Developmental Psychology
Developmental Psychology
section three
Babies are such a nice way to start people.
—Don Herold
American Writer, 20th Century
Infancy
As newborns, we were not empty-headed organisms. We had some basic reflexes, among them crying, kicking, and coughing. We slept a lot, and occasionally we smiled, although the meaning of our first smiles was not entirely clear. We ate and we grew. We crawled and then we walked, a journey of a thousand miles beginning with a single step. Sometimes we conformed; sometimes others conformed to us. Our development was a continuous creation of more complex forms. We needed the meeting eyes of love. We juggled the necessity of curbing our will with becoming what we could will freely. This section contains three chapters: “Physical Development in Infancy,” “Cognitive Development in Infancy,” and “Socioemotional Development in Infancy.”
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chapter 4
PHYSICAL DEVELOPMENT IN INFANCY
chapter outline
1 Physical Growth and Development in Infancy
Learning Goal 1 Discuss physical growth and development in infancy.
Learning Goal 2 Describe infants’ motor development.
3 Sensory and Perceptual Development
Learning Goal 3 Summarize the course of sensory and perceptual development in infancy.
What Are Sensation and Perception?
Nature, Nurture, and Perceptual Development
©Image Source/Getty Images
Latonya is a newborn baby inPage 105 Ghana. During her first days of life, she has been kept apart from her mother and bottle fed. Manufacturers of infant formula provide the hospital where she was born with free or subsidized milk powder. Her mother has been persuaded to bottle feed rather than breast feed her. When her mother bottle feeds Latonya, she overdilutes the milk formula with unclean water. Latonya’s feeding bottles have not been sterilized. Latonya becomes very sick. She dies before her first birthday.
Ramona was born in a Nigerian hospital with a “baby-friendly” program. In this program, babies are not separated from their mothers when they are born, and the mothers are encouraged to breast feed them. The mothers are told of the perils that bottle feeding can bring because of unsafe water and unsterilized bottles. They also are informed about the advantages of breast milk, which include its nutritious and hygienic qualities, its ability to immunize babies against common illnesses, and the role of breast feeding in reducing the mother’s risk of breast and ovarian cancer. Ramona’s mother is breast feeding her. At 1 year of age, Ramona is very healthy.
(Top) An HIV-infected mother breast feeding her baby in Nairobi, Kenya. (Bottom) A Rwandan mother bottle feeding her baby. What are some concerns about breast versus bottle feeding in impoverished African countries?(Top) ©Wendy Stone/Corbis/Getty Images; (bottom) ©Dave Bartruff/Corbis/Getty Images
For many years, maternity units in hospitals favored bottle feeding and did not give mothers adequate information about the benefits of breast feeding. In recent years, the World Health Organization and UNICEF have tried to reverse the trend toward bottle feeding of infants in many impoverished countries. They instituted “baby-friendly” programs in many countries (Grant, 1993). They also persuaded the International Association of Infant Formula Manufacturers to stop marketing their baby formulas to hospitals in countries where the governments support the baby-friendly initiatives (Grant, 1993). For the hospitals themselves, costs actually were reduced as infant formula, feeding bottles, and separate nurseries became unnecessary. For example, baby-friendly Jose Fabella Memorial Hospital in the Philippines reported saving 8 percent of its annual budget. Still, there are many places in the world where the baby-friendly initiatives have not been implemented.
The advantages of breast feeding in impoverished countries are substantial (UNICEF, 2017). However, these advantages must be balanced against the risk of passing the human immunodeficiency virus (HIV) to babies through breast milk if the mothers have the virusPage 106 (Croffut & others, 2018; Mnyani & others, 2017; Wojcicki, 2017). In some areas of Africa, more than 30 percent of mothers have HIV, but the majority of these mothers don’t know that they are infected (Mepham, Bland, and Newell, 2011). Later in the chapter, in the section on nutrition, we will look more closely at recent research on breast feeding in the United States, outlining the benefits for infants and mothers and discussing several life-threatening diseases that infants can contract as a result of malnutrition.
topical connections looking back
Previously, we followed the physical development that takes place from fertilization through the germinal, embryonic, and fetal periods of prenatal development. We learned that by the time the fetus has reached full gestational age (approximately 40 weeks), it has grown from a fertilized egg, barely visible to the human eye, to a fully formed human weighing approximately 8 pounds and measuring 20 inches in length. Also remarkable is the fact that by the end of the prenatal period the brain has developed approximately 100 billion neurons.
preview
It is very important for infants to get a healthy start. When they do, their first two years of life are likely to be a time of amazing development. In this chapter, we focus on the biological domain and the infant’s physical development, exploring physical growth, motor development, and sensory and perceptual development.
1 Physical Growth and Development in Infancy
LG1 Discuss physical growth and development in infancy.
Patterns of Growth
Height and Weight
The Brain
Sleep
Nutrition
Infants’ physical development in the first two years of life is extensive. Newborns’ heads are quite large in comparison with the rest of their bodies. They have little strength in their necks and cannot hold their heads up, but they have some basic reflexes. In the span of 12 months, infants become capable of sitting anywhere, standing, stooping, climbing, and usually walking. During the second year, growth decelerates, but rapid increases in such activities as running and climbing take place. Let’s now examine in greater detail the sequence of physical development in infancy.
A baby is the most complicated object made by unskilled labor.
—Anonymous
PATTERNS OF GROWTH
An extraordinary proportion of the total body is occupied by the head during prenatal development and early infancy (see Figure 1 ). The cephalocaudal pattern is the sequence in which the earliest growth always occurs at the top—the head—with physical growth and differentiation of features gradually working their way down from top to bottom (for example, shoulders, middle trunk, and so on). This same pattern occurs in the head area,Page 107because the top parts of the head—the eyes and brain—grow faster than the lower parts, such as the jaw.
FIGURE 1 CHANGES IN PROPORTIONS OF THE HUMAN BODY DURING GROWTH. As individuals develop from infancy through adulthood, one of the most noticeable physical changes is that the head becomes smaller in relation to the rest of the body. The fractions listed refer to head size as a proportion of total body length at different ages.
Motor development generally proceeds according to the cephalocaudal principle. For example, infants see objects before they can control their torso, and they can use their hands long before they can crawl or walk. However, development does not follow a rigid blueprint. One study found that infants reached for toys with their feet prior to reaching with their hands (Galloway & Thelen, 2004). On average, infants first touched the toy with their feet when they were 12 weeks old and with their hands when they were 16 weeks old.
Growth also follows the proximodistal pattern , the sequence in which growth starts at the center of the body and moves toward the extremities. For example, infants control the muscles of their trunk and arms before they control their hands and fingers, and they use their whole hands before they can control several fingers (Bindler & others, 2017).
HEIGHT AND WEIGHT
The average North American newborn is 20 inches long and weighs 7.6 pounds. Ninety-five percent of full-term newborns are 18 to 22 inches long and weigh between 5 and 10 pounds.
In the first several days of life, most newborns lose 5 to 7 percent of their body weight before they adjust to feeding by sucking, swallowing, and digesting. Then they grow rapidly, gaining an average of 5 to 6 ounces per week during the first month. They have doubled their birth weight by the age of 4 months and have nearly tripled it by their first birthday. Infants grow about 1 inch per month during the first year, approximately doubling their birth length by their first birthday.
Growth slows considerably in the second year of life (London & others, 2017). By 2 years of age, infants weigh approximately 26 to 32 pounds, having gained a quarter to half a pound per month during the second year to reach about one-fifth of their adult weight. At 2 years of age, infants average 32 to 35 inches in height, which is nearly half of their adult height.
An important point about growth is that it often is not smooth and continuous but rather is episodic, occurring in spurts (Adolph, 2018; Adolph & Berger, 2015). In infancy, growth spurts may occur in a single day and alternate with long time frames characterized by little or no growth for days and weeks (Lampl & Johnson, 2011; Lampl & Schoen, 2018). In two analyses, in a single day, infants grew seven-tenths of an inch in length in a single day (Lampl, 1993) and their head circumference increased three-tenths of an inch (Caino & others, 2010).
THE BRAIN
We have described the amazing growth of the brain from conception to birth. By the time it is born, the infant that began as a single cell is estimated to have a brain that contains approximately 100 billion nerve cells, or neurons. Extensive brain development continues after birth, through infancy and later (Sullivan & Wilson, 2018; Vasa & others, 2018). Because the brain is still developing so rapidly in infancy, the infant’s head should be protected from falls or other injuries and the baby should never be shaken. Shaken baby syndrome, which includes brain swelling and hemorrhaging, affects hundreds of babies in the United States each year (Hellgren & others, 2017). One analysis found that fathers were the most frequent perpetrators of shaken baby syndrome, followed by child care providers and boyfriends of the victim’s mother (National Center on Shaken Baby Syndrome, 2012).
Researchers have been successful in using the electroencephalogram (EEG), a measure of the brain’s electrical activity, to learn about the brain’s development in infancy (Bell & others, 2018; Hari & Puce, 2017) (see Figure 2 ). For example, a recent study found that higher-quality mother-infant interaction early in infancy predicted higher-quality frontal lobe functioning that was assessed with EEG later in infancy (Bernier, Calkins, & Bell, 2016).
FIGURE 2 MEASURING THE ACTIVITY OF AN INFANT’S BRAIN WITH AN ELECTROENCEPHALOGRAM (EEG). By attaching up to 128 electrodes to a baby’s scalp to measure the brain’s activity, researchers have found that newborns produce distinctive brain waves that reveal they can distinguish their mother’s voice from another woman’s, even while they are asleep. Why is it so difficult to measure infants’ brain activity?Courtesy of Vanessa Vogel Farley
Researchers also are increasingly using functional near-infrared spectroscopy (fNIRS), which uses very low levels of near-infrared light to monitor changes in blood oxygen, to study infants’ brain activity (de Oliveira & others, 2018; Emberson & others, 2017a, b; Taga, Watanabe, & Homae, 2018) (see Figure 3 ). Unlike fMRI, which uses magnetic fields or electrical activity, fNIRS is portable and allows the infants to be assessed as they explore the world around them. And recently Patricia Kuhl and her colleagues (Ferjan Ramirez & others, 2017) at the Institute for Learning and Brain Sciences at the University of Washington have been using magnetoencephalography,Page 108 or MEG, brain-imaging machines to assess infants’ brain activity. MEG maps brain activity by recording magnetic fields produced by electrical currents and is being used to assess such perceptual and cognitive activities as vision, hearing, and language in infants (see Figure 4 ).
FIGURE 3 FUNCTIONAL NEAR-INFRARED SPECTROSCOPY (fNRIS) Functional near-infrared spectroscopy is increasingly being used to examine the brain activity of infants. fNRIS is non-invasive and can assess infants as they move and explore their environment.©Oli Scarff/Getty Images
FIGURE 4 MEASURING THE ACTIVITY OF AN INFANT’S BRAIN WITH MAGNETOENCEPHALOGRAPHY (MEG). This baby’s brain activity is being assessed with a MEG brain-imaging device while the baby is listening to spoken words in a study at the Institute of Learning and Brain Sciences at the University of Washington. The infant sits under the machine and when he or she experiences a word, touch, sight, or emotion, the neurons working together in the infant’s brain generate magnetic fields and MEG pinpoints the location of the fields in the brain.©Dr. Patricia Kuhl, Institute for Learning and Brain Sciences, University of Washington
Among the researchers who are making strides in finding out more about the brain’s development in infancy are:
· Charles Nelson and his colleagues (Berens & Nelson, 2015; Bick & Nelson, 2018; Bick & others, 2017; Finch & others, 2017; McLaughlin, Sheridan, & Nelson, 2017; Nelson, 2007, 2012, 2013a, b; Nelson, Fox, & Zeanah, 2014; Vanderwert & others, 2016; Varcin & others, 2016) who are exploring various aspects of memory development, face recognition and facial emotion, and the role of experience in influencing the course of brain development;
· Martha Ann Bell and her colleagues (Bell, 2015; Bell & Cuevas, 2012, 2014, 2015; Bell & others, 2018; Bell, Ross, & Patton, 2018; Broomell & Bell, 2018; Li & others, 2017; MacNeill & others, 2018; Lusby & others, 2016) who are studying brain-behavior links, emotion regulation, inhibitory control, and the integration of cognition and emotion;
· Mark Johnson and his colleagues (Anzures & others, 2016; Gliga & others, 2017; Hakuno & others, 2018; Johnson, Jones, & Gliga, 2015; Johnson, Senju, & Tomalski, 2015; Milosavlijevic & others, 2017; Saez de Urabain & others, 2017; Senju & others, 2016), who are examining neuroconstructivist links between the brain, cognitive and perceptual processes, and environmental influences as well as studying the development of the prefrontal cortex and its functions, early identification of autism, face processing, and early social experiences; and
· John Richards and his colleagues (Emberson & others, 2071a; Lloyd-Fox & others, 2015; Richards, 2009, 2010, 2013; Richards & others, 2015; Richards, Reynolds, & Courage, 2010; Richards & Xie, 2015; Xie, Mallin, & Richards, 2018; Xie & Richards, 2016, 2017) who are examining sustained attention, perception of TV programs, and eye movements.
developmental connection
Brain Development
How does the brain change from conception to birth? Connect to “Prenatal Development and Birth.”
The Brain’s Development At birth, the newborn’s brain is about 25 percent of its adult weight. By the second birthday, the brain is about 75 percent of its adult weight. However, the brain’s areas do not mature uniformly.
Mapping the Brain Scientists analyze and categorize areas of the brain in numerous ways (Bell & others, 2018; Dean & others, 2018; Ferjan Ramirez & others, 2017). The portion farthest from the spinal cord is known as the forebrain. This region includes the cerebral cortex and several structures beneath it. The cerebral cortex covers the forebrain like a wrinkled cap. The brain has two halves, or hemispheres (see Figure 5 ). Based on ridges and valleys in the cortex, scientists distinguish four main areas, called lobes, in each hemisphere. Although the lobes usually work together, each has a somewhat different primary function (see Figure 6 ):
FIGURE 5 THE HUMAN BRAIN’S HEMISPHERES. The two hemispheres of the human brain are clearly seen in this photograph. It is a myth that the left hemisphere is the exclusive location of language and logical thinking and that the right hemisphere is the exclusive location of emotion and creative thinking.©A.Glauberman/Science Source
FIGURE 6 THE BRAIN’S FOUR LOBES. Shown here are the locations of the brain’s four lobes: frontal, occipital, temporal, and parietal.
· Frontal lobes are involved in voluntary movement, thinking, personality, and intentionality or purpose.
