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3.1 T H E N E W B O R N

The Newborn’s Reflexes

Assessing the Newborn

The Newborn’s States

Temperament

3.2 P H YS I C A L D E V E L O P M E N T

Growth of the Body

The Emerging Nervous System

3.3 M OV I N G A N D G R A S P I N G :

E A R LY M OTO R S K I L L S

Locomotion

Fine Motor Skills

3.4 C O M I N G TO K N OW T H E

WO R L D : P E R C E P T I O N

Smell, Taste, and Touch

Hearing

Seeing

❚ SPOTLIGHT ON RESEARCH:

How Infants Become Face Experts

Integrating Sensory Information

3.5 B E C O M I N G S E L F - AWA R E

Origins of Self-Concept

Theory of Mind

❚ REAL PEOPLE: APPLYING HUMAN DEVELOPMENT:

“Seeing Is Believing . . .” for 3-Year-Olds

S U M M A RY

K E Y T E R M S

L E A R N M O R E A B O U T I T

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C H A P T E R

Tools for Exploring the World Physical, Perceptual, and Motor Development

T hink about what you were like 2 years ago. Whatever you were doing, you probably look, act, think, and feel in much the same way today as you did then. Two years in an adult’s life usually doesn’t

result in profound changes, but 2 years makes a big difference early in life. The changes that occur in

the first few years after birth are incredible. In less than 2 years, an infant is transformed from a seem-

ingly helpless newborn into a talking, walking, havoc-wreaking toddler. No changes at any other point

in the life span come close to the drama and excitement of these early years.

In this chapter, our tour of these 2 years begins with the newborn and then moves to physical

growth—changes in the body and the brain. The third section of the chapter examines motor skills.

You’ll discover how babies learn to walk and how they learn to use their hands to hold and then

manipulate objects. In the fourth section, we’ll examine changes in infants’ sensory abilities that allow

them to comprehend their world.

As children begin to explore their world and learn more about it, they also learn more about

themselves. They learn to recognize themselves and begin to understand more about their thoughts

and others’ thoughts. We’ll explore these changes in the last section of the chapter.

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Lisa and Steve, proud but exhausted parents, are astonished at how their lives revolve around 10-day-old Dan’s eating and sleeping. Lisa feels as if she is feeding Dan around the clock. When Dan naps, Lisa thinks of many things she should do but usually naps herself because

she is so tired. Steve wonders when Dan will start sleeping through the night so that he and

Lisa can get a good night’s sleep themselves.

T H E N EW BO R N BABY T H AT T H R ILLS PAREN T S LIK E LISA AN D ST EVE IS AC T UALLY R AT H ER H O MELY. Newborns arrive covered with blood and vernix, a white-colored “wax” that protected the skin during the many months of prenatal development. In addition, the baby’s head is temporarily distorted from its journey through the birth canal, and the newborn has a beer belly and is bowlegged.

What can newborns like Dan do? We’ll answer that question in this section and, as we do, you’ll learn when Lisa and Steve can expect to resume getting a full night’s sleep.

| The Newborn’s Reflexes

Most newborns are well prepared to begin interacting with their world. The newborn is endowed with a rich set of reflexes, un- learned responses that are triggered by a specifi c form of stimulation. ● Table 3.1 shows the variety of refl exes commonly found in new- born babies.

You can see that some refl exes are designed to pave the way for newborns to get the nutrients they need to grow: The rooting and sucking refl exes ensure that the newborn is well prepared to begin a new diet of life-sustaining milk. Other refl exes seem designed to protect the newborn from danger in the environment. The eye blink, for example, helps newborns avoid unpleasant stimulation.

Still other refl exes serve as the foundation for larger, voluntary patterns of motor activity. For example, the stepping refl ex motions look like precursors to walking, so it probably won’t surprise you to learn that babies who practice the stepping refl ex often learn to walk earlier than those who don’t practice this (Zelazo, 1993).

Refl exes are also important because they can be a useful way to determine whether the newborn’s nervous system is working properly. For example, infants with damage to the sciatic nerve, which is found in the spinal cord, do not show the withdrawal refl ex. Infants who have problems with the lower part of the spine do not show the Babinski refl ex. If these or other refl exes are weak or missing altogether, a thorough physical and behavioral assessment is called for. Similarly, many of these refl exes nor- mally vanish during infancy; if they linger then this, too, indicates the need for a thor- ough physical examination.

L E A R N I N G O B J E C T I V E S

How do reflexes help newborns interact with the world? ❚

How do we determine whether a baby is healthy and adjust- ❚ ing to life outside the uterus?

What behavioral states are common among newborns? ❚

What are the different features of temperament? Do they ❚ change as children grow?

3.1 THE NEWBORN

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This newborn baby (Ben Kail at 20 seconds old)

is covered with vernix and is bow-legged; his

head is distorted from the journey down the

birth canal.

refl exes

unlearned responses triggered by specifi c

stimulation

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| Assessing the Newborn

Imagine that a mother has just asked you if her newborn baby is healthy. How would you decide? You would probably check to see whether the baby seems to be breathing and if her heart seems to be beating. In fact, breathing and heartbeat are two vital signs included in the Apgar score, which provides a quick, approximate assessment of the newborn’s status by focusing on the body systems needed to sustain life. The other vital signs are muscle tone, presence of refl exes such as coughing, and skin tone. Each of the fi ve vital signs receives a score of 0, 1, or 2, where 2 is the optimal score. For example, a newborn whose muscles are completely limp receives a 0; a baby who shows strong movements of arms and legs receives a 2. The fi ve scores are added to- gether, with a total score of 7 or more indicating a baby who is in good physi- cal condition. A score of 4–6 means that the newborn needs special attention and care. A score of 3 or less signals a life-threatening situation that requires emergency medical care (Apgar, 1953).

For a comprehensive evaluation of the newborn’s well-being, pediatri- cians and other child-development specialists sometimes administer the Neo- natal Behavioral Assessment Scale or NBAS for short (Brazelton & Nugent, 1995). The NBAS is used with newborns to 2-month-olds to provide a detailed portrait of the baby’s behavioral repertoire. The scale includes 28 behavioral items along with 18 items that test refl exes. The baby’s performance is used to evaluate the functioning of these four systems:

Autonomic ■ : the newborn’s ability to control body functions such as breathing and temperature regulation

Motor ■ : the newborn’s ability to control body movements and activity level

State ■ : the newborn’s ability to maintain a state (e.g., staying alert or staying asleep)

Social ■ : the newborn’s ability to interact with people

Newborns step reflexively when they are held

upright and moved forward.

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● TA B L E 3 . 1

Some Major Reflexes Found in Newborns

Name Response Age When Reflex Disappears Significance

Babinski A baby’s toes fan out when the sole 8–12 months Perhaps a remnant of evolution of the foot is stroked from heel to toe

Blink A baby’s eyes close in response to Permanent Protects the eyes bright light or loud noise

Moro A baby throws its arms out and 6 months May help a baby cling to its mother. then inward (as if embracing) in response to loud noise or when its head falls

Palmar A baby grasps an object placed 3–4 months Precursor to voluntary walking in the palm of its hand

Rooting When a baby’s cheek is stroked, 3–4 weeks (replaced Helps a baby find the nipple it turns its head toward the by voluntary head turning) stroking and opens its mouth

Stepping A baby who is held upright by 2–3 months Precursor to voluntary walking an adult and is then moved forward begins to step rhythmically

Sucking A baby sucks when an object 4 months (replaced by Permits feeding is placed in its mouth voluntary sucking)

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The NBAS is based on the view that newborns are remarkably competent individuals who are well prepared to interact with the environment. Refl ecting this view, exam- iners go to great lengths to bring out a baby’s best performance. They do everything possible to make a baby feel comfortable and secure during testing. And if the infant does not at fi rst succeed on an item, the examiner provides some assistance (Alberts, 2005).

The NBAS, along with a thorough physical examination, can determine whether a newborn is functioning normally. Scores from the NBAS can, for example, be used to diagnose disorders of the central nervous system.

| The Newborn’s States

Newborns spend most of each day alternating among four diff erent states (St. James- Roberts & Plewis, 1996; Wolff , 1987):

Alert inactivity ■ —The baby is calm with eyes open and attentive; the baby seems to be deliberately inspecting the environment.

Waking activity ■ —The baby’s eyes are open but they seem unfocused; the arms or legs move in bursts of uncoordinated motion.

Crying ■ —The baby cries vigorously, usually accompanied by agitated but unco- ordinated motion.

Sleeping ■ —The baby alternates from being still and breathing regularly to mov- ing gently and breathing irregularly; eyes are closed throughout.

Of these states, crying and sleeping have captured the attention of parents and re- searchers alike.

Crying Newborns spend 2–3 hours each day crying or on the verge of crying. If you’ve not spent much time around newborns, you might think that all crying is pretty much

alike. In fact, scientists and parents can identify three distinctive types of cries (Snow, 1998). A basic cry starts softly and then gradually becomes more intense; it usually occurs when a baby is hungry or tired. A mad cry is a more intense version of a basic cry; and a pain cry begins with a sudden, long burst of crying followed by a long pause and gasping. Thus, crying represents the newborn’s fi rst venture into interpersonal communication. By crying, babies tell their parents that they are hungry or tired, angry or hurt. By responding to these cries, parents are en- couraging their newborn’s eff orts to communicate.

Parents are naturally concerned when their baby cries, and if they can’t quiet a crying baby, their concern mounts and can easily give way to frustration and annoyance. It’s no surprise, then, that parents develop little tricks for soothing their babies. Many Western parents lift a baby to the shoulder and walk or gently rock the baby. Sometimes they will also sing lullabies, pat the baby’s back, or give the baby a pacifi er. Yet another method is to put a newborn into a car seat and go for a drive; this technique was used once, as a last resort, at 2 a.m. with Ben Kail when he was 10 days old. After about the 12th time around the block, he fi nally stopped crying and fell asleep!

Another useful technique is swaddling, in which an infant is wrapped tightly in a blanket. Swaddling is used in many cultures around the world, including Tur- key and Peru, as well as by Native Americans. Swaddling provides warmth and tactile stimulation that usually works well to soothe a baby (Delaney, 2000).

Parents are sometimes reluctant to respond to their crying infant for fear of producing a baby who cries constantly. Yet they hear their baby’s cry as a call for help that they shouldn’t ignore. What to do? Should parents respond? “Yes, usu-

ally” is probably the best answer (Hubbard & van Ijzendoorn, 1991). If parents respond immediately, every time their infant cries, the result may well be a fussy, whiny baby.

alert inactivity

state in which a baby is calm with eyes

open and attentive; the baby seems to be

deliberately inspecting the environment

waking activity

state in which a baby’s eyes are open but

seem unfocused while the arms or legs

move in bursts of uncoordinated motion

crying

state in which a baby cries vigorously, usu-

ally accompanied by agitated but uncoor-

dinated movement

sleeping

state in which a baby alternates from be-

ing still and breathing regularly to moving

gently and breathing irregularly; the eyes

are closed throughout

basic cry

cry that starts softly and gradually be-

comes more intense; often heard when

babies are hungry or tired

In many countries worldwide, infants are

wrapped tightly in blankets as a way to keep

them soothed.

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s T H I N K A B O U T I T

Newborns seem to be extremely well

prepared to begin to interact with their

environment. Which of the theories

described in Chapter 1 predict such

preparedness? Which do not?

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Instead, parents need to consider why their infant is crying and the intensity of the crying. When a baby wakes during the night and cries quietly, a parent might wait be- fore responding, giving the baby a chance to calm itself. However, when parents hear a loud noise from an infant’s bedroom followed by a mad cry, they should respond immediately. Parents need to remember that crying is actually the newborn’s fi rst at- tempt to communicate with others. They need to decide what the infant is trying to tell them and whether that warrants a quick response or whether they should let the baby soothe itself.

Sleeping Crying may get parents’ attention, but sleep is what newborns do more than anything else. They sleep 16–18 hours daily. The problem for tired parents is that newborns sleep in naps taken round-the-clock. Newborns typically go through a cycle of wake- fulness and sleep about every 4 hours. That is, they will be awake for about an hour, sleep for 3 hours, and then start the cycle anew. During the hour when newborns are awake, they regularly move between the diff erent waking states several times. Cycles of alert inactivity, waking activity, and crying are common.

As babies grow older, the sleep–wake cycle gradually begins to correspond to the day–night cycle (St. James-Roberts & Plewis, 1996). By 3 or 4 months, many babies sleep for 5–6 hours straight, and by 6 months many are sleeping for 10–12 hours at night, a major milestone for bleary-eyed parents like Lisa and Steve.

By six months, most North American infants are sleeping in a crib in their own room. Although this practice seems “natural” to North American parents, in much of the rest of the world children sleep with their parents throughout infancy and the preschool years. Such parent–child “co-sleeping” is commonly found in cultures where people defi ne themselves less as independent individuals and more as part of a group. For parents in cultures that value such interdependence—including Egypt, Italy, Japan, and Korea, as well as the Maya in Guatemala and the Inuit in Canada— co-sleeping is an important step in forging parent–child bonds, just as sleeping alone is an important step toward independence in cultures that value self-reliance (Morelli et al., 1992; Nelson, Schiefenhoevel, & Haimerl, 2000; Worthman & Brown, 2007).

How does co-sleeping work? Infants may sleep in a cradle placed next to their par- ents’ bed or in a basket that’s in their parents’ bed. When they outgrow this arrange- ment, they sleep in the bed with their mother; depending on the culture, the father may sleep in the same bed, in another bed in the same room, in another room, or in another house altogether!

You might think that co-sleeping would make children more dependent on their parents, but research provides no evidence of this (Cortesi et al., 2004; Okami, Weisner, & Olmstead, 2002). Plus, co-sleeping has the benefi t of avoiding the lengthy and elabo- rate rituals that are often required to get youngsters to sleep in their own room alone. With co-sleeping, children and parents simply go to bed together with few struggles.

Roughly half of newborns’ sleep is irregular or rapid-eye-movement (REM) sleep, a time when the body is quite active. During REM sleep, newborns move their arms and legs; they may grimace and their eyes may dart beneath their eyelids. Brain waves register fast activity, the heart beats more rapidly, and breathing is more rapid. In regular or nonREM sleep, breathing, heart rate, and brain activity are steady and newborns lie quietly without the twitching associated with REM sleep. REM sleep be- comes less frequent as infants grow. By 4 months, only 40% of sleep is REM sleep. By the fi rst birthday, REM sleep will drop to 25%—not far from the adult average of 20% (Halpern, MacLean, & Baumeister, 1995).

The function of REM sleep is still debated. Older children and adults dream dur- ing REM sleep, and brain waves during REM sleep resemble those of an alert, awake person. Consequently, many scientists believe that REM sleep provides stimulation for

T H I N K A B O U T I T

When Mary’s 4-month-old son cries,

she rushes to him immediately and does

everything possible to console him. Is

this a good idea?

Co-sleeping, in which infants and young children

sleep with their parents, is common in many

countries around the world.

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irregular or rapid-eye-movement (REM)

sleep

irregular sleep in which an infant’s eyes

dart rapidly beneath the eyelids while the

body is quite active

regular (nonREM) sleep

sleep in which heart rate, breathing, and

brain activity are steady

mad cry

more intense version of a basic cry

pain cry

cry that begins with a sudden long burst,

followed by a long pause and gasping

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the brain that fosters growth in the nervous system (Halpern et al., 1995; Roff warg, Muzio, & Dement, 1966).

By the toddler and preschool years, sleep routines are well established. Most 2-year- olds spend about 13 hours sleeping, compared to just under 11 hours for 6-year-olds. By age 4, most youngsters give up their afternoon nap and sleep longer at nighttime to compensate. This can be a challenging time for parents and caregivers who use nap- time as an opportunity to complete some work or to relax.

