives are more complex than Piaget believed.

Brain Development

Describe brain development during infancy. Give examples of the relationship between brain development and infant behavior. The brain develops through both experience-expectant and experience dependant processes: experience-expectant processes the brain expects that the world will present particular, species-universal experiences (ex: patterns of light and dark, various kinds of tastes and odors, language, and the like) and develops in response to those experiences. experience-dependent processes development occurs in response to specific experiences, hence the brain's amazing capacity to be changed by the unique experiences of each individual child. researchers have focused on answering two interconnected questions to try to understand infant brain development: Brain and Behavior What is the relationship between developments in certain parts of the brain and the onset of new skills or abilities? previous knowledge: the brain undergoes substantial development throughout infancy, although different parts grow at different times and rates cerebral cortex- associated with complex functions such as voluntary behavior, abstract thought, problem-solving, and language; very immature at birth; development is important to researchers trying to understand the brain-behavior relationship Bringing Up Babies in the Digital Age -interest in infant brain development has fueled a multimillion-dollar industry aimed at making babies smarter: 72 percent of the top-paid apps are in the Preschool/Toddler category; more than 80,000 apps are designated as educational; in 2013, a nationwide survey found that 58 percent of parents in the United States reported downloading apps for their children; the app industry rakes in enormous amounts of money, with current revenues estimated to be around $40 billion. - digital age has fundamentally altered the life experiences of infants and children throughout the world. -Electronic devices and digital applications are used increasingly with very young children for a variety of reasons: staying in touch with loved ones, distraction during periods of fussiness or distress, entertainment during daily routines, (ex: car rides, eating out), educational tools that promote academic skills (ex: reading and counting) But the scientific community has been struggling to keep up with the breakneck pace at which new devices and apps are developed, marketed, and adopted by parents of very young children, and there is no straightforward answer to the question of whether exposure to digital technologies is harmful or beneficial. Indeed, the answer depends on how and when the technologies are used. beneficial: raised hope for the educational potential of interactive media: harmful: raised concerns about the consequences of exposure during a crucial period of rapid brain development and the formation of social and attachment relationships: - Other research has focused on some positive consequences of interactive technologies such as distracting young children during stressful medical procedures or promoting language learning through video-chatting (McQueen, Cress, & Tothy, 2012 Roseberry, Hirsh-Pasek, & Golinkoff, 2014). - Some research has found that screen time, typically defined as exposure to television, may disrupt the sleep of infants and young children by causing them to take longer to fall asleep, or sleep less overall (Chonchaiya, Wilaisakditipakorn, Vijakkhana, & Pruksananonda, 2017; Cespedes et al., 2014). - Recent studies have focused on how digital technologies affect the quality of parent-infant interactions and indicate that quality suffers compared to interactions that involve traditional toys and books. - One study found that with electronic toys, parents used fewer words and responded less frequently to their infants' vocalizations and behaviors than they did with traditional toys and books (Sosa, 2016); the babies also vocalized less often. -Again, parent-child interactions were significantly affected by the nature of the toy, with the traditional sorter prompting a higher quality of parental language, overall, as well as more language specific to the types of shapes ("circle," "square") and spatial relationships ("Put it in there"). Thus, research supports critics' concerns that digital toys and apps may displace or dilute the quality of human interaction — a source of essential experiences for infant brain growth and emerging cognitive, social, and emotional development. As the prevalence of their use continues to explode, along with the industry's unfounded claims of their "educational" value, researchers continue to evaluate the risks and benefits to infant and child development (Hirsh-Pasek et al., 2015). Brain and Experience To what extent does experience or the lack thereof (that is, deprivation) enhance or impede brain development and function? Another important development, revealed by brain-imaging techniques, involves the language-related areas; frontal and temporal lobes; of the cortex, undergo significant myelination shortly before a characteristic spurt in toddlers' vocabulary. (Myelin, remember, is the fatty substance that covers axons, speeding the brain's communications.) At least as important as the growth of different brain areas is that the different areas increasingly function together (Fox, Levitt, & Nelson, 2010; Posner et al., 2016). Once again, myelination plays an important role. In fact, although myelination of the brain is ongoing from the second part of pregnancy through adolescence, there is a peak rate of myelination during the first postnatal year, resulting in the formation of neural networks that allow different parts of the brain to communicate and work together. For example, myelination of the neurons that link the prefrontal cortex and frontal lobes to the brain stem, where emotional responses are partially generated, creates a new potential for interaction between thinking and emotion. In general, the greater synchrony among brain areas appears vital to the emergence of functions that define late infancy, including [effects of experience]- more systematic problem solving, voluntary control of behavior, and the acquisition of language [Prolonged deprivation -Early life adversity -missing sensitive periods -sleeper effects: behavior, cognition, language] Toward the end of infancy, the length and the degree of branching of the neurons in the cerebral cortex approach adult magnitudes: Each neuron now has connections with other neurons, usually numbering in the thousands. Although brain structures mature at different rates, those that eventually will support adult behavior are present, and the pace of the brain's overall growth becomes slower and steadier until adolescence. prefrontal cortex (of the cortex); located behind the forehead; plays important role in development of voluntary behavior; begins to function in a new way between 7-9 months of age. With this change in functioning comes an increase in infants' ability to regulate themselves (Posner, Rothbart, Sheese, & Voelker, 2014). Infants can stop themselves from grabbing the first attractive thing they see; they can cuddle their teddy bear to keep from being upset when they are put down for a nap. With the emerging ability to inhibit action, they can also better control what they attend to. In effect, they begin to be able to stop and think (Posner, Rothbart, & Voelker, 2016). Brain and Experience everyday experience, as well as even brief periods of deprivation, can affect the brain's structures and functions. For instance, in discussing exuberant synaptogenesis and synaptic pruning (p. 130), we described how the infant's normal everyday experiences, such as exposure to a specific language, can affect which synapses are strengthened and which are eliminated, or pruned. We also discussed how newborns who are nearly blind due to congenital cataracts, despite corrective surgery that removes the cataracts and restores vision, may throughout their lives process auditory and visual information somewhat differently than individuals born with normal vision . If brain development is so readily influenced by the infant's daily experience and brief periods of deprivation, how might it be affected by situations in which an infant endures more severe forms of deprivation? early-life adversity: profound and pervasive deprivation; can have terrible consequences for development. conclusive evidence comes from research on infants & children who spent time in orphanages before being adopted into families or foster care. many orphans were abandoned/left without caregivers due to war or political violence and received basic physical care with little social & intellectual stimulation. typically confined to cribs most of the day, no social interaction & only looked at bare walls they were confined to cribs for most of each day, with no social interaction and nothing to look at but bare walls. many had significant delays in development by the time they were rescued. in general, research finds that children adopted early in infancy, before 6 months of age, fare better than those adopted at older ages. children adopted at older ages were much more likely to suffer significant developmental impairments. infant brain undergoes considerable development between 6-24 months, and during these phases of rapid growth, brain structures are sensitive to the infant's experiences (sensitive periods or periods of plasticity) The researchers point out that the infant brain undergoes considerable development between 6 and 24 months of age and that during such phases of rapid growth, brain structures are particularly sensitive to the infant's experiences. In Chapter 1, we described such phases as sensitive periods, or periods of plasticity, during which a particular experience (or lack of it) has a more pronounced effect on development than it would at another point in time. It is likely that during sensitive periods of brain development, the orphans lacked the species-universal experiences required for strengthening and fine-tuning normal experience-expectant neural connections. In addition, the infants' experience-dependent brain development may have been adversely affected by the deprived conditions of the orphanage. But even children who seem less affected by deprivation early in development may show evidence of impairment as they age. The detrimental effects of early-life adversity that occur only later in development are referred to as sleeper effects. Sleeper effects are evident in an interesting pattern of emotional development observed in some boys who had been institutionalized as infants: As young children, the boys were less adventurous than their non-institutionalized peers; however, as adolescents, such boys engaged in excessive levels of impulsiveness and risk-taking. This pattern suggests that deprivation may have altered the development of neural connections between areas of the brain associated with impulses and the processing of emotions (the limbic system), and those areas in the cerebral cortex responsible for higher levels of decision making and behavioral control. Aided by new brain-imaging technologies we have spectacular new insights into the relationships between the developing brain and the experiences and behaviors of infants. Indeed, brain scans of a group of these orphans showed significant deficits in the functioning of certain areas in the limbic system, which is involved in emotion and motivation. Interestingly, work with rats and other animals indicates that the specific limbic areas affected are especially vulnerable to stress, particularly when it is experienced early in development. As the findings involving the orphans suggest, advances in developmental neuroscience hold great promise for exploring how biological and environmental processes interact in the life of the developing child.