· Occipital lobes function in vision.
· Temporal lobes have an active role in hearing, language processing, and memory.
· Parietal lobes play important roles in registering spatial location, attention, and motor control.
To some extent, the type of information handled by neuronsPage 109 depends on whether they are in the left or right hemisphere of the cortex (Benjamin & others, 2017; Sidtis & others, 2018). Speech and grammar, for example, depend on activity in the left hemisphere in most people; humor and the use of metaphors depend on activity in the right hemisphere (Holler-Wallscheid & others, 2017). This specialization of function in one hemisphere of the cerebral cortex or the other is called lateralization . However, most neuroscientists agree that complex functions such as reading or performing music involve both hemispheres. Labeling people as “left-brained” because they are logical thinkers or “right-brained” because they are creative thinkers does not correspond to the way the brain’s hemispheres work. Complex thinking in normal people is the outcome of communication between both hemispheres of the brain (Nora & others, 2017; Raemaekers & others, 2018).
At birth, the hemispheres of the cerebral cortex already have started to specialize: Newborns show greater electrical brain activity in the left hemisphere than the right hemisphere when they are listening to speech sounds (Telkemeyer & others, 2011). How are the areas of the brain different in the newborn and the infant from those in an adult, and why do the differences matter? Important differences have been documented at both the cellular and the structural levels.
Changes in Neurons Within the brain, the type of nerve cells called neurons send electrical and chemical signals, communicating with each other. A neuron is a nerve cell that handles information processing (see Figure 7 ). Extending from the neuron’s cell body are two types of fibers known as axons and dendrites. Generally, the axon carries signals away from the cell body and dendrites carry signals toward it. A myelin sheath, which is a layer of fat cells, encases many axons (see Figure 7 ). The myelin sheath insulates axons and helps electrical signals travel faster down the axon (Cercignani & others, 2017; van Tilborg & others, 2018). Myelination also is involved in providing energy to neurons and in communication (Saab & Nave, 2017). At the end of the axon are terminal buttons, which release chemicals called neurotransmitters into synapses, which are tiny gaps between neurons’ fibers. Chemical interactions in synapses connect axons and dendrites, allowing information to pass from neuron to neuron (Ismail, Fatemi, & Johnson, 2017; Zhou & others, 2018). Think of the synapse as a river that blocks a road. A grocery truck arrives at one bank of the river, crosses by ferry, and continues its journey to market. Similarly, a message in the brain is “ferried” across the synapse by a neurotransmitter, which pours out information contained in chemicals when it reaches the other side of the river.
FIGURE 7 THE NEURON. (a) The dendrites of the cell body receive information from other neurons, muscles, or glands through the axon. (b) Axons transmit information away from the cell body. (c) A myelin sheath covers most axons and speeds information transmission. (d) As the axon ends, it branches out into terminal buttons.
Neurons change in two very significant ways during the first years of life. First, myelination, the process of encasing axons with fat cells, begins prenatally and continues after birth, even into adolescence and emerging adulthood (Juraska & Willing, 2017). Second, connectivity among neurons increases, creating new neural pathways (Eggebrecht & others, 2017; Zhou & others, 2018). New dendrites grow, connections among dendrites increase, and synaptic connections between axons and dendrites proliferate. Whereas myelination speeds up neural transmissions, the expansion of dendritic connections facilitates the spreading of neural pathways in infant development.
How complex are these neural connections? In a recent analysis, it was estimated that each of the billions of neurons is connected to as many as 1,000 other neurons, producing neural networks with trillions of connections (de Haan, 2015). As we have discussed previously, most of these billions of neurons essentially have been created, have traveled to their correct locations, and are connected to other neurons by the time of full-term birth. Nonetheless, they undergo further differentiation, and neural connectivity patterns continue to change at least into emerging adulthood (Vasa & others, 2018).
Researchers have discovered an intriguing aspect of synaptic connections: nearly twice as many of these connections are made as will ever be used (Huttenlocher & Dabholkar, 1997). The connections that are used survive and become stronger, while the unused ones are replaced by other pathways or disappear. In the language of neuroscience, these connections will be “pruned” (Gould, 2017). For example, the more babies engage in physical activity or use language, the more those pathways will be strengthened.
developmental connection
Brain Development
Changes in the prefrontal cortex in adolescents and older adults have important implications for their cognitive development. Connect to “Physical and Cognitive Development in Adolescence” and “Physical Development in Late Adulthood.”
The age at which “blooming” and subsequent “pruning” of synapses occurs varies by brain region. For example, the peak of synaptic overproduction in the visual cortex occurs at about the fourth postnatal month, followed by a gradual retraction until the middle to end of the preschool years. In areas of the brain involved in hearing and language, a similar, though somewhat later, course is detected. However, in the prefrontal cortex, the area of the brain where higher-level thinking and self-regulation occur, the peak of overproduction takes place at about 1 year of age; it is not until emerging adulthood that adult density of synapses is attained. Both heredity and environment are thought to influence the timing and course of synaptic overproduction and subsequent retraction.
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Early Experience and the Brain Children who grow up in a deprived environment may have depressed brain activity (Bick & Nelson, 2018; Bick & others, 2017; McLaughlin, Sheridan, & Nelson, 2017; Nelson, Fox, & Zeanah, 2014). As shown in Figure 8 , a child who grew up in the unresponsive and unstimulating environment of a Romanian orphanage showed considerably depressed brain activity compared with a child who grew up in a normal environment.
FIGURE 8 EARLY DEPRIVATION AND BRAIN ACTIVITY. These two photographs are PET (positron emission tomography) scans, which use radioactive tracers to image and analyze blood flow and metabolic activity in the body’s organs. These scans show the brains of (a) a typically developing child and (b) an institutionalized Romanian orphan who experienced substantial deprivation since birth. In PET scans, the highest to lowest brain activity is reflected in the colors of red, yellow, green, blue, and black, respectively. As can be seen, red and yellow show up to a much greater degree in the PET scan of the typically developing child than the deprived Romanian orphan.Courtesy of Dr. Harry T. Chugani, Children’s Hospital of Michigan
Are the effects of deprived environments reversible? There is reason to think that for some individuals the answer is “yes” (Dennis & others, 2014). The brain demonstrates both flexibility and resilience. Consider 14-year-old Michael Rehbein. At age 7, he began to experience uncontrollable seizures—as many as 400 a day. Doctors said the only solution was to remove the left hemisphere of his brain where the seizures were occurring. Recovery was slow, but his right hemisphere began to reorganize and take over functions that normally occur in the brain’s left hemisphere, including speech (see Figure 9 ).
FIGURE 9 PLASTICITY IN THE BRAIN’S HEMISPHERES. (a) Michael Rehbein at 14 years of age. (b) Michael’s right hemisphere (right) has reorganized to take over the language functions normally carried out by corresponding areas in the left hemisphere of an intact brain (left). However, the right hemisphere is not as efficient as the left, and more areas of the brain are recruited to process speech.Courtesy of The Rehbein Family
Neuroscientists believe that what wires the brain—or rewires it, in the case of Michael Rehbein—is repeated experience. Each time a baby tries to touch an attractive object or gazes intently at a face, tiny bursts of electricity shoot through the brain, knitting together neurons into circuits. The results are some of the behavioral milestones we discuss in this chapter.
The Neuroconstructivist View Not long ago, scientists thought that our genes determined how our brains were “wired” and that the cells in the brain responsible for processing information just maturationally unfolded with little or no input from environmental experiences. Whatever brain your heredity had dealt you, you were essentially stuck with. This view, however, turned out to be wrong. Research reveals that the brain has plasticity and its development depends on context (Bick & Nelson, 2018; D’Souza & Karmiloff-Smith, 2018; McLaughlin & Broihier, 2018; Snyder & Smith, 2018).
The infant’s brain depends on experiences to determine how connections are made. Before birth, it appears that genes mainly direct basic wiring patterns. Neurons grow and travel to distant places awaiting further instructions. After birth, the inflowing stream of sights, sounds, smells, touches, language, and eye contact help shape the brain’s neural connections.
In the increasingly popular neuroconstructivist view , (a) biological processes (genes, for example) and environmental conditions (enriched or impoverished, for example) influence the brain’s development; (b) the brain has plasticity and is context dependent; and (c) the child’s cognitive development is closely linked to development of the brain. These factors constrain or advance the construction of cognitive skills (Goldberg, 2017; Mucke & others, 2018; Schreuders & others, 2018; Westermann, Thomas, & Karmiloff-Smith, 2011). The neuroconstructivist view emphasizes the importance of considering interactions between experience and gene expression in the brain’s development, much as the epigenetic view proposes (Moore, 2017; Smith & others, 2018; Westermann, 2016).
developmental connection
Nature and Nurture
In the epigenetic view, development is an ongoing, bidirectional interchange between heredity and the environment. Connect to “Biological Beginnings.”
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SLEEP
Sleep restores, replenishes, and rebuilds our brains and bodies. What function does sleep have in people’s lives? How do sleep patterns change in infancy?
Why Do We Sleep? A number of theories have been proposed about why we sleep. From an evolutionary perspective, all animals sleep and this sleep likely is necessary for survival. Thus, sleep may have developed because animals needed to protect themselves at night. A second perspective is that sleep replenishes and rebuilds the brain and body, which the day’s waking activities can wear out. In support of this restorative function, many of the body’s cells show increased production and reduced breakdowns of proteins during sleep (Frank, 2017). Further, a current emphasis is that sleep is essential to clearing out waste in neural tissues, such as metabolites and cerebrospinal fluid (Aguirre, 2016). A third perspective is that sleep is critical for brain plasticity (Sterpenich, Ceravolo, & Schwartz, 2017). For example, neuroscientists recently have argued that sleep increases synaptic connections between neurons (Areal, Warby, & Mongrain, 2017). These increased synaptic connections during sleep have been linked to improved consolidation of memories (Gui & others, 2017). Further, a research review concluded that not only can sleep improve memory, but losing a few hours of sleep a night is related to negative effects on attention, reasoning, and decision making (Diekelmann, 2014).
In sum, sleep likely serves a number of functions with no one theory accounting for all of the functions. Let’s now turn our attention to sleep in infancy. In later chapters, we will explore sleep through the remainder of the life span.
Sleep that knits up the ravelled sleave of care . . . Balm of hurt minds, nature’s second course. Chief nourisher in life’s feast.
—William Shakespeare
English Playwright, 17th Century
Infant Sleep When we were infants, sleep consumed more of our time than it does now (Goh & others, 2017). The typical newborn sleeps approximately 18 hours a day, but newborns vary greatly in how much they sleep (Dias & others, 2018; Sadeh, 2008). The range is from about 10 hours to about 21 hours a day.
In a recent study, sleep sessions lasted approximately 3.5 hours during the first few months and increased to about 10.5 hours from 3 to 7 months (Mindell & others, 2016). A previous research review concluded that infants 0 to 2 years of age slept an average of 12.8 hours out of the 24, within a range of 9.7 to 15.9 hours (Galland & others, 2012). Another study revealed that by 6 months of age the majority of infants slept through the night, awakening their parents only once or twice a week (Weinraub & others, 2012).
Sleep problems have been estimated to affect 15 to 25 percent of infants. The most common infant sleep-related problem reported by parents is nighttime waking (Dias & others, 2018; Hospital for Sick ChildrenPage 112 & others, 2010). Surveys indicate that 20 to 30 percent of infants have difficulty going to sleep at night and staying asleep until morning (Sadeh, 2008). One study found that nighttime wakings at 1 year of age predicted lower sleep efficiency at 4 years of age (Tikotzky & Shaashua, 2012). Further research found that (1) maternal depression during pregnancy, (2) early introduction of solid foods, (3) infant TV viewing, and (4) child care attendance were related to shorter duration of infant sleep (Nevarez & others, 2010). And a recent study revealed that later bedtime and less sleep across a 24-hour period were linked to infants having more separation distress, greater inhibition, and higher anxiety and depression levels (Mindell & others, 2017).
Research also indicates that parental factors other than maternal depression are linked to infants’ sleep patterns (Field, 2017; Volkovich & others, 2018; Yu & others, 2017). A recent study found that maternal sleep when the infant was 3 months of age predicted the infant’s sleep patterns at 6 months of age and that increased involvement of the father in caregiving responsibilities improved the infant’s sleep (Tikotzky & others, 2015). And other recent research indicated that a higher level of maternal emotional availability at bedtime was associated with a lower level of infant distress at bedtime and longer infant sleep duration (Philbrook & Teti, 2016).
Cultural variations influence infant sleeping patterns (Field, 2017). For example, in the Kipsigis culture in Kenya, infants sleep with their mothers at night and are permitted to nurse on demand (Super & Harkness, 1997). During the day, they are strapped to their mothers’ backs, accompanying them on daily rounds of chores and social activities. As a result, the Kipsigis infants do not sleep through the night until much later than American infants do. During the first eight months of postnatal life, Kipsigis infants rarely sleep longer than three hours at a stretch, even at night. This sleep pattern contrasts with that of American infants, many of whom begin to sleep up to eight hours a night by 8 months of age.
REM Sleep In REM sleep, the eyes flutter beneath closed lids; in non-REM sleep, this type of eye movement does not occur and sleep is more quiet (Bathory & Tomopoulos, 2017). Figure 10 shows developmental changes in the average number of total hours spent in REM and non-REM sleep. By the time they reach adulthood, individuals spend about one-fifth of their night in REM sleep, and REM sleep usually appears about one hour after non-REM sleep. However, about half of an infant’s sleep is REM sleep, and infants often begin their sleep cycle with REM sleep rather than non-REM sleep. A much greater amount of time is taken up by REM sleep in infancy than at any other point in the life span. By the time infants reach 3 months of age, the percentage of time they spend in REM sleep falls to about 40 percent, and REM sleep no longer begins their sleep cycle.
FIGURE 10 DEVELOPMENTAL CHANGES IN REM AND NON-REM SLEEP
Why do infants spend so much time in REM sleep? Researchers are not certain. The large amount of REM sleep may provide infants with added self-stimulation, since they spend less time awake than do older children. REM sleep also might promote the brain’s development in infancy (Graven, 2006).
When adults are awakened during REM sleep, they frequently report that they have been dreaming, but when they are awakened during non-REM sleep, they are much less likely to report having been dreaming (Cartwright & others, 2006). Since infants spend more time than adults in REM sleep, can we conclude that they dream a lot? We don’t know whether infants dream or not, because they don’t have any way of reporting dreams.