Following an active day, most preschool children drift off to sleep easily. However, most children will have an occasional night when bedtime is a struggle. Furthermore, for approximately 20 to 30% of preschool children, bedtime struggles occur nightly (Lozoff , Wolf, & Davis, 1985). More often than not, these bedtime problems refl ect the absence of a regular bedtime routine that’s followed consistently. The key to a pleasant bedtime is to establish a nighttime routine that helps children to “wind down” from busy daytime activities. This routine should start at about the same time every night (“It’s time to get ready for bed . . .”) and end at about the same time (when the parent leaves the child and the child tries to fall asleep). This nighttime routine may be any- where from 15 to 45 minutes long, depending on the child. Also, as children get older, parents can expect them to perform more of these tasks independently. A 2-year-old

will need help all along the way, but a 5-year-old can do many of these tasks alone. But remember to follow the routine consistently; this way, children know that each step is getting them closer to bedtime and falling asleep.

Sudden Infant Death Syndrome For many parents of young babies, however, sleep is a cause of concern. In sud- den infant death syndrome (SIDS), a healthy baby dies suddenly for no apparent reason. Approximately 1–3 of every 1,000 American babies dies from SIDS. Most of them are between 2 and 4 months of age (Wegman, 1994).

Scientists don’t know the exact causes of SIDS, but one idea is that 2- to 4-month-old infants are particularly vulnerable to SIDS because many newborn refl exes are waning during these months and thus infants may not respond ef- fectively when breathing becomes diffi cult. They may not refl exively move their head away from a blanket or pillow that is smothering them (Lipsitt, 2003).

Researchers have also identifi ed several risk factors associated with SIDS. Ba- bies are more vulnerable if they were born prematurely or with low birth weight. They are also more vulnerable when their parents smoke. SIDS is more likely when a baby sleeps on its stomach (face down) than when it sleeps on its back (face up). Finally, SIDS is more likely during winter, when babies sometimes be- come overheated from too many blankets and sleepwear that is too heavy (Carroll & Loughlin, 1994). Evidently, SIDS infants, many of whom were born prematurely or with low birth weight, are less able to withstand physiological stresses and im- balances that are brought on by cigarette smoke, breathing that is temporarily interrupted, or overheating (Simpson, 2001).

In 1992, based on mounting evidence that SIDS occurred more often when infants slept on their stomachs, the American Academy of Pediatrics (AAP) began advising parents to put babies to sleep on their backs or sides. In 1994 the AAP joined forces with the U.S. Public Health Service to launch a national program to educate parents about the dangers of SIDS and the importance of putting babies to sleep on their backs. The “Back to Sleep” campaign was widely publi- cized through brochures, posters like the one shown in ❚ Figure 3.1, and videos. Since the Back to Sleep campaign began, research shows that far more infants are now sleeping on their backs and that the incidence of SIDS has dropped (NIH, 2000b).

However, it became clear that African American infants were still twice as likely to die from SIDS, apparently because they were much more likely to be placed on their stomachs to sleep. Consequently, in the 21st century the National Institutes of Health has partnered with groups such as the Women in the NAACP

sudden infant death syndrome (SIDS)

when a healthy baby dies suddenly for no

apparent reason

Figure 3.1 ❚ This poster is one part of an effective cam-

paign to reduce SIDS by encouraging parents

to have their babies sleep on their backs.

National Institute of Child Health and Development.

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and the National Council of 100 Black Women to train thousands of people to convey the Back to Sleep message in a culturally appropriate manner to African American communities (NICHD, 2004). The goal is for African American infants to benefi t from the life saving benefi ts of the Back to Sleep program. The message for all parents— particularly if their babies were premature or small-for-date—is to keep their babies away from smoke, to put them on their backs to sleep, and to not overdress them or wrap them too tightly in blankets (Willinger, 1995).

| Temperament

So far, we’ve talked as if all babies are alike. But if you’ve seen a number of babies to- gether, you know this isn’t true. Perhaps you’ve seen some babies who are quiet most of the time alongside others who cried often and impatiently? Maybe you’ve known infants who responded warmly to strangers next to others who seemed shy? These characteristics of infants indicate a consistent style or pattern to an infant’s behavior, and collectively they defi ne an infant’s temperament.

Alexander Thomas and Stella Chess (Thomas, Chess, & Birch, 1968) pioneered the study of temperament with the New York Longitudinal Study, in which they traced the lives of 141 individuals from infancy through adulthood. Thomas and Chess gathered their initial data by interviewing the babies’ parents and asking individuals unfamiliar with the children to observe them at home. Based on these interviews and observa- tions, Thomas and Chess suggested that infants’ behavior varied along nine tempera- mental dimensions. One dimension was activity, which referred to an infant’s typical level of motor activity. A second was persistence, which referred to the amount of time an infant devoted to an activity, particularly when obstacles were present.

The New York Longitudinal Study launched research on infant temperament, but today we know that Thomas and Chess overestimated the number of temperamental dimensions. Instead of nine dimensions, scientists now propose from two to six di- mensions. For example, Mary K. Rothbart (2004; Rothbart & Hwang, 2005) has devised an infl uential theory of temperament that includes three diff erent dimensions:

Surgency/extroversion ■ refers to the extent to which a child is generally happy, active, vocal, and regularly seeks interesting stimulation.

Negative aff ect ■ refers to the extent to which a child is angry, fearful, frus- trated, shy, and not easily soothed.

Effortful control ■ refers to the extent to which a child can focus attention, is not readily distracted, and can inhibit responses.

These dimensions of temperament emerge in infancy, con- tinue into childhood, and are related to dimensions of person- ality that are found in adolescence and adulthood (Gartstein, Knyazev, & Slobodskaya, 2005). However, the dimensions are not independent:, infants who are high on eff ortful control tend to be high on surgency/extroversion and low on negative aff ect. In other words, babies who can control their attention and inhibit responses tend to be happy and active but not an- gry or fearful.

Hereditary and Environmental Contributions to Temperament Most theories agree that temperament refl ects both heredity and experience. The infl uence of heredity is shown in twin stud- ies: Identical twins are more alike in most aspects of tempera- ment than fraternal twins, including activity level, extroversion,

temperament

consistent style or pattern of behavior

Twin studies show the impact of heredity on

temperament: If one identical twin is active, the

other one usually is.

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irritability, and persistence (Goldsmith, et al., 1999; Saudino & Cherny, 2001). If, for example, one identical twin is temperamentally active then the other usually is, too. However, the impact of heredity also depends on the temperamental dimension and the child’s age. For example, negative aff ect is more infl uenced by heredity than the other dimensions, and temperament in childhood is more infl uenced by heredity than is temperament in infancy (Wachs & Bates, 2001).

The environment also contributes to children’s temperament. Positive emotional- ity—youngsters who laugh often, seem to be generally happy, and express pleasure often—seems to refl ect environmental infl uences (Goldsmith et al., 1997). Conversely, infants more often develop intense, diffi cult temperaments when mothers are abrupt in dealing with them and lack confi dence (Belsky, Fish, & Isabella, 1991). And some temperamental characteristics are more common in some cultures than in others. Asian babies tend to be less emotional than European American babies. For instance, Asian babies cry less often and less intensely than European American babies, but Russian infants are more fearful and emotionally negative (Gartstein, Slobodskaya, & Kinsht, 2003; Kagan et al., 1994; Lewis, Ramsay, & Kawakami, 1993).

There’s no question that heredity and experience cause babies’ temperaments to diff er, but how stable is temperament? We’ll fi nd out in the next section.

Stability of Temperament Do calm, easygoing babies grow up to be calm, easygoing children, ado- lescents, and adults? Are diffi cult, irritable infants destined to grow up to be cranky, whiny children? The fi rst answers to these questions came from the Fels Longitudinal Project, a study of many aspects of physical and psychological development from infancy. Although not a study of temperament per se, Jerome Kagan and his collaborators (Kagan, 1989; Kagan & Moss, 1962) found that fearful preschoolers in the Fels project tended to be inhibited as older children and adolescents.

Spurred by fi ndings like this one, later investigators attempted to learn more about the stability of temperament. Their research shows that temperament is somewhat stable during the infant and toddler years (Jaff ari-Bimmel et al., 2006). An active fetus is more likely to be an active infant and is also more likely to be a diffi cult, unadap- tive infant (DiPietro et al., 1996). Newborns who cry under moderate stress tend, as 5-month-olds, to cry when they are placed in stress- ful situations (Stifter & Fox, 1990). In addition, inhibited 2-year-olds tend to be shy as 4-year-olds, particularly when their mothers are in- trusive (e.g., provide help when it’s not needed) or frequently make

snide remarks about their shyness, such as “Don’t be such a baby!” (Rubin, Burgess, & Hastings, 2002).

Thus, evidence suggests that temperament is at least somewhat stable throughout infancy and the toddler years (Lemery et al., 1999). Of course, the links are not per- fect. Sam, an emotional 1-year-old, is more likely to be emotional as a 12-year-old than Dave, an unemotional 1-year-old. However, it’s not a “sure thing” that Sam will still be emotional as a 12-year-old. Instead, think of temperament as a predisposition. Some infants are naturally predisposed to be sociable, emotional, or active; others can act in these ways, too, but only if the behaviors are nurtured by parents and others.

Though temperament is only moderately stable during infancy and toddlerhood, it can still shape development in important ways. For example, an infant’s tempera- ment may determine the experiences that parents provide. Parents may read more to quiet babies but play more physical games with their active babies. These diff erent experiences, driven by the infants’ temperament, contribute to each infant’s devel- opment despite the fact that the infants’ temperament may change over the years. Thus, although infants have many features in common, temperament characteristics remind us that each baby also seems to have its own unique personality from the very start.

T H I N K A B O U T I T

How would a learning theorist

explain why children have different

temperaments?

Children’s temperament influences the way that

adults treat them; for example, parents engage

in more vigorous play when their children are

temperamentally active.

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While crossing the street, 4-year-old Martin was struck by a passing car. He was in a coma for a week but then gradually became more alert. Now he seems to be aware of his surroundings. Needless to say, Martin’s mother is grateful that he survived the accident,

but she wonders what the future holds for her son.

FO R PAREN T S AN D C H ILD REN ALIK E, physical growth is a topic of great interest and a source of pride. Parents marvel at the speed with which babies add pounds and inches, and 2-year-olds proudly proclaim, “I bigger now!” In this section, we examine some of the basic features of physical growth, see how the brain develops, and discover how the accident aff ected Martin’s development.

| Growth of the Body

Growth is more rapid in infancy than during any other period after birth. Typically, infants double their birth weight by 3 months of age and triple it by their fi rst birth- day. This rate of growth is so rapid that, if continued throughout childhood, a typical 10-year-old boy would be nearly as long as an jumbo jet and weigh almost as much (McCall, 1979).

Average heights and weights for young children are represented by the lines marked 50th percentile in ❚ Figure 3.2. An average girl weighs about 7 pounds at

Recall answers: (1) serve as the basis for later motor behaviors, (2) Apgar score, (3) alert

inactivity, (4) REM sleep, (5) sleep on their backs, (6) temperament is moderately stable in

these years

Test Yourself

RECALL

1. Some refl exes help infants get necessary

nutrients, other refl exes protect infants

from danger, and still other refl exes

2. The is based on fi ve vital functions

and provides a quick indication of a newborn’s physical

health.

3. A baby lying calmly with its eyes open and focused is in a

state of .

4. Newborns spend more time asleep than awake, and about

half this time asleep is spent in ,

a time thought to foster growth in the central nervous

system.

5. The campaign to reduce SIDS emphasizes that infants

should .

6. Research on the stability of temperament in infants and

young children typically fi nds that .

INTERPRET

Compare the Apgar and the NBAS as measures of a newborn

baby’s well-being.

APPLY

Based on what you know about the stability of temperament,

what would you say to a parent who’s worried that her

15-month-old seems shy and inhibited?

3.2 PHYSICAL DEVELOPMENT

L E A R N I N G O B J E C T I V E S

How do height and weight change from birth to 2 years of ❚ age?

What nutrients do young children need? How are they best ❚ provided?

What are the consequences of malnutrition? How can it be ❚ treated?

What are nerve cells, and how are they organized in the ❚ brain?

How does the brain develop? When does it begin to ❚ function?

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birth, about 21 pounds at 12 months, and about 26 pounds at 24 months. If perfectly average, she would be 19–20 inches long at birth, grow to 29–30 inches at 12 months, and 34–35 inches at 24 months. Figures for an average boy are similar, but weights are slightly greater at ages 12 and 24 months.

These charts also highlight how much children of the same age vary in weight and height. The lines marked 90th percentile in Figure 3.2 represent heights and weights for children who are larger than 90% of their peers; the lines marked 10th percentile represent heights and weights for children who are smaller than 90% of their peers. Any heights and weights between these lines are considered normal. At age 1, for ex- ample, normal weights for boys range from about 19 to 27 pounds. This means that an extremely light but normal boy weighs only two thirds as much as his extremely heavy but normal peer!

The important message here is that average height and normal height are not one and the same. Many children are much taller or shorter than average but are still perfectly normal. This applies to all of the age norms that we mention in this book. Whenever we provide a typical or average age for a developmental milestone, remem- ber that the normal range for passing the milestone is much wider.

Whether an infant is short or tall depends largely on heredity. Both parents con- tribute to their children’s height. In fact, the correlation between the average of the

L e n

g th

( in

B 3 6 9 12 15 18 21 24 27 30 33 36

W e ig

h t

(l b

)

Age (months)

L e n

g th

( in

B 3 6 9 12 15 18 21 24 27 30 33 36

W e ig

h t

(l b

)

Age (months)

LengthLength

90th percentile90th percentile

50th percentile

10th percentile10th percentile

50th percentile

WeightWeight

Boys Girls

Figure 3.2 ❚ Boys and girls grow taller and heavier from birth to 3 years of age, but the range of normal heights and weights is quite wide.

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two parents’ heights and their child’s height at 2 years of age is about .7 (Plomin, 1990). As a general rule, two tall parents will have tall off spring; two short parents will have short off spring; and one tall parent and one short parent will have off spring of medium height.

So far we have emphasized the quantitative aspects of growth, such as height. This ignores an important fact: Infants are not simply scaled-down versions of adults. ❚ Figure 3.3 shows that, compared to adolescents and adults, infants and young chil- dren look top-heavy because their heads and trunks are disproportionately large. As growth of the hips, legs, and feet catches up later in childhood, their bodies take on more adult proportions. This pattern of growth, in which the head and trunk develop fi rst, follows the cephalocaudal principle introduced in Chapter 2 (page 56).

Growth of this sort requires energy. Let’s see how food and drink provide the fuel to grow.

“You Are What You Eat”: Nutrition and Growth In a typical 2-month-old, roughly 40% of the body’s energy is devoted to growth. Most of the remaining energy is used for basic bodily functions such as digestion and respi- ration. A much smaller portion is consumed in physical activity.

Because growth requires so much high energy, young babies must consume an enormous number of calories relative to their body weight. A typical 12-pound 3-month-old, for example, should ingest about 600 calories daily, or about 50 calories per pound of body weight. An adult, by contrast, needs to consume only about 15–20 calories per pound, depending on the person’s level of activity.

Breast-feeding is the best way to ensure that babies get the nourishment they need. Human milk contains the proper amounts of carbohydrates, fats, protein, vitamins, and minerals for babies. Breast-feeding also has several other advantages compared to bottle-feeding (Shelov, 1993; Sullivan & Birch, 1990). First, breast-fed babies are ill less often because breast milk contains the mother’s antibodies. Second, breast-fed babies are less prone to diarrhea and constipation. Third, breast-fed babies typically make the transition to solid foods more easily, apparently because they are accustomed to

T H I N K A B O U T I T

In Chapter 2 we explained how

polygenic inheritance is often involved

when phenotypes form a continuum.

Height is such a phenotype. Propose a

simple polygenic model to explain how

height might be inherited.

Figure 3.3 ❚ The head and trunk develop before the hips, legs, and feet, which gives young children a top-heavy appearance.

2 months

(fetal)

Based on Eichorn, 1969.