Looking Ahead

It is truly astonishing that babies undergo such enormous physical and cognitive changes in such a brief period of time. Equally amazing are the implications that these changes have for future development. Already, as a consequence of synaptogenesis and selective pruning, the baby's neural pathways are taking shape according to both species-universal and individual experiences. Whereas the crucial biological events during the newborn period (Chapter 4) involve changes in the connections between the sensory cortex of the brain and the brain stem, the remaining months of infancy are marked by increased myelination of the prefrontal cortex, which is associated with voluntary behavior and language, and myelination of pathways connecting different areas of the brain, which allows the brain to work in a more integrated way. Equally important are increases in height and weight, increases in the strength of muscles and bones, and a change in body proportion that shifts the baby's center of gravity — all of which are necessary to support developing motor skills. As we noted earlier, motor development appears to orchestrate the reorganization of many other functions that have been developing in parallel during infancy. For one thing, the acquisition of new motor skills leads infants to discover many properties of objects in their immediate environment. They become capable of reaching for objects efficiently and picking them up, feeling them, tasting them, moving around them, carrying them, and using them for various purposes of their own. Their growing autonomy and ability to explore the world advances further as gross motor skills emerge, especially the uniquely human form of locomotion — walking. These experiences would not amount to much, however, if babies were not able to represent them mentally or to remember them. The capacity to represent objects, people, events, and experiences mentally exerts a powerful influence on other areas of development that we explore in detail in later chapters, including symbolic play, imitation, and language. Indeed, as you will learn in later chapters, mental representation plays a pivotal role in how children make use of the material and symbolic tools of their culture. In the next chapter, we address the social and emotional domains of infancy and how they enter into the biocultural equation of children's development.

Motor development

One of the most dramatic developments between 3 and 24 months of age is the enormous increase in infants' ability to explore their environment by grasping and manipulating objects and by moving about. As their motor skills advance, babies gain important information about features of the world and how it is put together — for example, how objects feel to the touch and how they behave when they are poked, pulled, dropped, or banged together. Importantly, advances in motor skills give babies new opportunities to pursue people (quite literally) and to communicate to them and get feedback from them about interesting objects in the environment — from odd bits of trash ("No, don't touch — that's dirty") to the tail of the family dog ("Be careful, don't pull — that might hurt"), to a toy on a chair that was out of reach just a few months before ("What a big girl to reach that teddy bear!"). These changing motor abilities have widespread consequences for cognitive, social, and emotional development (Libertus, Joh, & Needham, 2016). For instance, infants' walking and grasping skills have been associated with the size of their vocabularies, as well as their language development at 3 years of age (He, Walle, & Campos, 2015; Wang, Lekhal, Aarø, & Schjølberg, 2014). One recent study found that 3-month-old-infants who received just 2 weeks of parent-guided training in reaching for objects engaged in higher levels of exploration and attention when they were 15-months-olds compared to infants who did not receive special training. All this suggests that the development of early motor skills may result in a cascade of developments in other areas (Libertus et al., 2016). fine motor skills: involve the development and coordination of small muscles (those that move the fingers and eyes) gross motor skills: involve the large muscles of the body and make locomotion possible. Fine Motor Skills We pointed out in Chapter 2 that human beings are highly distinctive in their ability to make and use tools. Such tool use would be impossible without the development of fine motor skills that allow us to grasp and manipulate objects. From the perspective of parents and caregivers, increasing fine motor control and coordination mean that their baby can participate more fully in such daily activities as feeding and dressing. It also means that the baby can get into drawers, cupboards, and other spaces that may contain dangerous objects. . FIGURE5.4 The development and coordination of the small muscles that control the fingers and hands are associated with a variety of important skills and follow a fairly predictable timetable. Early Skills: Reaching and Grasping Remember from Chapter 4 (p. 144) that very young infants reach for an object moving in front of them, a reflexlike motion we referred to as prereaching. As we discussed, at this initial stage, the perceptions and actions involved in reaching and grasping are not yet coordinated. Infants may reach for an object but fail to close their hands around it, usually because they close their hands too soon (see Figure 5.5a). Then, around 4 to 6 months of age, babies begin to gain voluntary control over their movements, so reaching and grasping occur in the proper sequence (Berthier & Keen, 2006). At first, their reaching and grasping is hit or miss (von Hofsten, 2001). With practice, their fine motor coordination gradually improves (see Figure 5.5b), and by 2 years of age, the overall speed and smoothness of their reaching approach adult levels. During this time, caretakers need to "baby proof" their homes by putting dangerous or fragile objects out of the infant's reach. They also have to watch out for the sudden appearance of unexpected items in the grocery cart if the baby is along for the ride! FIGURE5.5 At 3 months of age, the baby's reaching and grasping are not yet well coordinated, making it difficult to seize the object of interest (a). In contrast, by 8 months of age, motor skills are so advanced that the baby can not only grasp the object easily but also explore it intently (b). In the period between 7 and 12 months of age, fine motor movements of the hands and fingers become better coordinated. 7-month-olds are still unable to use their thumbs in opposition to their fingers to pick up object by 12 months of age, babies are able to move their thumbs and other fingers into positions appropriate to the size of the object they are trying to grasp. As their reaching and grasping become better coordinated and more precise, babies' explorations of objects become more refined. They are increasingly able to do such things as drink from a cup, eat with a spoon, and pick raisins out of a box. FIGURE5.6 Babies find ways to grasp objects from an early age, but good coordination of the thumb and forefinger requires at least a year to achieve. A 7-month old infant uses its palm to grasp a block and a tiny ball. A 9-month old infant uses its thumb and fingers to grasp the block and the tiny ball (scissors grasp). pincer grasp: 1yr old baby grasps the block and the tiny ball with thumb and forefinger. As babies gain control over their hands, different objects invite different kinds of exploration — banging, shaking, squeezing, and throwing. All these actions provide the baby with knowledge about the properties of the physical world. Rattles, for example, lend themselves to making noises, while soft dolls lend themselves to pleasurable touching. Perceptual-motor exploration is an all-important way to find out about the environment and to gain control over it. Later Skills: Manual Dexterity A lot of parents keep pictures of their babies' first efforts to feed themselves — pudgy faces all smeared with food. As amusing as these pictures can be, they illustrate the difficulty of mastering an act as elementary as using a spoon. Infants between 10 and 23 months of age attempt to hold a spoon in a variety of different ways as they try to learn the incredibly precise coordination that the effective use of a spoon entails. At 10 to 12 months of age, babies can do only simple things with a spoon, such as bang it on the table or repeatedly dip it into their bowl. Slightly older children can coordinate the action of dipping, opening their mouth, and bringing the spoon to it, but as often as not, the spoon is empty when it arrives. Once the baby masters the sequence of getting food on the spoon, carrying it to the mouth without spilling, and putting the food in the mouth, the sequence is adjusted until it is smooth and automatic. Coordination of fine motor movements increases significantly during the 2nd year of life. At age 1, infants can only roll a ball or fling it awkwardly; by the time they are age 2, they are more likely to throw it. By age 2, they can also turn the pages of a book without tearing or creasing them, snip paper with safety scissors, string beads with a needle and thread (although the bead hole usually has to be pretty big!), build a tower six blocks high with considerable ease, hold a cup of milk or a spoon of applesauce without spilling it, and dress themselves (as long as there are no buttons or shoelaces) (Bayley, 1993). Each of these accomplishments may seem minor on its own, but infants' growing ability to manipulate objects with their hands relates to one of the most sophisticated accomplishments of our species and the most effective way of transmitting and transforming culture — using and making tools. Using a spoon is a lot more complicated than you might think. It will take this baby many more months of practice before the fine motor skills involved in spoon use become smooth and automatic. Affordances= "the world offers experiences". the spoon is an affordance for the baby to practice hand movements, for the baby to practice putting it in its mouth. The floor is an affordance for the baby to crawl around. The crib is an affordance for the baby to fall asleep. (Early neuroscientist Gibson) Motor milestones youtube/watch (Baby Milestones Motor Development) Gross Motor Skills locomotion: the ability to move around on one's own; central developmental change that occurs toward the end of the 1st year. As we have noted, the development of gross motor skills greatly expands infants' opportunities to learn about the world and decreases their dependence on caregivers. Although there is wide variation in the age at which the various gross motor milestones are achieved, most babies throughout the world move through the same sequence of development, which begins with reflexive creeping and ends with purposeful walking, that uniquely human form of locomotion (Figure 5.7). FIGURE5.7 Despite wide variation in the ages at which specific gross motor skills are acquired, most children follow the same sequence of motor milestones, from sitting without support to independent walking. The horizontal axis represents the age in months and ranges from 3 to 21 months in increments of one month and the vertical axis represents the motor milestones. The time taken to achieve each milestone is listed below. Sitting w/o support — 4 to 9 months Standing w/ assistance — 4.5 to 12 months Hands-and-knees crawling — 5 to 14 months Walking w/ assistance — 6 to 15 months Standing alone — 6 to 18 months Walking alone — 8 to 19 months All data in the graph are approximate The horizontal axis represents the age in months and ranges from 3 to 21 months in increments of one month and the vertical axis represents the motor milestones. The time taken to achieve each milestone is listed below. Sitting w/o support — 4 to 9 months Standing w/ assistance — 4.5 to 12 months Hands-and-knees crawling — 5 to 14 months Walking w/ assistance — 6 to 15 months Standing alone — 6 to 18 months Walking alone — 8 to 19 months All data in the graph are approximate The horizontal axis represents the age in months and ranges from 3 to 21 months in increments of one month and the vertical axis represents the motor milestones. The time taken to achieve each milestone is listed below. Sitting without support — 4 to 9 months Standing with assistance — 4.5 to 12 months Hands-and-knees crawling — 5 to 14 months Walking with assistance — 6 to 15 months Standing alone — 6 to 18 months Walking alone — 8 to 19 months All data in the graph are approximate Creeping and Crawling During the 1st month of life, when their movements appear to be controlled primarily by subcortical areas of the brain, infants may occasionally creep short distances, propelled by the rhythmic pushing movements of their toes or knees (Figure 5.8). At about 2 months of age, this reflexive pushing disappears, and it is another 5 or 6 months before babies can crawl about on their hands and knees (World Health Organization, 2006). FIGURE5.8 Phases in the development of creeping and crawling. (a) Newborns creep by making pushing movements with their knees and toes. (b) The head can be held up, but leg movements diminish. (c) Control over movement of head and shoulders increases. (d) Ability to support the upper body with the