Shared Sleeping Sleeping arrangements for newborns vary from culture to culture (Field, 2017). For example, sharing a bed with a mother is a common practice in many cultures, such as Guatemala and China, whereas in others, such as the United States and Great Britain, newborns usually sleep in a crib, either in the same room as the parents or in a separate room. In some cultures, infants sleep with the mother until they are weaned, after which they sleep with siblings until middle and late childhood (Walker, 2006). Whatever the sleeping arrangements, it is recommended that the infant’s bedding provide firm support and that the crib has side rails (Kreth & others, 2018).
In the United States, shared sleeping remains a controversial issue (Burnham, 2014). Some experts recommend it and others argue against it, although recently the recommendation trend has been to avoid infant-parent bed sharing, especially if the infant is younger than 6 months of age (Byard, 2012a, b; Field, 2017; Mitchell & others, 2017; Weber & others, 2012). In a recent study, infant-parent bed sharing was associated with more night waking for mothers as wellPage 113 as infants, and more marital distress (Teti & others, 2016). The American Academy of Pediatrics Task Force on Infant Positioning and SIDS (AAPTFIPS) (2000) recommends against shared sleeping. Its members argue that in some instances bed sharing might lead to sudden infant death syndrome (SIDS), as could be the case if a sleeping mother rolls over on her baby (Moon & others, 2017). Recent studies have found that bed sharing is linked with a higher incidence of SIDS, especially when parents smoke (Adams, Ward, & Garcia, 2015). Further, a recent large-scale study in six countries (including the United States) found that parents of 6- to 12-month-old infants reported earlier bedtimes, shorter time to fall asleep, fewer sleep interruptions, and more total sleep when the infants slept in a separate room compared with infants sleeping in the same room or same bed with their parents (Mindell, Leichman, & Walters, 2018).
SIDS Sudden infant death syndrome (SIDS) is a condition that occurs when infants stop breathing, usually during the night, and die suddenly without any apparent reason. SIDS continues to be a leading cause of infant death in the United States, with more than 2,000 infant deaths annually attributed to SIDS (NICHD, 2018). Risk of SIDS is highest at 2 to 4 months of age.
developmental connection
Sleep
What are some sleep problems that children encounter in early childhood? Connect to “Physical and Cognitive Development in Early Childhood.”
Since 1992, the American Academy of Pediatrics (AAP) has recommended that infants be placed to sleep on their backs (supine position) to reduce the risk of SIDS, and the frequency of prone sleeping (on the stomach) among U.S. infants has dropped dramatically (AAPTFIPS, 2000). Researchers have found that SIDS does indeed decrease when infants sleep on their backs rather than their stomachs or sides (Bombard & others, 2018; Siren, 2017; Sperhake, Jorch, & Bajanowski, 2018). Why? Because sleeping on their backs increases their access to fresh air and reduces their chances of getting overheated.
developmental connection
Sleep
Sleep patterns change in adolescence and are linked to changes in the brain. Connect to “Physical and Cognitive Development in Adolescence.”
In addition to sleeping in a prone position, researchers have found that the following factors are linked to SIDS:
· SIDS occurs more often in infants with abnormal brain stem functioning involving the neurotransmitter serotonin (Rognum & others, 2014; Rubens & Sarnat, 2013).
· Heart arrhythmias are estimated to occur in as many as 15 percent of SIDS cases, and two studies found that gene mutations were linked to the occurrence of these arrhythmias (Brion & others, 2012; Van Norstrand & others, 2012).
· Six percent of infants with sleep apnea, a temporary cessation of breathing in which the airway is completely blocked, usually for 10 seconds or longer, die of SIDS (Ednick & others, 2010).
· Breast feeding is linked to a lower incidence of SIDS (Carlin & Moon, 2017).
· Low birth weight infants are 5 to 10 times more likely to die of SIDS than are their normal-weight counterparts (Horne & others, 2002).
· SIDS is more likely to occur in infants who do not use a pacifier when they go to sleep than in those who do use a pacifier (Carlin & Moon, 2017). A recent research review confirmed that pacifier use is linked to a lower incidence of SIDS (Alm & others, 2016).
· Infants whose siblings have died of SIDS are two to four times as likely to die of it (Lenoir, Mallet, & Calenda, 2000).
· African American and Eskimo infants are four to six times as likely as all others to die of SIDS (Kitsantas & Gaffney, 2010; Moon & others, 2017).
· SIDS is more common in lower socioeconomic groups (Hogan, 2014).
· SIDS is more common in infants who are passively exposed to cigarette smoke (Horne, 2018; Salm Ward & Balfour, 2016).
· SIDS is more common when infants and parents share the same bed (Carlin & Moon, 2017; Moon & others, 2017). A recent Swedish study confirmed that bed sharing was more common in SIDS cases than in other types of infant deaths (Mollborg & others, 2015).
· SIDS is more common if infants sleep in soft bedding (McGarvey & others, 2006).
· SIDS is less common when infants sleep in a bedroom with a fan. One study revealed that sleeping in a bedroom with a fan lowers the risk of SIDS by 70 percent (Coleman-Phox, Odouli, & Li, 2008).
Is this a good sleep position for infants? Why or why not?©Maria Teijeiro/Getty Images
It is generally accepted that the most critical factor in predicting whether an infant will develop SIDS is prone sleeping. As public awareness has grown regarding the importance of not letting infants sleep in a prone position, the number of infant deaths in the United States has decreased, although SIDS still is one of the leading causes of infant deathPage 114 (Bombard & others, 2018). In a recent research review, it was concluded that the two other factors that place infants at the highest risk for SIDS are (1) maternal smoking and (2) bed sharing (Mitchell & Krous, 2015).
One concern raised by critics of the “back to sleep movement” (ensuring that young infants sleep on their back rather than their stomach) is a decline in prone skills. To prevent this decline, many mothers provide their young infants with “tummy time” by periodically placing them on their stomachs when they are awake.
Sleep and Cognitive Development Might infant sleep be linked to children’s cognitive development? A recent research review indicated that there is a positive link between infant sleep and cognitive functioning, including memory, language, and executive function (Tham, Schneider, & Broekman, 2017). A study also revealed that a lower quality of sleep at 1 year of age was linked to lower attention regulation and more behavior problems at 3 to 4 years of age (Sadeh & others, 2015). And in another study, infants with poorer sleep patterns showed more distractibility during an attention task (Geva, Yaron, & Kuint, 2016). The link between infant sleep and children’s cognitive functioning likely occurs because of sleep’s role in brain maturation and memory consolidation, which may improve daytime alertness and learning.
NUTRITION
From birth to 1 year of age, human infants nearly triple their weight and increase their length by 50 percent. What do they need to sustain this growth?
Nutritional Needs and Eating Behavior Individual differences among infants in terms of their nutrient reserves, body composition, growth rates, and activity patterns make defining actual nutrient needs difficult (Borowitz & Borowitz, 2018; Rolfes & Pinna, 2018). However, because parents need guidelines, nutritionists recommend that infants consume approximately 50 calories per day for each pound they weigh—more than twice an adult’s caloric requirement per pound.
A number of developmental changes involving eating characterize the infant’s first year (Leow & others, 2017). As infants’ motor skills improve, they change from using suck-and-swallow movements with breast milk or formula to chew-and-swallow movements with semisolid and then more complex foods. As their fine motor control improves in the first year, they transition from being fed by others toward self-feeding. “By the end of the first year of life, children can sit independently, can chew and swallow a range of textures, are learning to feed themselves, and are making the transition to the family diet and meal patterns” (Black & Hurley, 2007, p. 1). At this point, infants need to have a diet that includes a variety of foods—especially fruits and vegetables.
Caregivers play very important roles in infants’ early development of eating patterns (Baye, Tariku, & Mouquet-Rivier, 2018; Brown, 2017). Caregivers who are not sensitive to developmental changes in infants’ nutritional needs, caregivers who are negligent, and conditions of poverty can contribute to the development of eating problems in infants (Black & Hurley, 2017; Perez-Escamilla & Moran, 2017). One study found that low maternal sensitivity when infants were 15 and 24 months of age was linked to a higher risk of obesity in adolescence (Anderson & others, 2012). And in a recent study, infants who were introduced to vegetables at 4 to 5 months of age showed less fussy eating behavior at 4 years of age than their counterparts who were introduced to vegetables after 6 months (de Barse & others, 2017).
A national study of more than 3,000 randomly selected 4- to 24-month-olds documented that many U.S. parents were feeding their babies too much junk food and not giving them enough fruits and vegetables (Fox & others, 2004). Up to one-third of the babies ate no vegetables and fruit but frequently ate French fries, and almost half of the 7- to 8-month-old babies were fed desserts, sweets, or sweetened drinks. By 15 months, French fries were the most common vegetable the babies ate.
Such poor dietary patterns early in development can result in more infants being overweight (Black & Hurley, 2017; Blake, 2017; Feldman-Winter & others, 2018). In addition to consuming too many French fries, sweetened drinks, and desserts, are there other factors that might explain increased numbers of overweight U.S. infants? A mother’s weight gain during pregnancy and a mother’s own high weight before pregnancy may be factors (Catalano & Shankar, 2017). Also, an important factor likely is whether an infant is breast fed or bottle fed (Uwaezuoke, Eneh, & Ndu, 2017). Breast-fed infants have lower rates of weight gain than bottle-fed infants in childhood and adolescence, and it is estimated that breast feeding reduces the risk of obesity by approximatelyPage 115 20 percent (Uwaezuoke, Eneh, & Ndu, 2017).
Breast versus Bottle Feeding For the first four to six months of life, human milk or an alternative formula is the baby’s source of nutrients and energy. For years, debate has focused on whether breast feeding is better for the infant than bottle feeding. The growing consensus is that breast feeding is better for the baby’s health (Blake, Munoz, & Volpe, 2019; DeBruyne & Pinna, 2017; Thompson & Manore, 2018). Since the 1970s, breast feeding by U.S. mothers has soared (see Figure 11 ). In 2016, 81 percent of U.S. mothers breast fed their newborns, and 52 percent breast fed their 6-month-olds (Centers for Disease Control and Prevention, 2016). The American Academy of Pediatrics Section on Breastfeeding (2012) reconfirmed its recommendation of exclusive breast feeding in the first six months followed by continued breast feeding as complementary foods are introduced, and further breast feeding for one year or longer as mutually desired by the mother and infant.
FIGURE 11 TRENDS IN BREAST FEEDING IN THE UNITED STATES: 1970–2016
What are some of the benefits of breast feeding? The following conclusions have been supported by research.
Outcomes for the Child
· Gastrointestinal infections. Breast-fed infants have fewer gastrointestinal infections (Bartick & others, 2017, 2018).
· Respiratory tract infections. Breast-fed infants have fewer infections of the lower respiratory tract (Bartick & others, 2018).
· Allergies. A recent research review found no support for breast feeding reducing the risk of allergies in young children (Heinrich, 2017).
· Asthma. Exclusive breast feeding for three months protects against wheezing in babies, but whether it prevents asthma in older children is unclear (Wang & others, 2018). However, a recent Japanese study found that breast feeding was linked to a lower incidence of asthma from 6 to 42 months of age (Yamakawa & others, 2015).
· Ear, throat, and sinus infections. One study found that infants who had been breast fed for 9 months or longer were less likely to have developed ear, throat, and sinus infections in the past year when they were 6 years old than their counterparts who had been breast fed for 3 months or less (Li & others, 2014). Breast-fed infants also are less likely to develop otitis media, a middle ear infection (Pelton & Leibovitz, 2009).
· Overweight and obesity. Consistent evidence indicates that breast-fed infants are less likely to become overweight or obese in childhood, adolescence, and adulthood (Catalano & Shankar, 2017; Uwaezuoke, Eneh, & Ndu, 2018).
· Diabetes. Breast-fed infants are less likely to develop type 1 diabetes in childhood (Lund-Blix & others, 2015) and type 2 diabetes in adulthood (Minniti & others, 2014).
· SIDS. Breast-fed infants have lower rates of SIDS (Bartick & others, 2017b; Wennergren & others, 2015).
· Hospitalization. A recent study of more than 500,000 Scottish children found that those who were breast fed exclusively at 6 to 8 weeks of age were less likely to have ever been hospitalized through early childhood than their formula-fed counterparts (Ajetunmobi & others, 2015). Other recent research has found that breast-fed infants had lower rates of hospitalization for a number of conditions, including gastrointestinal problems and lower respiratory tract infection, and breast-feeding mothers had lower rates of hospitalization for cardiovascular problems and diabetes (Bartick & others, 2018).
Human milk or an alternative formula is a baby’s source of nutrients for the first four to six months. The growing consensus is that breast feeding is better for the baby’s health, although controversy still swirls about the benefits of breast feeding in comparison with bottle feeding. Why is breast feeding strongly recommended by pediatricians?©JGI/Getty Images
In large-scale research reviews, no conclusivePage 116 evidence for the benefits of breast feeding was found for children’s cognitive development and cardiovascular health (Agency for Healthcare Research and Quality, 2007; Ip & others, 2009).
Outcomes for the Mother
· Breast cancer. Consistent evidence indicates a lower incidence of breast cancer in women who breast feed their infants (Bartick & others, 2017b; Mayor, 2015).
· Ovarian cancer. Evidence also reveals a reduction in ovarian cancer in women who breast feed their infants (Stuebe & Schwartz, 2010).
· Type 2 diabetes. Some evidence suggests that there is a reduction in type 2 diabetes in women who breast feed their infants (Bartick & others, 2017b).
In large-scale research reviews, no conclusive evidence could be found for maternal benefits of breast feeding involving return to prepregnancy weight, reduced rates of osteoporosis, and decreased risk of postpartum depression (Agency for Healthcare Research and Quality, 2007; Ip & others, 2009). However, one study revealed that women who breast fed their infants had a lower incidence of metabolic syndrome (a disorder characterized by obesity, hypertension, and insulin resistance) in midlife (Ram & others, 2008).
Many health professionals have argued that breast feeding facilitates the development of an attachment bond between the mother and infant (Britton, Britton, & Gronwaldt, 2006; Wittig & Spatz, 2008). However, a research review found that the positive role of breast feeding on the mother-infant relationship is not supported by research (Jansen, de Weerth, & Riksen-Walraven, 2008). The review concluded that recommending breast feeding should not be based on its role in improving the mother-infant relationship but rather on its positive effects on infant and maternal health. Also, researchers have not consistently found links between breast feeding and higher intelligence in children, although in two recent studies, breast feeding was associated with a small increase in children’s intelligence (Bernard & others, 2017; Kanazawa, 2015).
