Infancy: Physical
Development
Growth and Stability: Physical Growth
Over the first 2 years of a
human’s life, growth occurs at a
rapid pace.
Average birth weights
(progression through the 1st 2 years)
--By
age 5 months, the average infant's birthweight
has doubled to about 15 pounds.
--By age 1, the infants' birthweight has tripled to
approximately 22 pounds.
--By the end of its second year, the average child
weighs four times its birthweight.
--By age 1, the average baby stands 30 inches tall.
--By the end of the second year the average child is
three feet tall.
Decreasing Proportions…
At birth, the head is ¼ of the neonate’s body. By
adulthood, it is only 1/8th the size of the body.
 Not all parts of the body grow at the same rate.
The 4 Major Principles Governing Growth

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.

2) The PROXIMODISTAL PRINCIPLE states that
development proceeds from the center of the body
outward.

The PRINCIPLE OF HIERARCHICAL
INTEGRATION states that simple skills typically
develop separately and independently but are
later integrated into more complex skills.

The PRINCIPLE OF INDEPENDENCE OF
SYSTEMS suggests that different body systems
grow at different rates.
Maturation Rates
Different body systems mature at different rates.
For instance, the nervous system is highly developed during
infancy.
The nervous system comprises the brain and the nerves that extend
throughout the body.
 Infants are born with between 100 and 200 billion
NEURONS ( the nerve cells of the nervous
system).
 As the infant's experience in the world increases,
neurons that do not become interconnected
become unnecessary and die off.
The Neuron
The basic
element of the
nervous system
More About Neurons…
-- Neurons increase in size.
-- Neurons become coated with MYELIN, a fatty
substance that helps insulate neurons and speeds
transmission of nerve impulses.
-- The brain is made up of neurons, and triples its
weight in the first two years of life.
The infant's brain is 3/4 its adult size by age two
More About Neurons…
* As they grow, neurons become arranged by function.
* Some move into the CEREBRAL CORTEX, the upper layer of
the brain.
* Others move to subcortical levels, which regulate fundamental
activities such as breathing and heart rate (and are below
the cerebral cortex).
Networks of neurons become more complex
over the first few years of life.
Neuron Networks
Brain development occurs because of genetic
patterns and environmental influences.
PLASTICITY is the degree to which a developing
structure (e.g., the brain) or behavior is
susceptible to experience
The brain is relatively plastic
-- Infants who grow up in severely restricted
environments are likely to show differences
in brain structure and weight.
(brain development, continued)
-- 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.
Development of Body Rhythms
One of the major body rhythms is an infants state
-- An infant's STATE is the degree of awareness it displays
to both internal and external stimulation.
-- Includes various levels of wakeful behaviors (alertness,
crying, etc.) and various levels of sleep (active, quiet)
-- Changes in state are reflected in brain waves measured
by a device called an EEG, or electroencephalogram.
The major state occupying the infant is sleep.

On average, newborns sleep 16-17 hours
daily, ranging from 10-20 hours a day.

Sleep stages are fitful and "out of sync" during
early infancy.

By the end of the first year most infants are
sleeping through the night.
The Infant’s Cycle of Sleep
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 is associated with dreaming).

Brain waves are different than the dreaming sleep of adults.

This active REM-like sleep takes up half an infants sleep at first.

Researchers think the function of REM sleep in infants is to
provide a means for the brain to stimulate itself (autostimulation).
Motor Development
 Basic REFLEXES, unlearned, organized, involuntary
responses that occur automatically in the presence of
certain stimuli, represent behavior that has survival value
for the infant.

swimming reflex

eye blink reflex
More about reflexes in motor development…

Some reflexes stay throughout life; others disappear over time.

Some researchers believe reflexes stimulate the brain toward
development.

Reflexes are genetically determined and universal and may be
remnants from the past.

Reflexes can serve as helpful diagnostic tools for pediatricians
because they appear and disappear on a regular timetable
Gross Motor Skills
(rolling over, sitting upright, walking)

By 6 months infants can move by themselves.

Most can sit unsupported by 6 months

Crawling appears between 8-10 months.

Infants can walk holding on to furniture by 9
months and most can walk alone by 1 year.
Fine Motor Skills
(coordination, sophistication)

By 3 months infants can coordinate
movements of limbs.

Infants can grasp an object by 11 months.