arms improves. (e) Babies have difficulty coordinating shoulders and midsection; when the midsection is raised, the head lowers. (f) Babies can keep the midsection raised but are unable to coordinate arm and leg movements, so they tend to rock back and forth (Goldfield, 2000). (g) Coordinated arm and leg movements enable the baby to crawl. The first illustration shows an infant lying on its stomach and pushing its knees and toes forward. The second illustration shows the infant holding its head up and arms pressed down. The third illustration shows the baby lifting the head and shoulders by pressing down on the arms. The fourth illustration shows the upper body lifted up by pressing down on the arms. The fifth illustration shows the trying to rise by pressing down on the arms and legs. The sixth illustration shows the baby trying to kneel and move forward and backward by pressing down the arms. The sixth illustration shows the baby moving the arms and legs in coordination to start crawling. By the time they are 8 to 9 months of age, most infants can crawl on flat, smooth surfaces with some skill. Crawling allows babies to explore their environment in a new way and acquire new information about it, thus changing how they respond to the world. One manifestation of infants' new exploration of and response to the environment is the emergence of wariness of heights, typically about the same time that they begin to crawl — between 7 and 9 months of age among children in the United States (Dahl et al., 2013). This wariness is demonstrated by infants' behavior on a "visual cliff," a specially constructed apparatus that gives the illusion of a dangerous drop-off. As shown in Figure 5.9, the apparatus includes a strong sheet of clear acrylic that extends across two sides — one "shallow," and one "deep." On the shallow side, a checkered pattern is placed directly under the acrylic sheeting, so the surface seems solid and safe. On the deep side, the checkered pattern is placed at a distance below the sheeting, suggesting a cliff. A number of experiments conducted by Joseph Campos and his colleagues have demonstrated that infants are not afraid to cross over to the deep side until they have had a certain amount of experience trying to crawl about on their own (Bertenthal, Campos, & Kermoian, 1994). In addition to their reluctance to cross the cliff, infants with crawling experience express their wariness of depth by looking to their mothers for cues about what to do (Striano, Stahl, & Cleveland, 2009). (As discussed below, this kind of checking in with a caregiver for cues about how to behave is known as social referencing.) FIGURE5.9 Despite being encouraged to do so, this little boy is hesitant about crossing the transparent surface of the visual cliff. Associated with learning to crawl, his behavior indicates a fear of heights typical of 7- to 9-month-olds. Appreciating that when infants crawl, they not only move across flat surfaces but also gain experience moving — and sometimes falling — over various objects, obstacles, and steps, you might assume that wariness of heights is associated with the occasionally unhappy consequences of crawling. But research does not support this interpretation. Instead, it seems that visual proprioception: the visual feedback that one gets from moving around, may be critical to the development of wariness. To test this idea, a team of researchers placed pre-crawling babies in self-controlled go-carts (see Figure 5.10) for 10 minutes per day over a 15-day period (Dahl et al., 2013). These babies' heart rates increased significantly when they were held over the "deep" side of the visual cliff, in contrast to a control group of pre-crawling infants who had no go-cart experience. This suggests that visual proprioception does indeed contribute to the development of a fear of heights. FIGURE5.10 When babies who do not yet crawl get experience moving around their environments in self-controlled go-carts, they develop wariness of heights. This suggests that wariness is due to visual proprioception, rather than experiences falling in the course of learning to crawl. Walking A baby's first steps are a source of joy and marvel for caregivers as well as the babies themselves. As infants approach their first birthday, many become able to stand up and walk, which soon allows them to cover more distance than crawling did and frees their hands for carrying, exploring, and manipulating objects (Cole, Robinson, & Adolph, 2016). At first they need assistance of some kind in order to walk. This assistance can come in several forms. Many babies grasp onto furniture to pull themselves into a standing position (Berger & Adolph, 2003). Seeing such attempts, caregivers often help by holding both of the baby's arms to support the initial hesitant steps. Of course, it's a long road from a baby taking his or her first steps to being able to walk with ease around obstacles, up and down stairs, and on surfaces that are uneven or slippery. Indeed, a study of the motor behavior of 12- to 19-month-olds during free play documented an average of more than 2,000 steps and 17 falls per hour (Adolph et al., 2012). In addition to receiving a lot of assistance and encouragement from others throughout this process, babies become quite adept at responding to communications from others about their motor behavior. Karen Adolph's research shows an example of the ways infants use social referencing when walking down slopes that may put them at risk of falling (Adolph, Karasik, & Tamis-LeMonda, 2010). social referencing refers to infants' tendency to look to their caregiver for an indication of how to feel and act in unfamiliar circumstances. Placing infants on a walkway with an adjustable slope (see Figure 5.11), Adolph and her colleagues found that even when the slope was shallow and posed little risk of falling, babies proceeded with caution (if at all) when their mother discouraged them from walking. On the other hand, they refused to walk when the slope was steep and dangerous, even when their mother encouraged walking. The researchers concluded that when social signals from the caregiver conflict with the baby's own assessment of risk, the latter generally wins the day, which is probably good news. As the researchers point out: In everyday situations, parents cannot be so vigilant that they can protect infants from every potential danger. With the advent of independent locomotion comes increasing autonomy. Although mothers' advice can often be useful, especially under conditions of uncertainty, infants must eventually learn to navigate the world on their own. (p. 1041) FIGURE5.11 The transition from crawling to walking changes the way babies approach the task of going down a ramp. The toddler looks quite unsure, despite being lured by a toy. No one factor can be considered the key to walking; rather, as dynamic systems theorists point out, walking becomes possible only when all the component motor skills — upright posture, leg alternation, muscle strength, weight shifting, and sense of balance — have developed sufficiently and when the child has been able to practice combining them (Thelen, Fisher, & Ridley-Johnson, 2002). These new motor skills must then be combined with an increased sensitivity to perceptual input from the environment and social information from others about where, when, and how to walk. The Role of Practice in Motor Development Studies of motor development were among developmentalists' earliest strategies for investigating the relative roles of nature and nurture. During the 1930s and 1940s, it was commonly believed that the attainment of such motor milestones as sitting and walking were dictated by maturation, with learning and experience playing little or no role. One of the earliest studies to support this view was conducted by Wayne and Margaret Dennis among Hopi families in the southwestern United States (Dennis & Dennis, 1940). In traditional Hopi families, babies in the first several months after birth are tightly swaddled and strapped to a flat cradle board. They are unwrapped only once or twice a day so that they can be washed and their clothes can be changed. The wrapping allows infants very little movement of their arms and legs and no practice in such complex movements as rolling over. The Dennises compared the motor development of traditionally raised Hopi babies with that of the babies of less traditional Hopi parents who did not use cradle boards. They found that the two groups of babies did not differ in the age at which they began to walk by themselves, which is consistent with the notion that this basic motor skill does not depend on practice for its development. However, observations of babies from other cultural settings provide evidence that practice can affect the age at which babies reach motor milestones and may even alter the sequence of the milestones. Charles Super (1976) reported that among the Kipsigis people of rural Kenya, parents begin to teach their babies to sit up, stand, and walk not long after birth. To teach their children to sit up, for example, Kipsigis parents seat their babies in shallow holes in the ground that they have dug to support the infants' backs, or they nestle blankets around them to hold them upright. They repeat such procedures daily until the babies can sit up quite well by themselves. Training in walking begins in the 8th week after birth. The babies are held under the arms with their feet touching the ground and are gradually propelled forward. On average, Kipsigis babies reach the developmental milestones of sitting 5 weeks earlier and walking 3 weeks earlier than do babies in the United States. (Similar results have been reported among West Indian and Cameroonian children, whose mothers put them through a culturally prescribed sequence of motor exercises during the early months of infancy [Hopkins & Westen, 1988; Keller, 2003].) At the same time, Kipsigis infants are not advanced in skills they have not been taught or have not practiced. They learn to roll over or crawl no faster than children in the United States, and they lag behind children in the United States in their ability to negotiate stairs. Babies who are just beginning to stand up find other people and furniture to be handy aids. This Filipino baby who lives in a house on stilts is being trained at an early age in the essential skill of climbing a ladder. Further evidence about the impact that practice — or lack of it — can have on early motor development comes from the Ache, a nomadic people living in the rain forest of eastern Paraguay. Hilliard Kaplan and Heather Dove (1987) reported that Ache children under 3 years of age spend 80 to 100 percent of their time in direct physical contact with their mothers and are almost never seen more than 3 feet away from them. A major reason is that Ache hunter-gatherer groups do not create clearings in the forest when they stop to make camp. Rather, they remove just enough ground cover to make room to sit down, leaving roots, trees, and bushes more or less where they found them. For safety's sake, mothers either carry their infants or keep them within arm's reach. As a result of these cultural patterns, Ache infants are markedly slower than U.S. infants in acquiring gross motor skills such as walking. In fact, they begin walking, on the average, at about 23 months of age, almost a full year later than children in the United States. At about the age of 5, however, when Ache children are deemed old enough to be allowed to move around on their own, they begin to spend many hours in complex play activities that increase their motor skills. Within a few years, they are skilled at climbing tall trees and at cutting vines and branches while they balance high above the ground in a manner that bespeaks normal, perhaps even exceptional, motor skills. Intended to prevent sudden infant death syndrome, the practice of putting babies to sleep on their back has had the unexpected effect of delaying the onset of crawling. Pediatricians now encourage parents to provide young infants with plenty of "tummy time" in which to gain experiences important for learning to crawl. The influence of practice, and of cultural norms on physical development, is further highlighted by the "back-to-sleep" movement in the United States to eradicate SIDS (see Chapter 4, p. 155). The widespread success of getting parents to put their infants on their back to sleep rather than on their belly has had the unexpected effect of delaying the onset of crawling in babies in the United States by as much as 2 months (Majnemer & Barr, 2005). Because time spent in the prone position (facedown) provides babies with their earliest experiences of bearing their body weight with their arms, shifting their weight to reach for a toy, and trying out coordinated movements of their arms and legs, children who spend their waking as well as sleeping hours on their back miss out on developmentally appropriate experiences. As a consequence, pediatricians in the United States urge parents to provide their young infants with "tummy time" to play so that they can practice pushing themselves up as a precursor to crawling (Pontius et al., 2001). Indeed, researchers are finding that babies with more tummy time tend to roll, crawl, and sit at earlier ages than do those who spend less time in the prone position (Kuo et al., 2008).

