Transcript Infancy: Physical Development

CHAPTER 5
Infancy: Physical
Development
Learning Outcomes
LO1 Discuss tendencies in physical
growth in infancy.
LO2 Examine the development of the
brain and neurons in infancy.
LO3 Describe motor development in
infancy.
LO4 Discuss sensory and perceptual
development in infancy.
© Botanica/Jupiterimages
TRUTH OR FICTION?
• T F
The head of the newborn child doubles in
length by adulthood, but the legs increase in length
by about five times.
• T F
Infants triple their birth weight within a year.
• T F
A child’s brain reaches half its adult weight
by the age of 1 year.
• T F
The cerebral cortex—the outer layer of the
brain that is vital to human though and reasoning—is
only 1/8 inch thick.
• T F
Native American Hopi infants spend the first
year of life strapped to a board, yet they begin to
walk at about the same time as children who are
reared in other cultures.
© iStockphoto.com
LO1 Physical Growth and
Development
© Botanica/Jupiterimages
Sequences of Physical Development
• CEPHALOCAUDAL DEVELOPMENT
– The head doubles in length between birth and
maturity.
– The torso, arms, and legs increase in length by
ages 3, 4, 5 respectively.
• PROXIMODISTAL DEVELOPMENT
– Growth proceeds from trunk outward.
– Nerves must be in place before control of arms and
legs can develop.
– Infants gain control over trunks and shoulders prior
to arms, hands, and fingers; also hips and upper
legs come before lower legs, feet and toes
• DIFFERENTIATION
– As baby matures, physical reactions become more
specific.
Growth Patterns in Height and Weight
• Infants grow in spurts; 90-95% of time they are
not growing at all
• Infants double birth weight in about 5 months
and triple it by the first birthday
– Gain 4 to 7 pounds during 2nd year
• Height increases by 50% during first year
– Grow 4 to 6 inches during 2nd year
• Boys reach half adult height by 2nd birthday.
• Girls reach half adult height by 18 months.
Figure 5.1 – Growth Curves for Weight and
Height (Length) from Birth to Age 2 Years
Changes in Body Proportions
• Adult’s arms are nearly 3 times the length of
the head; legs 4 times as long.
• Neonates arms and legs are equal in length.
– Each are about 1.5 times length of head.
• Neck lengthens by first birthday.
• Arms grow more rapidly
than the legs at first.
– By 2nd birthday, arms are
longer than legs.
– But soon catch up and
surpass arms in length
© Barbara Penoyar/Getty Images
Failure to Thrive
• Defined as:
– A serious disorder impairing growth in
infancy and early childhood
– Infant does not make normal gains in
weight and size; also shows cognitive,
behavioral, & emotional problems (often
persists into older childhood)
– Feeding problems are central; infants often
described as “variable eaters”
• Biologically based: “organic”
– Caused by underlying health problems
• Non-biologically based: “non-organic”
– Based in psychological and/or social roots
Catch-up Growth
• Factors such as illness and malnutrition
can slow course of growth as genetically
predetermined.
• If problems are alleviated, rate of growth
frequently accelerates to normal pattern.
– This return to a genetically determined
pattern of growth is referred to as
canalization.
Nutrition: Fueling Development
• Nutritional needs of children in U.S. is for most
part better than developing countries.
• Infants from low-income families more likely to
display signs of poor nutrition such as anemia
and FTT.
• Infants need to be fed breast milk or ironfortified infant formula.
• Solid foods generally introduced 4–6 months
of age
• American Academy of Pediatrics recommends
infants be fed breast milk for at least the first
year or longer if possible.
• Whole cow’s milk delayed until 9–12 months of
age.
Helpful Hints for Infant Nutrition
1. Build up to a variety of foods. Introduce new
foods one at a time. This helps identify
possible food allergies.
2. Pay attention to baby’s appetite to avoid
over/underfeeding.
3. Do not over-restrict fat and cholesterol.
Baby needs calories and some fat for
growth.
4. Do not overdo high-fiber foods.
5. Generally avoid items with added sugar and
salt.
6. Encourage eating of high-iron foods; infants
need more iron pound for pound than adults.
