1. PSYC 50
SECTION 3: INFANCY
Chapter 5: Physical Development in Infancy
PHYSICAL GROWTH AND DEVELOPMENT IN INFANCY
Cephalocaudal and Proximodistal Patterns
o Cephalocaudal pattern: the sequence in which the
earliest growth always occurs at the top—the head—
with physical growth in size, weight, and feature
differentiation gradually working from top to bottom.
o Proximodistal pattern: the sequence in which growth
starts at the center of the body and moves toward the
Height and Weight
o The average North American newborn is 20 inches
long and weighs 7 ½ pounds.
o 95% of full term newborns are 18-22 inches long and
weigh between 5 ½ and 10 pounds.
o In the first several days of life, most newborns lose 5-
7% of their body weight. Once they adjust to sucking,
swallowing, and digesting, they grow rapidly, gaining
an average of 5-6 ounces per week during the 1st
o Doubled their birth weight by the age of 4 months and
have nearly tripled it by 1st birthday.
o Grow 1 inch per month during 1st
o Rate of growth is slower in the 2nd year.
o 2 years – 26 to 32 pounds, reached 1/5 of adult
o 2 years – 32 to 35 inches in height, nearly half of adult
o Neuron: nerve cell that handles information
processing at the cellular level.
o The Brain’s Development
Because the brain is still developing so rapidly in infancy,
the infant’s head should never be shaken.
Shaken baby syndrome – includes brain
swelling and hemorrhaging.
At birth, brain is about 25% of its adult
2nd birthday, 75% of adult weight
Myelin sheath – insulates nerve cells and
also helps nerve impulses travel faster.
Myelination –the process of encasing axons
with fat cells, begins prenatally and
continues after birth.
Myelination for visual pathways,
completed in 1st 6 months. Auditory
myelination, until 4 or 5 years of age. Some
continue even into adolescence.
One of the most dramatic changes in the 1st
2 years of life is the spreading connections
of dendrites to each other.
Another important aspect at the cellular
level is the dramatic increase in
connections between neurons.
Synapses – tiny gaps between neurons
where chemical interactions connect axons
and dendrites, allowing information to pass
from neuron to neuron.
Using the electroencephalogram (EEG),
which measures the brain’s electrical
activity, researchers have found that a
spurt in EEG activity occurs at about 1 ½ to
2 years of age. Other spurts seem to take
place at about 9, 12, 15, and 18 to 20 years.
Spurts of brain activity may coincide with
important changes in cognitive
Charles Nelson (1999, 2003), by attaching
up 128 electrodes to a baby’s scalp, he has
found that even newborns produce
distinctive brain waves that reveal they can
distinguish their mother’s voices from
another woman’s even while they are
o Brain’s Lobes and Hemispheres
Forebrain, the highest level of the brain.
Consists of a number of structures,
including the cerebral cortex-80% of the
brain’s volume and covers the lower
portions of the brain.
Cerebral cortex – perception, language,
The cerebral cortex is divided into 2 halves,
or hemispheres. Each hemisphere is divided
into 4 main areas called lobes:
Frontal – voluntary movement and thinking
Occipital – vision
Temporal – hearing
Parietal – processing information about
Lateralization – specialization of function in
one hemisphere of the cerebral cortex or
o Early Experience and the Brain
Neural connections are formed early in life.
The infant’s brain literally is waiting for
experiences to determine how connections
are made. Before birth, it appears that
genes mainly direct how the brain
establishes basic wiring patterns.
Neurons grow and travel to distant places
awaiting further instructions.
After birth, environmental experiences
guide the brain’s development.
Newborns sleep 16-17 hours a day, although some sleep more
and others less. The range is from about 10 hours to about 21
hours, and the longest period of sleep is not always between
11PM and 7AM.
o REM Sleep
Half of an infant’s sleep is REM sleep, and
infants often begin their sleep cycle with
REM sleep rather than non-REM sleep.
3 months-time spent in REM sleep falls to
40%, and REM sleep no longer begins their
REM sleep might promote the brain’s
development in infancy.
Infants sleep far more than children and
adults, and a much greater amount of time
is taken up by REM sleep in infancy that at
any other point in the life span.
o Shared Sleeping
Sharing a bed with a mother is a common
practice in many cultures, whereas in
others, newborns sleep in a crib, either in
the same room as the parents, or in a
Some child experts believe that shared
sleeping is beneficial, promoting breast
feeding, responding more quickly to the
baby’s cries, and detecting potentially
dangerous breathing pauses in the baby.
American Academy of Pediatrics Task Force
on Infant Positioning and SIDS (AAPTFIPS)
(2002) discourages shared sleeping.
Sudden Infant Death Syndrome – a
condition that occurs when an infant stops
breathing, usually during the night, and
suddenly dies without an apparent cause.
It is recommended that the infant’s
bedding provide firm support and cribs
should have side rails.