5 months

(fetal)

Newborn 2 years 6 years 12 years 25 years

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changes in the taste of breast milk that refl ect a mother’s diet. Fourth, breast milk cannot be contaminated, which is a signifi cant problem in developing countries when formula is used to bottle-feed babies.

Because of these many advantages, the American Academy of Pediatrics recom- mends that children be breast-fed for the fi rst year, with iron-enriched solid foods in- troduced gradually. Cereal is a good fi rst semi-solid food, followed by vegetables, fruits, and then meats. A good rule is to introduce only one food at a time. A 7-month-old having cheese for the fi rst time, for instance, should have no other new foods for a few days. In this way, allergies that may develop—skin rash or diarrhea—can be linked to a particular food, making it easier to prevent recurrences.

The many benefi ts of breast-feeding do not mean that bottle-feeding is harmful. Formula, when prepared in sanitary conditions, provides generally the same nutrients as human milk. But infants are more prone to develop allergies from formula, and formula does not protect infants from disease. Even so, bottle-feeding has advantages of its own. A mother who cannot readily breast-feed can still enjoy the intimacy of feeding her baby, and other family members can participate in feeding. In fact, long- term longitudinal studies typically fi nd that breast- and bottle-fed babies are similar in physical and psychological development (Fergusson, Horwood, & Shannon, 1987), so women in industrialized countries can choose either method and know that their babies’ dietary needs will be met.

In developing nations, bottle-feeding is potentially disastrous. Often the only water available to prepare formula is contaminated; the result is that infants have chronic diarrhea, leading to dehydration and sometimes death. Or, in an eff ort to conserve valuable formula, parents may ignore instructions and use less formula than indicated when making milk; the resulting “weak” milk leads to malnutrition. For these rea- sons, the World Health Organization strongly advocates breast-feeding as the primary source of nutrition for infants and toddlers in developing nations.

By 2 years, growth slows and so children need less to eat. This is also a time when many children become picky eaters, and toddlers and preschool children may fi nd that foods they once ate willingly are now “yucky.” As a toddler, Laura Kail loved green beans. When she reached 2, she decided that green beans were awful and ada- mantly refused to eat them. Though such fi nickiness can be annoy- ing, it may actually be adaptive for increasingly independent pre- schoolers. Because toddlers don’t know what is safe to eat and what isn’t, eating only familiar foods protects them from potential harm (Birch & Fisher, 1995).

Parents should not be overly concerned about this fi nicky period. Although some children do eat less than before (in terms of calories per pound), virtually all picky eaters get adequate food for growth. Nevertheless, picky-eating children can make mealtime miserable for all. What’s a parent to do? Experts recommend several guidelines for encouraging children to be more open-minded about foods and to deal with them when they aren’t (Leach, 1991).

When possible, allow children to choose among different healthy foods (e.g., ■ milk versus yogurt).

Allow children to eat foods in any order they want. ■

Off er children new foods one at a time and in small amounts; encourage but ■ don’t force children to eat new foods.

Don’t force children to “clean their plates.” ■

Don’t spend mealtimes talking about what the child is or is not eating; in- ■ stead, talk about other topics that interest the child.

Never use food to reward or punish children. ■

By following these guidelines, mealtimes can be pleasant and children can receive the nutrition they need to grow.

Toddlers and preschool children often become

picky eaters. This can be annoying but should not

concern parents.

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Malnutrition An adequate diet is only a dream to many of the world’s children. Worldwide, about one in four children under age 5 is malnourished, as indicated by being small for their age (UNICEF, 2006). Many are from third-world countries. In fact, nearly half of the world’s undernourished children live in India, Bangladesh, and Pakistan (UNICEF, 2006). But malnutrition is regrettably common in industrialized countries, too. Many American children growing up homeless and in poverty are malnourished. Approximately 10% of American households do not have adequate food (Nord, Andrews, & Carlson, 2007).

Malnourished children tend to develop less rapidly than their peers. Malnourishment is especially damaging during infancy, be- cause growth is ordinarily so rapid during these years. This is well illustrated by a longitudinal study conducted in Barbados in the West Indies (Galler & Ramsey, 1989; Galler, Ramsey, & Forde, 1986). Included were more than 100 children who were severely malnour- ished as infants as well as 100 children whose family environments were similar but who had adequate nutrition as infants. The children who experienced malnutrition during infancy were indistinguishable from their peers physically: they were just as tall and weighed just as much. However, children with a history of infant malnutrition had much lower scores on intelligence tests. Also, many of the children who were malnourished during infancy had diffi culty paying atten- tion in school and were easily distracted. Many similar studies sug- gest that malnourished youngsters tire easily, are more wary, and are often inattentive (Lozoff et al., 1998). In addition, malnutrition during rapid periods of growth may cause substantial and potentially irre- versible damage to the brain (Morgane et al., 1993).

Malnutrition would seem to have a simple cure—an adequate diet. But the solution is more complex than you might expect. Mal- nourished children are often listless and inactive (Ricciuti, 1993). They are unusually quiet and express little interest in what goes on around them. These behaviors are useful to children whose diet is inadequate because they conserve limited energy. Unfortunately, these behaviors may also deprive youngsters of experiences that would further their development. For example, when children are routinely unresponsive and lethargic, parents often come to believe that their actions have little impact on the children. That is, when children do not respond to parents’ eff orts to stimulate their development, this discourages par- ents from providing additional stimulation in the future. Over time, parents tend to provide fewer experiences that foster their children’s development. The result is a self- perpetuating cycle in which malnourished children are forsaken by parents who feel as if they can do little to contribute to their children’s growth. Thus, a biological infl uence (lethargy stemming from insuffi cient nourishment) causes a profound change in the experiences (parental teaching) that shape a child’s development (Worobey, 2005).

To break the vicious cycle, these children need more than an improved diet. Their parents must be taught how to foster their children’s development and must be encour- aged to do so. Programs that combine dietary supplements with parent training off er promise in treating malnutrition (Grantham-McGregor et al., 2001). Children in these programs often catch up with their peers in physical and intellectual growth, showing that the best way to reduce the eff ect of malnutrition on psychological forces is by ad- dressing both biological and sociocultural forces (Super, Herrera, & Mora, 1990).

| The Emerging Nervous System

The physical changes we see as infants grow are impressive. Even more awe-inspiring are the changes we cannot see—those involving the brain and the nervous system. An infant’s feelings of hunger or pain, its smiles or laughs, and its eff orts to sit upright

Many children around the world are

malnourished.

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nl ey

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O R

B IS

malnourished

being small for one’s age because of inad-

equate nutrition

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or to hold a rattle all refl ect the functioning of the brain and the rest of the emerging nervous system.

How does the brain accomplish these many tasks? To begin to answer this ques- tion, we need to look at the organization of the brain. The basic unit in the brain and the rest of the nervous system is the neuron, a cell that specializes in receiving and transmitting information. Neurons have the basic elements shown in ❚ Figure 3.4. The cell body, in the center of the cell, contains the basic biological machinery that keeps the neuron alive. The receiving end of the neuron, the dendrite, looks like a tree with its many branches. This structure allows one neuron to receive input from thousands of other neurons (Morgan & Gibson, 1991). The tubelike structure that emerges from the other side of the cell body, the axon, transmits information to other neurons. At the end of the axon are small knobs called terminal buttons, which release chemicals called neurotransmitters. These neurotransmitters are the messengers that carry informa- tion to nearby neurons.

Take 50–100 billion neurons like these, and you have the beginnings of a human brain. An adult’s brain weighs a little less than 3 pounds and would easily fi t into your hands. The wrinkled surface of the brain is the cerebral cortex; made up of 10 billion neurons, the cortex regulates many of the functions that we think of as dis- tinctly human. The cortex consists of left and right halves, called hemispheres, linked by a thick bundle of neurons called the corpus callosum. The characteristics you value the most—your engaging personality, your “way with words,” or your uncanny knack for “reading” others’ emotions—are all controlled by specifi c regions in the cortex. For example, your personality and your ability to make and carry out plans are largely

centered in an area in the front of the cortex called (appropriately enough) the frontal cortex. For most people, the ability to produce and understand language is mainly housed in neurons in the left hemisphere of the cortex. When you rec- ognize that others are happy or sad, neurons in your right hemisphere are usually at work.

Now that we know a bit about the organization of the mature brain, let’s look at how the brain grows and begins to function.

The Making of the Working Brain The brain weighs only three quarters of a pound at birth, which is roughly 25% of the weight of an adult brain. But the brain grows rapidly during infancy and the preschool years. At 3 years of age, for example, the brain has achieved 80% of its ultimate weight. Brain weight doesn’t tell us much, however, about the fascinating sequence of changes that take place to create a working brain. Instead, we need to move back to prenatal development.

neuron

basic cellular unit of the brain and ner-

vous system that specializes in receiving

and transmitting information

cell body

center of the neuron that keeps the

neuron alive

dendrite

end of the neuron that receives infor-

mation; it looks like a tree with many

branches

axon

tubelike structure that emerges from the

cell body and transmits information to

other neurons

terminal buttons

small knobs at the end of the axon that

release neurotransmitters

neurotransmitters

chemicals released by the terminal buttons

that allow neurons to communicate with

each other

cerebral cortex

wrinkled surface of the brain that regu-

lates many functions that are distinctly

human

hemispheres

right and left halves of the cortex

corpus callosum

thick bundle of neurons that connects the

two hemispheres

frontal cortex

brain region that regulates personality and

goal-directed behavior

Cell body

Dendrites

Terminal buttons

Direction of information flow

Axon

Figure 3.4 ❚ A nerve cell includes dendrites that receive

information, a cell body that has life-

sustaining machinery, and, for sending

information, an axon that ends in terminal

buttons.

The cortex is the outer, wrinkled surface of the

brain.

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Emerging Brain Structures The beginnings of the brain can be traced to the period of the zygote. At roughly 3 weeks after conception, a group of cells form a fl at structure known as the neural plate. At 4 weeks, the neural plate folds to form a tube that ultimately becomes the brain and spinal cord. When the ends of the tube fuse shut, neurons are produced in one small region of the neural tube. Production of neurons begins about 10 weeks after conception, and by 28 weeks the developing brain has virtually all the neurons it will ever have. During these weeks, neurons form at the incredible rate of more than 4,000 per second (Kolb, 1989).

From the neuron-manufacturing site in the neural tube, neurons migrate to their fi nal positions in the brain. The brain is built in stages, beginning with the innermost layers. Neurons in the deepest layer are positioned fi rst, followed by neurons in the second layer, and so on. This layering process continues until all six layers of the ma- ture brain are in place, which occurs about 7 months after conception (Rakic, 1995).

In the fourth month of prenatal development, axons begin to acquire myelin—the fatty wrap that speeds neural transmission. This process continues through infancy and into childhood and adolescence (Casaer, 1993). Neurons that carry sensory information are the fi rst to acquire myelin; neurons in the cortex are among the last. You can see the eff ect of more myelin in improved coordination and reaction times. The older the infant and (later) the child, the more rapid and coordinated his or her reactions.

In the months after birth, the brain grows rapidly. Axons and dendrites grow lon- ger, and, like a maturing tree, dendrites quickly sprout new limbs. As the number of dendrites increases, so does the number of synapses, reaching a peak at about the fi rst birthday. Soon after, synapses begin to disappear gradually, a phenomenon known as synaptic pruning. Thus, beginning in infancy and continuing into early adolescence, the brain goes through its own version of “downsizing,” weeding out unnecessary connections between neurons. This pruning depends on the activity of the neural cir- cuits: synapses that are active are preserved, but those that aren’t active are eliminated (Webb, Monk, & Nelson, 2001). Pruning is completed fi rst for brain regions associated with sensory and motor functions. Regions associated with basic language and spatial skills are completed next, followed by regions associated with attention and planning (Casey et al., 2005).

Structure and Function Since the mature brain is specialized, with diff erent psychological functions localized in particular regions, a natural question for developmental researchers is: “How early in development does brain functioning become localized?” To answer this question,

neural plate

fl at group of cells present in prenatal

development that becomes the brain and

spinal cord

myelin

fatty sheath that wraps around neurons

and enables them to transmit information

more rapidly

synaptic pruning

gradual reduction in the number of syn-

apses, beginning in infancy and continu-

ing until early adolescence

From birth to 2 years, neurons grow and create

many new synapses with other neurons.

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scientists have used many diff erent methods to map functions onto particular brain regions.

Studies of children with brain damage ■ : Children who suffer brain injuries provide valuable insights into brain structure and function. If a region of

the brain regulates a particular function (e.g., understanding speech), then damage to that region should impair the function.

Studies of electrical activity: Metal electrodes placed on an ■ infant’s scalp produce an electroencephalogram (EEG), a pattern of brain waves. If a region of the brain regulates a function, then the region should show distinctive EEG pat- terns while a child is using that function.

Studies using imaging techniques ■ : One method, functional magnetic resonance imaging (fMRI), uses magnetic fields to track the flow of blood in the brain. In this method the research participant’s brain is literally wrapped in an in- credibly powerful magnet that can track blood flow as participants perform different cognitive tasks (Casey et al., 2005).

None of these methods is perfect; each has drawbacks. When studying children with brain injuries, for example, multiple areas of the brain may be damaged, making it hard to link impaired functioning to a particular brain region. And fMRI is used sparingly because it’s expensive and participants must lie still for several minutes at a time.

Despite these limits, the combined outcome of research using these diff erent ap- proaches indicates that many areas of the cortex begin to function in infancy. Early specialization of the frontal cortex is shown by the fi nding that damage to this region in infancy results in impaired decision making and abnormal emotional responses (Anderson et al., 2001). Similarly, EEG studies show that a newborn infant’s left hemi- sphere generates more electrical activity than the right hemisphere in response to speech (Molfese & Burger-Judisch, 1991). Thus, by birth, the cortex of the left hemi- sphere is already specialized for language processing. Finally, studies of children with prenatal brain damage indicate that, by infancy, the right hemisphere is specialized for understanding certain kinds of spatial relations (Stiles et al., 2005).

Of course, this early specialization does not mean that the brain is functionally mature. During the remainder of childhood and into adulthood, these and other re-

gions of the brain continue to become more specialized. That is, with development the brain regions that are active during cognitive pro- cessing become more focused and less diff use; an analogy would be to a thunderstorm that covers a huge region versus one that packs the same power in a much smaller region (Durston et al., 2006). In Chap- ter 14, we’ll see that some regions of the brain continue to develop into old age whereas other areas are sometimes destroyed by diseases associated with aging.

Brain Plasticity Neuroplasticity refers to the extent to which brain organization is fl ex- ible. How plastic is the human brain? Answers to this question refl ect the familiar views on the nature–nurture issue (Nelson, 1999; Stiles, 2001). Some theorists believe that organization of brain function is predetermined genetically; it’s simply in most children’s genes that, for example, the left hemisphere will specialize in language process- ing. In this view, the brain is like a house: a structure that’s special- ized from the very beginning, with some rooms designed for cooking,

Electrodes placed on an infant’s scalp can de-

tect electrical activity that is used to create an

electroencephalogram, a pattern of the brain’s

response to stimulation.

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electroencephalogram (EEG)

pattern of brain waves recorded from elec-

trodes that are placed on the scalp

functional magnetic resonance imaging

(fMRI)

method of studying brain activity by using

magnetic fi elds to track blood fl ow in the

brain

In fMRI, a magnet is used to track the flow of

blood to different regions of the brain as chil-

dren and adults perform cognitive tasks.

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T H I N K A B O U T I T

When you’re trying to comprehend

a difficult paragraph in a textbook,

what part of your brain is probably

particularly active?

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others for sleeping, and others for bathing. In contrast, other theorists believe that few functions are rigidly assigned to specifi c brain sites at conception and that, instead, experience helps determine the functional organization of the brain. In this view, the brain is more like an offi ce building: an all-purpose structure with rooms designed to be used fl exibly to meet the diff erent business needs of the companies with offi ces in the building.