Which women are least likely to breast feed? They include mothers who work full-time outside the home, mothers under age 25, mothers without a high school diploma, African American mothers, and mothers in low-income circumstances (Merewood & others, 2007). In one study of low-income mothers in Georgia, interventions (such as counseling focused on the benefits of breast feeding and the free loan of a breast pump) increased the incidence of breast feeding (Ahluwalia & others, 2000). Increasingly, mothers who return to work during the infant’s first year of life use a breast pump to extract breast milk that can be stored for later feeding of the infant when the mother is not present.
As mentioned earlier, the American Academy of Pediatrics Section on Breastfeeding (2012) strongly endorses exclusive breast feeding for the first 6 months and further recommends breast feeding for another year. Are there circumstances when mothers should not breast feed? Yes, a mother should not breast feed (1) when she is infected with HIV or some other infectious disease that can be transmitted through her milk, (2) if she has active tuberculosis, or (3) if she is taking any drug that may not be safe for the infant (Brown & others, 2017; Schultz, Kostic, & Kharasch, 2018; Williams & others, 2016).
Some women cannot breast feed their infants because of physical difficulties; others feel guilty if they terminate breast feeding early. Mothers may also worry that they are depriving their infants of important emotional and psychological benefits if they bottle feed rather than breast feed. Some researchers have found, however, that there are no psychological differences between breast-fed and bottle-fed infants (Ferguson, Harwood, & Shannon, 1987; Young, 1990).
A further issue in interpreting the benefits of breast feeding was underscored in large-scale research reviews (Agency for Healthcare Research and Quality, 2007; Ip & others, 2009). While highlighting a number of breast feeding benefits for children and mothers, the report issued a caution about breast feeding research: None of the findings imply causality. Breast versus bottle feeding studies are correlational rather than experimental, and women who breast feed are wealthier, older, more educated, and likely more health-conscious than their bottle feeding counterparts, which could explain why breast-fed children are healthier.
developmental connection
Research Methods
How does a correlational study differ from an experimental study? Connect to “Introduction.”
Malnutrition in Infancy Many infants around the world are malnourished (UNICEF, 2018). Early weaning of infants from breast milk to inadequate sources of nutrients, such as unsuitable and unsanitary cow’s milk formula, can cause protein deficiency and malnutrition in infants. However, as we saw in the discussion following the chapter opening story, a concern in developing countries is the increasing number of women who are HIV-positive and the fear that they will transmit this virus to their offspring (Croffut & others, 2018). Breast feeding is more optimal for mothers and infants in developing countries, except for mothers who have or are suspected of having HIV/AIDS.
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connecting development to life
Improving the Nutrition of Infants and Young Children Living in Low-Income Families
Poor nutrition is a special concern in the lives of infants from low-income families. To address this problem in the United States, the WIC (Women, Infants, and Children) program provides federal grants to states for healthy supplemental foods, health care referrals, and nutrition education for women from low-income families beginning in pregnancy, and to infants and young children up to 5 years of age who are at nutritional risk (Chang, Brown, & Nitzke, 2017; Gilmore & others, 2017). WIC serves approximately 7,500,000 participants in the United States.
Positive influences on infants’ and young children’s nutrition and health have been found for participants in WIC (Chen & others, 2018; Gross & others, 2017; Lee & others, 2017; Martinez-Brockman & others, 2018; McCoy & others, 2018). One study revealed that a WIC program that introduced peer counseling services for pregnant women increased breast feeding initiation by 27 percent (Olson & others, 2010a, b). Another study found that entry during the first trimester of pregnancy to the WIC program in Rhode Island reduced rates of maternal cigarette smoking (Brodsky, Viner-Brown, & Handler, 2009). Also, a multiple-year literacy intervention with Spanish-speaking families in the WIC program in Los Angeles increased literacy resources and activities at home, which in turn led to a higher level of school readiness in children (Whaley & others, 2011). And in recent longitudinal studies, when mothers participated prenatally and in early childhood in WIC programs their young children showed short-term cognitive benefits and longer-term reading and math benefits (Jackson, 2015).
Participants in the WIC program. What are some changes the WIC program is trying to implement?Source: USDA Food and Nutrition Service, Supplemental Nutrition Assistance Program USDA Food and Nutrition Service “SNAP Photo Gallery/Jen Mitchell SNAP-Ed Connection http://snap.nal.usda.gov”
Why would the WIC program provide lactation counseling as part of its services?
A large-scale study that examined feeding practices in 28 developing countries found that the practices were far from optimal (Arabi & others, 2012). In this study, only 25 percent of infants 5 months of age and younger were breast fed. Also, feeding guidelines call for introducing complementary foods (solid and semisolid foods) beginning at 6 months. However, in this study, only 50 percent of the caregivers reported feeding their 6- to 8-month-olds complementary foods.
Even if it is not fatal, severe and lengthy malnutrition is detrimental to physical, cognitive, and social development (Donatelle & Ketcham, 2018; UNICEF, 2018; Wardlaw, Smith, & Collene, 2018). One study found that Asian Indian children who had a history of chronic malnutrition performed more poorly on tests of attention and memory than their counterparts who were not malnourished (Kar, Rao, & Chandramouli, 2008). And a longitudinal study revealed that Barbadians who had experienced moderate to severe protein/energy malnutrition during infancy had persisting attention deficits when they were 40 years old (Galler & others, 2012). Researchers also have found that interventions can benefit individuals who have experienced malnutrition in infancy. For example, in one study standard nutritional care combined with a psychosocial intervention (group meetings with mothers and play sessions with infants, as well as six months of home visits) reduced the negative effects of malnutrition on severely malnourished Bangladeshi 6- to 24-month-olds’ cognitive development (Najar & others, 2008).
To read about programs designed to improve infants’ and young children’s nutrition, see Connecting Development to Life .
Adequate early nutrition is an important aspect of healthy development (Rolfes & Pinna, 2018). In addition to sound nutrition, children need a nurturing, supportive environment (Black & Hurley, 2017; Blake, 2017). One individual who has stood out as an advocate of caring for children and who has been especially passionate about preventing child obesity is pediatrician Faize Mustafa-Infante, who is featured in Connecting with Careers .
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connecting with careers
Faize Mustafa-Infante
Dr. Mustafa-Infante grew up in Colombia, South America. Her initial profession was as an elementary school teacher in Colombia and then she obtained her medical degree with a specialty in pediatrics. Once she finished her medical training, she moved to San Bernardino, California, working as a health educator with a focus on preventing and treating child obesity in low-income communities. Dr. Mustafa-Infante currently works at Mission Pediatrics in Riverside, California, where she mainly treats infants. She continues her effort to prevent obesity in children and also serves as a volunteer for Ayacucho Mission, a nonprofit organization that provides culturally sensitive medical care for people living in poverty in Ayacucho, Peru. With regard to her cultural background, Dr. Mustafa-Infante describes herself as a Latino doctor with a middle-eastern name that reflects her strong family commitments to both heritages. Dr. Mustafa says that hard work and education have been the keys to her success and personal satisfaction.
For more information about what pediatricians do, see the Careers in Life-Span Development appendix.
Review Connect Reflect
LG1 Discuss physical growth and development in infancy.
Review
· What are cephalocaudal and proximodistal patterns?
· What changes in height and weight take place in infancy?
· What are some key features of the brain and its development in infancy?
· What changes occur in sleep during infancy?
· What are infants’ nutritional needs?
Connect
· What types of brain research technology can be used to study infants that cannot be used to study them before they are born? Which techniques can be used on adults but not infants? How might these limitations affect our understanding of brain development across the life span?
Reflect Your Own Personal Journey of Life
· What sleep and nutrition guidelines would you follow for enhancing the health and safety of your own infant?
2 Motor Development
LG2 Describe infants’ motor development.
The Dynamic Systems View
Reflexes
Gross Motor Skills
Fine Motor Skills
As a newborn, Ramona, whom you read about in the chapter opening story, could suck, fling her arms, and tightly grip a finger placed in her tiny hand. Within just two years, she would be toddling around on her own, opening doors and jars as she explored her little world. Are her accomplishments inevitable? How do infants develop their motor skills, and which skills do they develop at specific ages?
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THE DYNAMIC SYSTEMS VIEW
Developmentalist Arnold Gesell (1934) thought his painstaking observations had revealed how people develop their motor skills. He had discovered that infants and children develop rolling, sitting, standing, and other motor skills in a fixed order and within specific time frames. These observations, said Gesell, show that motor development comes about through the unfolding of a genetic plan, or maturation.
Later studies, however, demonstrated that the sequence of developmental milestones is not as fixed as Gesell indicated and not due as much to heredity as Gesell argued (Adolph, 2018; Adolph & Robinson, 2015). Beginning in the 1980s, the study of motor development experienced a renaissance as psychologists developed new insights about how motor skills develop (Adolph, 2018; Kretch & Adolph, 2018). One increasingly influential perspective is dynamic systems theory, proposed by Esther Thelen (Thelen & Smith, 1998, 2006).
According to dynamic systems theory , infants assemble motor skills for perceiving and acting. Notice that perception and action are coupled, according to this theory. To develop motor skills, infants must perceive something in their environment that motivates them to act and use their perceptions to fine-tune their movements. Motor skills assist infants in reaching their goals (Adolph, 2018).
Esther Thelen is shown conducting an experiment to discover how infants learn to control their arm movements to reach and grasp for objects. A computer device is used to monitor the infant’s arm movements and to track muscle patterns. Thelen’s research is conducted from a dynamic systems perspective. What is the nature of this perspective?Courtesy of Dr. David Thelen
How is a motor skill developed, according to this theory? When infants are motivated to do something, they might create a new motor behavior. The new behavior is the result of many converging factors: the development of the nervous system, the body’s physical properties and its possibilities for movement, the goal the child is motivated to reach, and availability of environmental support for the skill. For example, babies learn to walk only when maturation of the nervous system allows them to control certain leg muscles, when they want to move, when their legs have grown strong enough to support their weight, and when they have sufficient balance control to support their body on one leg.
Mastering a motor skill requires the infant’s active efforts to coordinate several components of the skill. Infants explore and select possible solutions to the demands of a new task; they assemble adaptive patterns by modifying their current movement patterns (Adolph, 2018). The first step occurs when the infant is motivated by a new challenge—such as the desire to cross a room—and gets into the “ballpark” of the task demands by taking a couple of stumbling steps. Then, the infant “tunes” these movements to make them smoother and more effective. The tuning is achieved through repeated cycles of action and perception of the consequences of that action. According to the dynamic systems view, even universal milestones, such as crawling, reaching, and walking, are learned through this process of adaptation: Infants modulate their movement patterns to fit a new task by exploring and selecting possible configurations (Adolph, 2018; Comalli, Persand, & Adolph, 2017).
To see how dynamic systems theory explains motor behavior, imagine that you offer a new toy to a baby named Gabriel (Thelen & others, 1993). There is no exact program that can tell Gabriel ahead of time how to move his arm and hand and fingers to grasp the toy. Gabriel must adapt to his goal—grasping the toy—and the context. From his sitting position, he must make split-second adjustments to extend his arm, holding his body steady so that his arm and torso don’t plow into the toy. Muscles in his arm and shoulder contract and stretch in a host of combinations, exerting a variety of forces. He improvises a way to reach out with one arm and wrap his fingers around the toy.
Thus, according to dynamic systems theory, motor development is not a passive process in which genes dictate the unfolding of a sequence of skills over time. Rather, the infant actively puts together a skill to achieve a goal within the constraints set by the infant’s body and environment. Nature and nurture, the infant and the environment, are all working together as part of an ever-changing system.
As we examine the course of motor development, we will describe how dynamic systems theory applies to some specific skills. First, though, let’s examine the beginning of motor development: the infant’s reflexes.
How might dynamic systems theory explain the development of learning to walk?©Di Studio/Shutterstock
REFLEXES
The newborn is not completely helpless. Among other things, it has some basic reflexes. For example, when submerged in water, the newborn automatically holds its breath and contracts its throat to keep water out.
Reflexes are built-in reactions to stimuli; they governPage 120 the newborn’s movements, which are automatic and beyond the newborn’s control. Reflexes are genetically carried survival mechanisms. They allow infants to respond adaptively to their environment before they have had the opportunity to learn. The rooting and sucking reflexes are important examples. Both have survival value for newborn mammals, who must find a mother’s breast to obtain nourishment. The rooting reflex occurs when the infant’s cheek is stroked or the side of the mouth is touched. In response, the infant turns its head toward the side that was touched in an apparent effort to find something to suck. The sucking reflex occurs when newborns automatically suck an object placed in their mouth. This reflex enables newborns to get nourishment before they have associated a nipple with food and also serves as a self-soothing or self-regulating mechanism.
Another example is the Moro reflex , which occurs in response to a sudden, intense noise or movement (see Figure 12 ). When startled, the newborn arches its back, throws back its head, and flings out its arms and legs. Then the newborn rapidly draws in its arms and legs. The Moro reflex is believed to be a way of grabbing for support while falling; it would have had survival value for our primate ancestors.
FIGURE 12 NEWBORN REFLEXES. Young infants have several reflexes, including the Moro reflex (top) and grasping reflex (bottom).(Top) ©Petit Format/Science Source; (bottom) ©Stockbyte/PunchStock
Some reflexes—coughing, sneezing, blinking, shivering, and yawning, for example—persist throughout life. They are as important for the adult as they are for the infant. Other reflexes, though, disappear several months following birth, as the infant’s brain matures and voluntary control over many behaviors develops. The rooting and Moro reflexes, for example, tend to disappear when the infant is 3 to 4 months old.
The movements of some reflexes eventually become incorporated into more complex, voluntary actions. One important example is the grasping reflex , which occurs when something touches the infant’s palms (see Figure 12 ). The infant responds by grasping tightly. By the end of the third month, the grasping reflex diminishes and the infant shows a more voluntary grasp. As its motor coordination becomes smoother, the infant will grasp objects, carefully manipulate them, and explore their qualities.
The old view of reflexes is that they were exclusively genetic, built-in mechanisms that governed the infant’s movements. The new perspective on infant reflexes is that they are not automatic or completely beyond the infant’s control. For example, infants can alternate the movement of their legs to make a mobile jiggle or change their sucking rate to listen to a recording (Adolph & Robinson, 2015).
GROSS MOTOR SKILLS
Ask any parents about their baby, and sooner or later you are likely to hear about one or more motor milestones, such as “Cassandra just learned to crawl,” “Jesse is finally sitting alone,” or “Angela took her first step last week.” Parents proudly announce such milestones as their children transform themselves from babies unable to lift their heads to toddlers who grab things off the grocery store shelf, chase a cat, and participate actively in the family’s social life (Thelen, 2000). These milestones are examples of gross motor skills , which involve large-muscle activities such as moving one’s arms and walking.
