body size
CHAPTER 5 PHYSICAL DEVELOPMENT IN INFANCY AND TODDLERHOOD
BRIEF CHAPTER SUMMARY
During the first two years, body size dramatically, following organized patterns of growth. The skull also grows rapidly, accommodating large increases in brain size. Nincreases eurons in the brain form an elaborate communication system. Myelination improves the efficiency of message transfer. Neurophysiological measures of brain functioning allow researchers to identify relationships between the brain and psychological development.
The cerebral cortex is the largest brain structure, containing the greatest number of neurons and synapses. The two hemispheres specialize in different functions, but brain plasticity allows some recovery of abilities lost to damage in one hemisphere. Stimulation of the brain is essential during sensitive periods, when the brain is developing most rapidly.
The interplay between genetic and environmental factors affects physical growth. Nutrition is crucial to development of the rapidly growing brain and body. Breast milk, which is ideally suited to infants’ needs, is especially important in promoting survival and health in poverty-stricken regions. Recent evidence indicates a relationship between rapid weight gain in infancy and later overweight and obesity. Malnutrition in the early years can lead to permanent stunting of physical growth and of brain development. Parental affection is essential for normal physical growth.
Babies are born with built-in learning capacities that allow them to benefit from experience immediately. Infants are capable of classical and operant conditioning. They also learn through their natural preference for novel stimulation and through imitation.
Large individual differences exist in babies’ rate of motor development. According to dynamic systems theory, each new motor skill is a joint product of central nervous system development, the body’s movement capacities, the child’s goals, and environmental supports for the skill. Reaching, which plays a vital role in infant cognitive development, is affected by early experience and babies’ visual surroundings.
In the first year, babies start to organize sounds into complex patterns, detecting regularities that facilitate later language learning. Infants’ remarkable statistical learning capacity allows them to extract patterns from complex, continuous speech, preparing them to utter their first words around age 12 months. Visual development is supported by maturation of the eye and visual centers in the cerebral cortex. Pattern perception begins at birth; babies’ tendency to look for structure in a pattern stimulus also applies to face perception. Through intermodal perception, babies perceive input from different sensory systems in a unified way. Perception is guided by the discovery of affordances—the action possibilities that a situation allows.
LECTURE OUTLINE
I. BODY GROWTH (pp. 159–161)
A. Changes in Body Size and Muscle–Fat Makeup (pp. 159–160)
1. Birth weight doubles by 5 months of age, triples by 1 year, and quadruples by 2 years.
2. The early rise in body fat peaks at about 9 months. During the second year, most toddlers slim down.
3. Muscle tissue increases slowly during infancy and does not peak until adolescence.
B. Changes in Body Proportions (p. 161)
1. Growth of the head and chest occurs before that of the trunk and legs, following the cephalocaudal trend.
2. Following the proximodistal trend, the arms and legs grow ahead of the hands and feet.
C. Individual and Group Differences (p. 161)
1. In infancy, sex differences and ethnic differences in body size are apparent.
2. The best estimate of a child’s physical maturity is skeletal age, a measure of bone development.
II. BRAIN DEVELOPMENT (pp. 161–171)
A. Development of Neurons (pp. 161–163)
1. The human brain contains 100 to 200 billion neurons. Between them are synapses—tiny gaps where fibers from different neurons come close together but do not touch.
2. Neurons send messages to one another by releasing chemicals called neurotransmitters, which cross the synapse.
3. Neurons that are stimulated by input from the surrounding environment continue to establish new synapses; those that are seldom stimulated soon lose their synapses, in a process called synaptic pruning.
4. About half the brain’s volume is made up of glial cells, which are responsible for myelination, the coating of neural fibers with myelin, which improves the efficiency of message transfer.
5. After neurons and synapses are overproduced, cell death and synaptic pruning sculpt away excess building material to form the mature brain.
B. Measures of Brain Functioning (pp. 163–164)
1. An electroencephalogram (EEG) detects changes in electrical activity in the cerebral cortex.
2. Event-related potentials (ERPs) are used to study responsiveness to stimuli and atypical brain functioning.
3. Neuroimaging techniques, such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), provide precise information about which brain regions are specialized for certain capacities.
4. In near-infrared spectroscopy (NIRS), infrared light is beamed at regions of the cerebral cortex to measure blood flow and oxygen metabolism while the child attends to a stimulus.