Research designed to test these views shows that the brain has some plasticity. Remember Martin, the preschooler whose brain was damaged when he was hit by a car? His language skills were impaired after the accident. This was not surprising because the left hemisphere of Martin’s brain had absorbed most of the force of the accident. But within several months Martin had completely recovered his language skills. Apparently other neurons took over language-related processing from the dam- aged neurons. This recovery of function is not uncommon—particularly for young children—and shows that the brain is plastic. In other words, young children often recover more skills after brain injury than do older children and adults, apparently because functions are more easily reassigned in the young brain (Stiles et al., 2005).

However, the brain is not completely plastic, because brains have a similar struc- ture and similar mapping of functions on those structures. Visual cortex, for example, is almost always near the back of the brain. Sensory and motor cortex always run across the middle of the brain. But if a neuron’s function is not specifi ed at conception, how do diff erent neurons take on diff erent functions and in much the same pattern for most people? Researchers are trying to answer this question, and many details still need to be worked out. The answer probably lies in complex biochemical processes (Barinaga, 1997; Kunzig, 1998). You can get an idea of what’s involved by imagining people arriving for a football game at a stadium where there are no reserved seats. As fans enter the stadium, they see others wearing their own school colors and move in that direction. Of course, not everyone does this. Some fans sit with friends from the other team. Some pick seats based on other factors (e.g., to avoid looking into the sun, to be close to the concession stand). In general, though, by game time most fans have taken seats on their respective sides of the fi eld.

In much the same way, as neurons are created and begin migrating through the layers of cortex, cellular biochemistry makes some paths more attractive than oth- ers. Yet, just as each fan can potentially sit anywhere because there are no reserved seats, an individual neuron can end up in many diff erent locations because genetic instructions do not assign specifi c brain regions. Thus, the human brain is plastic—its organization and function can be aff ected by experience—but its development follows some general biochemical instructions ensuring that most people end up with brains organized along similar lines.

Finally, it’s important to emphasize the role of environmental stimulation in normal brain development. To return to the analogy of the brain as a building, the newborn’s brain is perhaps best conceived as a partially fi nished, partially furnished house: A general organizational framework is there, with preliminary neural path- ways designed to perform certain functions. The left hemisphere no doubt has some language pathways and the frontal cortex has some emotion-related pathways. How- ever, completing the typical organization of the mature brain requires input from the environment (Greenough & Black, 1992). In this case, environmental input infl uences experience-expectant growth—over the course of evolution, human infants have typi- cally been exposed to some forms of stimulation that are used to adjust brain wiring, strengthening some circuits and eliminating others. For example, under normal condi- tions, healthy human infants experience moving visual patterns (e.g., faces) and varied sounds (e.g., voices). Just as a newly planted seed depends on a water-fi lled environ- ment for growth, a developing brain depends upon environmental stimulation to fi ne- tune circuits for vision, hearing, and other systems (Black, 2003).

What’s more, just as a seed’s growth is stunted without adequate water, brain circuits are altered when deprived of the expected stimulation. As a case in point, adults who have been blind since birth are extremely skilled at many auditory tasks: Apparently

neuroplasticity

extent to which brain organization is

fl exible

experience-expectant growth

process by which the wiring of the brain

is organized by experiences that are com-

mon to most humans

experience-dependent growth

process by which an individual’s unique

experiences over a lifetime aff ect brain

structures and organization

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brain regions that process visual stimuli in sighted people are, in the absence of vi- sual stimulation, converted to auditory circuits (Collignon et al., 2007; Gougoux et al., 2004). Thus, experience is the catalyst that converts the partially furnished, partially fi nished newborn brain into a mature, specialized brain (Johnson, 2000; Webb et al., 2001).

Of course, experiences later in life also sculpt the brain (and we’ll see this in sev- eral chapters later in this book). Experience-dependent growth denotes changes in the brain that are not linked to specifi c points in development and that vary across individuals and across cultures. Experience-dependent growth is illustrated by a pre- school child’s learning of a classmate’s name, an elementary school child’s discovery of a shortcut home from school, and an adolescent’s mastery of the functions of a new cell phone. In each case, brain circuits are modifi ed in response to an individual’s ex- periences. With today’s technology, we can’t see these daily changes in the brain. But when they accumulate over many years—as when individuals acquire expertise in a skill—brain changes can be detected. For example, skilled cellists have extensive brain regions devoted to controlling the fi ngers of the left hand as they are positioned on the strings (Elbert et al., 1995). And years of driving a taxicab produces changes in the hip- pocampus, a region of the brain implicated in navigation and way-fi nding (Maguire, Woollett, & Spiers, 2006).

Recall answers: (1) disproportionately large, (2) more, (3) parent training, (4) cell body,

(5) goal-directed behavior, (6) left hemisphere, (7) they often regain their earlier skills

over time

Test Yourself

RECALL

1. Compared to older children and

adults, an infant’s head and trunk are

2. Because of the high demands of growth, infants need

calories per pound than adults.

3. The most eff ective treatment for malnutrition is improved

diet and .

4. The is the part of the neuron that

contains the basic machinery to keep the cell alive.

5. The frontal cortex is the seat of personality and regulates

6. Human speech typically elicits the greatest electrical activ-

ity from the of an infant’s brain.

7. A good example of brain plasticity is that, although chil-

dren with brain damage often have impaired cognitive

processes, .

INTERPRET

Compare growth of the brain before birth with growth of the

brain after birth.

APPLY

How does malnutrition illustrate the infl uence on develop-

ment of life-cycle forces in the biopsychosocial framework?

L E A R N I N G O B J E C T I V E S

What are the component skills involved in learning to walk? ❚ At what age do infants master them?

How do infants learn to coordinate the use of their hands? ❚

3.3 MOVING AND GRASPING: EARLY MOTOR SKILLS

Nancy is 14 months old and a world-class crawler. Using hands and knees, she can go just about anywhere she wants to. Nancy does not walk and seems uninterested in learn- ing how. Nancy’s dad wonders whether he should be doing something to help Nancy progress

From years of practice, the region of the brain

that controls the fingers of the left hand is prob-

ably well developed in this skilled cellist. This

demonstrates experience-dependent growth.

A V

ID L

. P O

K R

ES S

/ A

FP /

G et

ty Im

ag es

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beyond crawling. Deep down, he worries that perhaps he was negligent in not providing more

exercise for Nancy when she was younger.

D O YO U REMEMBER W H AT IT W AS LIK E T O LEAR N T O T YPE, to drive a car with a stick shift, to play a musical instrument, or to play a sport? Each of these activities involves motor skills: coordinated movements of the muscles and limbs. Success demands that each movement be done in a precise way, in exactly the right sequence, and at exactly the right time. For example, in the few seconds that it takes you to type “human devel- opment,” if you don’t move your fi ngers in exactly the correct sequence to the precise location on the keyboard, you might get “jinsj drveo;nrwnt.”

These activities are demanding for adults, but think about similar challenges for infants. Infants must learn to move about in the world, to locomote. At fi rst unable to move independently, infants soon learn to crawl, to stand, and to walk. Once the child can move through the environment upright, the arms and hands are free. To take ad- vantage of this arrangement, the human hand has fully independent fi ngers (instead of a paw), with the thumb opposing the remaining four fi ngers. Infants must learn the fine motor skills associated with grasping, holding, and manipulating objects. In the case of feeding, for example, infants progress from being fed by others, to holding a bottle, to feeding themselves with their fi ngers, to eating with utensils.

Together, locomotion and fi ne motor skills give children access to an enormous va- riety of information about shapes, textures, and features in their environment. In this section, we’ll see how locomotion and fi ne motor skills develop and, as we do, we’ll see whether Nancy’s dad should worry about her lack of interest in walking.

| Locomotion

Advances in posture and locomotion transform the infant in little more than a year. ❚ Figure 3.5 shows some of the important milestones in motor development and the age by which most infants have achieved them. By about 5 months of age, most babies will have rolled from back to front and will be able to sit upright with support. By 7 months infants can sit alone, and by 10 months they can creep. A typical 14-month- old is able to stand alone briefl y and walk with assistance. This early, unsteady form of walking is called toddling (hence the term toddler). Of course, not all children walk at exactly the same age. Some walk before their fi rst birthday; others—like Nancy, the world-class crawler in the vignette—take their fi rst steps as late as 18 or 19 months of age. By 24 months, most children can climb steps, walk backwards, and kick a ball.

Researchers once thought these developmental milestones refl ected maturation (e.g., McGraw, 1935). Walking, for example, emerged naturally when the necessary muscles and neural circuits matured. Today, however, locomotion—and, in fact, all of motor development—is viewed from a new perspective. According to dynamic sys- tems theory, motor development involves many distinct skills that are organized and reorganized over time to meet the demands of specifi c tasks. For example, walking includes maintaining balance, moving limbs, perceiving the environment, and having a reason to move. Only by understanding each of these skills and how they are com- bined to allow movement in a specifi c situation can we understand walking (Thelen & Smith, 1998).

Posture and Balance The ability to maintain an upright posture is fundamental to walking. But upright pos- ture is virtually impossible for newborns and young infants because of the shape of their body. Cephalocaudal growth means that an infant is top-heavy. Consequently, as soon as a young infant starts to lose her balance, she tumbles over. Only with growth of the legs and muscles can infants maintain an upright posture (Thelen, Ulrich, & Jensen, 1989).

Once infants can stand upright, they must continuously adjust their posture to avoid falling down (Metcalfe et al., 2005). By a few months after birth, infants begin

motor skills

coordinated movements of the muscles

and limbs

locomote

ability to move around in the world

fi ne motor skills

motor skills associated with grasping,

holding, and manipulating objects

toddling

early, unsteady form of walking done by

infants

toddlers

young children who have just learned to

walk

dynamic systems theory

theory that views motor development as

involving many distinct skills that are

organized and reorganized over time to

meet specifi c needs

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to use visual cues and an inner-ear mechanism to adjust their posture. To show the use of visual cues for balance, researchers had babies sit in a room with striped walls that moved. When adults sit in such a room, they perceive themselves (not the walls) as moving and adjust their posture accordingly; so do infants, which shows that they use vision to maintain upright posture (Bertenthal & Clifton, 1998). In addition, when 4-month-olds who are propped in a sitting position lose their balance, they try to keep their head upright. They do this even when blindfolded, which means they are us- ing cues from their inner ear to maintain balance (Woollacott, Shumway-Cook, & Williams, 1989).

Balance is not, however, something that infants master just once. Instead, infants must relearn balancing for sitting, crawling, walking, and other postures. Why? The body rotates around diff erent points in each posture (e.g., the wrists for crawling ver- sus the ankles for walking), and diff erent muscle groups are used to generate com- pensating motions when infants begin to lose their balance. Consequently, it’s hardly surprising that infants who easily maintain their balance when sitting still topple over time after time when crawling. And once they walk, infants must adjust their posture further when they carry objects, because these aff ect balance (Garciaguirre, Adolph, & Shrout, 2007). Infants must recalibrate the balance system as they take on each

Figure 3.5 ❚ Locomotor skills improve rapidly in the 15 months after birth, and progress can be measured by many developmental milestones.

Pull to stand by furniture 12 months

Fetal posture 0 months

Walk when led 11 months

Creep 10 months

Stand holding furniture 9 months

Stand with help 8 months

Sit alone 7 months

Sit on high chair; grasp dangling object 6 months

Chin up 1 month

Chest up 2 month

Reach and miss 3 month

Sit with support 4 month

Sit on lap; grasp object 5 month

Climb stair steps 13 months

Stand alone 14 months

Walk alone 15 months

Based on Shirley, 1931, and Bayley, 1969.

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new posture, just as basketball players recalibrate their muscle movements when they move from dunking to shooting a three pointer (Adolph, 2000, 2003).

Stepping Another essential element of walking is moving the legs alternately, repeatedly trans- ferring the weight of the body from one foot to the other. Children don’t step sponta- neously until approximately 10 months because they must be able to stand in order to step.

Can younger children step if they are held upright? Thelen and Ulrich (1991) de- vised a clever procedure to answer this question. Infants were placed on a treadmill and held upright by an adult. When the belt on the treadmill started to move, infants could respond in one of several ways. They might simply let both legs be dragged rearward by the belt. Or they might let their legs be dragged briefl y, then move them forward together in a hopping motion. Many 6- and 7-month-olds demonstrated the mature pattern of alternating steps on each leg. Even more amazing is that—when the treadmill was equipped with separate belts for each leg that moved at diff erent speeds—babies adjusted, stepping more rapidly on the faster belt.

Apparently, the alternate stepping motion that is essential for walking is evident long before infants walk alone. Walking unassisted is not possible, though, until other component skills are mastered.

Perceptual Factors Many infants learn to walk in the relative security of fl at, unclut- tered fl oors at home. But they soon discover that the environment off ers a variety of surfaces, some more conducive to walking than others. Infants use perceptual information to judge whether a sur- face is suitable for walking. When placed on a surface that gives way underfoot (e.g., a waterbed), they quickly judge it unsuitable for walking and resort to crawling (Gibson et al., 1987). When toddlers encounter a surface that slopes down steeply, few try to walk down (which would result in a fall); instead, they slide or scoot backwards (Adolph, Eppler, & Gibson, 1993; Adolph, 1997). And infants are more likely to cross a wide bridge with a rigid handrail than a nar- row bridge with a wobbly handrail (Berger, Adoph, & Lobo, 2005). Results like these show that infants use perceptual cues to decide whether a surface is safe for walking.

Coordinating Skills Dynamic systems theory emphasizes that learning to walk demands orchestration of many individual skills. Each component skill must fi rst be mastered alone and then integrated with the other skills (Werner, 1948). That is, mastery of intricate motions requires both differentiation (mastery of component skills) and integration— combining the motions in proper sequence into a coherent, working whole. In the case of walking, not until 12 to 15 months of age have children mastered the component skills to be coordinated and so al- low independent, unsupported walking.

Mastering individual skills and coordinating them well does not happen over- night. Instead, they take time and repeated practice. When parents give their infants daily practice in sitting, for example, their infants master sitting at a younger age. However, such practice has no eff ect on stepping because diff erent muscles and move- ments are involved (Zelazo et al., 1993). Similarly, when infants practice crawling on their bellies, this helps them crawl on hands and feet because many of the motions are the same (Adolph, Vereijken, & Denny, 1998); yet when infants practice crawling on steep slopes, there is no transfer to walking on steep slopes because the motions

Infants are capable of stepping—moving the legs

alternately—long before they can walk alone. D

ex te

r G

or m

le y

diff erentiation

distinguishing and mastering individual

motions

integration

linking individual motions into a coher-

ent, coordinated whole

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diff er (Adolph, 1997). Thus, experience can improve the rate of motor development, but the improvement is limited to the movements that were trained. In other words, just as daily practice kicking a soccer ball won’t improve your golf game, infants who receive much practice in one motor skill usually don’t improve in others.

These fi ndings from laboratory research are not the only evidence that practice promotes motor development; cross-cultural research points to the same conclusion. In Europe and North America, most infants typically walk alone near their fi rst birth- day. But infants in other cultures often begin to walk (and reach the other milestones listed on page 102) at an earlier age because child-care practices allow children to practice their emerging motor skills. For example, in some traditional African cul- tures, infants sit and walk at younger ages. Why? Infants are commonly carried by their parents “piggyback” style, which helps develop muscles in the infants’ trunk and legs.

Some cultures even take a further step. They believe that practice is essential for motor skills to develop normally and so they (or siblings) provide daily training ses- sions. For example, the Kipsigis of Kenya help children learn to sit by having them sit while propped up (Super, 1981). And among the West Indians of Jamaica, mothers have an elaborate exercise routine that allow babies to practice walking (Hopkins & Westra, 1988). This training provides additional opportunities for children to learn the elements of diff erent motor skills; not surprisingly, infants with these opportuni- ties learn to sit and walk earlier.

