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Chapter 5
Body Growth and Development
Physical growth and development of motor skills influence cognitive, social, and other
dimensions of development. Cognitive and social factors, such as how an individual is
perceived by others, can in turn influence the physical growth and development of motor
skills.
Growth refers specifically to the increase in physical size of the body.
Development refers to the orderly patterns and levels of functioning associated with
growth.
Norms of Growth To determine whether rate of growth in an individual is proceeding
satisfactorily, physical characteristics such as weight and height are measured
quantitatively in a sample of the population at different ages to establish norms.
normative data indicate that while males and females grow at a similar rate in infancy and
childhood, an adolescent growth spurt occurs in girls about two years earlier than it
occurs in boys.
Patterns in Body Growth The rate of growth for various body systems differs and
depends on the functional importance of the particular system.
the brain grows rapidly early in infancy, whereas maturity of the reproductive system is
delayed until adolescence.
The pattern of development for individual systems of the body is cephalocaudal—parts of
the body near the head grow more rapidly than parts more distant from the head.
proximodistal—parts of the body near the middle develop before those near the
periphery. Considerable variability occurs in the rate of physical growth and development
among individuals within a group as well as among ethnic and cultural groups.
The brain and nervous system
The brain grows rapidly during the prenatal period and continues to grow after birth,
though at a slower rate. Different brain areas grow at different rates; the brainstem and
midbrain are almost complete at birth, while the cerebral cortex continues to develop
postnatally. The brain consists of neurons and glial cells
Parts of many neurons become surrounded by myelin, a sheath of fatty material that
insulates and speeds up neural impulses. Neuron proliferation, neuron migration, and
neuron differentiation are all part of prenatal brain development.
After birth, additional brain development is due largely to neuron differentiation, which
increases the number of connections between neurons. Both the number of neurons and
the density of their synapses with other neurons are probably greater in infancy in many
regions of the brain than at other times in development.
Plasticity in brain development Certain brain areas and the individual neurons within
these areas possess plasticity, the ability of a brain structure to replace the functions
normally controlled by other brain areas should these other areas become damaged. Some
neurons are sensitive to experience-expectant information, such as in the development of
depth or pattern vision in many animals. Other neurons are sensitive to experiencedependent information.
Cognitive neuroscientists utilize a number of different procedures including positron
emission tomography (PET), functional magnetic resource imaging (fMRI), and eventrelated potentials (ERP) to determine which regions of the brain are functioning during
the processing of various kinds of information.
Brain lateralization The cerebral cortex is divided into right and left hemispheres. In
general, each hemisphere has specialized functions. The process by which one
hemisphere dominates the other is called lateralization. For example, in most righthanded people the left hemisphere is especially involved in language, while the right
hemisphere is involved in spatial processing. Studies suggest that infants display
behaviors that indicate lateralization at birth; however, lateralization may increase later in
development.
Motor Skill Development Motor development follows cephalocaudal and proximodistal
patterns.
differentiation and integration of motor abilities occur with development.
The First Actions: Reflexes The earliest movements of the newborn are reflexes,
involuntary responses to environmental stimuli such as touch, sound, and light. Primitive
reflexes are necessary for survival and include reflexes that provide nourishment, such as
rooting and sucking. Postural reflexes maintain body orientation and include stepping and
body righting.
Motor Milestones During the first year of life, infants exhibit rhythmical stereotypies,
repeated sequences of movements that do not appear to be goal directed but may be
integrated into later voluntary behaviors. Directed, voluntary behaviors gradually emerge
in the first year. Some of these behaviors can be described as motor milestones because
they provide the infant with new ways to interact with the environment. Among these are
the ability to maintain postural control and locomotion, including the ability to walk
independently.
Learning about the many objects in the world improves when progress in eye-hand
coordination and prereaching behavior develops into the ability to control objects
manually.
Determinants of Motor Development Evidence consistent with a maturational view of
motor development is suggested by the tendency in all children to undergo predictable
and orderly patterns of motor development. Even developmentally disabled babies
achieve milestones in the same sequence as normal babies, although somewhat more
slowly.