Highest cause of infant death in the US
with nearly 3,000 infant deaths annually
attributed to SIDS.
Risk is highest at 4-6 weeks of age.
Since 1992, the AAP has recommended
that infants be placed to sleep on their
backs to reduce the risk of SIDS.
In addition to sleeping in a prone position, researchers have found that the
following are risk factors for SIDS:
Low birth weight infants are 5 to 10 times more likely to die of
Infants whose siblings have died of SIDS are 2-4 times as likely to
die of it.
6% of infants with sleep apnea, a temporary cessation of
breathing in which the airway is completely blocked, usually 10
seconds or longer, die of SIDS.
More common in lower socioeconomic status.
More common in infants who are passively exposed to cigarette
More common if infants sleep in soft bedding.
o Nutritional Needs and Eating Behavior
From birth to 1 year, human infants nearly
triple their weight and increase their length
Nutritionists recommend that infants
consume approximately 50 calories/day for
each pound they weigh.
Scheduled feeding versus demand feeding
Does the same type of nutrition that makes
us healthy adults also make young infants
For growing infants, high-calorie, high-
energy foods are part of a balanced diet.
French fries were the most common
vegetables the babies ate.
o Breast versus Bottle Feeding
Human milk or an alternative formula is the
baby’s source of nutrients and energy for
the first 4 to 6 months of life.
The growing consensus is that breast
feeding is better for the baby’s health.
Which women are least likely to breast
feed? They include mothers who work full
time outside of the home, under age 25,
without a high school education, African
American mothers, and mothers in low-
Intervention – counseling focused on the
benefits of breast feeding; free loan of a
Circumstances when mothers should not
1. Infected with AIDS or some other
infectious disease that can be
transmitted through her milk.
2. Active tuberculosis
3. 3. Taking any drug that may not be safe
for the infant.
What are some of the benefits of breast feeding?
They include these benefits during the first two years of life and later:
Appropriate weight gain and lowered risk of childhood obesity.
Prevention or reduction of diarrhea, respiratory infections (such
as pneumonia and bronchitis), bacterial and urinary tract
infections, and otitis media (a middle ear infection).
Denser bones in childhood and adulthood.
Reduced childhood cancer and reduced incidence of breast
cancer in mothers and their female offspring.
Lower incidence of SIDS
Improved neurological and cognitive development
Improved visual acuity
o Malnutrition in Infancy
Marasmus: a wasting away of body tissues
in the infant’s first year, caused by severe
Kwashiorkor: a conditioned caused by a
deficiency in protein in which the child’s
abdomen and feet become swollen with
water; usually appears between 1 to 3
years of age.
o The ability to control elimination depends on both
muscular maturation and motivation.
o Many toddlers are physically unable to control
elimination at 2 years of age. When toilet training is
initiated, it should be accomplished in a warm,
relaxed, supportive manner.
Dynamic Systems Theory: the perspective on motor development
that seeks to explain how motor behaviors are assembled for
perceiving and acting.
o In order to develop motor skills, infants must perceive
something in the environment that motivates them to
act and use their perceptions to fine-tune their
o When infants are motivated to do something, they
create a new motor behavior to complete the new
desired act. The new behavior is the result of many
1. The development of the nervous system and the
body’s physical properties, including its
possibilities for movement
2. The goal the child is motivated to reach.
3. The environmental support for the skill.
o Infants explore and select possible solutions to the
demands of the new task; they assemble adaptive
patterns by modifying their current movement
Reflexes are built-in reactions to stimuli; they govern the
newborn’s movements, which are automatic and beyond the
o Sucking reflex – occurs when newborns automatically
suck an object placed in their mouth. This enables
newborns to get nourishment before they have
associated a nipple with food.
o Rooting reflex – occurs when the infant’s cheek is
stroked or the side of the mouth is touched. In
response, the infant turns his head toward the side
that was touched in an apparent effort to find
something to suck.
o Moro reflex – a neonatal startle response that occurs in
reaction to a sudden, intense noise or movement.
When startled, the newborn arches its back, throws its
head back, and flings out its arms and legs. Then the
newborn rapidly closes its arms and legs to the center
of the body.
o The moro reflex is believed to be a way of grabbing for
support while falling.
o Grasping reflex – occurs when something touches the
infant’s palms. The infant responds by grasping tightly.
Reflex Stimulation Infant’s Response Developmental
Flash of light,
puff of air
Sole of foot
noise or being
or side of
face down in
Closes both eyes
Fans out toes, twists
Startles, arches back,
throws head back,
flings out arms and legs
and then rapidly closes
them to center of body
Turns head, opens
mouth, begins sucking
Moves feet as if to walk
Forms fists with both
hands and usually turns
head to the right
9 months-1 year
Weakens after 3
Gross Motor Skills: motor skills that involve large-muscle
activities, such as walking.
o The Development of Posture
Within a few weeks, can hold their heads
erect, and soon they can lift their heads
By 2 months, babies can sit while supported
on a lap or an infant seat
6 or 7 months, can sit independently
1st year, standing develops gradually
4. 8 months, learn to pull themselves up and
hold on to a chair.