You may be surprised that some cultures do just the opposite—they have prac- tices that discourage motor development. The Ache, an indigenous group in Paraguay, protect infants and toddlers from harm by carrying them constantly (Kaplan & Dove, 1987). In Chinese cities, parents often allow their children to crawl only on a bed sur- rounded by pillows, in part because they don’t want their children crawling on a dirty fl oor (Campos et al., 2000). In both cases, infants reach motor milestones a few months later than the ages listed in the chart on page 102.

Even European and North American infants are crawling at older ages today than they did in previous generations (Dewey et al., 1998). This generational diff erence refl ects the eff ectiveness of the Back to Sleep campaign described on page 88. Because today’s babies spend less time on their tummies, they have fewer opportunities to discover that they can propel themselves by creeping, which would otherwise prepare them for crawling.

Thus, cultural practices can accelerate or delay the early stages of motor develop- ment, depending on the nature of practice that infants and toddlers receive. In the long run, however, the age of mastering various motor milestones is not critical for children’s development. All healthy children learn to walk, and whether this happens a few months before or after the “typical” ages shown on page 102 has no bearing on children’s later development.

Beyond Walking If you can recall the feeling of freedom that accompanied your fi rst driver’s license, you can imagine how the world expands for infants and toddlers as they learn to move independently. The fi rst tentative steps are soon followed by others that are more skilled. With more experience, infants take longer, straighter steps. And, like adults, they begin to swing their arms, rotating the left arm forward as the right leg moves then repeating with the right arm and left leg (Ledebt, 2000; Ledebt, van Wieringen, & Savelsbergh, 2004).

Most children learn to run a few months after they walk alone. Most 2-year-olds have a “hurried walk” instead of a true run; they move their legs stiffl y (rather than bending them at the knees) and are not “airborne” as is the case with true running. By 5 or 6 years, children run easily, quickly changing directions or speed. Hopping also shows young children’s growing skill: A typical 2- or 3-year-old will hop a few times on one foot, typically keeping the upper body very stiff ; by 5 or 6, children can hop long distances on one foot or alternate hopping fi rst on one foot a few times, then on the other.

In many African cultures, infants are routinely

carried piggyback style; this strengthens the

infant’s legs, which allows them to walk at a

younger age.

O R

G EN

S C

H Y

TT E

/ Pe

te r

A rn

ol d

In c.

T H I N K A B O U T I T

How does learning to hop on one

foot demonstrate differentiation and

integration of motor skills?

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With their advanced motor skills, older preschoolers delight in unstructured play. They enjoy swinging, climbing over jungle gyms, and balancing on a beam. Some learn to ride a tricycle or to swim.

| Fine Motor Skills

A major accomplishment of infancy is skilled use of the hands (Ber- tenthal & Clifton, 1998). Newborns have little apparent control of their hands, but 1-year-olds are extraordinarily talented.

Reaching and Grasping At about 4 months, infants can successfully reach for objects (Ber- tenthal & Clifton, 1998). These early reaches often look clumsy—and for good reason. When infants reach, they don’t move their arm and hand directly and smoothly to the desired object (as older children and adults do). Instead, the infant’s hand moves like a ship under the direction of an unskilled navigator: It moves a short distance, slows, then moves again in a slightly diff erent direction—a process that’s repeated until the hand fi nally contacts the object (McCarty & Ash- mead, 1999). As infants grow, their reaches have fewer movements, though they are still not as continuous and smooth as reaches by older children and adults (Berthier, 1996).

Reaching requires that an infant move the hand to the location of a desired object. Grasping poses a diff erent challenge: Now the infant must coordinate movements of individual fi ngers to grab an object. Grasping, too, becomes more effi cient during infancy. Most 4-month- olds just use their fi ngers to hold objects, wrapping the object tightly with their fi ngers alone. Not until 7 or 8 months do most infants use their thumbs to hold objects (Siddiqui, 1995). At about this same age, infants begin to position their hands to make it easier to grasp an object. If trying to grasp a long thin rod, for example, infants place their fi ngers perpendicular to the rod, which is the best position for grasping (Wentworth, Benson, & Haith, 2000). In- fants need not see their hand to position it correctly: They position the hand just as accurately in reaching for a lighted object in a darkened room as when reaching in a lighted room (McCarty et al., 2001).

Infants’ growing control of each hand is accompanied by greater coordination of the two hands. Although 4-month-olds use both hands, their motions are not coor- dinated; rather, each hand seems to have a mind of its own. Infants may hold a toy motionless in one hand while shaking a rattle in the other. At roughly 5 to 6 months of age, infants can coordinate the motions of their hands so that each hand performs diff erent actions that serve a common goal. So a child might, for example, hold a toy animal in one hand and pet it with the other (Karniol, 1989). These skills continue to improve after the child’s fi rst birthday: 1-year-olds reach for most objects with one hand; by 2 years, they reach with one or two hands, as appropriate, depending on the size of the object (van Hof, van der Kamp, & Savelsbergh, 2002).

These gradual changes in fi ne motor coordination are well illustrated by the ways children feed themselves. Beginning at roughly 6 months of age, many infants experiment with “fi nger foods” such as sliced bananas and green beans. Infants can eas- ily pick up such foods, but getting them into their mouths is another story. The hand grasping the food may be raised to the cheek, then moved to the edge of the lips, and fi nally shoved into the mouth. Mission accomplished, but only after many de-

Locomotor skills develop rapidly in preschool

children, making it possible for them to play

vigorously.

ic B

id er

/ P

ho to

Ed it

A typical 4-month-old grasps an object with

fingers alone.

au ra

D w

ig ht

/ P

ho to

Ed it

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tours along the way! However, infants’ eye–hand coordination improves rapidly, and foods varying in size, shape, and texture are soon placed directly in the mouth.

At about the fi rst birthday, many parents allow their children to try eating with a spoon. Youngsters fi rst simply play with the spoon, dipping it in and out of a dish

fi lled with food or sucking on an empty spoon. Soon they learn to fi ll the spoon with food and place it in their mouth, but the motions are awkward. For example, most 1-year-olds fi ll a spoon by fi rst placing it directly over a dish. Then, they lower it until the bowl of the spoon is full. In contrast, 2-year-olds typically scoop food from a dish by rotating their wrist, which is the same motion adults use.

As preschoolers, children become much more dextrous and are able to make many precise and delicate movements with their hands and fi ngers. Greater fi ne motor skill means that preschool children can begin to care for themselves. No longer must they rely primarily on parents to feed and clothe them; instead, they become increasingly skilled at feed- ing and dressing themselves. A 2- or 3-year-old, for example, can put on some simple clothing and use zippers but not buttons; by 3 or 4 years, children can fasten buttons and take off their clothes when going to the bathroom; and most 5-year-olds can dress and undress themselves— except for tying shoes, which children typically master at about age 6.

Greater fi ne motor coordination also leads to improvements in pre- school children’s printing and drawing. Given a crayon or marker, 2-year- olds will scribble, expressing delight in the simple lines that are created just by moving a crayon or marker across paper. By 4 or 5 years of age, children use their drawings to depict recognizable objects.

All of these actions illustrate the principles of diff erentiation and integration that were introduced in our discussion of locomotion. Complex acts involve many simple movements. Each must be performed correctly and in the proper sequence. Develop- ment involves fi rst mastering the separate elements and then assembling them into a smoothly functioning whole.

Handedness Are you right-handed or left-handed? If you’re right-handed, you’re in the majority. About 90% of the people worldwide prefer to use their right hand, although this fi gure varies somewhat from place to place, refl ecting cultural infl uences. Most of the remaining 10% are left-handed; a relatively small percentage of people are truly ambidextrous.

When young babies reach for objects, they don’t seem to prefer one hand over the other; they use their left and right hands interchangeably. They may shake a rattle with their left hand and, moments later, pick up blocks with their right. In one study, infants and toddlers were videotaped as they played with toys that could be manipu- lated with two hands, such as a pinwheel (Cornwell, Harris, & Fitzgerald, 1991). The 9-month-olds used their left and right hands equally, but by 13 months, most grasped the toy with their right hand. Then they used their left hand to steady the toy while the right hand manipulated the object.

This early preference for one hand becomes stronger and more consistent dur- ing the toddler and preschool years. By age 2 a child’s hand preference is clear; most children use their right hand in fi ne motor skills such as coloring, brushing teeth, or zipping a jacket. At this age, youngsters occasionally use their nonpreferred hand for tasks, but by age 5 children typically use their nonpreferred hand only when the pre- ferred hand is doing something else. By the time children are ready to enter kindergar- ten, handedness is well established and diffi cult to reverse (McManus et al., 1988).

What determines whether children become left- or right-handed? Some scientists believe that a gene biases children toward right-handedness (Annett, 2006). Consistent with this idea, identical twins are more likely than fraternal twins to have the same handedness—both are right-handed or both are left-handed (Sicotte, Woods, & Mazzi- otta, 1999). But experience also contributes to handedness. Modern industrial cultures

By age 5, fine-motor skills are developed to the

point that most youngsters can dress themselves.

M ed

io Im

ag es

/ G

et ty

Im ag

T H I N K A B O U T I T

Jenny and Ian are both left-handed and

they fully expected their son, Tyler, to

prefer his left hand, too. But he’s

8 months old already and seems to use

both hands to grasp toys and other

objects. Should Jenny and Ian give up

their dream of being the three left-

handed musketeers?

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favor right-handedness. School desks, scissors, and can openers, for example, are de- signed for right-handed people and can be used by left-handers only with diffi culty. In the United States, elementary school teachers used to urge left-handed children to use their right hands. As this practice has diminished in the last 50 years, the percentage of left-handed children has risen steadily (Levy, 1976). Thus, handedness seems to have both hereditary and environmental infl uences.

Recall answers: (1) dynamic systems theory, (2) the inner ear, (3) using perceptual

information, (4) 4, (5) 1 year

Test Yourself

RECALL

1. According to ,

motor development involves many

distinct skills that are organized and re-

organized over time, depending on task

demands.

2. When 4-month-olds tumble from a sitting position, they

usually try to keep their head upright. This happens even

when they are blindfolded, which means that the impor-

tant cues to balance come from .

3. Skills important in learning to walk include main-

taining upright posture and balance, stepping, and

4. Akira uses both hands simultaneously, but not in a coordi-

nated manner; each hand seems to be “doing its own thing.”

Akira is probably months old.

5. Before the age of , children show

no signs of handedness; they use their left and right hands

interchangeably.

INTERPRET

Compare and contrast the milestones of locomotor develop-

ment in the fi rst year with the fi ne motor milestones.

APPLY

Describe how the mastery of a fi ne motor skill—such as

learning to use a spoon or a crayon—illustrate the integration

of biological, psychological, and sociocultural forces in the

biopsychosocial framework.

Darla is mesmerized by her newborn daughter, Olivia. Darla loves holding Olivia, talking to her, and simply watching her. Darla is certain that Olivia is already getting to know her and is coming to recognize her face and the sound of her voice. Darla’s husband, Steve,

thinks she is crazy: “Everyone knows that babies are born blind, and they probably can’t hear

much either.” Darla doubts Steve and wishes someone could tell her the truth about Olivia’s

vision and hearing.

T O AN SW ER D AR LA’S Q UEST IO N S, we need to defi ne what it means for an infant to expe- rience or sense the world. Humans have several kinds of sense organs, each of which is receptive to a diff erent kind of physical energy. For example, the retina at the back of the eye is sensitive to some types of electromagnetic energy, and sight is the result. The eardrum detects changes in air pressure, and hearing is the result. Cells at the top of the nasal passage detect the passage of airborne molecules, and smell is the result. In each case, the sense organ translates the physical stimulus into nerve impulses that are sent to the brain. The processes by which the brain receives, selects, modifi es, and

3.4 COMING TO KNOW THE WORLD: PERCEPTION

L E A R N I N G O B J E C T I V E S

Are infants able to smell, to taste, and to experience pain? ❚

Can infants hear? How do they use sound to locate objects? ❚

How well can infants see? Can they see color and depth? ❚

How do infants coordinate information between different ❚ sensory modalities, such as between vision and hearing?

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organizes these impulses is known as perception. This is simply the fi rst step in the complex process of accumulating information that eventually results in “knowing.”

Darla’s questions are really about her newborn daughter’s perceptual skills. By the end of this section, you’ll be able to answer her questions because we’re going to look at how infants use diff erent senses to experience the world.

| Smell, Taste, and Touch

Newborns have a keen sense of smell. Infants respond positively to pleasant smells and negatively to unpleasant smells (Mennella & Beauchamp, 1997). They have a relaxed and contented facial expression when they smell honey or choc- olate, but they frown or turn away when they smell rotten eggs or ammonia. Young babies can also recognize familiar odors. Newborns will look in the direc- tion of a pad that is saturated with their own amniotic fl uid (Schaal, Marlier, & Soussignan, 1998). They will also turn toward a pad saturated with the odor of their mother’s breast or her perfume (Porter & Winburg, 1999).

Newborns also have a highly developed sense of taste. They readily diff erenti- ate salty, sour, bitter, and sweet tastes (Rostenstein & Oster, 1997). Most infants seem to have a “sweet tooth.” They react to sweet substances by smiling, sucking, and licking their lips (Steiner et al., 2001) but grimace when fed bitter or sour substances (Kaijura, Cowart, & Beauchamp, 1992). Infants are also sensitive to changes in the taste of breast milk that refl ect a mother’s diet and will nurse more after their mother has consumed a sweet-tasting substance such as vanilla (Men- nella & Beauchamp, 1996).

Newborns are sensitive to touch. As we saw earlier in this chapter, many areas of the newborn’s body respond refl exively when touched. Touching an in- fant’s cheek, mouth, hand, or foot produces refl exive movements, documenting that infants perceive touch.

If babies react to touch, does this mean they experience pain? This is diffi cult to answer because pain has such a subjective element to it. The same pain-eliciting stimulus that leads some adults to complain of mild discomfort causes others to report that they are in agony. Since infants cannot express their pain to us directly, we must use indirect evidence.

The infant’s nervous system defi nitely is capable of transmitting pain, because receptors for pain in the skin are just as plentiful in in- fants as they are in adults (Anand & Hickey, 1987). Furthermore, babies’ behavior in response to apparent pain-provoking stimuli also suggests that they experience pain (Buchholz et al., 1998). For example, babies receiving an inoculation lower their eyebrows, purse their lips, and (of course) cry. Although we can’t hear the baby in the photo, the sound of her cry is probably the unique pattern associated with pain. The pain cry begins suddenly, is high-pitched, and is not easily soothed. The baby is also agitated, moving her hands, arms, and legs (Craig et al., 1993; Gou- bet, Clifton, & Shah, 2001). All together, these signs strongly suggest that babies experience pain.

Perceptual skills are extraordinarily useful to newborns and young babies. Smell and touch help them recognize their mothers. Smell and taste make it much easier for them to learn to eat. Early development of smell, taste, and touch prepares newborns and young babies to learn about the world.

| Hearing

Do you remember, from Chapter 2, the study in which mothers read aloud The Cat in the Hat late in pregnancy? This research showed that the fetus can hear at 7 or 8 months after conception. As you would expect from these results, newborns typically respond

perception

processes by which the brain receives,

selects, modifi es, and organizes incoming

nerve impulses that are the result of physi-

cal stimulation

Infants and toddlers do not like bitter and sour

tastes!

D io

n O

gu st

/ T

he Im

ag e

W or

An infant’s response to an inoculation—a distinc-

tive facial expression coupled with a distinctive

cry—clearly suggests that the baby feels pain.

S at

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to sounds in their surroundings. If a parent is quiet but then coughs, an infant may startle, blink his eyes, and move his arms or legs. These responses may seem natural, but they do indeed indicate that infants are sensitive to sound.

Overall, adults can hear better than infants (Saff ran, Werker, & Werner, 2006). Adults can hear some very quiet sounds that infants can’t. More interestingly, infants best hear sounds that have pitches in the range of human speech: neither very high- nor very low-pitched. Infants can diff erentiate speech sounds, such as vowels from consonant sounds, and by 4 or 5 months they can recognize their own names (Jusczyk, 1995; Mandel, Jusczyk, & Pisoni, 1995).