The Development of Posture How do gross motor skills develop? As a foundation, these skills require postural control. For example, to track moving objects, you must be able to control the movement of your head in order to stabilize your gaze; before you can walk, you must be able to balance on one leg.
Posture is more than just holding still and straight. Posture is a dynamic process that is linked with sensory information in the skin, joints, and muscles, which tell us where we are in space; in vestibular organs in the inner ear that regulate balance and equilibrium; and in vision and hearing (Soska, Robinson, & Adolph, 2015).
Newborn infants cannot voluntarily control their posture. Within a few weeks, though, they can hold their heads erect, and soon they can lift their heads while prone. By 2 months of age, babies can sit while supported on a lap or an infant seat, but they cannot sit independently until they are 6 or 7 months of age. Standing also develops gradually during the first year of life. By about 8 to 9 months of age, infants usually learn to pull themselves up and hold on to a chair, and they often can stand alone by about 10 to 12 months of age.
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Learning to Walk Locomotion and postural control are closely linked, especially in walking upright (Kretch & Adolph, 2018). To walk upright, the baby must be able both to balance on one leg as the other is swung forward and to shift weight from one leg to the other.
Even young infants can make the alternating leg movements that are needed for walking. The neural pathways that control leg alternation are in place from a very early age, even at birth or before. Indeed, researchers have found that alternating leg movements occur during the fetal period and at birth (Adolph & Robinson, 2015). Both alternating leg movements and forward stepping movements occur early in development and are precursors to walking.
If infants can produce forward stepping movements so early, why does it take them so long to learn to walk? The key skills in learning to walk appear to be stabilizing balance on one leg long enough to swing the other forward and shifting weight without falling. These are difficult biomechanical problems to solve, and it takes infants about a year to do it.
In learning to locomote, infants learn what kinds of places and surfaces are safe for locomotion (Adolph, 2018; Karasik, Tamis-LeMonda, & Adolph, 2016). Karen Adolph (1997) investigated how experienced and inexperienced crawling infants and walking infants go down steep slopes (see Figure 13 ). Newly crawling infants, who averaged about 8½ months in age, rather indiscriminately went down the steep slopes, often falling in the process (with their mothers next to the slope to catch them). After weeks of practice, the crawling babies became more adept at judging which slopes were too steep to crawl down and which ones they could navigate safely. New walkers also could not judge the safety of the slopes, but experienced walkers accurately matched their skills with the steepness of the slopes. They rarely fell downhill, either refusing to go down the steep slopes or going down backward in a cautious manner. Experienced walkers perceptually assessed the situation—looking, swaying, touching, and thinking before they moved down the slope. With experience, both the crawlers and the walkers learned to avoid the risky slopes where they would fall, integrating perceptual information with the development of a new motor behavior. In this research, we again see the importance of perceptual-motor coupling in the development of motor skills. Thus, practice is very important in the development of new motor skills (Adolph & Berger, 2015).
FIGURE 13 THE ROLE OF EXPERIENCE IN CRAWLING AND WALKING INFANTS’ JUDGMENTS OF WHETHER TO GO DOWN A SLOPE. Karen Adolph (1997) found that locomotor experience rather than age was the primary predictor of adaptive responding on slopes of varying steepness. Newly crawling and walking infants could not judge the safety of the various slopes. With experience, they learned to avoid slopes where they would fall. When expert crawlers began to walk, they again made mistakes and fell, even though they had judged the same slope accurately when crawling. Adolph referred to this as the specificity of learning because it does not transfer across crawling and walking.Courtesy of Dr. Karen Adolph, New York University
Practice is especially important in learning to walk (Adolph, 2018; Adolph & Robinson, 2015). “Thousands of daily walking steps, each step slightly different from the last because of variations in the terrain and the continually varying biomechanical constraints on the body, may help infants to identify the relevant” combination of strength and balance required to improve their walking skills (Adolph, Vereijken, & Shrout, 2003, p. 495). In one study, Adolph and her colleagues (2012) observed 12- to 19-month-olds during free play. Locomotor experience was extensive, with the infants averaging 2,368 steps and 17 falls per hour.
A recent study explored how infants plan and guide their locomotion in the challenging context of navigating a series of bridges varying in width (Kretch & Adolph, 2018). Infants’ visual exploration (direction of their gaze) was assessed using a head-mounted eye-tracking device, and their locomotor actions were captured using video. The 14-month-olds engaged in visual exploration from a distance as an initial assessmentPage 122 before they crossed almost every bridge. The visual information led to modifications in their gait when approaching narrow bridges, and they used haptic (touch) information at the edge of the bridges. As they gained more walking experience, their exploratory behaviors became more efficient and they became more adept at deciding which bridges were safe to walk across.
Might the development of walking be linked to advances in other aspects of development? Walking allows the infant to gain contact with objects that were previously out of reach and to initiate interaction with parents and other adults, thereby promoting language development (Adolph & Robinson, 2015; He, Walle, & Campos, 2015). Thus, just as with advances in postural skills, walking skills can produce a cascade of changes in the infant’s development (Marrus & others, 2018).
The First Year: Motor Development Milestones and Variations Figure 14 summarizes the range of ages at which infants accomplish various gross motor skills during the first year, culminating in the ability to walk easily. After studying Figure 14 , you should be able to order the milestones and describe the typical ages at which babies reach these milestones.
FIGURE 14 MILESTONES IN GROSS MOTOR DEVELOPMENT. The horizontal red bars indicate the range of ages at which most infants reach various milestones in gross motor development.(Photo credit left to right) ©Barbara Penoyar/Getty Images; ©StephaneHachey/Getty Images; ©Image Source/Alamy; ©Victoria Blackie/Getty Images; ©Digital Vision; ©Fotosearch/Getty Images; ©Corbis/PictureQuest; ©amaviael/123RF
A recent study found a number of factors that are linked to motor development in the first year of life (Flensborg-Madsen & Mortensen, 2017). Twelve developmental milestones were assessed, including grasping, rolling, sitting, and crawling; standing and walking; and overall mean of milestones. A larger size at birth (such as birth weight, birth length, and head circumference) was the aspect of pregnancy and delivery that showed the strongest link to reaching motor milestones earlier. Mother’s smoking in the last trimester of prenatal development was associated with reaching the motor milestones later. Also, increase in size (weight increase, length increase, and head increase) in the first year were related to reaching the motor milestones earlier. Breast feeding also was linked to reaching the milestones earlier.
However, the timing of these milestones, especially the later ones, may vary by as muchPage 123 as two to four months, and experiences can modify the onset of these accomplishments (Adolph, 2018). For example, since 1992, when pediatricians began recommending that parents place their babies on their backs to sleep, fewer babies crawled, and those who crawled did so later (Davis & others, 1998). Also, some infants do not follow the standard sequence of motor accomplishments. For example, many American infants never crawl on their belly or on their hands and knees. They may discover an idiosyncratic form of locomotion before walking, such as rolling or scooting, or they might never locomote until they are upright (Adolph & Robinson, 2015). In the African Mali tribe, most infants do not crawl (Bril, 1999). And in Jamaica, approximately one-fourth of babies skip crawling (Hopkins, 1991).
A baby is an angel whose wings decrease as his legs increase.
—French Proverb
According to Karen Adolph and Sarah Berger (2005), “the old-fashioned view that growth and motor development reflect merely the age-related output of maturation is, at best, incomplete. Rather, infants acquire new skills with the help of their caregivers in a real-world environment of objects, surfaces, and planes.”
Development in the Second Year The motor accomplishments of the first year bring increasing independence, allowing infants to explore their environment more extensively and to initiate interaction with others more readily. In the second year of life, toddlers become more motorically skilled and mobile. Motor activity during the second year is vital to the child’s competent development, and few restrictions, except for safety, should be placed on their adventures.
By 13 to 18 months, toddlers can pull a toy attached to a string and use their hands and legs to climb a number of steps. By 18 to 24 months, toddlers can walk quickly or run stiffly for a short distance, balance on their feet in a squatting position while playing with objects on the floor, walk backward without losing their balance, stand and kick a ball without falling, stand and throw a ball, and jump in place.
Can parents give their babies a head start on becoming physically fit and physically talented through structured exercise classes? Most infancy experts recommend against structured exercise classes for babies. But there are other ways to guide infants’ motor development.
Mothers in developing countries tend to stimulate their infants’ motor skills more than mothers in more developed countries (Hopkins, 1991; Karasik & others, 2015). In many African, Indian, and Caribbean cultures, mothers massage and stretch their infants during daily baths (Adolph, Karasik, & Tamis-LeMonda, 2010). Mothers in the Gusii culture of Kenya also encourage vigorous movement in their babies.
(Top) In the Algonquin culture in Quebec, Canada, babies are strapped to a cradle board for much of their infancy. (Bottom) In Jamaica, mothers massage and stretch their infants’ arms and legs. To what extent do cultural variations in the activity infants engage in influence the time at which they reach motor milestones?(Top) ©Michael Greenlar/The Image Works; (bottom) ©Pippa Hetherington/Earthstock/Newscom
Do these cultural variations make a difference in the infant’s motor development? When caregivers provide babies with physical guidance by physically handling them in special ways (such as stroking, massaging, or stretching) or by giving them opportunities for exercise, the infants often reach motor milestones earlier than infants whose caregivers have not provided these activities (Adolph, 2018; Adolph, Karasik, & Tamis-LeMonda, 2010; Karasik & others, 2015). For example, Jamaican mothers expect their infants to sit and walk alone two to three months earlier than English mothers do (Hopkins & Westra, 1990). And in sub-Saharan Africa, traditional practices in many villages involve mothers and siblings engaging babies in exercises, such as frequent exercise for trunk and pelvic muscles (Super & Harkness, 1997).
Many forms of restricted movement—such as Chinese sandbags, orphanage restrictions, and failure of caregivers to encourage movement in Budapest—have been found to produce substantial delays in motor development (Adolph, Karasik, & Tamis-LeMonda, 2010). In some rural Chinese provinces, for example, babies are placed in a bag of fine sand, which acts as a diaper and is changed once a day. The baby is left alone, face up, and is visited only when being fed by the mother (Xie & Young, 1999).
Some studies of swaddling (wrapping an infant tightly in a blanket) show slight delays in motor development, but other studies show no delays. Cultures that do swaddle infants usually do so early in the infant’s development when the infant is not yet mobile; when the infant becomes more mobile, swaddling decreases.
FINE MOTOR SKILLS
Whereas gross motor skills involve large muscle activity, fine motor skills involve finely tuned movements. Grasping a toy, using a spoon, buttoning a shirt, or any activity that requires finger dexterity demonstrates fine motor skills. Infants have hardly any control over fine motor skills at birth, but newborns do have many components of whatPage 124 will become finely coordinated arm, hand, and finger movements (McCormack, Hoerl, & Butterfill, 2012).
The onset of reaching and grasping marks a significant achievement in infants’ ability to interact with their surroundings (Rachwani & others, 2015). During the first two years of life, infants refine how they reach and grasp (Dosso, Herrera, & Boudreau, 2017; Needham, 2009). Initially, infants reach by moving their shoulders and elbows crudely, swinging their arms toward an object. Later, when infants reach for an object they move their wrists, rotate their hands, and coordinate their thumb and forefinger. Infants do not have to see their own hands in order to reach for an object (Clifton & others, 1993). Cues from muscles, tendons, and joints, not sight of the limb, guide reaching by 4-month-old infants. Recent research studies found that short-term training involving practice of reaching movements increased both preterm and full-term infants’ reaching for and touching objects (Cunha & others, 2016; Guimaraes & Tudelia, 2015).
A young girl uses a pincer grip to pick up puzzle pieces.©Newstockimages/SuperStock
Infants refine their ability to grasp objects by developing two types of grasps. Initially, infants grip with the whole hand, which is called the palmar grasp. Later, toward the end of the first year, infants also grasp small objects with their thumb and forefinger, which is called the pincer grip. Their grasping system is very flexible. They vary their grip on an object depending on its size, shape, and texture, as well as the size of their own hands relative to the object’s size. Infants grip small objects with their thumb and forefinger (and sometimes their middle finger too), but they grip large objects with all of the fingers of one hand or both hands.
Perceptual-motor coupling is necessary for the infant to coordinate grasping (Barrett, Traupman, & Needham, 2008). At different stages of development, infants use different perceptual systems to coordinate grasping. Four-month-old infants rely greatly on touch to determine how they will grip an object; 8-month-olds are more likely to use vision as a guide (Newell & others, 1989). This developmental change is efficient because vision lets infants preshape their hands as they reach for an object.
Experience plays a role in reaching and grasping. In a recent study, 3-month-olds who were not yet engaging in reaching behavior were provided with reaching experiences. These experiences were linked to increased object exploration and attention focusing skills at 15 months of age (Libertus, Joh, & Needham, 2016). In another study, 3-month-old infants participated in play sessions wearing “sticky mittens”—“mittens with palms that stuck to the edges of toys and allowed the infants to pick up the toys” (Needham, Barrett, & Peterman, 2002, p. 279) (see Figure 15 ). Infants who participated in sessions with the mittens grasped and manipulated objects earlier in their development than a control group of infants who did not receive the “mitten” experience. The infants who had worn the sticky mittens looked at the objects longer, swatted at them more during visual contact, and were more likely to mouth the objects. In a later study, 5-month-old infants whose parents trained them to use the sticky mittens for 10 minutes a day over a two-week period showed advances in their reaching behavior at the end of the two weeks (Libertus & Needham, 2010). Also, in a recent study, 3-month-old infants participated in active motor training using sticky mittens that allowed them to pick up toys, and these infants engaged in more sophisticated object exploration at 5.5 months of age (Wiesen, Watkins, & Needham, 2016).
FIGURE 15 INFANTS’ USE OF “STICKY MITTENS” TO EXPLORE OBJECTS. Amy Needham and her colleagues (2002) found that “sticky mittens” enhanced young infants’ object exploration skills.Courtesy of Dr. Amy Needham
Just as infants need to exercise their gross motor skills, they also need to exercise their fine motor skills (Needham, 2009). Especially when they can manage a pincer grip, infants delight in picking up small objects. Many develop the pincer grip and begin to crawl at about the same time, and infants at this time pick up virtually everything in sight, especially on the floor, and put the objects in their mouth. Thus, parents need to be vigilant in regularly monitoring what objects are within the infant’s reach (Keen, 2005).