Breast Feeding versus Bottle Feeding
• Breast milk considered to be the best nourishment for
infants.
• 70% of American mothers now breast feed.
– 2 in 5 after 6 mos / 1 in 5 after 1 yr
• Many mothers bottle
feed when returning to
work due to convenience.
• Some use breast pumps
to store for use when
nursing is not possible.
• Some parents opt for
bottle feeding to allow
fathers to share in feeding.
Advantages to Breast-Milk
(for baby)
•
•
•
•
It conforms to human digestion processes
(less likely to upset baby’s stomach).
Alone, it is adequate for first 6 mos. Other
foods only supplement breast milk for 1st yr.
As infant matures, composition of breast milk
changes to help meet the infant’s needs.
Breast milk contains mother’s antibodies and
helps infant ward off health problems.
Advantages of Breast-Milk
(for baby)
• Breast Milk helps protect against a form of
childhood cancer (lymphoma: cancer of the
lymph nodes).
• Breast milk decreases likelihood of developing
serious cases of diarrhea.
• Infants nourished by breast milk are less likely
to develop allergies and constipation.
• Breast-fed infants less likely to develop
obesity later in life.
• Breast feeding is associated with better neural
and behavioral organization in babies.
Breast Feeding and Moms
• Advantages:
– Reduces risk of early breast and ovarian cancer
– Builds strength of bones; reducing risk of
osteoporosis in menopause
– Helps to shrink uterus after delivery
Breast Feeding and Moms
• Disadvantages:
– Breast milk is a bodily fluid and can transmit HIV
– Alcohol, many other drugs, and environmental
hazards such as PCB’s can also be transmitted via
breast milk
– Breast feeding places higher demands on mother’s
nutrient base; she must stay adequately nourished
herself.
– There is a tendency for soreness in the breasts.
– It can be “inconvenient” and demanding to continue
to meet feeding needs of baby.
LO2 Development of
the Brain and Nervous
System
© Botanica/Jupiterimages
Neurons
• Neurons are the basic building blocks of
the nervous system.
• They receive and send messages from
one part of the body to another.
• People are born with approx. 100 billion,
most in the brain.
• They vary in length from a fraction of an
inch to several feet.
Neurons
• Anatomy of a Neuron:
– Cell Body
• Maintains working order of entire neuron
– Dendrites
• Short root-like fibers receiving incoming
messages
– Axon
• Single threadlike structure that sends outgoing
messages to other neurons
– Neurotransmitters
• Chemical messengers released at end bulbs of
a neuron that transmit information between
neurons
Neurons
• Anatomy of a Neuron (con’t):
– Myelin
• Myelin Sheaths: white fatty segments covering axon
insulating neurons from electrically charged atoms in
surrounding fluids, making transmission more
efficient
• Myelination: process of growth of myelin on axons,
not complete at birth, allows for more advances in
cognitive and motor skills to develop
• Multiple sclerosis
– A disease where the myelin is replaced by hard,
fibrous tissue that disrupts neural transmission
and interferes with muscle control. PKU causes
mental retardation by inhibiting formation of
myelin
Figure 5.2 – Anatomy of a Neuron
Development of the Brain
• Size
– A neonate’s brain weighs a little less than
one pound.
– Nearly 1/4 its adult weight
– It will triple to nearly 70% of its adult
weight by one year.
Figure 5.3 – Growth of Body Systems as a
Percentage of Total Postnatal Growth
Development of the Brain
• Structures of the Brain:
– Medulla
• Area in the brain stem (hindbrain) involved in
heartbeat and respiration
– Cerebellum
• Part of the brain stem (hindbrain) involved in
coordination and balance
– Cerebrum
• Part of brain responsible for learning, thought,
memory, and language
• Consists of two hemispheres (left and right)
• Covered with a surface of tissue about 1/8 inch
thick that develops into fissures (the cerebral
cortex)
Figure 5.4 – Structures of the Brain
Development of the Brain
• Growth Spurts of the Brain
– First major growth takes place in 4th & 5th months
of Prenatal Development
• Due primarily to formation of neurons
– Second spurt occurs between 25th week of
Prenatal Development and the end of the 2nd year
after birth
• Due mainly to proliferation of dendrites and axons
Figure 5.5 – Increase in Neural Connections
in the Brain
Development of the Brain
• Brain Development in Infancy
– Growth in infants is strongly related to the process
of myelination.