C. Development of the Cerebral Cortex (pp. 164–167)
1. The cerebral cortex, which surrounds the rest of the brain, accounts for 85 percent of the brain’s weight and contains the greatest number of neurons and synapses.
2. Regions of the Cortex
a. The order in which cortical regions develop corresponds to the order in which various capacities emerge in infancy and childhood.
b. The cortical regions with the most extended period of development are the frontal lobes; the prefrontal cortex is responsible for thought.
3. Lateralization and Plasticity of the Cerebral Cortex
a. Lateralization refers to the specialization of functions of the left and right hemispheres of the cerebral cortex.
b. Brain plasticity refers to the ability of areas of the brain to take over functions of a damaged region.
D. Sensitive Periods in Brain Development (pp. 167–169)
1. Human Evidence: Victims of Deprived Early Environments
a. The experiences of children placed in orphanages and later exposed to ordinary family rearing confirm the importance of a generally stimulating environment for psychological development.
b. Neurobiological findings indicate that early, prolonged institutionalization leads to a generalized decrease in activity of the cerebral cortex, especially the prefrontal cortex.
2. Appropriate Stimulation
a. Appropriate early intervention helps to protect the young brain from potentially damaging effects of both excessive and inadequate stress-hormone exposure.
b. In addition to impoverished environments, ones that overwhelm children with expectations beyond their current capacities interfere with the brain’s potential.
c. Experience-expectant brain growth depends on ordinary experiences, such as opportunities to explore the environment, interact with people, and hear language and other sounds.
d. Experience-dependent brain growth is a lifelong process consisting of additional growth and refinement of established brain structures as a result of specific learning experiences.
E. Changing States of Arousal (pp. 169–171)
1. Rapid brain growth means that the organization of sleep and wakefulness changes substantially between birth and 2 years, increasingly conforming to a night–day schedule.
2. These changing arousal patterns are due to brain development, but they are also affected by cultural beliefs and practices and by parents’ needs.
III. INFLUENCES ON EARLY PHYSICAL GROWTH (pp. 171–176)
A. Heredity (p. 171)
1. When diet and health are adequate, height and rate of physical growth are largely determined by heredity.
2. Catch-up growth refers to physical growth that is delayed by temporary environmental influences but returns to a genetically determined path once conditions improve.
3. Weight is also affected by genetic makeup, but environment, especially nutrition, also plays an important role.
B. Nutrition (pp. 171–174)
1. Twenty-five percent of an infant’s total caloric intake is devoted to growth; babies need extra calories to keep developing organs functioning properly.
2. Breastfeeding versus Bottle-Feeding
a. Breastfeeding offers many nutritional and health advantages over bottle-feeding.
b. Breastfed babies in poverty-stricken regions of the world are less likely to be malnourished and more likely to survive the first year of life.
c. Although 77 percent of American mothers begin breastfeeding after birth, more than one-third stop by 6 months.
d. Breastfed and bottle-fed infants in industrialized nations do not differ in emotional adjustment.
3. Are Chubby Babies at Risk for Later Overweight and Obesity?
a. Infants and toddlers can eat nutritious foods freely without risk of becoming overweight, but recent evidence does show a strengthening relationship between rapid weight gain in infancy and later obesity.
b. Breastfeeding for the first six months, limiting unhealthy foods, promoting energetic play, and limiting television viewing time are ways that parents can prevent their infants from becoming overweight children.
C. Malnutrition (p. 175)
1. About one-third of the world’s children suffer from malnutrition before age 5, with 8 percent severely affected, suffering from two dietary diseases:
a. Marasmus is a wasted condition of the body caused by a diet low in all essential nutrients.
b. Kwashiorkor is caused by an unbalanced diet very low in protein.
2. Children who survive these extreme forms of malnutrition often grow to be smaller in all body dimensions and suffer lasting damage to the organs; when their diets improve, they tend to gain excessive weight.
3. Malnutrition seriously affects learning and behavior, with lasting negative effects on fine-motor coordination, attention, behavior, and intelligence.
4. Iron-deficiency anemia, common among poverty-stricken infants and children, interferes with many central nervous system processes.
5. An estimated 22 percent of U.S. children suffer from food insecurity—uncertain access to enough food for a healthy, active life.
D. Emotional Well-Being (p. 176)
1. Growth faltering refers to infants whose weight, height, and head circumference are substantially below age-related growth norms and who are withdrawn and apathetic.
2. In many such cases, a disturbed parent–infant relationship contributes to this failure to grow normally.
3. If the disorder is not corrected in infancy, most of these children remain small and show lasting cognitive and emotional difficulties.