Rachel Keen (2011; Keen, Lee, & Adolph, 2014) emphasizes that tool use is an excellent context for studying problem solving in infants because tool use provides information about how infants plan to reach a goal. Researchers in this area have studied infants’ intentional actions, which range from picking up a spoon in different orientations to retrieving rakes from inside tubes. One study explored motor origins of tool use by assessing developmental changes in banging movements in 6- to 15-month-olds (Kahrs, Jung, & Lockman, 2013). In this study, younger infants were inefficient and variable when banging an object but by one year of age infants showed consistent straight up-and-down hand movements that resulted in precise aiming and consistent levels of force.
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Review Connect Reflect
LG2 Describe infants’ motor development.
Review
· What is the dynamic systems view?
· What are some reflexes that infants have?
· How do gross motor skills develop in infancy?
· How do fine motor skills develop in infancy?
Connect
· What are the differences between the grasping reflex present at birth and the fine motor grasping skills an infant develops between 4 and 12 months of age?
Reflect Your Own Personal Journey of Life
· Think of a motor skill that you perform. How would dynamic systems theory explain your motor skill performance?
3 Sensory and Perceptual Development
LG3 Summarize the course of sensory and perceptual development in infancy.
What Are Sensation and Perception?
The Ecological View
Visual Perception
Other Senses
Intermodal Perception
Nature, Nurture, and Perceptual Development
Perceptual-Motor Coupling
How do sensations and perceptions develop? Can a newborn see? If so, what can it perceive? What about the other senses—hearing, smell, taste, and touch? What are they like in the newborn, and how do they develop? Can an infant put together information from two modalities, such as sight and sound? These are among the intriguing questions that we will explore in this section.
WHAT ARE SENSATION AND PERCEPTION?
How does a newborn know that her mother’s skin is soft rather than rough? How does a 5-year-old know what color his hair is? Infants and children “know” these things as a result of information that comes through the senses. Without vision, hearing, touch, taste, and smell, we would be isolated from the world; we would live in dark silence, a tasteless, colorless, feelingless void.
Sensation occurs when information interacts with sensory receptors—the eyes, ears, tongue, nostrils, and skin. The sensation of hearing occurs when waves of pulsating air are collected by the outer ear and transmitted through the bones of the inner ear to the auditory nerve. The sensation of vision occurs as rays of light contact the eyes, become focused on the retina, and are transmitted by the optic nerve to the visual centers of the brain.
The experiences of the first three years of life are almost entirely lost to us, and when we attempt to enter into a small child’s world, we come as foreigners who have forgotten the landscape and no longer speak the native tongue.
—Selma Fraiberg
Developmentalist and Child Advocate, 20th Century
Perception is the interpretation of what is sensed. The air waves that contact the ears might be interpreted as noise or as musical sounds, for example. The physical energy transmitted to the retina of the eye might be interpreted as a particular color, pattern, or shape, depending on how it is perceived.
THE ECOLOGICAL VIEW
For the past several decades, much of the research on perceptual development in infancy has been guided by the ecological view of Eleanor and James J. Gibson (E. J. Gibson, 1969, 1989, 2001; J. J. Gibson, 1966, 1979). They argue that we do not have to take bits and pieces of data from sensations and build up representations of the world in our minds. Instead, our perceptual system can select from the rich information that the environment itself provides.
According to the Gibsons’ ecological view , we directly perceive informationPage 126 that exists in the world around us. This view is called ecological “because it connects perceptual capabilities to information available in the world of the perceiver” (Kellman & Arterberry, 2006, p. 112). Thus, perception brings us into contact with the environment so we can interact with and adapt to it (Kretch & Adolph, 2017). Perception is designed for action. Perception gives people information such as when to duck, when to turn their bodies as they move through a narrow passageway, and when to put their hands up to catch something.
In the Gibsons’ view, objects have affordances , which are opportunities for interaction offered by objects that fit within our capabilities to perform activities. A pot may afford you something to cook with, and it may afford a toddler something to bang. Adults typically know when a chair is appropriate for sitting, when a surface is safe for walking, or when an object is within reach. An infant who runs down a steep slope or crawls across a narrow beam is determining the affordances of the slope or beam. We directly and accurately perceive these affordances by sensing information from the environment—the light or sound reflecting from the surfaces of the world—and from our own bodies through muscle receptors, joint receptors, and skin receptors, for example (Adolph & Kretch, 2015).
How would you use the Gibsons’ ecological theory of perception and the concept of affordance to explain the role that perception is playing in this baby’s activity?©Ryan KC Wong/Getty Images
An important developmental question is: What affordances can infants or children detect and use? In one study, for example, when babies who could walk were faced with a squishy waterbed, they stopped and explored it, then chose to crawl rather than walk across it (Gibson & others, 1987). They combined perception and action to adapt to the demands of the task.
Similarly, as we described earlier in the section on motor development, infants who were just learning to crawl or just learning to walk were less cautious when confronted with a steep slope than experienced crawlers or walkers were (Adolph, 1997). The more experienced crawlers and walkers perceived that a slope affords the possibility for not only faster locomotion but also for falling. Again, infants coupled perception and action to make a decision about what to do in their environment. Through perceptual development, children become more efficient at discovering and using affordances (Kretch & Adolph, 2017).
Studying infants’ perceptions has not been an easy task. For instance, if newborns have limited communication abilities and are unable to verbalize what they are seeing, hearing, smelling, and so on, how can we study their perception? Connecting Through Research describes some of the ingenious ways researchers study infants’ perceptions.
VISUAL PERCEPTION
What do newborns see? How does visual perception develop in infancy?
Visual Acuity and Human Faces Psychologist William James (1890/1950) called the newborn’s perceptual world a “blooming, buzzing confusion.” More than a century later, we can safely say that he was wrong (Bremner & others, 2017; Damon & others, 2018; Singarajah & others, 2017; Weatherhead & White, 2017). Even the newborn perceives a world with some order. That world, however, is far different from the one perceived by the toddler or the adult.
Just how well can infants see? At birth, the nerves and muscles and lens of the eye are still developing. As a result, newborns cannot see small things that are far away. The newborn’s vision is estimated to be 20/240 on the well-known Snellen chart used for eye examinations, which means that a newborn can see at 20 feet what an adult with normal vision can see at 240 feet (Aslin & Lathrop, 2008). In other words, an object 20 feet away is only as clear to the newborn as it would be if it were 240 feet away from an adult with normal vision (20/20). By 6 months of age, though, on average vision is 20/40 (Aslin & Lathrop, 2008).
Faces are possibly the most important visual stimuli in children’s social environment, and it is important that they extract key information from others’ faces (Singarajah & others, 2017; Sugden & Moulson, 2017). Infants show an interest in human faces soon after birth (Johnson & Hannon, 2015). Research shows that within hours after infants are born, they prefer to look at faces rather than other objects and to look at attractive faces more than at unattractive ones (Lee & others, 2013).
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connecting through research
How Can Newborns’ Perception Be Studied?
The creature has poor motor coordination and can move itself only with great difficulty. Although it cries when uncomfortable, it uses few other vocalizations. In fact, it sleeps most of the time, about 16 to 17 hours a day. You are curious about this creature and want to know more about what it can do. You think to yourself, “I wonder if it can see. How could I find out?”
You obviously have a communication problem with the creature. You must devise a way that will allow the creature to “tell” you that it can see. While examining the creature one day, you make an interesting discovery. When you move an object horizontally in front of the creature, its eyes follow the object’s movement.
The creature’s eye movement suggests that it has at least some vision. In case you haven’t already guessed, the creature you have been reading about is the human infant, and the role you played is that of a researcher interested in devising techniques to learn about the infant’s visual perception. After years of work, scientists have developed research methods and tools sophisticated enough to examine the subtle abilities of infants and to interpret their complex actions (Bendersky & Sullivan, 2007).
Following are six research techniques that are used to study sensory and perceptual development: (1) visual preference method, (2) habituation/dishabituation, (3) high-amplitude sucking, (4) orienting response, (5) eye tracking, and (6) equipment.
Visual Preference Method
Robert Fantz (1963) was a pioneer in this effort. Fantz made an important discovery that advanced the ability of researchers to investigate infants’ visual perception: Infants look at different things for different lengths of time. Fantz placed an infant in a “looking chamber,” which had two visual displays on the ceiling above the infant’s head. An experimenter viewed the infant’s eyes by looking through a peephole. If the infant was fixating on one of the displays, the experimenter could see the display’s reflection in the infant’s eyes. This allowed the experimenter to determine how long the infant looked at each display. Fantz (1963) found that infants only 2 days old looked longer at patterned stimuli, such as faces and concentric circles, than at red, white, or yellow discs. Infants 2 to 3 weeks old also preferred to look at patterns—a face, a piece of printed matter, or a bull’s-eye—longer than at red, yellow, or white discs (see Figure 16 ). Fantz’s research method—studying whether infants can distinguish one stimulus from another by measuring the length of time they attend to different stimuli—is referred to as the visual preference method.
FIGURE 16 FANTZ’S EXPERIMENT ON INFANTS’ VISUAL PERCEPTION. (a) Infants 2 to 3 weeks old preferred to look at some stimuli more than others. In Fantz’s experiment, infants preferred to look at patterns rather than at color or brightness. For example, they looked longer at a face, a piece of printed matter, or a bull’s-eye than at red, yellow, or white discs. (b) Fantz used a “looking chamber” to study infants’ perception of stimuli.©David Linton, Courtesy of the Linton Family
Habituation and Dishabituation
Another way that researchers have studied infant perception is to present a stimulus (such as a sight or a sound) a number of times. If the infant decreases its response to the stimulus after several presentations, it indicates that the infant is no longer interested in looking at the stimulus. If the researcher now presents a new stimulus, the infant’s response will recover—indicating the infant can discriminate between the old and new stimulus (Messinger & others, 2017).
Habituation is the name given to decreased responsiveness to a stimulus after repeated presentations of the stimulus. Dishabituation is the recovery of a habituated response after a change in stimulation. Newborn infants can habituate to repeated sights, sounds, smells, or touches (Rovee-Collier, 2004). Among the measures researchersPage 128 use in habituation studies are sucking behavior (sucking stops when the young infant attends to a novel object), heart and respiration rates, and the length of time the infant looks at an object. Figure 17 shows the results of one study of habituation and dishabituation with newborns (Slater, Morison, & Somers, 1988).
FIGURE 17 HABITUATION AND DISHABITUATION. In the first part of one study, (a) 7-hour-old newborns were shown a stimulus. As indicated, the newborns looked at it an average of 41 seconds when it was first presented to them (Slater, Morison, & Somers, 1988). Over seven more presentations of the stimulus, they looked at it less and less. In the second part of the study, (b) infants were presented with both the familiar stimulus to which they had just become habituated and a new stimulus (which was rotated 90 degrees). The newborns looked at the new stimulus three times as long as the familiar stimulus.
High-Amplitude Sucking
To assess an infant’s attention to sound, researchers often use a method called high-amplitude sucking. In this method, infants are given a nonnutritive nipple to suck, and the nipple is connected to a sound-generating system. The researcher computes a baseline high-amplitude sucking rate in a one-minute silent period. Following the baseline, presentation of a sound is made contingent on the rate of high-amplitude sucking. Initially babies suck frequently so the sound occurs often. Gradually they lose interest in hearing the same sound, so they begin to suck less often. Then the researcher changes the sound that is being presented. If the babies renew their vigorous sucking, the inference is that they have noticed the sound change and are sucking more because they want to hear the interesting new sound (Menn & Stoel-Gammon, 2009).
The Orienting Response and Eye-Tracking
A technique that can be used to determine whether an infant can see or hear is the orienting response, which involves turning one’s head toward a sight or sound. However, the most important recent advance in measuring infant perception is the development of sophisticated eye-tracking equipment (Boardman & Fletcher-Watson, 2017; Kretch & Adolph, 2017; van Renswoude & others, 2018). Eye-tracking consists of measuring eye movements that follow (track) a moving object and can be used to evaluate an infant’s early visual ability, or a startle response can determine an infant’s reaction to a noise (Bendersky & Sullivan, 2007). Figure 18 shows an infant wearing an eye-tracking headgear in a recent study on visually guided motor behavior and social interaction. Most studies of infant development use remote optics eye trackers that have a camera that is not attached to the infant’s head.
FIGURE 18 AN INFANT WEARING EYE-TRACKING HEADGEAR. Photo from Karen Adolph’s laboratory at New York University.Courtesy of Dr. Karen Adolph, New York University
One of the main reasons that infant perceptionPage 129 researchers are so enthusiastic about the availability of sophisticated eye-tracking equipment is that looking time is among the most important measures of infant perceptual and cognitive development (Aslin, 2012). The new eye-tracking equipment allows for far greater precision in assessing various aspects of infant looking and gaze than is possible with human observation (Boardman & Fletcher-Watson, 2017; Law & others, 2018). Among the areas of infant perception in which eye-tracking equipment is being used are attention (Jia & others, 2017; Meng, Uto, & Hashiya, 2017), memory (Kingo & Krojgaard, 2015), and face processing (Chhaya & others, 2018). Further, eye-tracking equipment is improving our understanding of atypically developing infants, such as those who have autism or who were born preterm (Falck-Ytter & others, 2018; Finke, Wilkinson, & Hickerson, 2017; Liberati & others, 2017).
One eye-tracking study shed light on the effectiveness of TV programs and DVDs that claim to educate infants (Kirkorian, Anderson, & Keen, 2012). In this study, 1-year-olds, 4-year-olds, and adults watched Sesame Street and the eye-tracking equipment recorded precisely what they looked at on the screen. The 1-year-olds were far less likely to consistently look at the same part of the screen as their older counterparts, suggesting that the 1-year-olds showed little understanding of the Sesame Street video but instead were more likely to be attracted by what was salient than by what was relevant.
Equipment
Technology can facilitate the use of most methods for investigating the infant’s perceptual abilities. Video-recording equipment allows researchers to investigate elusive behaviors. High-speed computers make it possible to perform complex data analysis in minutes. Other equipment records respiration, heart rate, body movement, visual fixation, and sucking behavior, which provide clues to what the infant is perceiving. For example, some researchers use equipment that detects whether a change in infants’ respiration follows a change in the pitch of a sound. If so, it suggests that the infants heard the pitch change.
Scientists have had to be very creative when assessing the development of infants, discovering ways to “interview” them even though they cannot yet talk. Other segments of the population, such as adults who have suffered from a stroke, have difficulty communicating verbally. What kinds of methods or equipment do you think researchers might use to evaluate their perceptual abilities?