10 – 12 months, can stand alone
o Learning to Walk
Walking upright requires balancing on one
leg while swinging the other leg forward
and simultaneously shifting the weight from
one leg to the other.
If infants can produce forward stepping
movements so early, why does it take them
so long to learn to walk? Because the key
skills in learning to walk require so many
concurrent movements, infants need about
a year to solve this difficult biomechanical
o Development in the Second Year
Become more motorically skilled and
mobile. No longer content with being in a
playpen, they want to move all over the
Pediatricians also recommend that exercise
for infants should not be of the intense,
aerobic variety. Babies cannot adequately
stretch their bodies to achieve aerobic
o Cultural Variations in Guiding Infant’s Motor
Jamaican mothers regularly massage their
infants and stretch their arms and legs; this
practice is linked to advanced motor
Mothers in the Gusii culture of Kenya also
encourage vigorous movement in their
Algonquin infants in Quebec, Canada, spend
much of their first year strapped to a
Fine Motor Skills: motor skills that involve more finely tuned
movements, such as finger dexterity.
o A significant achievement in their interactions with
their surroundings comes with the onset of reaching
SENSORY AND PERCEPTUAL DEVELOPMENT
What Are Sensation and Perception
o Sensation: the product of interaction between
information and the sensory receptors—the eyes, ears,
tongue, nostrils, and skin.
o Perception: the interpretation of what is sensed.
The Ecological View
o Ecological view: the view that perception functions to
bring organisms in contact with the environment and
to increase adaptation.
o Affordances: opportunities for interaction offered by
objects that are necessary to perform functional
o Visual preference method: a method used to
determine whether infants can distinguish one
stimulus from another by measuring the length of time
they attend to different stimuli.
In Robert Fantz (1963) experiment, infants
preferred to look at patterns rather than at
color or brightness. Fantz used a looking
chamber to study infant’s perception on
o Habituation: decreased responsiveness to a stimulus
after repeated presentation of the stimulus.
o Dishabituation: recovery of a habituated response
after a change in stimulation.
o Tracking: a technique to determine if an infant can see
or hear. Newborns typically turn their eyes and heads
in the direction of an interesting sound or sight,
especially the human voice and face.
o Equipment: videotape equipment allows the
researchers to investigate elusive behaviors.
o Visual perception
Visual acuity and color
Newborns cannot see small
things that are far away. The
newborn’s vision is estimated to
be 20/600 on the well-known
Snellen chart. In other words, an
object 20 feet away is only as
clear to the newborn as it would
be if it were 600 feet away from
an adult with normal vision
By 6 months, vision is 20/100 or
better, and by about the 1st
birthday, the infant’s vision
approximates that of an adult.
At birth, babies can distinguish
between green and red. Cones
are present by 2 months.
What does the world look like to
Perceptual constancy: in which sensory
stimulation is changing but perception of
the physical world remains constant.
Size constancy: the recognition
that an object remains the same
even though the retinal image of
the object changes.
Shape constancy: the recognition
that an object’s shape remains
the same even though its
orientation to us changes.
An important contributor to
depth perception is binocular
vision, which involves the fact
that we have two eyes separated
by several inches that give us
slightly different views of the
Newborns do not have binocular
vision; it develops at about 3 to 4
months of age.
Infants not only see forms and
figures at an early age but also
develop expectations about
future events in their world by
5. the time they are 3 months of
During the last two months of pregnancy,
the fetus can hear sounds as it nestles in its
mother’s womb: It hears the mother’s
voice, music, and so on.
o Touch and pain
Newborns do respond to touch.
Newborns can differentiate odors.
Sensitivity to taste might be present even
Intermodal Perception: the ability to relate and integrate
information from two or more sensory modalities, such as vision
o In one study, as early as 3 ½ months old, infants looked
more at their mother when they also heard her voice
and longer at their father when they also heard his
o Thus, babies are born into the world with some innate
abilities to perceive relations among sensory
modalities, but their intermodal abilities improve
considerably through experience.
o Locomoting in the environment teaches babies about
how objects and people look from different
perspectives, or whether surfaces will support their
weight. Individuals perceive in order to move and
move in order to perceive. Perceptual and motor
development do not occur in isolation from one
another but instead are coupled.
1. What three pieces of advice about the infant’s physical
development would you want to give a friend who has just had a
baby? Why those three?
2. How much sensory stimulation should caregivers provide for
infants? A little? A lot? Could an infant be given too much sensory
Santrock, J.W. (2006). Life-Span Perspective.10th Edition. McGraw-Hill. New York.
Mrs. Maria Angela L. Diopol