By age 2, infants can drink from a cup
without spilling.
Milestones of
Motor
Development
50% of children are
able to perform
each skill at the
month indicated,
but the specific
timing varies
widely!
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.
(Norms are based on scales developed by
developmental psychologists & pediatricians)
A common technique to determine infants’
normative standing:
BRAZELTON NEONATAL BEHAVIORAL ASSESSMENT
SCALE (NBAS)
 NBAS is a measure used to determine infants'
neurological and behavioral responses to their
environment.
a. supplements the Apgar
b. 27 categories of responses
c. interactions with others
d. motor behavior
e. physiological control
f. response to stress
More about norms

Norms should be based on large,
heterogeneous samples.

The time at which specific motor skills
appear is in part determined by cultural
factors.

There are certain genetic constraints on how
early a skill can emerge
Nutrition in Infancy Fuels Motor
Development
Nutrition during infancy is extremely
important. Without proper
nutrition, infants cannot reach
their physical potential and also
may suffer cognitive and social
consequences.
Malnutrition & It’s Effects
Malnutrition, the condition of having an improper
amount and balance of nutrients produces
several results.
--slower growth
--susceptibility to disease
--lower IQ scores
Malnutrition & It’s Effects, continued
--Malnutrition can also cause MARASMUS, a
disease characterized by the cessation of
growth in infants.
--Older children are susceptible to
KWASHIORKOR, a disease in which a
child's stomach, limbs, and face swell with
water.
 Risks of malnutrition are greater
in underdeveloped countries and
in areas with high poverty rates.
 Undernutrition is more common
in developed countries
(deficiency in the diet).
Nutrition as Fuel for Motor Development: Breast or Bottle??
For the first four to six months of life there is no better food for an
infant than breast milk! Why?
all essential nutrients
b. natural immunity to childhood diseases
c. more easily digested
d. health advantages for mother (lower cancer)
e. emotional advantages for both mother and child
f.
bonding?
In spite of this, only half of mothers in U.S. breast-feed
a.
Breast Milk Advantages
Introducing Solid Foods
Most babies can begin to eat solid foods at
about 4-6 months.

Foods are introduced gradually.

Weaning, the cessation of breast-feeding, occurs on
average in the U.S. at 3-4 months.
Experts recommend infants be breast-fed for
6-12 months.
Development of the Senses
Infants come to understand the world around them
through sensation & perception

SENSATION is the stimulation and responsiveness
of the sense organs.

PERCEPTION is the sorting out, interpretation,
analysis, and integration of stimuli involving the
sense organs and brain.
Visual Perception: Seeing the World


Newborn infants cannot see beyond a distance of 20
feet.
By 6 months, the average infant's vision is 20/20.
Binocular vision, the ability to combine both eyes' vision to
see depth and motion is achieved at 14 weeks.

Gibson's "visual cliff" experiments showed that most
infants between 6-14 months would not crawl over the
apparent cliff .

The “visual cliff” experiment examines the depth
perception of infants

Infants show clear visual preferences that are
present at birth

Infants prefer to look at patterns and complex stimuli.

Infants prefer to look at faces.

Minutes after birth they show a preference for certain
colors, shapes, configurations
May support the existence of specialized brain cells
(genetic influence on visual preferences)—but
environmental influences too.
Auditory Perception: The World of Sound

It is clear that infants hear from the time
they are born—and even before!
(prenatally)

Infants are more sensitive than adults to
high and low frequencies but not to the
middle ranges.

Sound localization permits infants to discern
direction from which a sound is emanating.

This skill is poorer in infants than adults
because of infants' smaller heads.

It reaches adult level at 1 year.

Infants can differentiate changes in melodies
and sounds - a requirement for language - and
their mother's voice from other voices
Smell and Taste in Infancy

Infants react to unpleasant tastes and smells
from birth.

Newborns can detect their mother's smell, but
only when breastfed.

Infants have an innate sweet tooth.
Sensitivity to Pain and Touch

Infants are born with the capacity to feel pain.

Touch is one of the most highly developed
sensory systems in a newborn.

The rooting reflex is strong.

Infants gain information about the world through touch.

Even the youngest infants respond to gentle touches and
are calmed by them
Initially, information is collected and interpreted by individual
sensory systems, but…
Eventually infants use the MULTIMODAL
APPROACH TO PERCEPTION in which
information collected by various individual sensory
systems is integrated and coordinated.
This approach is evidence of the sophisticated
perceptual abilities of infants (combining sensory
inputs)
 The infants growing perceptual ability is aided
by the development of affordances (action
possibilities connected to a situation or
stimulus).
 Example:
Julissa learns that her toy truck has
several affordances: It can be grabbed and
squeezed, chewed, thrown across the room at
the cat, etc.)