Chapter 4


Physical Development in Infancy



Chapter Outline



I.        Growth and Stability

A.     Physical Growth:  the Rapid Advances of Infancy

1.      By age 5 months, the average infant's birthweight has doubled to about 15 pounds.

2.      By age 1, the infants' birthweight has tripled to approximately 22 pounds.

3.      By the end of its second year, the average child weighs four times its birthweight.

4.      By age 1, the average baby stands 30 inches tall.

5.      By the end of the second year the average child is three feet tall.

6.      Not all parts of the body grow at the same rate.

7.      The CEPHALOCAUDAL PRINCIPLE states that growth follows a pattern that begins with the head and upper body parts and then proceeds to the rest of the body.

8.      The PROXIMODISTAL PRINCIPLE states that development proceeds from the center of the body outward.

9.      The PRINCIPLE OF HIERARCHICAL INTEGRATION states that simple skills typically develop separately and independently but are later integrated into more complex skills.

10.  The PRINCIPLE OF INDEPENDENCE OF SYSTEMS suggests that different body systems grow at different rates.

B.     The Nervous System and Brain:  The Foundations of Development

1.      The nervous system comprises the brain and the nerves that extend throughout the body.

2.      Infants are born with between 100 and 200 billion NEURONS, the nerve cells of the nervous system.

a)      Neurons communicate with other neurons by means of chemical transmitters that travel across the small gaps between neurons, known as synapses.

3.      As the infant's experience in the world increases, neurons that do not become interconnected become unnecessary and die off – a process called synaptic pruning.

4.      Neurons increase in size.

a)      Neurons become coated with MYELIN, a fatty substance that helps insulate neurons and speeds transmission of nerve impulses.

b)      The brain triples its weight in the first two years of life.

c)      The infant's brain is 3/4 its adult size by age two.

5.      As they grow, neurons become arranged by function.

a)      Some move into the CEREBRAL CORTEX, the upper layer of the brain.

b)      Others move to subcortical levels, which regulate fundamental activites such as breathing and heart rate and are below the cerebral cortex.

6.      PLASTICITY is the degree to which a developing structure (e.g., the brain) or behavior is susceptible to experience and is relatively great for the brain.

a)      Infants who grow up in severely restricted environments are likely to show differences in brain structure and weight.

b)      Research with non-humans reveals that a SENSITIVE PERIOD exists which is a specific but limited time span, usually early in an organism's life, during which the organism is particularly susceptible to environmental influences relating to some particular facet of development.

C.     Integrating the Bodily Systems:  The Life Cycles of Infancy

1.      Behavior becomes integrated through the development of various body RHYTHMS, which are repetitive, cyclical patterns of behavior.

2.      An infant's STATE is the degree of awareness it displays to both internal and external stimulation.

3.      Changes are reflected in brain waves measured by a device called an EEG, or electroencephalogram.

4.      The major state occupying the infant is sleep.

a)      On average, newborns sleep 16 - 17 hours daily, ranging from 10 to 20 hours a day.

b)      Sleep stages are fitful and "out of sync" during early infancy.

c)      By the end of the first year most infants are sleeping through the night for a total of about 15 hours.

d)      Infants have a cycle of sleep similar to but different than REM - RAPID EYE MOVEMENT, the period of sleep found in adults and children and associated with dreaming.

(1)   Brain waves are different than the dreaming sleep of adults.

(2)   This active REM-like sleep takes up half an infant’s sleep at first.

(3)   Researchers think the function of REM sleep in infants is to provide a means for the brain to stimulate itself – a process called autostimulation.

(4)   Cultural practices affect the sleep patterns of infants.

e)      SUDDEN INFANT DEATH SYNDROME (SIDS) is a disorder in which seemingly healthy infants die in their sleep.

(1)   affects 1 in 1,000 infants in the U.S. annually.

(2)   no cause found

(3)   leading cause of death in children under 1 year old

(4)   Boys, African Americans, and low birthweight and low Apgar scorers, and babies whose mothers smoked during pregnancy, babies with certain brain defects, and children who are abused are at higher risk.

II.                 Motor Development

A.     Reflexes:  Our Inborn Physical Skills

1.    Basic REFLEXES, unlearned, organized, involuntary responses that occur automatically in the presence of certain stimuli, represent behavior that has survival value for the infant.

a)      swimming reflex

b)      eye blink reflex

c)      Some reflexes stay throughout life; others disappear over time.

d)      Some researchers believe reflexes stimulate the brain toward development.

e)      Reflexes can serve as helpful diagnostic tools for pediatricians because they appear and disappear on a regular timetable.

f)       Reflexes are genetically determined and universal and may be remnants from the past.

B.     Motor Development in Infancy:  Landmarks of Physical Achievement

1.      Gross Motor Skills

a)      By six months infants can move by themselves.

b)      Crawling appears between 8 and 10 months.

c)      Infants can walk holding on to furniture by 9 months and most can walk alone by 1 year.

d)      Most can sit unsupported by six months.

2.      Fine Motor Skills

a)      By three months infants can coordinate movements of limbs.

b)      Infants can grasp an object by 11 months.

c)      By age two, infants can drink from a cup without spilling.

3.      It is important to keep in mind that developmental NORMS are the average performance of a large sample of individuals of a certain age and mask substantial individual differences.

a)      BRAZELTON NEONATAL BEHAVIORAL ASSESSMENT SCALE (NBAS) is a measure used to determine infants' neurological and behavioral responses to their environment.