Summary

Physical Growth Height and weight increase rapidly throughout infancy, especially during the 1st year. Body proportions shift, too, with the head coming to account for relatively less of the infant's length and the legs for relatively more. Soft bones gradually ossify, and muscle mass increases. Although boys tend to be larger than girls, girls tend to develop more quickly. Norms for children's growth can be enormously helpful in determining whether a child's physical development is on track and whether a child may be at risk for later problems. Significantly slower growth rates, known as infant growth restriction or stunting, are associated with developmental delay, infections, and poor nutrition, whereas significantly faster growth rates are associated with the risk of obesity in later childhood. Brain Development Increased myelination of axons, along with other changes, such as the formation of neural networks that allow different parts of the brain to communicate and work together, leads to substantial development of the cerebral cortex, including the prefrontal and language-related areas, and to greater synchrony among the brain areas. These changes appear to be vital to the emergence in late infancy of more systematic problem solving, voluntary control of behavior, and the acquisition of language. By late infancy, most of the brain structures that will support adult behavior are present. As shown by studies of orphans who experienced early life adversity, prolonged deprivation in infancy leads to ongoing impairments in intellectual functioning. Because the brain undergoes considerable development between 6 and 24 months of age, lack of experiences during this sensitive period appears to affect both experience-expectant and experience-dependent brain development. Motor Development Made possible by physical changes, the development of fine and gross motor skills enables infants to reduce their dependence on caregivers to get around and allows them to increasingly explore their environment. As the movements of their hands and fingers become better coordinated during the 1st year, infants perfect their reaching and grasping. With continuing increases in coordination of fine motor movements, by age 2 infants can do much in the way of feeding and dressing themselves and can turn book pages, cut paper, string beads, and stack blocks. Progress in locomotion leads to the emergence of crawling by 8 to 9 months of age, at which time wariness of heights appears. Walking begins at around 1 year and is made possible by the development of component motor skills and by practice. Studies in different cultures reveal that practice or lack of it can affect the age at which infants reach motor milestones. Cognitive Development: The Great Debate For some developmentalists, including Piaget, young infants are limited to sensorimotor intelligence until about 18 months of age, when they become capable of representational thinking — thinking that is truly conceptual. For other developmentalists, very early in development, if not from birth, infants are capable of representing and understanding the world conceptually. A rudimentary conceptual system develops separately from, although in close association with, the sensorimotor system. In Piaget's stage of sensorimotor development, infants acquire knowledge exclusively through motor actions directed at their immediate environment and guided by their senses. Following the first two of Piaget's substages, in which infants learn to control reflexes and then to modify and repeat actions involving their bodies, infants move through four additional sensorimotor substages:In substage 3, infants 4 to 8 months of age become capable of secondary circular reactions, repeating actions that involve objects, not simply those that involve their own body.In substage 4, at 8 to 12 months of age, infants begin to display intentionality, engaging in goal-directed behavior.In substage 5, the stage of tertiary circular reactions, infants 12 to 18 months of age deliberately vary their actions, thus experimenting in order to explore the world.In substage 6, which occurs between 18 and 24 months of age, infants begin to base their actions on representations. The ability to represent mentally is crucial to problem solving, symbolic play, deferred imitation, and the use of language. The sequence and timing of the behaviors associated with Piaget's sensorimotor stages have been replicated with infants in a wide range of societies. However, critics of Piaget argue that young infants have representational competence that traditional Piagetian tests do not enable them to reveal. Conceptual Development For Piaget, object permanence — the understanding that objects continue to exist when out of sight — emerges only gradually, beginning at about 8 months. Thus, 8- to 12-month-olds continue to search for an object in a location where they discovered it even when they have seen it hidden again in a different location. Piaget claimed that these infants still did not have true representations. Other developmentalists have argued that the infants' behavior reflects not a lack of representational competence but performance problems — specifically, memory limitations or a tendency to perseverate, repeating the same movement or the same successful strategy. Using the violation-of-expectations method, in which babies are habituated to an event and then presented with possible and impossible variants, researchers have obtained results suggesting that infants as young as 2½ months are capable of representations. According to the dynamic systems approach, cognitive development in infancy involves not a shift from sensorimotor to conceptual intelligence but the growing abilities to coordinate all the various systems involved in sensorimotor and conceptual intelligence. The formation of representations may depend heavily on experience. In experiments, infants' typical preference for a novel object over a familiar object is reversed when the room is darkened, perhaps because experience with an object leads to a stronger representation of it. Experiments using the violation-of-expectations method suggest that infants as young as 3 months of age have an initial grasp of various physical laws concerning the behavior of objects, such as the law of gravity. Other experiments using simplified tests suggest that, contrary to Piaget's view, young infants may be capable of understanding basic numbers and cause-effect relationships. Of particular interest is infants' abilities to categorize, evident as early as 3 months of age. Developmentalists are uncertain whether changes in categorization abilities during infancy simply reflect improved perceptual abilities or signal a change from categorization based only on perceptual features to categorization that is also conceptually based. The Growth of Attention and Memory Developments in attention and memory are crucial to all the other cognitive changes of infancy. Infants are increasingly able to sustain their attention; in addition, they are increasingly fast at processing information about the targets of their attention. These changes are reflected in experiments showing that attention to simple visual displays decreases after the first few months but attention to complex stimuli increases. Memory increases rapidly during the 1st year, as shown by the increase in the length of time over which infants are able to remember procedures such as how to make a mobile move. Looking Ahead Infancy is a brief period of enormous physical and cognitive changes with significant implications for development in other domains and for future development. Brain development and increases in height and weight support developing motor skills, which help make the cognitive changes possible. Among cognitive changes crucial to development is the growing capacity for mental representation and memory.