The serious developmental delays seen in institutionalized children who are severely
deprived of experiences with motor activity demonstrate that environmental factors are
also crucial for proper motor development. Some types of experiences may promote the
acquisition of motor milestones.
Cross-Cultural Differences Cross-cultural differences in the onset of motor milestones
may indicate genetic differences as the source of cultural dissimilarities in motor
development. However, differences in child rearing across cultures cannot be ruled out as
a contributor to such cultural dissimilarity.
Sleep Infants display a wide variety of behavioral states: regular and irregular sleep,
drowsiness, alert inactivity, and crying. But it is sleep that is usually of greatest concern
to parents. Part of the process of physical development includes changes in sleep patterns
that bring the cycles of infants and caregivers into alignment with each other.
Patterns of Sleep Although individual differences are great, newborns average sixteen
to seventeen hours of sleep a day. Sleep and wake cycles are short, and babies are easily
disrupted by external stimulation. Over time, patterns shift so that infants are sleeping
less, but for longer periods of time.
sleep patterns differs across cultures--- industrialized countries, babies are often sleeping
through the night by three to four months. In cultures such as the Kipsigi of Kenya,
infants are permitted more flexibility and do not sleep through the night until much older.
Infants (even before birth) display two distinct sleep states, REM and NREM. As a
newborn the infant spends about eight in sixteen hours of sleep in REM, but adults spend
only two in seven hours of sleep in REM.
It is not clear whether young infants dream; however, REM sleep is believed to be
important for normal brain activity. Autostimulation theory proposes that REM sleep
provides powerful stimulation to the central nervous system, compensating for the
relatively brief number of hours each day the infant is awake.
Sleeping Arrangements Where should infants sleep? Historically, and in most cultures
today (such as Japan), infants and mothers sleeping together (co-sleeping) is the norm.
American mothers typically justify putting very young children in a separate room as a
way to encourage self-reliance and independence. Even so, co-sleeping has become more
common in American households with forty-seven percent of mothers in a recent survey
reporting sharing a bed either sometimes or frequently.
In co-sleeping arrangements, mothers and infants engage in greater synchronized sleep,
protecting infants from apnea, potentially reducing the risk of unexplained deaths. Other
research suggests that co-sleeping can put an infant at risk for death, especially if the
infant is younger than 11 weeks of age. The American Academy of Pediatrics does not
recommend bed sharing with infants.
Research Applied to Parenting: Reducing Sudden Infant Death Syndrome
The ability to modify reflexes and integrate them with voluntary motor skills is an
important developmental process. Sudden infant death syndrome (SIDS), the abrupt,
unexplained death of an otherwise healthy infant, may be a result of an unsuccessful
integration of reflexive and voluntary control of breathing. Although no single cause has
been identified, several factors have been correlated with SIDS. The steps parents can
take to help reduce the likelihood of SIDS include placing the infant on his or her back or
side to sleep, eliminating exposure to cigarette smoke, providing firm bedding and good
ventilation, and breast feeding, along with timely immunizations. Some researchers also
suggest that having the infant sleep in the same room as the caregiver during the first few
months of development also helps reduce the risk of SIDS.
Basic Learning Processes Developmental psychologists have found evidence for a
number of basic learning processes in early infancy and childhood.
Habituation--the gradual decline in responding following repeated occurrences of the
same stimulus. When a response reoccurs after a change in the familiarized stimulus, an
individual is displaying recovery from habituation, or dishabituation. Nearly all infants
demonstrate habituation, but premature, brain-damaged, and younger infants show less
rapid habituation and less rapid recovery from habituation than older, more mature
infants.
Imitation--the process where infant repeats a response that another individual, the model,
has made.
Some researchers have reported that one- or two-day-old newborns can imitate facial
expressions. Even before one year of age, the infant demonstrates deferred imitation, the
ability to imitate a model’s behavior hours, days, or even weeks later. After one year of
age, they also differentiate behaviors that are intentional compared to those that are
unintentional.