Infants also can distinguish diff erent musical sounds and can remember lullabies and songs that parents sing to them (Trainor, Wu, & Tsang, 2004). They can distin- guish diff erent melodies and prefer melodies that are pleasant sounding over those that are unpleasant sounding or dissonant (Trainor & Heinmiller, 1998). And infants are sensitive to the rhythmic structure of music: After hearing a simple sequence of notes, they can tell the diff erence between another sequence that matches the original versus one that doesn’t (Hannon & Trehub, 2005). This early sensitivity to music is remarkable but perhaps not so surprising when you consider that music is (and has been) central in all cultures.

In addition to carrying a message through words or music, sound can reveal much about its source. When we hear a person speak, the pitch of the speech can be used to judge the age and sex of the speaker; if the speech contains many relatively lower- pitched sounds, then the speaker is probably a man. The loudness of the speech tells us about the speaker’s distance; if it can barely be heard, the speaker is far away. Also, diff erences in the time it takes sound to travel to the left and right ears tell us about the speaker’s location; if the sounds arrive at exactly the same time, the speaker must be directly ahead or directly behind us.

Even infants can extract much of this information in sound. Young babies can distinguish sounds of diff erent pitches, and 6-month-olds do so nearly as accurately as adults (Spetner & Olsho, 1990). They are also able to diff erentiate speech sounds, such as diff erent vowel and consonant sounds (a topic we examine in more detail in Chapter 4).

Like adults, infants use sound to locate objects, looking toward the source of sound (Morrongiello, Fenwick, & Chance, 1990). Infants also use sound to decide whether objects are near or far. In one study (Clifton, Perris, & Bullinger, 1991), 7-month-olds were shown a rattle. Next, the experimenters darkened the room and shook the rattle either 6 inches away from the infant or about 2 feet away. Infants would often reach for the rattle in the dark when it was 6 inches away but not when it was 2 feet away. These 7-month-olds were quite capable of using sound to estimate distance—in this case, distinguishing a toy they could reach from one they could not.

Thus, by the middle of the fi rst year, infants are responding to much of the infor- mation that is provided by sound. In Chapter 4, we will reach the same conclusion when we examine the perception of language-related sounds.

| Seeing

If you’ve ever watched infants, you’ve probably noticed that they spend much of their waking time looking around. Sometimes they seem to be generally scanning their en- vironment, and sometimes they seem to be focusing on nearby objects. What do they see as a result? Perhaps their visual world is a sea of confusing gray blobs. Or maybe they see the world essentially as adults do. Actually, neither of these descriptions is entirely accurate, but the second is closer to the truth.

The various elements of the visual system—the eye, the optic nerve, and the brain—are relatively well developed at birth. Newborns respond to light and can track moving objects with their eyes. How well do infants see? The clarity of vision, called visual acuity, is defi ned as the smallest pattern that can be distinguished depend- ably. You’ve undoubtedly had your acuity measured, probably by being asked to read rows of progressively smaller letters or numbers from a chart. To assess newborns’

visual acuity

smallest pattern that one can distinguish

reliably

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acuity we use the same approach, adjusted somewhat because we can’t use words to explain to infants what we’d like them to do. Most infants will look at patterned stimuli instead of plain, patternless stimuli (Snow, 1998). For example, if we were to show the two stimuli in ❚ Figure 3.6 to an infant, most babies would look longer at the striped pattern than at the gray pattern. As we make the lines narrower (along with the spaces between them), there comes a point at which the black and white stripes become so fi ne that they simply blend together and appear gray—just like the other pattern.

To estimate an infant’s acuity, we pair the gray square with squares in which the widths of the stripes diff er, like the ones in ❚ Figure 3.7: When infants look at the two stimuli equally, this indicates that they are no longer able to distinguish the stripes of the patterned stimulus. By measuring the width of the stripes and their distance from an infant’s eye, we can estimate acuity, with detection of thinner stripes indicating better acuity. Measurements of this sort indicate that newborns and 1-month-olds see at 20 feet what normal adults would see at 200–400 feet. But by the fi rst birthday, an infant’s acuity is essentially the same as that of an adult with normal vision (Kellman & Arterberry, 2006).

Color Not only do infants begin to see the world with greater acuity during the fi rst year, they also begin to see it in color! How do we perceive color? The wavelength of light is the basis of color perception. In ❚ Figure 3.8, light that we see as red has a relatively long wavelength, whereas violet (at the other end of the color spectrum) has a much shorter wavelength. Concentrated in the back of the eye, along the retina, are special- ized neurons called cones. Some cones are particularly sensitive to short-wavelength light (blues and violets). Others are sensitive to medium-wavelength light (greens and yellows), and still others are sensitive to long-wavelength light (reds and oranges). These diff erent kinds of cones are linked by complex circuits of neurons, and this circuitry is responsible for our ability to see the world in colors.

These circuits gradually begin to function in the fi rst few months after birth. New- borns and young babies can perceive few colors, but by 3 months the three kinds of cones and their associated circuits are working and infants are able to see the full range of colors (Kellman & Arterberry, 2006). In fact, by 3 to 4 months, infants’ color perception seems similar to that of adults (Adams & Courage, 1995; Franklin, Pilling, & Davies, 2005). In particular, infants, like adults, tend to see categories of color: they see the spectrum as a group of reds, a group of yellows, a group of greens, and the like (Dannemiller, 1998). By 3 months, infants prefer red and blue over other colors (Zem- ach, Chang, & Teller, 2007).

Depth People see objects as having three dimensions: height, width, and depth. The retina of the eye is fl at, so height and width can be represented directly on its two-dimensional surface. But the third dimension, depth, cannot be represented directly on this fl at surface, so how do we perceive depth? We use perceptual processing to infer depth.

Figure 3.6 ❚ Infants usually prefer looking at striped pat-

terns to plain ones, a preference that can be

used to measure an infant’s visual acuity.

Figure 3.7 ❚ Visual acuity can be measured by determining

the thinnest stripes that the infant prefers

to view.

cones

specialized neurons in the back of the eye

that sense color

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Depth perception tells us whether objects are near or far, which was the basis for some classic research by Eleanor Gibson and Richard Walk (1960) on the origins of depth perception. In their work, babies were placed on a glass-covered platform, a device known as the visual cliff. On one side of the platform, a checkerboard pattern appeared directly under the glass; on the other side, the pattern appeared several feet below the glass. The result was that the fi rst side looked shallow but the other looked deep, like a cliff .

Mothers stood on each side of the visual cliff and tried to coax their infants across the deep or the shallow side. Most babies willingly crawled to their moth- ers when they stood on the shallow side. In contrast, almost every baby refused to cross the deep side, even when the mothers called them by name and tried to lure them with an attractive toy. Clearly, infants can perceive depth by the time they are old enough to crawl.

What about younger babies who cannot yet crawl? When babies as young as 6 weeks are simply placed on the visual cliff , their hearts beat more slowly when they are placed on the deep side of the cliff . Heart rate often decelerates when people notice something interesting, so this would suggest that 6-week-olds notice that the deep side is diff erent. At 7 months, infants’ heart rate accelerates, a sign of fear. Thus, although young babies can detect a diff erence between the shallow and the deep sides of the visual cliff , only older, crawling babies are actu- ally afraid of the deep side (Campos et al., 1978).

How do infants infer depth, on the visual cliff or anywhere? They use several kinds of cues. Among the fi rst are kinetic cues, in which motion is used to estimate depth. Visual expansion refers to the fact that as an object moves closer, it fi lls an ever-greater proportion of the retina. Visual expansion is why we fl inch when someone unexpectedly tosses a soda can toward us, and it’s what allows a batter to estimate when a baseball will arrive over the plate. Another cue, motion parallax, refers to the fact that nearby moving objects move across our visual fi eld faster than those at a distance. Motion parallax is in action when you look out the side window in a moving car: Trees next to the road move rapidly across the visual fi eld, but mountains in the distance move much more slowly. Babies use these cues in the fi rst weeks after birth; for example, a 1-month-old baby will blink if a moving object looks as if it’s going to hit him in the face (Nanez & Yonas, 1994).

Another cue becomes important at about 4 months. Retinal disparity is based on the fact that the left and right eyes often see slightly diff erent versions of the same scene. You can demonstrate retinal disparity by touching your nose with your fi nger. If you look at your fi nger with one eye (closing the other eye), each eye has a very dif- ferent view of your fi nger. But if you hold your fi nger at arm’s length from your nose and repeat the demonstration, each eye has very similar views of your fi ngers. Thus,

500 600

Visible light

X-rays

.1 10 100 1000

Ultra-

violet

rays

Infrared rays

Wavelength of light in nanometers (billionths of a meter)

400 700

Figure 3.8 ❚ The visible portion of light ranges from a

wavelength of about 400 nanometers (which

looks violet) to nearly 700 nanometers

(which looks red).

visual cliff

glass-covered platform that appears to

have a “shallow” and a “deep” side; used to

study infants’ depth perception

kinetic cues

cues to depth perception in which motion

is used to estimate depth

visual expansion

kinetic cue to depth perception that is

based on the fact that an object fi lls an

ever-greater proportion of the retina as it

moves closer

motion parallax

kinetic cue to depth perception based on

the fact that nearby moving objects move

across our visual fi eld faster than

do distant objects

retinal disparity

way of inferring depth based on diff er-

ences in the retinal images in the left and

right eyes

Infants avoid the “deep side” of the visual cliff,

indicating that they perceive depth.

ar k

R ic

ha rd

s /

Ph ot

oE di

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greater disparity in retinal images signifi es that an object is close. By 4–6 months of age, infants use retinal disparity as a depth cue, cor- rectly inferring that objects are nearby when disparity is great (Kell- man & Arterberry, 2006).

By 7 months, infants use several cues for depth that depend on the arrangement of objects in the environment. These are sometimes called pictorial cues because they’re the same cues that artists used to convey depth in drawings and paintings. Here are two examples of pictorial cues that 7-month-olds use to infer depth.

Linear perspective ■ : Parallel lines come together at a single point in the dis- tance. Thus, we use the space between the lines as a cue to distance and, con- sequently, decide the train is far away because the parallel tracks grow close together.

Texture gradient ■ : The texture of objects changes from coarse and distinct for nearby objects to finer and less distinct for distant objects. We judge that dis- tinct flowers are close and that blurred ones are distant.

Not only do infants use visual cues to judge depth, they also use sound. Remember that infants correctly judge quieter objects to be more distant than louder objects. Given such an assortment of cues, it is not surprising that infants gauge depth so accurately.

Perceiving Objects Perceptual processes enable us to interpret patterns of lines, textures, and colors as ob- jects. That is, our perception actually creates an object from sensory stimulation. This is particularly challenging because we often see only parts of objects—nearby objects often obscure parts of more distant objects. Nevertheless, we recognize these objects despite this complexity in our visual environment.

Perception of objects is limited in newborns, but it develops rapidly in the fi rst few months after birth (Johnson, 2001). By 4 months, infants use a number of cues to deter- mine which elements go together to form objects. One important cue is motion: Ele- ments that move together are usually part of the same object (Kellman & Arterberry, 2006). For example, at the left of ❚ Figure 3.9, a pencil appears to be moving back and forth behind a colored square. If the square were removed, you would be surprised to see a pair of pencil stubs, as shown on the right side of the diagram. The common movement of the pencil’s eraser and point leads us to believe that they’re part of the same pencil.

pictorial cues

cues to depth perception that are used to

convey depth in drawings and paintings

linear perspective

a cue to depth perception based on the

fact that parallel lines come together at a

single point in the distance

texture gradient

perceptual cue to depth based on the fact

that the texture of objects changes from

coarse and distinct for nearby objects to

fi ner and less distinct for distant objects

T H I N K A B O U T I T

Psychologists often refer to “perceptual-

motor skills,” which implies that the two

are closely related. Based on what you’ve

learned in this chapter, how might motor

skills influence perception? How could

perception influence motor skills?

Linear perspective is one cue to depth: We

interpret the railroad tracks that are close to-

gether as being more distant than the tracks that

are far apart.

is io

ns o

f A

m er

ic a

/ Jo

e S

oh m

/ G

et ty

Im ag

Texture gradient is used to infer depth: We interpret the distinct flowers as

being closer than the flowers with the coarse texture.

os e

Fu st

e R

ag a

/ C

or bi

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Young infants, too, are surprised by demonstrations like this. If they see a dis- play like the moving pencils, they will then look very briefl y at a whole pencil, apparently because they expected it. In contrast, if after seeing the moving pencil they’re shown the two pencil stubs, they look much longer—as if trying to fi gure out what happened (Amso & Johnson & Aslin, 2006; Eizenman & Bertenthal, 1998). Evidently, even very young babies use common motion to create objects from dif- ferent parts.

Motion is one clue to object unity, but infants use others including color, texture, and aligned edges. As you can see in ❚ Figure 3.10, infants more often group features together (i.e., believe they’re part of the same object) when they’re the same color, have the same texture, and have their edges are aligned (Johnson, 2001).

Perceiving Faces One object that’s particularly important for infants is the human face. Some scientists argue that babies are innately attracted to stimuli that are facelike. The claim here is that some aspect of the face—perhaps three high-contrast blobs close together— constitutes a distinctive stimulus that is readily recognized, even by newborns. For example, newborns turn their eyes to follow a moving face more than they turn their eyes for nonface stimuli (Johnson, Grossman, & Farroni, 2008). This preference for faces and facelike stimuli supports the view that infants are innately attracted to faces. However, preference for tracking a moving face changes abruptly at about 4 weeks of

When you look at this pattern, what do you

see? You probably recognize it as part of a

human eyeball, even though all that’s physi-

cally present in the photo are many different

colored dots.

au l G

on za

le z

Pe re

z /

Ph ot

o R

es ea

rc he

rs , I

nc .

Many cues tell us that these are two objects, not

one unusually shaped object: The two objects

differ slightly in color, the glass of juice has a dif-

ferent texture than the orange, and the glass has

a well-defined edge.

G oo

d S

ho ot

/ S

up er

S to

Figure 3.9 ❚ After infants have seen the pencil ends mov-

ing behind the square, they are surprised to

see two pencils when the square is removed;

this shows that babies use common motion

as a way to determine what makes up an

object.

T H I N K A B O U T I T

When 6-month-old Sebastian watches

his mother type on a keyboard, how

does he know that her fingers and the

keyboard are not simply one big unusual

object?

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age—infants now track all moving stimuli. One idea is that newborns’ face tracking is a refl ex, based on primitive circuits in the brain, that is designed to enhance attention to facelike stimuli. Starting at about 4 weeks, circuits in the brain’s cortex begin to control infants’ looking at faces and other stimuli (Morton & Johnson, 1991).

By 7 or 8 months, infants process faces in much the same way that adults do: as a confi guration in which the internal elements (e.g., eyes, nose, mouth) are arranged and spaced in a unique way. Younger infants, in contrast, often perceive faces as an independent collection of facial features, as if they have not yet learned that the ar-

Cue

Color

Infants believe this display has one pencil…

…but believe this display has two pencils

Texture

Aligned edges

Figure 3.10 ❚ In addition to common motion, infants use

common color, common texture, and aligned

edges as clues to object unity.

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rangement and spacing of features is critical (Bhatt et al., 2005; Schwarzer, Zauner, & Jovanic, 2007).

As infants gain more and more experience with faces, their perception of facial confi gurations becomes further refi ned. In the Spotlight on Research feature, we’ll see that this age-related refi nement of facial confi gurations results in a highly unusual outcome—6-month-olds outperform adults!