– Neonates have certain reflexes but other physical
activities are random and unorganized.
– By age 2, myelination of nerves to muscles become
well developed and affords better motor control
– Myelination of sensory neurons begins around 6th
month of pregnancy and continues to about age 4.
• By 5-6 months after birth, vision becomes the
dominant sense.
Development of the Brain
• Nature and Nurture in Brain Development
– Development of the brain is strongly affected by the
course of natural physical maturation (nature).
– It is also affected by the experiences of the
individual (nurture).
– Infants have more neural connections than adults.
– Connections that are activated by experience
survive; the others do not.
– Dichotomy of Adaptability:
• Adaptability allows development of neural
connections to meet demands of variations in
environments.
• But lack of stimulation, especially during critical
periods, can lead to impairment of neural
connections.
LO3 Motor Development
© Botanica/Jupiterimages
Motor Development
• Involves:
– Activity of muscles and coordination of movements
in conjunction with the infant’s sensory
development
– Like physical growth, motor development follows
the same cephalocaudal and proximodistal
patterns and differentiation
• Control of head and torso comes before arms
(cephalocaudal)
• Control of trunks and shoulders come before
hands and fingers (proximodistal)
Motor Development
• Lifting and Holding the Torso and Head
– Newborns
• Can move head slightly side to side
• Helps avoid suffocation if an obstruction presents itself
– 1 month
• Can raise head
– 2 months
• Can also lift chests while lying on tummy
– 3-6 months
• Generally manage head well without support
– Caution
• Even after attaining ability to support head on own, if lifted
improperly or jerked, neck injuries are possible
Motor Development
• Control of the Hands: “Getting a Grip”
– Voluntary reaching and grasping require visualmotor coordination
– 3-4 months
• Begin to make clumsy attempts to swipe at objects
• Ulnar grasping: hold objects with fingers and palm only;
no thumbs
– 4-6 months
• Begin to grasp but may hold object indefinitely until
attention is diverted or hand accidentally opens
• Can transfer items from one hand to another
– 9-12 months
• Pincer grasping: use of oppositional thumb
– Stacking blocks
• 2 blocks at 15 mos; 3 blocks at 18 mos; 5 blocks at 24
mos
Motor Development
• Locomotion
– Movement from one place to another; ages of
accomplishment vary with individuals but “usually”
follows sequence of development, as in crawling
before walking (some may skip a stage)
Motor Development
• Sequence of Locomotion
– 6 months
• Can roll over (back to tummy and vice versa)
– 7 months
• Begin to sit up alone
– 8-9 months
• Begin to crawl; lie on tummy and use arms to pull
• About a month later begin to creep; up onto hands and
knees
• Standing while holding on to something; rudimentary
walking with support
– 10-11 months
• Can stand briefly without holding on
– 12-15 months
• Begin to walk unaided; earning name of toddler
Figure 5.6 – Motor Development
in Infancy
Toddlers: Nature & Nurture
• Nature (Maturation)
– Provides the limits (reaction range) for the
expression of inherited traits
– As child matures, so does muscle strength,
bone density, balance, and coordination.
– Certain voluntary motor skills not possible
until brain has matured in terms of
myelination and differentiation of motor
areas in cortex.
– By age 2, can run, walk backward, kick, and
jump
Toddlers: Nature & Nurture
• Nurture (Experience)
– Determines if a child will develop skills that reach
upper limits of their range
– Environmental effects on motor skills
• Native American Hopi babies are strapped to a cradle
board first year of life.
– Catch up to walking early in 2nd year
Toddlers: Nature & Nurture
– Environmental effects on motor skills (cont.)
• Identical Twin Study
– One received motor skill training the other none;
trained baby had better skills at first, but untrained
baby soon caught up with equal skills
• Iranian and Lebanese Orphanages
– Iranian infants experiencing severe social & physical
neglect showed significant retardation in motor skill
development
– Children with similar deprivations and results were
shown to make dramatic improvements with minimal
interventions.