IV. LEARNING CAPACITIES (pp. 176–180)
A. Learning refers to changes in behavior as the result of experience.
B. Classical Conditioning (pp. 176–177)
1. Newborn reflexes make classical conditioning possible in young infants. In this form of learning, a neutral stimulus is paired with a stimulus that leads to a reflexive response, as follows:
a. An unconditioned stimulus (UCS) consistently produces a reflexive, or unconditioned response (UCR).
b. A neutral stimulus that does not lead to the reflexive response is presented just before, or at about the same time as, the UCS.
c. The neutral stimulus, now called a conditioned stimulus (CS), produces the reflexive response, now called a conditioned response (CR).
2. Extinction is a decline in the CR as a result of presenting the CS repeatedly without the UCS.
C. Operant Conditioning (p. 178)
1. Operant conditioning is a form of learning in which infants act, or operate, on the environment, and stimuli that follow their behavior change the probability that the behavior will occur again.
2. A reinforcer is a stimulus that increases the occurrence of a response.
3. Punishment refers to removing a desirable stimulus or presenting an unpleasant one to decrease the occurrence of a response.
D. Habituation (pp. 178–179)
1. Habituation refers to a gradual reduction in the strength of a response due to repetitive stimulation.
2. Recovery is an increase in responsiveness after a new stimulus appears.
3. Habituation and recovery promote learning by focusing our attention on those aspects of the environment we know least about.
E. Imitation (pp. 179–180)
1. Imitation is learning by copying the behavior of another person.
2. Research indicates that newborns can imitate adult facial expressions and certain gestures.
3. Some researchers argue that certain newborn “imitative” responses are actually mouthing—a common early exploratory response to interesting stimuli, but others claim that newborns imitate diverse facial expressions and head movements with effort and determination.
4. Specialized cells in motor areas of the cerebral cortex in primates, called mirror neurons, may underlie the infant’s capacity to imitate.
V. MOTOR DEVELOPMENT (pp. 181–186)
A. The Sequence of Motor Development (pp. 181, 182)
1. Gross-motor development refers to control over actions that help an infant get around in the environment, such as crawling, standing, and walking.
2. Fine-motor development involves smaller movements, such as reaching and grasping.
3. Large individual differences exist in rate of motor progress.
B. Motor Skills as Dynamic Systems (pp. 181–183)
1. According to dynamic systems theory of motor development, mastery of motor skills involves acquiring increasingly complex systems of action.
2. Each new skill is a joint product of central nervous system development, the body’s movement capacities, the goals of the child, and environmental supports for the skill.
3. Because motor development is motivated by exploration and the desire to master new tasks and, therefore, varies with context, heredity can map it out only at a general level.
C. Dynamic Motor Systems in Action (pp. 183–184)
1. To find out how infants acquire motor capabilities, researchers conduct microgenetic studies, following babies from their first attempts at a skill until it becomes smooth and effortless.
2. Research illustrates that rather than following a strict, predetermined pattern, the order in which motor skills develop depends on the anatomy of the body part being used, the surrounding environment, and the baby’s efforts.
D. Cultural Variations in Motor Development (pp. 184–185)
1. Cross-cultural research illustrates how early movement opportunities and a stimulating environment contribute to motor development.
2. Cultural beliefs vary concerning the advisability of deliberately teaching motor skills to babies.
E. Fine-Motor Development: Reaching and Grasping (pp. 185–186)
1. Reaching plays a vital role in infant cognitive development because, by manipulating things, infants learn a great deal about the sights, sounds, and feel of objects.
2. Motor skills start out as gross, diffuse activity and move toward mastery of fine movements.
3. Prereaching refers to the poorly coordinated swipes of newborns.
4. Development of Reaching and Grasping
a. Voluntary reaching appears at about 3 to 4 months and improves as depth perception advances and as infants gain greater control of body posture and arm and hand movements.
b. The ulnar grasp is a clumsy motion in which the young infant’s fingers close against the palm.
c. The well-coordinated pincer grasp, using the index finger and thumb, appears by the end of the first year.
5. Early Experience and Reaching
a. In cultures where mothers carry their infants on their hips or in slings, babies have rich opportunities to explore with their hands, and they are advanced in development of reaching and grasping.
b. Research shows that infants given a moderate amount of visual stimulation reached for objects earlier than those given nothing to look at.