Sensory Capacities
Sensation refers to the basic units of information recorded by a sensory receptor and the
brain.
Perception refers to the process of organizing and interpreting sensations.
Vision The human infant is an active perceiver of the visual information in the
environment. Visual accommodation is the process whereby the lens changes its shape so
that objects at different distances from the eye can be brought into focus on the retina.
Newborns have limited accommodation and best discriminate objects located
approximately 8–20 inches away.
Smooth visual pursuit consists of following a slowly moving target with smooth,
continuous movements of the eyes. By six to eight months of age, this capacity appears
adultlike.
How well an infant can see is determined by measures of visual acuity, the ability to
make discriminations among contours, borders, and edges in the visual array. Visual
acuity improves rapidly in the first six months after birth.
Kinetic cues are helpful in identifying objects. Three-month-olds (but not newborns) will
perceive a partially occluded object as a unified whole if the visible pieces of the object
are seen moving together. Kinetic cues are also used in the perception of biological
motion. When a pattern of lights simulates a person walking, five-month-olds (but not
three-month-olds) seem to give special meaning to this pattern.
By three months of age, and possibly before, infants possess adultlike color vision.
Visual information processing in infants under two months of age is governed primarily
by relatively simple elements such as contours, angles, and motion. After two months of
age, scanning becomes more systematic
The ability to perceive depth is partly a result of binocular vision, the reception of slightly
different visual inputs by the two eyes. Studies using the visual cliff have found that
infants who are able to crawl usually will not crawl to the deep side of the cliff.
Audition Babies begin responding to sound stimuli several weeks before birth.
newborns prefer sounds they heard prenatally. Prenatal familiarity helps to explain why
newborns prefer to listen to a recording of their mothers’ voices rather than to a
stranger’s voice.
Deafness and hearing disabilities strike one to three of every thousand infants.
Although infants can detect sound before birth, their hearing improves after birth.
Newborns display sound localization, the ability to locate a sound by turning the head or
eyes in the direction of the sound; less precise in locating the position of a noise than
children or adults.
Infants under six months have the perceptual capacities to discriminate the basic
distinctive speech sounds called phonemes in any of the hundreds of languages spoken
around the world. Theoretical accounts of these findings suggest that infants either are
born with a “speech module,” an innate capacity to detect and process speech sound, or
make use of general auditory capacities and quickly learn to use these abilities to process
speech sounds.
Infants as young as one month demonstrate categorical perception for many speech
sounds. by about one year of age, infants who have not heard certain phonemes in their
language environment lose the ability to perceive them.
Smell, Taste, and Sensitivity to Pain Newborns can detect many odors, as measured by
their facial expressions in response to odor stimuli. By five days of age, breast-fed infants
prefer their own mothers’ breast pads over other mothers’ breast pads.
Infants respond differentially to taste stimuli shortly after birth, Innate taste preferences
may help infants meet nutritional needs and avoid harmful substances.
Stimulation of the skin of newborns elicits a variety of reflexes. Regulating their body
temperature is difficult because newborns cannot sweat.
Traditionally, newborns and very young infants have seldom received medication to
reduce pain. Infants were thought not to experience pain or to remember it if experienced.
Research indicates, however, that the neurological mechanisms for detecting pain
develop early, and behavioral responses suggest sensitivity to pain, and even some
memory of it, in young infants.
Atypical Development: Visual Problems in Infancy
Approximately 1 in 10,000 babies are born with cataracts, which is a clouding of all or part of the
eye that impairs the ability to see patterned stimuli. Cataracts can impair the baby’s visual acuity
as well as other visual abilities. In addition, as many as 5 percent of infants have amblyopia, or
“lazy eye.” This results in the failure of vision to develop in one because of suppression of visual
input by the other eye. A common cause of amblyopia is strabismus, which is the inability of the
two eyes to display vergence. Infants and children with strabismus may appear “cross-eyed.”