Physical growth

The changes in body size and proportions and in the muscles and bones, as well as in the brain are connected both with each other and with the development of the new behavioral capacities babies display. example: babies' greater weight requires larger and stronger bones to support them and stronger muscles to enable movement. - developing cognitive capacities make babies want to explore new aspects of the world, but to explore the world, they must coordinate their constantly changing size and strength in new ways. Size and Shape - During 1st year of life: most healthy babies triple in weight & grow approx. 10 inches; in the U.S., the typical 1-year-old weighs 20-22 lbs and stands 28-30 inches tall. -During the 2nd year of life: children's bodies continue to grow rapidly, though at a much slower rate; in the U.S., children on average gain 5 pounds and grow 4 inches to about 27 pounds and about 34 inches (This tapering off of the growth rate continues until adolescence when there is a noticeable growth spurt for children growing up in many, but not all, parts of the world) by 2 years of age, most children have all their baby teeth. U.S. babies' lengths roughly double and their weights increase around 200 percent during the first 2 years of life. Note that at this stage, boys tend, on average, to be heavier and taller than girls. Boys @ birth: length= around 50 cm/ grow up to 85 cm in 2 years weight= 3.5 kg/ increase to 12kg in 2 years Girls @ birth: length= around 48 cm/ grow to 82 cm in 2 years of age. weight= 2.5 kg/ increase to 11 kg in 2 yrs Increases in babies' height and weight are accompanied by changes in their body proportions. At birth, the baby's head is 70 percent of its adult size and accounts for about 25 percent of the baby's total length. By 1 year of age, the head accounts for 20 percent of body length, and by adulthood, 12 percent. Infants' legs at birth are not much longer than their heads; by adulthood, the legs account for about half of a person's total height. By 12 months, the changes in body proportions have led to a lower center of gravity, making it easier for the child to balance on two legs and begin to walk. As their bodies stretch out, most babies lose the potbellied look so characteristic of early infancy; they begin to look more like children than infants. FIGURE5.3 These drawings show the proportions of body length accounted for by the head, trunk, and legs at different stages of development. During the fetal period, the head accounts for as much as 50 percent of body length. The head decreases from 25 percent of body length at birth to 12 percent in adulthood. The first illustration shows a 2-month old fetus. The head is nearly half the size of the whole body. The second illustration shows the fetus in the fifth month. The size of the body truck is increased, proportionally reducing the size of the head. The next illustration shows a newborn baby. The size of the head of a newborn is approximately one-third the body size. The proportion of the head size steadily decreases in relative to the increasing size of the body truck over the years. The norms for children's growth can be enormously helpful in determining whether a child's physical development is on track. Physical growth that differs substantially from the norms may signal illness or risk for disease. For example, infant growth restriction, or stunting: significantly slower growth rates: associated with # of serious problems, including developmental delay, infections, and poor nutrition significantly faster growth rates are associated with risk of obesity in later childhood However, most standard growth norms are derived by averaging large samples of children who are developing in Western, technologically advanced countries; consequently, they should be used with caution in determining whether children's growth is on track. First, babies who are growing up in societies within developing nations or challenging environments may develop differently than indicated in standard growth charts. In many areas of the Amazon, for example, infants tend to grow rapidly during the first few months, but their rates of growth, especially in height, slow substantially after that, likely due to some combination of genetics, infectious diseases, and poor-quality diets (Urlacher et al., 2016). The Musculoskeletal System As babies grow, the bones and muscles needed to support their increasing bulk and mobility undergo corresponding growth. Most of a newborn's bones are relatively soft, and they harden (ossify) only gradually, as minerals are deposited in them in the months after birth. The bones in the hand and wrist are among the first to ossify. They harden by the end of the 1st year, making it easier for a baby to grasp objects, pick them up, and play with them. At the same time, infants' muscles increase in length and thickness, a process that continues throughout childhood and into late adolescence. In infancy, increases in muscle mass are closely associated with the development of the baby's ability to crawl, stand alone, and walk. Although boys are generally larger than girls, as Figure 5.2 clearly indicates, research supports the common wisdom that girls mature faster than boys. In fact, sex differences in growth rates are apparent even before birth: Halfway through the prenatal period, the skeletal development of female fetuses is some 3 weeks more advanced than that of male fetuses. At birth, the female skeleton is 4 to 6 weeks more mature than that of the male; by puberty, it is 2 years more advanced. (Girls are more advanced in the development of other organ systems as well. They get their permanent teeth, go through puberty, and reach their full body size earlier than boys do [Bogin, 1999].) The physical changes of infancy described above open wholly new ways of exploring and learning about the environment. Equally significant in making these possible are the changes taking place in the brain.

Conceptual Development

s we have seen, Piaget maintained that before the onset of representations, infants have no knowledge that endures beyond the immediate here and now. Although they can form primitive associations as, for example, in classical and operant conditioning (see Chapter 4, pp. 147 - 149), it is not until the end of the sensorimotor stage of intelligence that infants gain a conceptual understanding of the characteristics of objects and events. The distinction between sensorimotor and conceptual intelligence was cleverly highlighted by Jean Mandler when she characterized the sensorimotor infant as an "absent-minded professor" who, finding herself in the kitchen unable to remember what she wanted there, searches around for a clue and, upon seeing a cup by the sink, thinks, "Aha, I came for coffee!" (2004, p. 21). From Piaget's perspective, the sensorimotor infant can be similarly cued by perceptual features of the immediate environment to "remember" past associations but cannot grasp them conceptually in the absence of such prompts. In the sections that follow, we explore the ways that infants demonstrate capacities to understand the world in more conceptual, abstract terms. As you will see, there is strong evidence that Piaget underestimated the conceptual intelligence of infants. As yet, however, there is no unifying theory that accounts for conceptual development during the first 2 years. Should such a unifying theory take shape, the accumulating evidence indicates that it will need to account for the infant's biological preparedness to construct a typically "human" understanding of the world as well as for the consequences of the infant's experiences in specific contexts. Understanding the Permanence of Objects Observation 1. A baby seated at a table is offered a soft toy (see Figure 5.12). He grasps it. While he is still engrossed in the toy, the experimenter takes it from him and places it on the table, behind a screen. The baby may begin to reach for the toy, but as soon as it disappears from sight, he stops short, stares for a moment, and then looks away without attempting to move the screen (Piaget, 1954). Observation 2. A baby is placed in an infant seat in a bare laboratory room. Her mother, who has been playing with her, disappears for a moment. When the mother reappears, the baby sees three of her, an illusion the experimenter has created through the use of carefully arranged mirrors. The baby displays no surprise as she babbles happily to her multiple mothers (Bower, 1982). Observation 3. A baby watches a toy train as it chugs along a track (see Figure 5.13). When the train disappears into a tunnel, the child's eyes remain fixed on the tunnel's entrance rather than following the train's expected progress through the tunnel. When the train reappears at the other end of the tunnel, it takes the child a few seconds to catch up with it visually, and the child shows no surprise when the train that comes out of the tunnel is a different color or shape (Bower, 1982). FIGURE5.12 Instead of searching behind the screen when his toy disappears, this infant looks dumbfounded. This kind of behavior led Piaget to conclude that objects no longer in view cease to exist for infants younger than 8 months of age. The first photo shows a baby looking at a monkey soft toy. The second photo shows the baby looking stunned when a sheet is placed between the baby and the monkey soft toy. FIGURE5.13 Infants who have yet to gain a firm understanding of object permanence, according to Piaget's criteria, fail to track the motion of a toy train when it enters a tunnel. In the first illustration, the baby is shown smiling and watching the train approaching the tunnel. In the second illustration, the baby is shown happily looking at the toy train entering the tunnel. In the third and the fourth illustrations, the baby's eyes remains fixed at the point where the train entered the tunnel. The baby's face shows a sad confused expression. In the final illustration, the baby notices the train leaving the tunnel from the other end and smiles happily. Each of these observations was recorded in the context of studying object permanence, a full and stable grasp of which is, according to Piaget, a clear indicator that the development of mental representation and conceptual thinking is under way. As noted, Piaget contended that babies demonstrate object permanence only when they begin to search actively for an absent object, as when they uncover a toy they have just seen the experimenter hide under a cloth or behind a barrier. His research indicated that although this active searching behavior first appears at around 8 months of age, infants' mastery of object permanence is incomplete until the second half of their 2nd year. He discovered, for example, that babies between 8 and 12 months tend to make a characteristic mistake when searching for objects: If, after they have successfully searched for an object hidden in one location, A, the object is then hidden, right before their eyes, in a new location, B (Figure 5.14), they will still search for the object in location A, where they previously found it! FIGURE5.14 In this movie sequence, an object is placed in the circle on the left (position B), and then both circles (positions A and B) are covered with a cloth while the baby watches. In a previous trial, the object had been placed in the right-hand circle (position A), and the baby had correctly retrieved it. This time, while remaining oriented toward the hidden object at position B, the baby nonetheless picks up the cloth at position A, where the object was hidden before. In the first video screenshot, the baby is shown looking at the object placed in position B , which is to the child's right side. In the second part, circles marking both positions are shown covered with cloth. The baby is shown looking at the covers. In the third video screenshot, the child is trying to grab the covering cloth on its left, but is looking at the cloth on its right side. In the fourth video screenshot, the baby is shown holding the cloth covering the circle to its left and still looking at and reaching out to cloth on its right. Piaget interpreted this pattern of responding — referred to as the A-not-B error — as evidence that the child remembers the existence of the object but cannot reason systematically about it. He believed that true representation requires the ability both to keep in mind the existence of an absent object and to