VI. PERCEPTUAL DEVELOPMENT (pp. 187–197)
A. Hearing (pp. 187–189)
1. During the first year, babies start to organize sounds into complex patterns.
2. Around 6 to 7 months, babies can distinguish musical tunes on the basis of variations in rhythmic patterns
3. Speech Perception
a. Newborns prefer listening to human speech over nonspeech sounds.
b. Around 5 months, they become sensitive to syllable stress patterns in their own language; between 6 and 8 months, they start to “screen out” sounds not used in their native tongue.
c. Around 7 to 9 months, infants begin to divide the speech stream into wordlike units.
4. Analyzing the Speech Stream
a. Infants’ impressive statistical learning capacity enables them to analyze the speech stream for patterns and acquire speech structures for which they will later learn meanings.
b. Adults’ style of communicating with infants greatly facilitates analysis of the structure of speech.
B. Vision (pp. 189–193)
1. Around 2 months, infants can focus on objects about as well as adults; color vision is adultlike by 4 months.
2. Babies’ visual acuity reaches 20/80 by 6 months and an adult level of about 20/20 by 4 years.
3. The infant’s ability to scan and track moving objects improves over the first half-year.
4. Depth Perception
a. Depth perception—the ability to judge the distance of objects from one another and from ourselves—is important for guiding motor activity.
b. Emergence of Depth Perception
(1) Motion is the first depth cue to which infants are sensitive.
(2) Sensitivity to binocular depth cues emerges between 2 and 3 months and improves rapidly over the first year.
(3) Sensitivity to pictorial depth cues, such as changes in texture and overlapping objects, begins between 3 and 4 months and strengthens between 5 and 7 months.
c. Independent Movement and Depth Perception
(1) From extensive crawling experience, babies figure out how to use depth cues to detect the danger of falling.
(2) As they master each new body posture, babies must undergo new learning about depth.
5. Pattern Perception
a. Contrast sensitivity explains newborns’ preference for looking at patterned rather than plain stimuli.
b. Combining Pattern Elements
(1) Newborn infants respond to the separate parts of a pattern.
(2) At 2 to 3 months, infants begin to integrate the parts of a pattern into a unified whole.
(3) At 12 months, infants can detect familiar objects represented by incomplete drawings.
c. Face Perception
(1) Newborns are more responsive to faces and facelike patterns than to other patterns and show a preference for faces judged by adults as attractive.
(2) From repeated exposures, babies learn to prefer their mother’s face to that of an unfamiliar woman.
(3) Around 3 months, infants readily make fine distinctions among the features of different faces.
(4) At 5 months, infants perceive emotional expressions as meaningful wholes.
(5) Through early experience, babies form group biases, preferring female to male faces and faces of members of their own race to members of other races.
(6) As babies recognize and respond to the expressive behavior of others, face perception supports their earliest social relationships.
C. Object Perception (pp. 193–195)
1. Size and Shape Constancy
a. Size constancy— perception of an object’s size as the same, despite changes in the size of its retinal image—is evident in the first week of life, as is shape constancy: perception of an object’s shape as stable, despite changes in the shape projected on the retina.
b. Both size and shape constancy seem to be built-in capacities that help babies detect a coherent world of objects.
2. Perception of Object Identity
a. At first, babies rely heavily on motion and spatial arrangement to identify objects.
b. As infants become familiar with many objects, they rely more on shape, color, and pattern and less on motion to identify objects as unified wholes.
c. From 4 to 11 months, infants increasingly use featural information to detect the identity of an object traveling behind a screen.
D. Intermodal Perception (pp. 195–196)
1. Intermodal perception combines information from more than one modality, or sensory system.
2. Babies perceive input from different sensory systems in a unified way by detecting amodal sensory properties—information that overlaps two or more sensory systems.
3. Detection of amodal relations, such as the common tempo and rhythm in sights and sounds, provides the basis for detecting more specific intermodal matches.
4. In addition to easing perception of the physical world, intermodal perception facilitates processing of the social world and supports diverse aspects of learning.
E. Understanding Perceptual Development (pp. 196–197)
1. Eleanor and James Gibson’s differentiation theory states that infants actively search for invariant features of the environment—those that remain stable—in a constantly changing perceptual world.
2. Perception is guided by the discovery of affordances—the action possibilities that a situation offers an organism with certain motor capabilities.
3. Some researchers believe that babies impose meaning on what they perceive, constructing categories of objects and events in the surrounding environment, while others believe that this shift from a perceptual to a cognitive emphasis p