Spotlight on Research How Infants Become Face Experts

Who were the investiga-

tors, and what was the

aim of the study? Over

the first year, infants rapidly become more skilled

at recognizing human faces, presumably because

they are exposed to an ever-larger number of

faces and thus are able to fine-tune their face

recognition processes. If this argument is correct,

then infants might also lose the ability to recog-

nize some facelike stimuli. For example, a mon-

key’s face has many of the same basic features of

a human face: eyes, nose, and mouth in the famil-

iar configuration. A young infant’s broadly tuned

face recognition processes might work well for

monkey faces, but an older infant’s more finely

tuned processes might not. Testing this hypoth-

esis was the aim of a study by Olivier Pascalis,

Michelle de Haan, and Charles A. Nelson (2002).

How did the investigators measure the topic of

interest? Pascalis and colleagues wanted to deter-

mine whether 6-month-olds, 9-month-olds, and

adults could recognize human faces and monkey

faces. Consequently, they had infants and adults

view a photo of a monkey face or a human face.

Then that face was paired with a novel face of

the same species. Experimenters recorded par-

ticipants’ looking at the two faces. The expecta-

tion was that, if the participants recognized the

familiar stimulus, they would look longer at the

novel stimulus.

Who were the participants in the study? The

study included 30 6-month-olds, 30 9-month-

olds, and 11 adults. Half the infants at each age

saw human faces; the others saw monkey faces.

Adults saw both human and monkey faces.

What was the design of the study? This study

was experimental. The independent variables

included the type of face (human vs. monkey) and

the familiarity of the face on the test trial (novel

vs. familiar). The dependent variable was the

participants’ looking at the two faces on the test

trials. The study was cross-sectional because it

included 6-month-olds, 9-month-olds, and adults,

each tested once.

Were there ethical concerns with the study? No.

There was no obvious harm associated with

looking at pictures of faces.

What were the results? If participants recog-

nized the familiar face, they should look more at

the novel face; if they did not recognize the fa-

miliar face, they should look equally at the novel

and familiar faces. ❚ Figure 3.11 shows the per- centage of time that participants looked at the

novel face. When human faces were shown, all

three age groups looked longer at the novel face

(more than 50% preference for the novel face).

But when monkey faces were shown, 6-month-

olds looked longer at the novel face whereas

9-month-olds and adults looked at novel and

familiar faces equally. Remarkably, 6-month-olds

showed greater skill than older infants and adults,

as they were the only group to recognize a mon-

key face that had been shown before.

What did the investigators conclude? Pascalis

and colleagues (2002) concluded that their find-

ings “support the hypothesis that the perceptual

window narrows with age and that during the

first year of life the face processing system is

tuned to a human template” (p. 1322). That is,

from experience infants fine-tune their face pro-

cessing systems to include only human faces.

What converging evidence would strengthen

these conclusions? These findings show that

6-month-olds’ face processing systems work

equally well on human and monkey faces. The

investigators could determine how broadly

the system is tuned by studying young infants’

recognition of other species that have faces in

a humanlike configuration. In addition, it would

be beneficial to use brain mapping methods (de-

scribed on page 98) to determine whether the

brain regions associated with face recognition

change as face processing systems become more

finely tuned between 6 and 9 months.

Pascalis and colleagues had participants in their study view one of the human faces

or one of the monkey faces. Then that face was shown with the other face of the

same type (e.g., both human faces if the participant had seen the human face first). If

participants remember the first face then they should look longer at the novel face.

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[continued]

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The fi ndings from the Spotlight on Research study show that experience leads infants to a more precise confi guration of faces, one that includes human faces but not monkey faces. This experience-based fi ne-tuning is also shown in infants’ ability to recognize faces from diff erent racial groups. Most adults recognize faces from their own race better than faces from other races, refl ecting greater exposure to faces of their own race. An interesting reversal of the usual pattern documents the importance of experience: Adults born in Korea but adopted by European parents recognized European American faces better than Asian faces (Sangrigoli et al., 2005). Kelly et al. (2007) showed that European American 3-month-olds recognized African and Asian faces just as readily as they recognized European American faces. At 9 months, how- ever, European American infants recognized European American faces but not Afri- can and Asian faces. Evidently, by 9 months of age the facial template is modifi ed to refl ect the kinds of faces that infants see frequently, which usually are faces from their own race.

Rapid changes in face recognition skill show the role of experience in fi ne-tuning infants’ perception, a theme that will emerge again in the early phases of language learning (Chapter 4). And these improved face recognition skills are adaptive, for they provide the basis for social relationships (see Chapter 5) that infants form during the rest of their fi rst year of life. There’s a practical benefi t as well: If you see a giant ape in New York City and wonder whether it’s really King Kong or an imposter, just ask a 6-month-old.

| Integrating Sensory Information

So far, we have discussed infants’ sensory systems separately. In reality, of course, most infant experiences are better described as “multimedia events.” For example, a nursing mother provides visual and taste cues to her baby. A rattle stimulates vision, hearing, and touch. In fact, much stimulation is not specifi c to one sense but spans multiple senses. Temporal information, such as duration or tempo, can be seen or heard. For example, you can detect the rhythm of a person clapping by seeing the hands meet or by hearing the sound of hands striking. Similarly, the texture of a surface—whether it’s rough or smooth—can be detected by sight or by feel.

Infants readily perceive many of these relations. For example, infants can recog- nize visually an object that they have only touched previously (Sann & Streri, 2007).

To enhance your understanding of this

research, go to www.cengage.com/

psychology/kail/ to complete critical thinking

questions and explore related websites.

Figure 3.11 ❚ Infants and adults recognize faces of individual humans (indicated by

looking at a novel face more than 50% of the time), but only 6-month-

old infants recognize faces of individual monkeys. Data from Pascalis

et al. (2002).

H u

m a n

f a ce

s M

o n

k e y f

a ce

5045 6055 65

Percent of time spent looking at novel face

6-month-olds 9-month-olds adults

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Similarly, they can detect relations between information presented visually and auditorily. They know, for example, that an object mov- ing into the distance looks smaller and is harder to hear (Bahrick & Lickliter, 2002). They can also link the temporal properties of visual and auditory stimulation, such as duration and rhythm (Lewkowicz, 2000a). Finally, they even link their own body movement to their per- ceptions of musical rhythm, giving new meaning to the phrase “feel the beat, baby!” (Phillips-Silver & Trainor, 2005).

Traditionally, coordinating information from diff erent senses (e.g., vision with hearing, vision with touch) was thought to be a chal- lenging task for infants. More recently, however, some researchers have argued that the infant’s sensory systems are particularly attuned to intersensory redundancy, that is, to information that is presented simultaneously to diff erent sensory modes (Bahrick & Lickliter, 2002, 2004). Perception is best when information is presented redundantly to multiple senses. When an infant sees and hears the mother clapping (visual, auditory informa- tion), he focuses on the information conveyed to both senses and pays less attention to information that’s only available in one sense, such as the color of the mother’s nail polish or the sounds of her humming along with the tune. Or the infant can learn that the mom’s lips are chapped from seeing the fl aking skin and by feeling the rough- ness as the mother kisses him. According to intersensory redundancy theory, it’s as if infants follow the rule “Any information that’s presented in multiple senses must be important, so pay attention to it!” (Flom & Bahrick, 2007).

Integrating information from diff erent senses is yet another variation on the theme that has dominated this chapter: Infants’ sensory and perceptual skills are im- pressive. Darla’s newborn daughter, from the opening vignette, can defi nitely smell, taste, and feel pain. She can distinguish sounds, and at about 7 months she will use sound to locate objects. Her vision is a little blurry now but will improve rapidly; in a few months, she’ll see the full range of colors and perceive depth. In short, Darla’s daughter, like most infants, is exceptionally well prepared to begin to make sense out of her environment.

A mother who breast-feeds provides her baby

with a multimedia event: the baby sees, smells,

hears, feels, and tastes her!

ig it

al V

is io

n /

G et

ty Im

ag es

intersensory redundancy

infants’ sensory systems are attuned to

information presented simultaneously to

diff erent sensory modes

Recall answers: (1) bitter, (2) pain, (3) the use of sound to judge distances, (4) 1 year,

(5) Cones, (6) retinal disparity, (7) part of the same object, (8) information presented

redundantly to multiple senses

Test Yourself

RECALL

1. Infants respond negatively to sub-

stances that taste sour or .

2. Infants respond to with a high-

pitched cry that is hard to soothe.

3. If an infant seated in a completely darkened room hears

the sound of her favorite rattle nearby, she will reach for it;

this demonstrates .

4. At age , infants’ acuity is like that

of an adult with normal vision.

5. are specialized neurons in the

retina that are sensitive to color.

6. The term refers to the fact that im-

ages of an object in the left and right eyes diff er for nearby

objects.

7. When elements consistently move together, infants decide

that they are .

8. Infants readily integrate information from diff erent senses,

and their sensory systems seem to be particularly attuned

to .

INTERPRET

Compare the impact of nature and nurture on the develop-

ment of infants’ sensory and perceptual skills.

APPLY

Perceptual skills are quite refi ned at birth and mature rap-

idly. What evolutionary purposes are served by this rapid

development?

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When Ximena brushes her teeth, she puts her 20-month-old son, Christof, in an infant seat facing the bathroom mirror. She’s been doing this for months, and Christof always seems to enjoy looking at the images in the mirror. Lately, he seems to pay special at-

tention to his own refl ection. Ximena thinks that sometimes Christof deliberately frowns or

laughs just to see what he looks like. Is this possible, Ximena wonders, or is her imagination

simply running wild?

AS IN FAN T S’ PHYSIC AL, MO T O R, AN D PERC EPT UAL SK ILLS G RO W , they learn more and more about the world around them. As part of this learning, infants and toddlers begin to realize that they exist independently of other people and objects in the environment and that their existence continues over time. In this last section, you’ll see how chil- dren become self-aware and learn what Christof knows about himself.

| Origins of Self-Concept

When do children begin to understand that they exist? Measuring the onset of this awareness is not easy. Obviously, we can’t simply ask a 3-year-old, “So, tell me, when did you fi rst realize you existed and weren’t just part of the furniture?” Investigators need a less direct approach, and a mirror off ers one route. Babies sometimes touch the face in the mirror or wave at it, but none of their behaviors indicates that they recog- nize themselves in the mirror. Instead, babies act as if the face in the mirror is simply a very interesting stimulus.

How would we know that infants recognize themselves in a mirror? One clever approach is to have mothers place a red mark on their infant’s nose; they do this surreptitiously, while wiping the baby’s face. Then the infant is returned to the mir- ror. Many 1-year-olds touch the red mark on the mirror, showing that they notice the

mark on the face in the mirror. By 15 months, however, an important change occurs: Babies see the red mark in the mirror, then reach up and touch their own noses. By age 2, virtually all children do this (Bullock & Lütkenhaus, 1990; Lewis & Brooks-Gunn, 1979). When these older children notice the red mark in the mirror, they understand that the funny looking nose in the mirror is their own!

We don’t need to rely solely on the mirror task to know that self-awareness emerges between 18 and 24 months. During this same period, toddlers look more at photo- graphs of themselves than at photos of other children. They also refer to themselves by name or with a personal pronoun, such as “I” or “me,” and sometimes they know their age and their gender. These changes, which often occur together, suggest that self-awareness is well estab- lished in most children by age 2 (Lewis & Ramsay, 2004; Pinquart, 2005).

Soon toddlers and young children begin to recognize continuity in the self over time; the “I” in the present is linked to the “I” in the past

L E A R N I N G O B J E C T I V E S

When do children begin to realize that they exist? ❚

What are toddlers’ and preschoolers’ self-concepts like? ❚

When do preschool children begin to acquire a theory ❚ of mind?

3.5 BECOMING SELF-AWARE

Not until 15 to 18 months of age do babies

recognize themselves in the mirror, which is an

important step in becoming self-aware.

PT S

an ta

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G et

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ag es

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(Nelson, 2001). Awareness of a self that is extended in time is fostered by conversa- tions with parents about the past and the future. Through such conversations, a 3-year- old celebrating a birthday understands that she’s an older version of the same person who had a birthday a year previously.

Children’s growing awareness of a self extended in time is also revealed by their understanding of ownership (Fasig, 2000). When a toddler sees his favorite toy and says “mine,” this implies awareness of continuity of the self over time: “In the past, I played with that.” And when toddlers say “Mine!” they are often not being aggressive or selfi sh; instead, “mine” is a way of indicating ownership in the process defi ning themselves. They are not trying to deny the toy to another but simply saying that playing with this toy is part of who they are (Levine, 1983).

Once children fully understand that they exist, they begin to wonder who they are. They want to defi ne themselves. Through- out the preschool years, possessions continue to be one of the ways in which children defi ne themselves. Preschoolers are also likely to mention physical characteristics (“I have blue eyes”), their preferences (“I like spaghetti”), and their competencies (“I can count to 50”). What these features have in common is a fo- cus on a child’s characteristics that are observable and concrete (Damon & Hart, 1988).

As children enter school, their self-concepts become even more elaborate (Harter, 1994), changes that we’ll explore in Chapter 9.

| Theory of Mind

As youngsters gain more insights into themselves as thinking beings, they begin to realize that people have thoughts, beliefs, and intentions. They also understand that thoughts, beliefs, and intentions often cause people to behave as they do. Amazingly, even infants understand that people’s behavior is often intentional—designed to achieve a goal. Imagine a father who says, “Where are the crackers?” in front of his 1-year-old daughter and then begins opening kitchen cabinets, moving some objects to look behind them. Finding the box of crackers, he says, “There they are!” An in- fant who understands intentionality would realize how her father’s actions (searching, moving objects) were related to the goal of fi nding the crackers.

Many clever experiments have revealed that 1-year-olds do indeed have this un- derstanding of intentionality (Sommerville & Woodward, 2005). For example, Bell- agamba, Camaioni, and Colonnesi (2006) had 15-month-olds watch an experimenter perform an action but fail to achieve an apparent goal. The experimenter might, for example, look as if she wanted to drop a bead necklace in a jar but instead it falls onto the table. Or an experimenter looks as if she wants to use a stick to push a button, but she misses. When 15-month-olds were given the same objects, they typically imitated the experimenter’s intended action—placing the necklace in the jar or pushing the button—and not what she actually did. Infants’ interpretations emphasized what the actions were meant to accomplish, not the actions per se.

From this early understanding of intentionality, young children’s naïve psychology expands rapidly. Between 2 and 5, children develop a theory of mind, a naïve under- standing of the relations between mind and behavior. One of the leading researchers on theory of mind, Henry Wellman (1993, 2002), believes that children’s theory of mind moves through three phases during the preschool years. In the earliest phase, 2-year- olds are aware of desires and often speak of their wants and likes, as in “Lemme see” or “I wanna sit.” And they often link their desires to their behavior, such as “I happy there more cookies” (Wellman, 1993). Thus, by age 2, children understand that people have desires and that desires can cause behavior.

By about age 3, children clearly distinguish the mental world from the physical world. For example, if told about a girl who has a cookie and another who is thinking

Preschool children use their toys to define

themselves; saying “Mine” is shorthand for “This

is my doll and I like to play with dolls a lot!”

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di t

theory of mind

ideas about connections between thoughts,

beliefs, intentions, and behavior that cre-

ate an intuitive understanding of the link

between mind and behavior

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about a cookie, 3-year-olds know that only the fi rst girl can see, touch, and eat her cookie (Harris et al., 1991). Most 3-year-olds also use “mental verbs” like “think,” “believe,” “re- member,” and “forget,” which suggests that they have some understanding of diff erent mental states (Bartsch & Wellman, 1995). Although 3-year-olds talk about thoughts and beliefs, they nevertheless emphasize desires when trying to explain why people act as they do.

Not until 4 years of age do mental states really take center stage in children’s un- derstanding of their own actions and the actions of others. That is, by age 4, children understand that behavior is often based on a person’s beliefs about events and situa- tions, even when those beliefs are wrong. This developmental transformation is par- ticularly evident when children are tested on false-belief tasks such as the one shown in ❚ Figure 3.12. In all false-belief tasks, a situation is set up so that the child being tested has accurate information but someone else does not. For example, in the story in Figure 3.12, the child being tested knows the ball is really in the box but Sally, the girl in the story, believes that the ball is still in the basket. Remarkably, although 4-year- olds correctly say that Sally will look for the ball in the basket (i.e., will act on her false belief), most 3-year-olds claim that she will look for the ball in the box. The 4-year-olds understand that Sally’s behavior is based on her beliefs even though her beliefs are incorrect (Frye, 1993).