reason about that absent object mentally, an achievement he did not think occurs until late in the 2nd year, during the sixth substage of the sensorimotor period. Alternative Explanations of Infants' Difficulties Other developmentalists have disagreed with Piaget's interpretation of young infants' A-not-B error. They believe that the error is due not to a failure to represent and reason about the object but to other developmental limitations, including limitations of memory or motor skills (Cuevas & Bell, 2010; Marcovitch et al., 2016). The Role of Memory. In an influential series of studies, Adele Diamond (1991) suggested that young infants may be capable of representation but fail Piaget's A-not-B task because they simply do not remember where the object was hidden. Diamond varied the time between the switching of an object from location A to location B and the moment when children were allowed to reach for the hidden object (Diamond, 1991, 2000). She found that, if they were allowed to reach immediately, 7½-month-old babies correctly located the object at position B, but if they were prevented from reaching for as little as 2 seconds, they exhibited the A-not-B error. By 9 months of age, infants could withstand a delay of 5 seconds before beginning to make mistakes, and by 12 months of age, they could withstand a delay of 10 seconds. These results suggest that young infants are capable of representing objects they cannot see but quickly forget their location and become confused (which may explain the behavior of the baby in Figure 5.14 on page 181). Other studies documenting a relationship between the delay of reaching and successful searching (Bremner et al., 2005; Johansson et al., 2014; Ruffman, Slade, & Redman, 2005) further suggest that the A-not-B task may impose significant demands on infants' memory system, masking their representational abilities. The Role of Perseveration. Have you ever tried to push your ill-fitting glasses up the bridge of your nose (again), only to remember that you're wearing your contact lenses? If so, then you are familiar with perseveration — the persistent repetition of a particular behavior. Diamond believed that young infants may exhibit the A-not-B error not only because of their memory limitations but also because of their tendency to engage in motor perseveration, in which they repeat a movement rather than modify it to fit new events. She noted that some infants who make the A-not-B error in fact look at location B but reach toward location A. Research suggests that such perseveration (which could also explain the behavior of the baby in Figure 5.15) may be due to the tendency of certain motor behaviors to become habits (Clearfield et al., 2009) or may be related to immature brain development that makes it difficult for infants to inhibit responses (Diamond & Amso, 2008; Marcovitch et al., 2016). FIGURE5.15 Using this version of the violation-of-expectations method, researchers find that infants as young as 2½ months look longer at the impossible event, suggesting that they are capable of mentally representing their past experiences. The first and second illustrations are titled Habituation Events. The first illustration representing Short-carrot event shows a small carrot placed to the left of a black screen. Dotted forward arrows point from the carrot to the screen and from the screen to the edge of the illustration. The arrows are drawn close to the base. The second illustration representing Tall-carrot event shows a tall carrot placed to the left of a black screen. Dotted forward arrows point from the carrot to the screen and from the screen to the edge of the illustration. The arrows are drawn at close to the top of the screen. The third and fourth illustrations are titled Test Events. The illustrations shows screen with part of the top half cut out. In the third illustration titled Possible event, a small carrot is shown to the left of the screen. Dotted forward arrows point from the carrot to the screen and from the screen to the edge of the illustration. The arrows are drawn close to the base. In the fourth illustration, a tall carrot is shown to the left of the screen. forward arrows point from the carrot to the screen and from the screen to the edge of the illustration. The arrows are drawn at close to the top of the screen through the cutout part. The first and second illustrations are titled Habituation Events. The first illustration representing Short-carrot event shows a small carrot placed to the left of a black screen. Dotted forward arrows point from the carrot to the screen and from the screen to the edge of the illustration. The arrows are drawn close to the base. The second illustration representing Tall-carrot event shows a tall carrot placed to the left of a black screen. Dotted forward arrows point from the carrot to the screen and from the screen to the edge of the illustration. The arrows are drawn at close to the top of the screen. The third and fourth illustrations are titled Test Events. The illustrations shows screen with part of the top half cut out. In the third illustration titled Possible event, a small carrot is shown to the left of the screen. Dotted forward arrows point from the carrot to the screen and from the screen to the edge of the illustration. The arrows are drawn close to the base. In the fourth illustration, a tall carrot is shown to the left of the screen. forward arrows point from the carrot to the screen and from the screen to the edge of the illustration. The arrows are drawn at close to the top of the screen through the cutout part. The A-not-B error may also involve another type of perseveration that is not specifically linked to motor behavior: Babies may reach incorrectly for the object at location A because of their previous success in finding it there. This is an example of a capture error, a tendency of people at all ages to continue using a once-successful solution whenever possible. Memory limitations, motor perseveration, and capture errors are all explanations for why infants may fail the A-not-B task, even though they may possess the ability to form mental representations. In other words, many developmentalists believe that infants have representational competence but lack the performance skills required to successfully demonstrate that competence on the task (Hespos & Baillargeon, 2008). Alternative Approaches to Measuring and Understanding Object Permanence Prompted by evidence that the performance demands of the A-not-B task obscure the young infant's representational competence about objects, several developmentalists have proposed alternative ways of measuring and understanding object permanence. Some designed new tests of Piaget's theory, arguing that if infants were not required to demonstrate their understanding by reaching for and manipulating things, it might be possible to show that infants are capable of representational thought at or near birth. Others have taken a much more radical stance, proposing that the whole idea of competence in the absence of performance is irrelevant to infants' performance on the A-not-B test. As you will see, these developmentalists do not call for new measures of object permanence as much as for a new theory about how infants behave in various testing situations. Violation-of-Expectations Method. To challenge Piaget's theory of when representation develops, Renée Baillargeon and her colleagues devised an object permanence test that exploits the well-known tendency of infants (in fact, of everyone) to stare at events that violate their expectations (Hespos & Baillargeon, 2008; Wang, Baillargeon, & Brueckner, 2004). This test, the violation-of-expectations method, involves a bit of research trickery. Basically, babies are habituated to a particular event and then presented two variants of the event — one that is "possible" under normal circumstances and one that is "impossible" and comes about only through an illusion created by the researcher. The premise is that if infants are capable of mentally representing their experiences, they should develop specific expectations during the habituation phase and then look longer at events that violate those expectations — that is, at the impossible events. In one study, infants were habituated to two events. In one, a short carrot moved behind a screen and reappeared on the other side; in the other, a tall carrot moved behind the screen and likewise reappeared (Figure 5.15). Once the infants were habituated to these two events, they were presented with two test events in which a window had been cut out of the screen. In the possible event, a short carrot again moved behind the screen and reappeared on the other side. The window in the screen was high enough that the small carrot was hidden from view as it passed behind the screen. In the impossible event, a tall carrot moved behind the screen and reappeared on the other side. In this case, the tall carrot should have appeared in the window as it passed behind the screen — but, in violation of anyone's expectations, it did not (thanks to the experimenter's secret manipulations). Using this method, Baillargeon demonstrated that infants as young as 2½ months of age looked longer at the impossible event than at the possible event, suggesting that they had, indeed, formed mental representations of their past experiences with the habituation events. As you will see later in this chapter, developmentalists have used similar tricks to figure out what infants do and do not understand about the physical world. Dynamic Systems Approach. While many developmentalists have focused on untangling infants' underlying conceptual competence from the performance demands of the tasks, Esther Thelen and her colleagues have offered an entirely different approach to thinking about the nature of knowledge and its development in infants (Thelen, Schoener, Scheier, & Smith, 2001). According to their dynamic systems perspective (see Chapter 1, p. 27), it is unnecessary to invoke the idea of performance limitations to explain infants' failures on the A-not-B task or to invoke the idea of mental concepts such as object permanence to account for their ultimate success. In their view, infants' behaviors on tests of object permanence — indeed, all human action in any context — are the result of the dynamics that emerge from the "immediate circumstances and the [individual's] history of perceiving and acting in similar circumstances" (p. 34). Thus, infants' experiences with specific objects, their current memory of those experiences, and their current motor skills all interact in their solving the specific problems posed by whatever task they face. From this perspective, the critical developmental process is not, as Piaget contended, a shift from sensorimotor intelligence to conceptual intelligence. Rather, it is infants' growing abilities to better coordinate all the various systems involved in both sensorimotor and conceptual intelligence (looking, reaching, perceiving, remembering, and so on) required by the task at hand (Clearfield, Diedrich, Smith, & Thelen, 2006). The Role of Experience. Noting that infants' performance on tests of object permanence is highly sensitive to the particulars of the test itself — such as the search method (reaching or looking) and the amount of time between hiding and searching — Jeanne Shinskey and her colleagues (Shinskey & Jachens, 2014; Shinskey & Munakata, 2005, 2010) wondered if infants gradually develop stronger representations of objects through their experience with them and if stronger representations are required for some tasks than for others. In line with the dynamic systems approach, the researchers focused on the process through which infants build mental representations rather than on whether and at what age infants reliably demonstrate the capacity to represent objects mentally. Reasoning that infants' representations of objects gradually strengthen as babies gain experience perceiving and interacting with them, Shinskey and Munakata predicted that object permanence would be stronger for familiar objects than for novel objects. To test their prediction, the researchers used an inventive method in which 7-month-olds were presented with novel and familiar objects under "visible" and "hidden" conditions (Shinskey & Munakata, 2005). In the "visible" condition, either a novel object or a familiar object was set in front of the babies. (An object was made