Figure 19 shows a computer estimation of what a picture of a face looks like to an infant at different ages from a distance of about 6 inches. Infants spend more time looking at their mother’s face than a stranger’s face as early as 12 hours after being born (Bushnell, 2003). By 3 months of age, infants (1) match voices to faces, (2) distinguish between male and female faces, and (3) discriminate between faces of their own ethnic group and those of other ethnic groups (Gaither, Pauker, & Johnson, 2012; Kelly & others, 2005, 2007; Lee & others, 2013; Liu & others, 2011, 2015).
FIGURE 19 VISUAL ACUITY DURING THE FIRST MONTHS OF LIFE. The four photographs represent a computer estimation of what a picture of a face looks like to a 1-month-old, 2-month-old, 3-month-old, and 1-year-old (which approximates the visual acuity of an adult).©Kevin Peterson/Getty Images; Simulation by Vischek
Experience plays an important role in face processing in infancy and later in development. One aspect of this experience involves the concept of perceptual narrowing, in which infants are more likely to distinguish between faces to which they have been exposed than faces that they have never seen before (Kobayashi & others, 2018; Minar & Lewkowicz, 2018; Tham, Bremner, & Hayes, 2017).
Color Vision The infant’s color vision also improves (Yang & others, 2015). By 8 weeks, and possibly as early as 4 weeks, infants can discriminate between some colors (Kelly, Borchert, & Teller, 1997). By 4 months of age, they have color preferencesPage 130 that mirror adults’ in some cases, preferring saturated colors such as royal blue over pale blue, for example (Bornstein, 1975). In part, the changes in vision described here reflect biological origins and maturation (Skelton & others, 2017). Experience, however, is also necessary for color vision to develop normally (Sugita, 2004).
Perceptual Constancy Some perceptual accomplishments are especially intriguing because they indicate that the infant’s perception goes beyond the information provided by the senses (Bremner & others, 2017). This is the case in perceptual constancy, in which sensory stimulation is changing but perception of the physical world remains constant. If infants did not develop perceptual constancy, each time they saw an object at a different distance or in a different orientation, they would perceive it as a different object. Thus, the development of perceptual constancy allows infants to perceive their world as stable. Two types of perceptual constancy are size constancy and shape constancy.
Size constancy is the recognition that an object remains the same even though the retinal image of the object changes as you move toward or away from the object. The farther away from us an object is, the smaller its image is on our eyes. Thus, the size of an object on the retina is not sufficient to tell us its actual size. For example, you perceive a bicycle standing right in front of you as smaller than the car parked across the street, even though the bicycle casts a larger image on your eyes than the car does. When you move away from the bicycle, you do not perceive it to be shrinking even though its image on your retinas shrinks; you perceive its size as constant.
But what about babies? Do they have size constancy? Researchers have found that babies as young as 3 months of age show size constancy (Bower, 1966; Day & McKenzie, 1973). However, at 3 months of age, this ability is not full-blown. It continues to develop until 10 or 11 years of age (Kellman & Banks, 1998).
Shape constancy is the recognition that an object remains the same shape even though its orientation to us changes. Look around the room you are in right now. You likely see objects of varying shapes, such as tables and chairs. If you get up and walk around the room, you will see these objects from different sides and angles. Even though your retinal image of the objects changes as you walk and look, you will still perceive the objects as having the same shape.
Do babies have shape constancy? As with size constancy, researchers have found that babies as young as 3 months of age have shape constancy (Bower, 1966; Day & McKenzie, 1973). Three-month-old infants, however, do not have shape constancy for irregularly shaped objects such as tilted planes (Cook & Birch, 1984).
Perception of Occluded Objects Look around where you are now. You likely see that some objects are partly occluded by other objects that are in front of them—possibly a desk behind a chair, some books behind a computer, or a car parked behind a tree. Do infants perceive an object as complete when it is occluded by an object in front of it?
In the first two months of postnatal development, infants don’t perceive occluded objects as complete; instead, they perceive only what is visible (Johnson & Hannon, 2015). Beginning at about 2 months of age, infants develop the ability to perceive that occluded objects are whole (Slater, Field, & Hernandez-Reif, 2007). How does perceptual completion develop? In Scott Johnson’s research (2010, 2011, 2013), learning, experience, and self-directed exploration via eye movements play key roles in the development of perceptual completion in young infants.
Many objects that are occluded appear and disappear behind closer objects, as when you are walking down the street and see cars appear and disappear behind buildings as they move or you move. Infants develop the ability to track briefly occluded moving objects at about 3 to 5 months of age (Bertenthal, 2008). One study explored the ability of 5- to 9-month-old infants to track moving objects that disappeared gradually behind an occluded partition, disappeared abruptly, or imploded (shrank quickly in size) (Bertenthal, Longo, & Kenny, 2007) (see Figure 20 ). In this study, the infants were more likely to accurately predict the reappearance of the moving object when it disappeared gradually than when it vanished abruptly or imploded.
FIGURE 20 INFANTS’ PREDICTIVE TRACKING OF A BRIEFLY OCCLUDED MOVING BALL. The top picture shows the visual scene that infants experienced. At the beginning of each event, a multicolored ball bounced up and down with an accompanying bouncing sound, and then rolled across the floor until it disappeared behind the partition. The other three pictures show the three stimulus events that the 5- to 9-month-old infants experienced: (a) Gradual occlusion—the ball gradually disappears behind the right side of the occluding partition located in the center of the display. (b) Abrupt occlusion—the ball abruptly disappears when it reaches the location of the white circle and then abruptly reappears two seconds later at the location of the second white circle on the other side of the occluding partition. (c) Implosion—the rolling ball quickly decreases in size as it approaches the occluding partition and rapidly increases in size as it reappears on the other side of the occluding partition.
Depth Perception Might infants even perceive depth? To investigate this question, Eleanor Gibson and Richard Walk (1960) constructed a miniature cliff with a drop-off covered by glass in their laboratory. They placed infants on the edge of this visual cliff and had their mothers coax them to crawl onto the glass (see Figure 21 ). Most infants would not crawl out on the glass, choosing instead to remain on the shallow side, an indication that they could perceive depth.
FIGURE 21 EXAMINING INFANTS’ DEPTH PERCEPTION ON THE VISUAL CLIFF. Eleanor Gibson and Richard Walk (1960) found that most infants would not crawl out on the glass, which, according to Gibson and Walk, indicated that they had depth perception. However, some critics point out that the visual cliff is a better indication of the infant’s social referencing and fear of heights than of the infant’s perception of depth.©Mark Richard/PhotoEditPage 131
OTHER SENSES
Other sensory systems besides vision also develop during infancy. We will explore development in hearing, touch and pain, smell, and taste.
Hearing During the last two months of pregnancy, as the fetus nestles in its mother’s womb, it can hear sounds such as the mother’s voice, music, and so on (Kisilevsky & others, 2009). Two psychologists wanted to find out if a fetus who heard Dr. Seuss’ classic story The Cat in the Hat while still in the mother’s womb would prefer hearing the story after birth (DeCasper & Spence, 1986). During the last months of pregnancy, 16 women read The Cat in the Hat to their fetuses. Then shortly after the babies were born, they listened to recordings of their mothers reading either The Cat in the Hat or a story with a different rhyme and pace, The King, the Mice and the Cheese (which was not read to them during prenatal development). The infants sucked on a nipple in a different way when they listened to the recordings of the two stories, suggesting that the infants recognized the pattern and tone of The Cat in the Hat (see Figure 22 ). This study illustrates not only that a fetus can hear but also that it has a remarkable ability to learn and remember even before birth. An fMRI study confirmed capacity of the fetus to hear at 33 to 34 weeks into the prenatal period by assessing fetal brain response to auditory stimuli (Jardri & others, 2012).
FIGURE 22 HEARING IN THE WOMB. (a) Pregnant mothers read The Cat in the Hat to their fetuses during the last few months of pregnancy. (b) When they were born, the babies preferred listening to a recording of their mothers reading The Cat in the Hat, as evidenced by their sucking on a nipple that produced this recording, rather than another story, The King, the Mice and the Cheese.(a) ©McGraw Hill Companies/Jill Braaten, Photographer; (b) Courtesy of Dr. Melanie J. Spence
The fetus can also recognize the mother’s voice, as one study demonstrated (Kisilevsky & others, 2003). Sixty term fetuses (mean gestational age, 38.4 weeks) were exposed to a tape recording either of their mother or of a female stranger reading a passage. The sounds of the tape were delivered through a loudspeaker held just above the mother’s abdomen. Fetal heart rate increased in response to the mother’s voice but decreased in response to the stranger’s voice.
What kind of changes in hearing take place during infancy? They involve perception of a sound’s loudness, pitch, and localization:
· Loudness. Immediately after birth, infants cannot hear soft sounds quite as well as adults can; a stimulus must be louder to be heard by a newborn than by an adult (Trehub & others, 1991). For example, an adult can hear a whisper from about 4 to 5 feet away, but a newborn requires that sounds be closer to a normal conversational level to be heard at that distance. By three months of age, infants’ perception of sounds improves, although some aspects of loudness perception do not reach adult levels until 5 to 10 years of age (Trainor & He, 2013).
· Pitch. Infants are also less sensitive to the pitch of a sound than adults are. Pitch is the perception of the frequency of a sound. A soprano voice sounds high-pitched, a bass voice low-pitched. Infants are less sensitive to low-pitched sounds and are more likely to hear high-pitched sounds (Aslin, Jusczyk, & Pisoni, 1998). One study revealed that by 7 months of age, infants can process simultaneous pitches when they hear voices but they are more likely to encode the higher-pitched voice (Marie & Trainor, 2013). By 2 years of age, infants have considerably improved their ability to distinguish sounds of different pitch.
· Localization. Even newborns can determine the general location from which a sound is coming, but by 6 months of age, they are more proficient at localizing sounds or detecting their origins. Their ability to localize sounds continues to improve during the second year (Burnham & Mattock, 2010).
Although infants can process variations in sound loudness, pitch, and localization, these aspects of hearing continue to improve during the childhood years (Trainor & He, 2013).
Touch and Pain Do newborns respond to touch? Can they feel pain?
Newborns do respond to touch. A touch to the cheek produces a turning of the head; a touch to the lips produces sucking movements.
Regular gentle tactile stimulation prenatally may have positive developmental outcomes. For example, a recent study found that 3-month-olds who had regular gentle tactile stimulation as fetuses were more likely to have an easy temperament than their counterparts who had irregular gentle or no tactile stimulation as fetuses (Wang, Hua, & Xu, 2015).
Newborns can also feel painPage 132 (Bellieni & others, 2016). If you have a son and consider whether he should be circumcised, the issue of an infant’s pain perception probably will become important to you. Circumcision is usually performed on infant boys about the third day after birth. Will your son experience pain if he is circumcised when he is 3 days old? An investigation by Megan Gunnar and her colleagues (1987) found that newborn infant males cried intensely during circumcision. Circumcised infants also display amazing resiliency. Within several minutes after the surgery, they can nurse and interact in a normal manner with their mothers. And, if allowed to, the newly circumcised newborn drifts into a deep sleep, which seems to serve as a coping mechanism.
developmental connection
Sensation and Perception
Kangaroo care and massage therapy are associated with many positive outcomes in preterm and low birth weight infants. Connect to “Prenatal Development and Birth.”
For many years, doctors performed operations on newborns without anesthesia. This practice was accepted because of the dangers of anesthesia and because of the supposition that newborns do not feel pain. As researchers demonstrated that newborns can feel pain, the practice of operating on newborns without anesthesia has been challenged. Anesthesia now is used in some circumcisions (Morris & others, 2012).
Recent neuroimaging studies indicate that newborn infants likely experience some aspects of pain similarly to adults (Ranger & Grunau, 2015). Magnetic resonance imaging (MRI) studies of adults have found that there is a complex brain activity network that underlies pain, which is called the “pain matrix.” The pain matrix brain regions consist of areas located in the thalamus, somatosensory cortex, and amygdala (Denk, McMahon, & Tracey, 2014). In a recent study, researchers discovered that 18 of the 20 regions in the adult pain matrix also are present in the newborn’s pain matrix (Goksan & others, 2015). However, a major brain region in the adult’s pain matrix that was not present in the infant’s was the amygdala, which involves emotional responses. Also in this study, the MRI information revealed that the pain threshold in newborns occurs at a lower level of stimulation than for adults, confirming newborns’ heightened pain sensitivity that has been found in earlier behavioral studies. And in a recent study, kangaroo care was effective in reducing neonatal pain, especially indicated by the significantly lower level of crying when the care was instituted after the newborn’s blood had been drawn by a heel stick (Seo, Lee, & Ahn, 2016).
Smell Newborns can differentiate odors (Doty & Shah, 2008). The expressions on their faces seem to indicate that they like the way vanilla and strawberries smell but do not like the way rotten eggs and fish smell (Steiner, 1979). In one investigation, 6-day-old infants who were breast fed showed a clear preference for smelling their mother’s breast pad rather than a clean breast pad (MacFarlane, 1975) (see Figure 23 ). However, when they were 2 days old they did not show this preference, indicating that they require several days of experience to recognize this odor.
FIGURE 23 NEWBORNS’ PREFERENCE FOR THE SMELL OF THEIR MOTHER’S BREAST PAD. In the experiment by MacFarlane (1975), 6-day-old infants preferred to smell their mother’s breast pad rather than a clean one that had never been used, but 2-day-old infants did not show this preference, indicating that odor preference requires several days of experience to develop.©Jean Guichard
Taste Sensitivity to taste is present even before birth (Doty & Shah, 2008). Human newborns learn tastes prenatally through the amniotic fluid and in breast milk after birth (Beauchamp & Mennella, 2009). In one study, even at only 2 hours of age, babies made different facial expressions when they tasted sweet, sour, and bitter solutions (Rosenstein & Oster, 1988). At about 4 months of age, infants begin to prefer salty tastes, which as newborns they had found to be aversive (Doty & Shah, 2008).
INTERMODAL PERCEPTION
Imagine yourself playing basketball or tennis. You are experiencing many visual inputs: the ball coming and going, other players moving around, and so on. However, you are experiencing many auditory inputs as well: the sound of the ball bouncing or being hit, the grunts and groans of other players, and so on. There is good correspondence between much of the visual and auditory information: When you see the ball bounce, you hear a bouncing sound; when a player stretches to hit a ball, you hear a groan. When you look at and listen to what is going on, you do not experience just the sounds or just the sights—you put all these things together. You experience a unitary episode. This is intermodal perception , which involves integrating information from two or more sensory modalities, such as vision and hearing (Bremner & Spence, 2017; Hannon, Schachner, & Nave-Blodgett, 2017; Nomikou, Koke, & Rohlfing, 2017). Most perception is intermodal (Bahrick, 2010).