This basic developmental progression is remarkably robust. Wellman, Cross, and Watson (2001) conducted a meta-analysis of approximately 175 studies in which more than 4,000 young children were tested on false-belief tasks. Before 3½ years, children typically make the false-belief error: Attributing their own knowledge of the ball’s

Sally has a ball.

Sally goes out for a walk.

Anne takes the ball from the basket and puts it into the box.

Now Sally comes back. She wants to play with her ball. Where will she look for her ball?

She puts the ball in her basket.

This is Sally. Sally has a basket.

This is Anne. Anne has a box.

Figure 3.12 ❚ In a false-belief task, most 3-year-olds say that

Sally will look for the ball in the box, showing

that they do not understand how people can

act on their beliefs (where the ball is) even

when those beliefs are wrong.

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T H I N K A B O U T I T

Suppose you believe that a theory of

mind develops faster when preschoolers

spend much time with other children.

What sort of correlational study would

you devise to test this hypothesis? How

could you do an experimental study to

test the same hypothesis?

location to Sally, they say she will search in the correct location. Yet a mere six months later, children now understand that Sally’s false belief will cause her to look for the ball in the box. This rapid developmental transition from incorrect to correct performance is unaff ected by many procedural variables (e.g., whether Sally is a doll, a picture, a person in a videotape, or a real person).

Even more remarkably, the same developmental pattern is evident in many diff er- ent cultures. Callaghan and colleagues (2005) tested understanding of false belief in preschool children from fi ve diff erent cultural settings: Canda, India, Peru, Samoa, and Thailand. In all fi ve settings, the majority of 3-year-olds made the false-belief error, at 4 years about half made the error, and by 5 years almost no children did.

This pattern therefore signifi es a fundamental change in children’s understanding of the centrality of beliefs in a person’s thinking about the world. By age 4 children “realize that people not only have thoughts and beliefs, but also that thoughts and beliefs are crucial to explaining why people do things; that is, actors’ pursuits of their desires are inevitably shaped by their beliefs about the world” (Bartsch & Wellman, 1995, p. 144).

You can see preschool children’s growing understanding of false belief in the next Real People feature.

The early stages of children’s theory of mind seem clear. But just how this hap- pens is very much a matter of debate. According to one view, theory of mind is based on an innate, specialized module that automatically recognizes behaviors associated with diff erent mental states such as wanting, pretending, and believing. Supporting this modular view are fi ndings from children with autism, a severe disorder in which individuals are uninterested in other people and have extremely limited social skills. Children with autism lag far behind typically developing children in understanding false belief, as if an “understanding other people” module is not working properly (Peterson, Wellman, & Liu, 2005).

Another view is that growth of theory of mind refl ects change in language skills (e.g., Harris, de Rosnay, & Pons, 2005; Milligan, Astington, & Dack, 2007), which de- velop rapidly during the same years that theory of mind emerges. Growing language skills provide a preschooler with an expanded vocabulary that includes verbs describ- ing mental states (e.g., “think,” “know,” “believe”) as well as more grammatical forms that can be used to describe a setting where a person knows that another person has a false belief.

Yet another view is that a child’s theory of mind emerges from interactions with other people, interactions that provide children with insights into diff erent mental states. Through conversations with parents and older siblings that focus on other people’s mental states, children learn facts of mental life and this helps them see that others often have diff erent perspectives than they do. In other words, when children frequently participate in conversations that focus on other people’s moods, feelings, and intentions, this helps them learn that people’s behavior is based on their beliefs

Real People: Applying Human Development “Seeing Is Believing . . .” for 3-Year-Olds

Preschoolers gradually

recognize that people’s

behavior is sometimes

guided by mistaken beliefs. We once witnessed

an episode at a day-care center that docu-

mented this growing understanding. After lunch,

Karen, a 2-year-old, saw ketchup on the floor

and squealed, “blood, blood!” Lonna, a 3-year-

old, said in a disgusted tone, “It’s not blood—it’s

ketchup.” Then, Shenan, a 4-year-old, interjected,

“Yeah, but Karen thought it was blood.” A similar

incident took place a few weeks later, on the

day after Halloween. This time Lonna put on a

monster mask and scared Karen. When Karen

began to cry, Lonna said, “Oh stop. It’s just a

mask.” Shenan broke in again, saying, “You know

it’s just a mask. But she thinks it’s a monster.” In

both cases, only Shenan understood that Karen’s

behavior was based on her beliefs (that the

ketchup is blood and that the monster is real),

even though her beliefs were false.

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regardless of the accuracy of those beliefs (Dunn & Brophy, 2005; Taumoepeau & Ruff , 2006).

Of course, preschool children’s growing knowledge of the mind is not an isolated accomplishment. This understanding is simply part of the profound cognitive growth that occurs during the preschool years. We’ll examine this cognitive growth next, in Chapter 4.

Recall answers: (1) personal pronouns such as “I” and “me,” (2) possessions, (3) false beliefs

Test Yourself

RECALL

1. Apparently children are fi rst self-aware

at age 2 because this is when they fi rst

recognize themselves in a mirror and in

photographs and when they fi rst

use .

2. During the preschool years, children’s self-concepts

emphasize , physical characteris-

tics, preferences, and competencies.

3. Unlike 4-year-olds, most 3-year-olds don’t understand

that other people’s behavior is sometimes based on

INTERPRET

Compare and contrast diff erent explanations of the growth of

theory of mind during the preschool years.

APPLY

Self-concept emerges over the same months that toddlers

show rapid gains in locomotor skills. How might changes in

locomotor skill contribute to a toddler’s emerging sense of

self?

3.1 The Newborn

How do reflexes help newborns interact with the world?

Babies are born with a number of different reflexes. ■ Some help them adjust to life outside of the uterus, some help protect them from danger, and some serve as the ba- sis for later voluntary motor behavior.

How do we determine whether a baby is healthy and adjusting

to life outside the uterus?

The Apgar scale measures five vital signs to determine a ■ newborn baby’s physical well-being. The Neonatal Behav- ioral Assessment Scale provides a comprehensive evalua- tion of a baby’s behavioral and physical status.

What behavioral states are common among newborns?

Newborns spend their day in one of four states: alert ■ inactivity, waking activity, crying, and sleeping. A new- born’s crying includes a basic cry, a mad cry, and a pain cry. The best way to calm a crying baby is by putting it on the shoulder and rocking.

Newborns spend approximately two thirds of every day ■ asleep and go through a complete sleep–wake cycle once every 4 hours. By 3 or 4 months, babies sleep through the night. Newborns spend about half of their time asleep in REM sleep, an active form of sleep that may stimulate growth in the nervous system.

Some healthy babies die from sudden infant death syn- ■ drome. Factors that contribute to SIDS are prematurity, low birth weight, and smoking. Also, babies are vulner- able to SIDS when they sleep on their stomach and when they are overheated. The goal of the Back to Sleep cam- paign is to prevent SIDS by encouraging parents to have infants sleep on their backs.

What are the different features of temperament? Do they

change as children grow?

Temperament refers to a consistent style or pattern to an ■ infant’s behavior. Modern theories list two to six dimen- sions of temperament, including (for example) extrover- sion and negative affect. Temperament is influenced both by heredity and by environment and is a reasonably stable characteristic of infants and young children.

3.2 Physical Development

How do height and weight change from birth to 2 years of age?

Physical growth is particularly rapid during infancy, but ■ babies of the same age differ considerably in their height and weight. Size at maturity is largely determined by heredity.

Growth follows the cephalocaudal principle, in which the ■ head and trunk develop before the legs. Consequently,

S U M M A RY

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infants and young children have disproportionately large heads and trunks.

What nutrients do young children need? How are they best

provided?

Infants must consume a large number of calories relative ■ to their body weight, primarily because of the energy re- quired for growth. Breast-feeding and bottle-feeding both provide babies with adequate nutrition.

Malnutrition is a worldwide problem that is particularly ■ harmful during infancy, when growth is so rapid. Treat- ing malnutrition adequately requires improving chil- dren’s diets and training their parents to provide stimu- lating environments.

What are nerve cells, and how are they organized in the brain?

A nerve cell, called a neuron, includes a cell body, a ■ dendrite, and an axon. The mature brain consists of billions of neurons, organized into nearly identical left and right hemispheres connected by the corpus callosum. The cerebral cortex regulates most of the functions we think of as distinctively human. The frontal cortex is associated with personality and goal-directed behavior; the left hemisphere of the cortex with language; and the right hemisphere of the cortex with nonverbal pro- cesses such as perceiving music and regulating emotions.

How does the brain develop? When does it begin to function?

The brain specializes early in development. During in- ■ fancy, the left hemisphere is specialized for language, the right hemisphere is specialized for some forms of spatial processing, and the frontal cortex is specialized for emotionality.

The brain is moderately plastic. Most brains are orga- ■ nized in much the same way, but following a brain injury, cognitive processes are sometimes transferred to undam- aged neurons.

3.3 Moving and Grasping: Early Motor Skills

What are the component skills involved in learning to walk? At

what age do infants master them?

Infants acquire a series of locomotor skills during their ■ first year, culminating in walking a few months after the first birthday. Like most motor skills, learning to walk involves differentiation of individual skills, such as main- taining balance and using the legs alternately, and then integrating these skills into a coherent whole.

How do infants learn to coordinate the use of their hands?

Infants first use only one hand at a time, then both hands ■ independently, then both hands in common actions, and finally, at about 5 months of age, both hands in different actions with a common purpose.

Most people are right-handed, a preference that emerges ■ after the first birthday and becomes well established dur- ing the preschool years. Handedness is determined by heredity but can also be influenced by cultural values.

3.4 Coming to Know the World: Perception

Are infants able to smell, to taste, and to experience pain?

Newborns are able to smell, and some can recognize their ■ mother’s odor; they also taste, preferring sweet substances and responding negatively to bitter and sour tastes.

Infants respond to touch. They probably experience pain ■ because their responses to painful stimuli are similar to those of older children.

How well can infants hear?

Babies can hear. More important, they can distinguish dif- ■ ferent sounds and use sound to locate objects in space.

How well can infants see? Can they see color and depth?

A newborn’s visual acuity is relatively poor, but ■ 1-year-olds can see as well as an adult with normal vision.

Color vision develops as different sets of cones-begin to ■ function, a process that seems to be complete by 3 or 4 months of age. Infants perceive depth based on kinetic cues, retinal disparity, and pictorial cues. They also use motion to recognize objects.

Infants are attracted to faces and experience leads infants ■ to form a face template based on faces they see often.

How do infants process and combine information from differ-

ent sensory modalities, such as between vision and hearing?

Infants coordinate information from different senses. ■ They can recognize, by sight, an object they’ve felt previ- ously. Infants are often particularly attentive to informa- tion presented redundantly to multiple senses.

3.5 Becoming Self-Aware

When do children begin to realize that they exist?

Beginning at about 15 months, infants begin to recognize ■ themselves in the mirror, which is one of the first signs of self-recognition. They also begin to prefer looking at pictures of themselves, begin referring to themselves by name (or using personal pronouns), and sometimes know their age and gender. Evidently, by 2 years of age, most children are self-aware.

What are toddlers’ and preschoolers’ self-concepts like?

Preschoolers often define themselves in terms of observ- ■ able characteristics, such as possessions, physical charac- teristics, preferences, and competencies.

When do preschool children begin to acquire a theory of

mind?

Theory of mind—which refers to a person’s ideas about ■ connections between thoughts, beliefs, intentions, and behavior—develops rapidly during the preschool years. Most 2-year-olds know that people have desires and that desires can cause behavior. By age 3, children distinguish the mental world from the physical world but still em- phasize desire in explaining others’ actions. By age 4, however, children understand that behavior is based on beliefs about the world, even when those beliefs are wrong.

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K E Y T E R M S

Websites

Visit the Human Development companion website for all URLs.

The Human Development Book Companion Website ■

See www.cengage.com/psychology/kail for practice quiz questions, Internet exercises, glossary, fl ashcards, and more. Also accessible from the Wadsworth Psychology Study Center (www.cengage.com/psychology/kail).

Human Development and Family Science Extension, ■ Ohio State University

Visit this website for more information about infants and toddlers.

Kidshealth ■

This website, maintained by the Nemours Foundation, has information about children’s growth and nutrition.

Total Baby Care ■

Pampers (the diaper company) maintains this web- site, which has information about infant and toddler development.

Kids Nutrition ■

The Baylor College of Medicine maintains this website with information about children’s nutrition.

Society for Neuroscience, “Brain Briefings” ■

The society’s website has a feature called “brain brief- ings,” which features newsletters summarizing research fi ndings, including topics related to the developing brain.

Go to www.cengage.com/login to link to CengageNOW, your online study tool. First take the Pre-Test for this chapter to get your Personalized Study Plan, which will identify topics you need to review and direct you to online resources. Then take the Post-Test to determine what concepts you have mas- tered and what you still need to work on.

Readings

ACREDOLO, L., & GOODWYN, S. (2000). Baby minds: Brain-building games your baby will love. New York: Bantam. The authors, both child psychologists, use modern research on child development as the basis for techniques and activi- ties that foster children’s cognitive development.

AMERICAN ACADEMY OF PEDIATRICS. (2004). Your baby’s fi rst year. New York: Bantam. This book covers every- thing a parent needs to know about a baby’s fi rst year, includ- ing milestones of infant development, child care, health care, and more.

BRAZELTON, T. B., & SPARROW, J. D. (2006). Touchpoints birth to 3: Your child’s emotional and behavioral develop- ment. Cambridge, MA: De Capo Press. The fi rst author is a famous pediatrician and creator of the Neonatal Behavioral Assessment Scale (NBAS); the second author is a child psy-

L E A R N M O R E A B O U T I T

refl exes (84)

alert inactivity (86)

waking activity (86)

crying (86)

sleeping (86)

basic cry (86)

mad cry (87)

pain cry (87)

irregular or rapid-eye-movement (REM) sleep (87)

regular (nonREM) sleep (87)

sudden infant death syndrome (SIDS) (88)

temperament (89)

malnourished (95)

neuron (96)

cell body (96)

dendrite (96)

axon (96)

terminal buttons (96)

neurotransmitters (96)

cerebral cortex (96)

hemispheres (96)

corpus callosum (96)

frontal cortex (96)

neural plate (97)

myelin (97)

synaptic pruning (97)

electroencephalogram (EEG) (98)

functional magnetic resonance imaging (fMRI) (98)

neuroplasticity (98)

experience-expectant growth (99)

experience-dependent growth (100)

motor skills (101)

locomote (101)

fi ne motor skills (101)

toddling (101)

toddlers (101)

dynamic systems theory (101)

diff erentiation (103)

integration (103)

perception (108)

visual acuity (109)

cones (110)

visual cliff (111)

kinetic cues (111)

visual expansion (111)

motion parallax (111)

retinal disparity (111)

pictorial cues (112)

linear perspective (112)

texture gradient (112)

intersensory redundancy (117)

theory of mind (119)

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chiatrist. The fi rst part of the book describes the landmarks of development during the fi rst three years; the second part addresses common challenges to an infant’s development, including bedwetting and sleep problems.

ELIOT, L. (2000). What’s going on in there? How the brain and mind develop in the fi rst fi ve years of life. New York: Bantam. The author, a neurobiologist, provides a comprehen- sive but readable account of the development of the brain and the senses.

KOPP, C. (2003). Baby steps: The “whys” of your child’s behavior in the fi rst two years (2nd ed.). New York: Henry Holt. As the title indicates, this book is not only about newborns. However, we recommend the book because the author begins with newborn babies and traces the changes that occur in physical, motor, mental, and socioemotional development.

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