familiar by providing an infant several opportunities to reach for it.) Infants reached more for the novel object, demonstrating a preference for novelty. In the "hidden" condition — the condition that actually tests for object permanence — the babies were presented with a novel or familiar object and then the lights were turned off, shrouding the room and the object in darkness. (The babies had been given some experience with the lights going out so that they wouldn't be surprised or scared during the test phase.) In this hidden condition, the babies tended to reverse their previous novelty preference, reaching more for the familiar object than for the novel object. What does this shift from a novelty preference in the visible condition to a familiarity preference in the hidden condition tell us about the process of forming mental representations? As Shinskey and Munakata point out, once infants have mastered information contained in one stimulus, seeking the novelty of a new stimulus is an adaptive strategy for acquiring new information about the world — a strategy that has likely evolved in our species because of its useful role in helping us explore, learn about, and respond to changes in our environments. When the infants in their study showed a preference for the novel object in the visible condition, they were demonstrating that they had processed the familiar object sufficiently well that it had become less interesting to explore, so they were more inclined to reach for the novel object. Furthermore, the fact that the infants were more inclined to reach for the familiar object in the hidden condition suggests that their experience with the object had helped them develop a stronger representation of it than of the novel object. Evidence such as this leads some developmentalists to argue that the formation of mental representations depends heavily on experience (Shinskey & Jachens, 2014; Shinskey & Munakata, 2010; Wang & Baillargeon, 2008). Thus, it seems likely that infants' developing representations and knowledge of the world is a joint consequence of human evolutionary processes and experiences available to babies in the specific cultural contexts in which they are brought up. Developmentalists continue to debate questions about when object permanence emerges in development and whether it is innate, learned through experience, or some combination of the two. As you will now see, these fundamental questions also inspire research on how infants understand other properties of the physical world. Understanding Other Properties of the Physical World There are, of course, properties of the physical world other than objects' continuing existence when out of sight. As adults, we are so thoroughly familiar with the properties of our physical world that is it easy for us to overlook their significance for our behavior and development. We walk around obstacles rather than attempt to walk through them; we expect an apple that falls from a tree to land on the ground and not fly around crazily and hit someone on the nose; we may playfully smack a friend with a pillow but would never do so with a brick; when we reach into the back of a closet, we expect to find a wall, not the land of Narnia. What is the source of our knowledge of the physical world? Are we born with the knowledge that objects are solid and conform to physical laws, such as the law of gravity, or does that knowledge emerge from experience? By what process do we come to reason about objects, recognizing, for example, that they can be counted, that there are often cause-and-effect relationships between them, or that certain objects share some of their features with other objects and can be categorized accordingly? As they have done in their research on object permanence, developmentalists have turned to infants to explore these fundamental questions. And, as they do in their research on object permanence, developmentalists often employ the violation-of-expectations method, generally in the form of research trickery, to good advantage. A number of such experiments found that between 3 and 9 months of age, and sometimes earlier, infants appear to have at least an initial grasp of a wide variety of physical laws concerning the behavior of objects. For instance, 5-month-old babies expect liquid and granular (sand) substances to be "pourable" when transferred from one glass to another, and they are surprised when researchers cunningly arrange for the apparently pourable substance to plop into the second glass like an ice cube; similarly, the babies expect solid substances to plop when transferred from one glass to another, they and are surprised when they pour like liquids (Hespos et al., 2016). Other research conducted by Renee Baillargeon and her colleagues has explored whether infants would expect an object that is suspended unsupported in midair would fall (Wang, Zhang, & Baillargeon, 2016). In an early study, the experimenters repeatedly presented 4½-month-old infants with the habituation event shown at the top of Figure 5.16 (p. 186), in which a hand reaches out and places one block on another before being withdrawn (Needham & Baillargeon, 1993). Then the researchers presented either an event that defies the law of gravity, in which the top block is left dangling in midair as the hand withdraws (bottom part of Figure 5.16), or a control event (not shown), in which the hand withdraws partway and continues holding the top block, which is not supported by the bottom block. Infants looked longer when the block appeared to be suspended in midair without any visible support, indicating to the researchers that the babies expected the block to fall. Similar studies have demonstrated that by 4 months of age, infants appear to believe that objects cannot move behind one screen and reappear from a separate screen without appearing in the space between screens, and they also appear to believe that if a container with an object inside is moved, the object will move with it (Figure 5.17) (Baillargeon, 2004; Spelke, Breinlinger, Macomber, & Jacobson, 1992). FIGURE5.16 Evidence that very young infants have some appreciation of the laws of gravity is demonstrated by the fact that they stare longer at impossible "gravity" events, such as a block remaining suspended in air, than at possible events, such as a block being supported by a block underneath it. The first series of three illustrations is titled Possible event. The first illustration shows a large block with a small colored block placed to its right. A hand holding another colored block is shown in this illustration. In the second illustration, the second colored block is shown placed on the first block. In the third illustration, the hand is moved away from the stacked blocks. The second set of three illustrations is titled Impossible Event. The first illustration shows a large block with a small colored block placed to its right. The size of this block is smaller than the one show in the previous set of illustrations. A hand holding another colored block is shown in this illustration. In the second illustration, the second colored block is shown being placed on the first block. A gap is seen between the two blocks. In the third illustration, the hand is moved away from the blocks that have a gap between them. The first event shows a person placing an object over the other. The second event shows the person suspending the object in the air. The former is termed as a possible event and the latter as an impossible event. The first series of three illustrations is titled Possible event. The first illustration shows a large block with a small colored block placed to its right. A hand holding another colored block is shown in this illustration. In the second illustration, the second colored block is shown placed on the first block. In the third illustration, the hand is moved away from the stacked blocks. The second set of three illustrations is titled Impossible Event. The first illustration shows a large block with a small colored block placed to its right. The size of this block is smaller than the one show in the previous set of illustrations. A hand holding another colored block is shown in this illustration. In the second illustration, the second colored block is shown being placed on the first block. A gap is seen between the two blocks. In the third illustration, the hand is moved away from the blocks that have a gap between them. The first event shows a person placing an object over the other. The second event shows the person suspending the object in the air. The former is termed as a possible event and the latter as an impossible event. FIGURE5.17 Studies using the violation-of-expectations method find that infants as young as 4 months look longer at events that violate certain physical laws. The first sequence shown here depicts the impossible event of an object passing behind a screen and then reappearing from behind a separate screen, without showing up in the space between the screens. The second sequence shows the impossible event of an object inside a container failing to change position when the container is moved. The first set of three illustrations shows an impossible event. The illustration shows two vertical bars with a mouse play toy placed to the left of the first vertical bar with an arrow pointing from the toy to the bar. In the second illustration, only the vertical bars are shown. In the third illustration, two vertical bars are shown. The mouse toy is shown to the right of the second vertical bar, and an arrow is shown pointing from the vertical bar to the toy on the right. The second set of three illustrations also shows an impossible event. The first illustration shows a set of curtains with a hand emerging out of each curtain. The left hand is shown holding a large cylinder and the right hand is shown holding a smaller cylinder with a checked pattern. In the second illustration, the small cylinder with checked pattern is not shown. In the third illustration, the large cylinder is moved slightly to the right, and the checked cylinder is seen near the right curtain. The first set of three illustrations shows an impossible event. The illustration shows two vertical bars with a mouse play toy placed to the left of the first vertical bar with an arrow pointing from the toy to the bar. In the second illustration, only the vertical bars are shown. In the third illustration, two vertical bars are shown. The mouse toy is shown to the right of the second vertical bar, and an arrow is shown pointing from the vertical bar to the toy on the right. The second set of three illustrations also shows an impossible event. The first illustration shows a set of curtains with a hand emerging out of each curtain. The left hand is shown holding a large cylinder and the right hand is shown holding a smaller cylinder with a checked pattern. In the second illustration, the small cylinder with checked pattern is not shown. In the third illustration, the large cylinder is moved slightly to the right, and the checked cylinder is seen near the right curtain. Reasoning About Objects Piaget's theory about knowledge of objects: even after children begin to be aware of the physical properties of objects, they cannot reason about those objects; example, they cannot count them, understand cause-effect relations between them, or categorize them according to some feature they have in common. Counting The question of whether young babies can count has puzzled researchers for decades. In an early study conducted by Karen Wynn (1992), 4-month-old infants were shown the events depicted in Figure 5.18. First, a mouse doll was placed on an empty stage while the baby watched. Then a screen was raised to hide the doll from the baby's view. Next, the baby saw a hand holding a doll identical to the first one go behind the screen and then reappear without the doll. The screen was then lowered, in half the trials revealing two dolls (the possible event) and in the other half revealing only one doll (the impossible event). The infants looked longer when there was only one doll, suggesting that they had mentally calculated the number of dolls that ought to be behind the screen. Similarly, when the experiment began with two dolls on the stage and the hand removed one doll from behind the screen, the infants seemed surprised when the screen was lowered to reveal two dolls. FIGURE5.18 After 4-month-olds observe the sequence