Early, exploratory forms of intermodal perception exist even in newborns (Bahrick & Hollich, 2008; Bremner, 2017; Guellai & others, 2016). For example, newborns turn their eyes and their head toward the sound of a voice or rattle when the soundPage 133 is maintained for several seconds (Clifton & others, 1981), but the newborn can localize a sound and look at an object only in a crude way (Bechtold, Bushnell, & Salapatek, 1979). These early forms of intermodal perception become sharpened with experience in the first year of life (Bremner & Spence, 2017; Kirkham & others, 2012). In one study, infants as young as 3 months old looked longer at their parents when they also heard their voices (Spelke & Owsley, 1979). Thus, even young infants can coordinate visual-auditory information involving people.
What is intermodal perception? Which two senses is this infant using to integrate information about the blocks?©Kaori Ando/Getty Images
Can young infants put vision and sound together as precisely as adults do? In the first six months, infants have difficulty connecting sensory input from different modes, but in the second half of the first year they show an increased ability to make this connection mentally (Hannon, Schachner, & Nave-Blodgett, 2017).
NATURE, NURTURE, AND PERCEPTUAL DEVELOPMENT
Now that we have discussed many aspects of perceptual development, let’s explore one of developmental psychology’s key issues in relation to perceptual development: the nature-nurture issue. There has been a longstanding interest in how strongly infants’ perception is influenced by nature or nurture (Bremner, 2017; Chen & others, 2017; Johnson & Hannon, 2015). In the field of perceptual development, nature proponents are referred to as nativistsand those who emphasize learning and experience are called empiricists.
In the nativist view, the ability to perceive the world in a competent, organized way is inborn or innate. A completely nativist view of perceptual development no longer is accepted in developmental psychology.
The Gibsons argued that a key question in infant perception is what information is available in the environment and how infants learn to generate, differentiate, and discriminate the information—certainly not a nativist view. The Gibsons’ ecological view also is quite different from Piaget’s constructivist view. According to Piaget, much of perceptual development in infancy must await the development of a sequence of cognitive stages for infants to construct more complex perceptual tasks. Thus, in Piaget’s view the ability to perceive size and shape constancy, a three-dimensional world, intermodal perception, and so on, develops later in infancy than the Gibsons envision.
The longitudinal research of Daphne Maurer and her colleagues (Chen & others, 2017; Lewis & Maurer, 2005, 2009; Maurer, 2016; Maurer & Lewis, 2013; Maurer & others, 1999) has focused on infants born with cataracts—a thickening of the lens of the eye that causes vision to become cloudy, opaque, and distorted and thus severely restricts infants’ ability to experience their visual world. Studying infants whose cataracts were removed at different points in development, they discovered that those whose cataracts were removed and new lenses placed in their eyes in the first several months after birth showed a normal pattern of visual development. However, the longer the delay in removing the cataracts, the more their visual development was impaired. In their research, Maurer and her colleagues (2007) have found that experiencing patterned visual input early in infancy is important for holistic and detailed face processing after infancy. Maurer’s research program illustrates how deprivation and experience influence visual development, revealing an early sensitive period when visual input is necessary for normal visual development (Chen & others, 2017; Maurer & Lewis, 2013).
Today, it is clear that just as an extreme nativist position on perceptual development is unwarranted, an extreme empiricist position also is unwarranted. Much of very early perception develops from innate (nature) foundations, and the basic foundation of many perceptual abilities can be detected in newborns (Bornstein, Arterberry, & Mash, 2015). However, as infants develop, environmental experiences (nurture) refine or calibrate many perceptual functions, and they may be the driving force behind some functions (Amso & Johnson, 2010). The accumulation of experience with and knowledge about their perceptual world contributes to infants’ ability to process coherent perceptions of people and things (Bremner & others, 2016; Johnson & Hannon, 2015). Thus, a full portrait of perceptual development includes the influence of nature, nurture, and a developing sensitivity to information (Bremner & others, 2016; Chen & others, 2017; Maurer, 2016).
What roles do nature and nurture play in the infant’s perceptual development?©Boris Ryaposov/ShutterstockPage 134
PERCEPTUAL-MOTOR COUPLING
As we come to the end of this chapter, we return to the important theme of perceptual-motor coupling. The distinction between perceiving and doing has been a time-honored tradition in psychology. However, a number of experts on perceptual and motor development question whether this distinction makes sense (Adolph, 2018; Thelen & Smith, 2006). The main thrust of research in Esther Thelen’s dynamic systems approach is to explore how people assemble motor behaviors for perceiving and acting. The main theme of the ecological approach of Eleanor and James J. Gibson is to discover how perception guides action. Action can guide perception, and perception can guide action. Only by moving one’s eyes, head, hands, and arms and by moving from one location to another can an individual fully experience his or her environment and learn how to adapt to it. Perception and action are coupled (Kretch & Adolph, 2018).
How are perception and action coupled in children’s development?©Kevin Liu/Getty Images
Babies, for example, continually coordinate their movements with perceptual information to learn how to maintain balance, reach for objects in space, and move across various surfaces and terrains (Bremner & others, 2017). They are motivated to move by what they perceive. Consider the sight of an attractive toy across the room. In this situation, infants must perceive the current state of their bodies and learn how to use their limbs to reach the toy. Although their movements at first are awkward and uncoordinated, babies soon learn to select patterns that are appropriate for reaching their goals.
Equally important is the other part of the perception-action coupling. That is, action educates perception (Adolph, 2018). For example, watching an object while exploring it manually helps infants to determine its texture, size, and hardness. Locomoting in the environment teaches babies about how objects and people look from different perspectives, or whether various surfaces will support their weight.
The infant is by no means as helpless as it looks and is quite capable of some very complex and important actions.
—Herb Pick
Developmental Psychologist, University of Minnesota
How do infants develop new perceptual-motor couplings? Recall from our discussion earlier in this chapter that in the traditional view of Gesell, infants’ perceptual-motor development is prescribed by a genetic plan to follow a fixed and sequential progression of stages in development. The genetic determination view has been replaced by the dynamic systems view that infants learn new perceptual-motor couplings by assembling skills for perceiving and acting. New perceptual-motor coupling is not passively accomplished; rather, the infant actively develops a skill to achieve a goal within the constraints set by the infant’s body and the environment (Kretch & Adolph, 2018).
Children perceive in order to move and move in order to perceive. Perceptual and motor development do not occur in isolation from each other but instead are coupled.
Review Connect Reflect
LG3 Summarize the course of sensory and perceptual development in infancy.
Review
· What are sensation and perception?
· What is the ecological view of perception?
· How does visual perception develop in infancy?
· How do hearing, touch and pain, smell, and taste develop in infancy?
· What is intermodal perception?
· What roles do nature and nurture play in perceptual development?
· How is perceptual-motor development coupled?
Connect
· Perceptual-motor coupling was discussed in the previous section as well as in this section. Describe how this concept could be linked to the concept of nature versus nurture.
Reflect Your Own Personal Journey of Life
· How much sensory stimulation would you provide your own baby? A little? A lot? Could you overstimulate your baby? Explain.
Page 135
topical connections looking forward
In the next chapter, you will read about the remarkable cognitive changes that characterize infant development and how soon infants are able to competently process information about their world. Advances in infants’ cognitive development—together with the development of the brain and perceptual-motor advances discussed in this chapter—allow infants to adapt more effectively to their environment. Later in this text, we will further explore physical development when we examine how children progress through early childhood (ages 3 to 5). Young children’s physical development continues to change and to become more coordinated in early childhood, although gains in height and weight are not as dramatic in early childhood as in infancy.
reach your learning goals
Physical Development in Infancy
1 Physical Growth and Development in Infancy
LG1 Discuss physical growth and development in infancy.
Patterns of Growth
Height and Weight
The Brain
Sleep
Nutrition
· The cephalocaudal pattern is the sequence in which growth proceeds from top to bottom. The proximodistal pattern is the sequence in which growth starts at the center of the body and moves toward the extremities.
· The average North American newborn is 20 inches long and weighs 7.6 pounds. Infants grow about 1 inch per month in the first year and nearly triple their weight by their first birthday. The rate of growth slows in the second year.
· One of the most dramatic changes in the brain in the first two years of life is dendritic spreading, which increases the connections between neurons. Myelination, which speeds the conduction of nerve impulses, continues through infancy and even into adolescence.
· The cerebral cortex has two hemispheres (left and right). Lateralization refers to specialization of function in one hemisphere or the other. Early experiences play an important role in brain development.
· Neural connections are formed early in an infant’s life. Before birth, genes mainly direct neurons to different locations. After birth, the inflowing stream of sights, sounds, smells, touches, language, and eye contact helps to shape the brain’s neural connections, as does stimulation from caregivers and others. The neuroconstructivist view, in which brain development is influenced by a person’s environment and experiences, is an increasingly popular perspective.
· Newborns usually sleep about 18 hours a day. By 6 months of age, many American infants approach adult-like sleeping patterns. REM sleep—during which dreaming occurs—is present more in early infancy than in childhood and adulthood.
· Sleeping arrangements for infants vary across cultures. In America, infants are more likely to sleep alone than in many other cultures. Some experts believe shared sleeping can lead to sudden infant death syndrome (SIDS), a condition that occurs when a sleeping infant suddenly stops breathing and dies without an apparent cause. However, it is generally accepted that the most critical factor in predicting whether an infant will develop SIDS is prone sleeping.
· Infants need to consume about 50 calories per day for each pound they weigh. The growing consensus is that in most instances breast feeding is superior to bottle feeding for both the infant and the mother, although the correlational nature of studies must be considered.
· Severe infant malnutrition is still prevalent in manyPage 136 parts of the world. A special concern in impoverished countries is early weaning from breast milk and the misuse and hygiene problems associated with bottle feeding in these countries. The Women, Infants, and Children (WIC) program has produced positive benefits in low-income families in the United States.
2 Motor Development
LG2 Describe infants’ motor development.
The Dynamic Systems View
Reflexes
Gross Motor Skills
Fine Motor Skills
· Thelen’s dynamic systems theory seeks to explain how motor behaviors are assembled for perceiving and acting. Perception and action are coupled. According to this theory, motor skills are the result of many converging factors, such as the development of the nervous system, the body’s physical properties and its movement possibilities, the goal the child is motivated to reach, and environmental support for the skill. In the dynamic systems view, motor development is far more complex than the result of a genetic blueprint.
· Reflexes—automatic movements—govern the newborn’s behavior. They include the sucking, rooting, and Moro reflexes. The rooting and Moro reflexes disappear after three to four months. Permanent reflexes include coughing and blinking. For infants, sucking is an especially important reflex because it provides a means of obtaining nutrition.
· Gross motor skills involve large-muscle activities. Key skills developed during infancy include control of posture and walking. Although infants usually learn to walk by their first birthday, the neural pathways that allow walking begin forming earlier. The age at which infants reach milestones in the development of gross motor skills may vary by as much as two to four months, especially for milestones in late infancy.
· Fine motor skills involve finely tuned movements. The onset of reaching and grasping marks a significant accomplishment, and this skill becomes more refined during the first two years of life.
3 Sensory and Perceptual Development
LG3 Summarize the course of sensory and perceptual development in infancy.
What Are Sensation and Perception?
The Ecological View
Visual Perception
Other Senses
Intermodal Perception
Nature, Nurture, and Perceptual Development
Perceptual-Motor Coupling
· Sensation occurs when information interacts with sensory receptors. Perception is the interpretation of sensation.
· Created by the Gibsons, the ecological view states that we directly perceive information that exists in the world around us. Perception brings people in contact with the environment to interact with and adapt to it. Affordances provide opportunities for interaction offered by objects that fit within our capabilities to perform activities.
· Researchers have developed a number of methods to assess the infant’s perception, including the visual preference method (which Fantz used to determine young infants’ preference for looking at patterned over nonpatterned displays), habituation and dishabituation, and tracking.
· The infant’s visual acuity increases dramatically in the first year of life. Infants’ color vision improves as they develop. Young infants systematically scan human faces. As early as 3 months of age, infants show size and shape constancy. At approximately 2 months of age, infants develop the ability to perceive that occluded objects are complete. In Gibson and Walk’s classic study, infants as young as 6 months of age indicated they could perceive depth.
· The fetus can hear during the last two months of pregnancy. Immediately after birth, newborns can hear, but their sensory threshold is higher than that of adults. Developmental changes in the perception of loudness, pitch, and localization of sound occur during infancy. Newborns can respond to touch and feel pain. Newborns can differentiate odors, and sensitivity to taste may be present before birth.
· Early, exploratory forms of intermodal perception—the ability to relate and integrate information from two or more sensory modalities—are present in newborns and become sharper over the first year of life.
· In describing the sources of perceptualPage 137 development, nature advocates are referred to as nativists and nurture proponents are called empiricists. The Gibsons’ ecological view that has guided much of perceptual development research leans toward a nativist approach but still allows for developmental changes in distinctive features. Piaget’s constructivist view leans toward an empiricist approach, emphasizing that many perceptual accomplishments must await the development of cognitive stages in infancy. A strong empiricist approach is unwarranted. A full account of perceptual development includes the roles of nature, nurture, and the developing sensitivity to information.
· Perception and action are often not isolated but rather are coupled. Individuals perceive in order to move and move in order to perceive.
key terms
sudden infant death syndrome (SIDS)
key people
Karen Adolph
Martha Ann Bell
Robert Fantz
Eleanor Gibson
James J. Gibson
William James
Mark Johnson
Scott Johnson
Rachel Keen
Patricia Kuhl
Daphne Maurer
Charles Nelson
John Richards
Esther Thelen
Richard Walk
chapter 5
COGNITIVE DEVELOPMENT IN INFANCY
chapter outline
1 Piaget’s Theory of Infant Development
Learning Goal 1 Summarize and evaluate Piaget’s theory of infant development.
Evaluating Piaget’s Sensorimotor Stage
2 Learning, Attention, Remembering, and Conceptualizing
Learning Goal 2 Describe how infants learn, focus attention, remember, and conceptualize.
Concept Formation and Categorization
Learning Goal 3 Describe the nature of language and how it develops in infancy.
Biological and Environmental Influences
©DreamPictures/Getty Images
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