(1)   supplements the Apgar

(2)   27 categories of responses

(a)    interactions with others

(b)   motor behavior

(c)    physiological control

(d)   response to stress

b)      Norms should be based on large, heterogeneous samples.

c)      The time at which specific motor skills appear is in part determined by cultural factors.

d)      There are certain genetic constraints on how early a skill can emerge.

C.     Developmental Diversity:  The Cultural Dimensions of Motor Development

1.      The time at which specific motor skills appear is in part determined by cultural factors.

2.      Activities that are intrinsic to a culture are more apt to be purposely taught to infants in that culture, leading to their earlier emergence.

3.      However, there are certain genetically determined constraints on how early a skill can emerge.

D.     Nutrition in Infancy:  Fueling Motor Development

1.      Without proper nutrition, infants cannot reach their physical potential and also may suffer cognitive and social consequences.                                

2.      Malnutrition, the condition of having an improper amount and balance of nutrients, produces several results.

a)      slower growth

b)      susceptibility to disease

c)      lower IQ scores

3.      Risks are greater in underdeveloped countries and in areas with high poverty rates.

4.      Undernutrition is where there is some deficiency in the diet.

5.      Malnutrition can cause MARASMUS, a disease characterized by the cessation of growth in infants.

6.      Older children are susceptible to KWASHIORKOR, a disease in which a child's stomach, limbs, and face swell with water.

7.      In some cases, NONORGANIC FAILURE TO THRIVE is a disorder in which infants stop growing due to a lack of stimulation and attention as the result of inadequate parenting.

8.      There appears to be no correlation between obesity, defined as weight greater than 20 percent above the average for a given height, and later weight at age 16.

9.      For the first four to six months of life there is no better food for an infant than breast milk.

a)      all essential nutrients

b)      natural immunity to childhood diseases

c)      more easily digested

d)      it is sterile, warm, and convenient for mother to dispense

e)      some evidence it may enhance cognitive growth

f)       health advantages for mother

g)      emotional advantages for both mother and child

10.  Only half of mothers in U.S. breast-feed

a)      Issues of age, social status, and race influence the decision to breast-feed.

b)      Infectious disease, or medication may preclude breast-feeding.

c)      Working women find breast-feeding inconvenient.

d)     Lack of education is also an issue.

11.  Most babies can begin to eat solid foods at about 4 - 6 months.

a)      Foods are introduced gradually.

b)      Weaning, the cessation of breast-feeding, occurs on average in the U.S. at 3 to 4 months.

c)      Experts recommend infants be breast-fed for 6 to 12 months.

III.               Development of the Senses

A.     SENSATION is the stimulation of the sense organs.

B.     PERCEPTION is the sorting out, interpretation, analysis, and integration of stimuli involving the sense organs and brain.

C.     Visual Perception:  Seeing the World

1.      Newborn infants cannot see beyond 20 feet.

2.      By 6 months, the average infant's vision is 20/20.

3.      Binocular vision, the ability to combine both eyes' vision to see depth and motion is achieved at 14 weeks.

a)      Gibson's "visual cliff" experiments showed that most infants between 6 and 14 months would not crawl over the apparent cliff .

b)      We do not know how early this depth perception occurs in infancy.

4.      Infants prefer to look at patterns and complex stimuli.

5.      Infants prefer to look at faces.

D.     Auditory Perception:  The World of Sound

1.      The ability to hear begins prenatally.

2.      Infants are more sensitive than adults to high and low frequencies but not to the middle ranges.

3.      Sound localization permits infants to discern direction from which a sound is emanating.

a)      This skill is poorer in infants than adults because of infants' smaller heads.

b)      It reaches adult level at 1 year.

4.      Infants can differentiate changes in melodies and sounds - a requirement for language - and their mother's voice from other voices.

E.      Smell and Taste

1.      Infants react to unpleasant tastes and smells from birth.

2.      Newborns can detect their mother's smell, but only when breastfed.

3.      Infants have an innate sweet tooth.

4.      Infants also develop taste preferences based on what their mothers drank while they were in the womb.

F.      Sensitivity to Pain and Touch

1.      Infants are born with the capacity to feel pain.

a)      There seems to be a developmental progression in reactions to pain.

b)      Research with rats suggests that exposure to pain in infancy may lead to permanent rewiring of the nervous system that results in greater sensitivity to pain during adulthood.

2.      Touch is one of the most highly developed sensory systems in a newborn.

a)      The rooting reflex is strong.

b)      Infants gain information about the world through touch.

c)      Even the youngest infants respond to gentle massages and are calmed by them.

G.     Multimodal Perception:  Combining Individual Sensory Inputs

1.      Eventually infants use the MULTIMODAL APPROACH TO PERCEPTION in which information collected by various individual sensory systems is integrated and coordinated.

2.      Infant’s perceptual growth is aided by AFFORDANCES, the action possibilities that a given situation provides.




Key Terms and Concepts

Cephalocaudal principle

Proximodistal principle

Principle of hierarchical integration

Principle of the independence of systems




Cerebral cortex


Sensitive period



Rapid eye movement (REM) sleep

Sudden infant death syndrome (SIDS)



Brazelton Neonatal Behavioral

Assessment (NBAS)



Nonorganic failure to thrive



Multimodal approach to perception