of events depicted at the top of the figure, they show surprise when the screen is removed and only one mouse remains. Apparently the babies not only remember the presence of the first mouse hidden behind the screen but mentally add the second mouse and expect to see two mice. The first illustration shows an object being placed on a stage that has a screen below. Text below reads, "Object is placed on a stage." In the second illustration, the screen is raised up partially obscuring the object. Text below reads, "Screen comes up." In the third illustration, the object is moved to the right end of the stage. Text below reads, "Second object placed behind screen." The fourth illustration shows the screen on the stage and the empty hand at the right end of the stage. An arrow from this illustration points to text "Outcomes." Two types of outcomes are possible - Possible and Impossible. Two illustrations depict the possible outcome. The two illustrations show the screen dropping and revealing the two objects. The two illustrations depicting the impossible outcome show the screen dropping and revealing one object. More recent research has confirmed that young babies recognize when the number of objects in an array increases or decreases, and there is some indication that the recognition of numerical change is associated with the activation of specific brain areas (Edwards, Wagner, Simon, & Hyde, 2016; Mou & van Marle, 2014). In light of the fact that counting is a fundamental skill of the human species, researchers are not surprised that the brain may have evolved to include areas that are dedicated to processing number. In addition to perceiving changes in the numbers of objects, babies seem to "match" number across sensory modalities (see the discussion of multimodal perception in Chapter 4, p. 140). For example, when 7-month-olds hear a recording of three voices speaking, they look longer at a video that shows three faces than at a video that shows only two (Jordan & Brannon, 2006). This preference for correspondence is evident at a more complex level when older babies respond to correct and incorrect counting (Slaughter, Itakura, Kutsuki, & Siegal, 2011). Eighteen-month-olds were shown a video depicting six fish. In one instance — the correct counting condition — a hand pointed to each fish while a voice counted each one, from one to six. In the other instance — the incorrect counting condition — the hand moved back and forth between only two of the six fish while the voice counted to six. The babies looked significantly longer at the correct, compared to the incorrect, counting sequence, indicating a preference for correct counting. Such experiments appear to demonstrate that infants are capable of understanding certain features of counting far ahead of Piaget's timetable regarding their ability to reason about objects. However, as with other research suggesting precocious, possibly innate, infant abilities (such as whether infants understand the permanence of objects), research claiming to demonstrate that infants can count has not gone unchallenged. For example, Leslie Cohen and Kathryn Marks (2002) found that the infants looked longer the more objects there were and that they looked longer at a familiar display, no matter how many objects were in it. Developmentalists are still trying to reach conclusions about competence based on performance, wondering whether young babies are truly able to count objects or whether they only appear to do so in the context of specific tasks (Cordes & Brannon, 2009). Cause-Effect Relationships Another way of reasoning about the physical world is through cause-effect relationships. When one object has contact with another object, and the second object moves away or falls down, we perceive that the first object pushed the second one. When an object is dragged across another object, and the second object falls into two pieces, we perceive that the first object cuts the second one. Physical causality is fundamental to human experience and behavior, and developmentalists are keen to understand whether knowledge of cause-effect relationships comes from experience or is an innate capacity present early in life (Leslie, 2002). In an experiment to test this idea, Elena Mascalzoni and her colleagues presented newborns with two computer displays in which one gray disc appeared to bump into a second disc, which then moved (commonly referred to as the "launching task"; Mascalzoni, Regolin, Vallortigara, & Simion, 2013). In one, the causal version, the second disc moved immediately, an event that adults perceive as the result of its being pushed by the first disc. In the other, the noncausal version, there was a delay in the movement of the second disc, suggesting that being pushed did not cause its movement. The newborns looked significantly longer at the causal version, suggesting their preference for cause-effect relationships over noncausal events. Although research with newborns suggests that the perception of physical causality may be present at birth, other research indicates that experience can have a significant impact on infants' understanding of cause-effect relationships. An example is a clever study conducted with 4½-month-olds wearing mittens (Rakison & Krogh, 2012). Some of the babies wore regular mittens and were placed in front of several balls glued to a tray. The other babies wore mittens made of Velcro and were placed in front of a tray of loose balls that stuck easily to the mittens. Clearly, the regular-mittened babies did not experience cause-effect relationships; even if they succeeded in touching the balls by batting or swiping at them, the balls, glued to the tray, did not move. On the other hand (so to speak), babies wearing the sticky mittens experienced cause-effect relationships when their batting and swiping resulted in "catching" a ball. After some experience in wearing either regular or sticky mittens, the infants were presented with causal and noncausal displays similar to the launching task described above. As predicted, babies who had special experiences with causal relationships were more likely to show evidence of causal perception on the launching task. Categorizing Imagine 2-year-old Sylvie playing "bedtime" with her toys. She has put her Dora doll under a cover on the table, along with Bitty Kitty and Pooh Bear. Excluded from the makeshift bed, however, are several other toys that she had just been playing with, among them Dora's truck and Pooh Bear's honey pot. Sylvie has appropriately categorized her toys into two groups: those that need sleep and those that do not. The process of categorizing — that is, of seeing similarities in different objects and events — is an essential feature of how we make sense of the world. Without the ability to categorize, we would need to learn about each new detail of our experience from scratch. We would not be able to take knowledge gained in one situation and apply it to another similar situation, and this would make learning about the world a very slow and inefficient process. The adults of our species, however, are incredibly adept at categorization. Developmentalists are interested in when this ability emerges and how it changes over time. Infants display an ability to form categories remarkably early in life (Cimpian, 2016). For example, if 3-month-olds are shown a series of pairs of pictures of different cats and then shown a pair consisting of a picture of a cat and a picture of a dog, the infants will look longer at the picture of the dog than they will at the picture of the new cat (Figure 5.19). This preferential looking indicates that the infants had formed a category for what they had been viewing and that a dog did not fit it (Quinn & Eimas, 1996; Quinn, Eimas, & Rosenkrantz, 1993). Brain studies have shown that when young babies form categories, the electrical activity of their brains changes in ways which suggest that basic neurological processes have evolved to support early categorizing abilities (Quinn, Westerlund, & Nelson, 2006). In addition, brain research suggests that young babies 4 to 6 months of age may categorize and process faces differently than they process other visually complex objects (de Heering, Van Belle, & Rossion, 2014). FIGURE5.19 When 3-month-olds are shown a sequence of pictures of cats, they are surprised at the presence of a dog in the sequence, indicating that they are sensitive to the category cats. In Trail one, two and three, two photos of cats are shown. In the test trail, a photo of a cat and a photo of a dog are shown. Most research on categorization, however, has been conducted with somewhat older infants and has focused on the bases infants use to form categories. Do they rely primarily on perceptual similarities — that is, on similarities in how objects look, feel, or sound — or are they able to categorize according to more abstract, conceptual features, such as how objects function or behave? The framing of this question may remind you of the general theme that has permeated much of our discussion of infant intelligence: the extent to which an infant's knowledge is primarily perceptual and sensorimotor in nature and the extent to which it is also abstract and conceptual. Evidence that infants form conceptual categories before the 1st year comes from an intriguing study of "generalized imitation" (Mandler, 2004; Mandler & McDonough, 1996). In this study, 9- and 11-month-old babies observed an adult model performing an action that would be appropriate either for animals as a category or for vehicles as a category — for example, giving a toy dog a drink from a cup or turning a key in a toy car door (Figure 5.20, p. 190). Then, in the imitation phase, either the dog or the car was put away, and the infants were presented with a different item that was placed next to the prop (the cup or the key). Sometimes the new item was from the same category as the previous one (a bunny was placed next to the cup or a truck was placed next to the key); sometimes it was from the other category (the bunny was placed next to the key or the truck was placed next to the cup). The researchers found that the babies would give a drink to the bunny but not to the truck, and likewise would use the key with the truck but not with the bunny. That is, while the babies were likely to imitate the action with the appropriate object, they rarely performed the action on the item from the incorrect category. FIGURE5.20 Illustrating infants' ability to categorize objects is the finding that when 7- to 11-month-olds (a) observe an adult give a toy dog a drink, they (b) do not imitate the action with a toy truck but (c) imitate the adult's action with a toy bunny. The first illustration shows a baby watching an adult giving a toy dog a drink. The second illustration shows a toy truck and a glass placed in front of the child. The third illustration shows the baby giving a drink to a toy rabbit. There is still uncertainty among developmentalists about the basis for the changes in categorization observed across infancy (Booth, Schuler, & Zajicek, 2010; Rostad, Yott, & Poulin-Dubois, 2012). Some researchers believe that perceptual similarity — whether the object has legs versus wheels, for example — remains fundamental to category formation for the entire period. Thus, older infants show improved categorization skills because their sensory systems are more developed, and they have greater experience, making them sensitive to more subtle characteristics and to relationships between characteristics (Cohen & Cashon, 2006; Quinn, 2002). Others believe that before the end of the 1st year, infants become capable of forming genuine conceptual categories — categories based on such meaningful features as what things do and how they come to be the way they are — in addition to perceptual categories (Mandler, 2004). For instance, 14-month-olds continue to categorize toy replicas of people and animals as animate objects, even though their legs have been replaced by wheels; similarly, toy wagons and boats are categorized as inanimate, even though they have been given legs (Rostad et al., 2012). Although developmentalists are continuing to test different theories about how infants form categories, it is clear that by the end of infancy, babies are able to use them categories organize their own behavior in relation to their environments, as did Sylvie when she put some of her toys to bed but not others.