LO4 Sensory and
Perceptual Development
© Botanica/Jupiterimages
Sensory and Perceptual Development
• Vision - Sight
– Development of Visual Acuity & Peripheral
Vision
• Newborns
– Extremely nearsighted: acuity about 20/600
– Poor peripheral vision: perception of objects to side
about at 30 degree angle (adults are nearly 90
degrees)
» By 7 wks peripheral expands to about 45 degrees
• 6 months
– Acuity: about 20/50
– Peripheral: about equal to adult
• 3-5 years
– Acuity: approximate adult levels of 20/20 in best cases
Sensory and Perceptual Development
• Vision – Sight, con’t.
– Visual Preferences
• 8-12 weeks
– Distinct preference for curved lines over
straight lines
– Can discriminate mother’s face from a
stranger’s
– Pay most attention to outer “edges”:
peripheral features (chin - ears) rather
than inner ones (nose - eyes)
– Focus more on “where” things are
• 2 months
– Infants fixate significantly longer on the
human face & begin to focus on inner
features more, especially eyes, but also
mouth and nose
– Focus more on “what” things are doing
• “Reading” faces (interpreting facial
expressions) is important to infants
because they do not understand verbal
information communicated through
language (non-verbal communication is
our first language).
© Jarek Szymanski/iStockphoto.com
• 1 month
Figure 5.7 – Preferences for Visual Stimuli in
2-Month-Olds
Figure 5.8 – Eye Movement of 1- and 2Month-Olds
Sensory and Perceptual Development
• Vision – Sight, con’t.
– Development of Depth Perception
• Infants generally respond to depth cues by the
time they are crawling (6-8 mos).
Sensory and Perceptual Development
• Classic Study: The Visual Cliff
– Infants of different ages are tested on a
table-top device that simulates a drop off (or
cliff) of about 4 feet.
– They are encouraged to crawl over the drop
off (which is actually covered by Plexiglas).
– 1 month
» Display no change in heart rate; no fear
or perception of depth
– 2 months
» Show decrease in heart rate; sign of
interest
– 9 months
» Increase in heart rate; fear response to
perception of depth and ability to fall
Figure 5.9 – The Visual Cliff
Sensory and Perceptual Development
• Vision – Sight, con’t.
– Development of Perceptual Constancies
• Perceptual Constancy: the ability to perceive
objects as maintaining their identity although
our senses tell us they are different
© Dmitriy Tereschenko/iStockphoto.com
Sensory and Perceptual Development
– Perceptual Constancies
• Size Constancy: tendency to perceive an
object as being the same size even when retinal
sizes vary according to the distance of the
object
– Infants usually achieve by 2.5-3 months
– Some research indicates even neonates possess
rudimentary size constancy.
• Shape Constancy: tendency to perceive an
object as having the same shape even when
viewing it from another angle
– By 4-5 months, under certain conditions
Sensory and Perceptual Development
• Development of Hearing
– Newborns
• Can turn head in the direction of a sound
• Infants hearing can be quite acute; it is good to
habituate them to a moderate noise level so
they are less likely to waken or startle at
sudden, sharp noises
– 1 month
• Perceive differences between very similar
speech sounds
– 2-3 months
• Can reliably discriminate three-syllable words
Sensory and Perceptual Development
• Development of Hearing (cont.)
– 3.5 months
• Can identify sounds of parent’s voices over
others
– 6 months
• Can screen out meaningless sounds and
variations of their native language
• After exposure to one’s native language, infants
gradually lose the capacity to discriminate
sounds of other languages.
– 18 months
• Accuracy of sound-localizing close to that of
adults
• As infants mature, the range of pitch they can
sense expands to that of adults (20-20,000
cycles per second).
Figure 5.10 – Declining Ability to Discriminate
the Sounds of Foreign Languages
Sensory and Perceptual Development
• Development of Coordination of the
Senses
– Infants can recognize that objects
experienced by one sense (e.g., vision) are
the same as those experienced through
another sense (e.g., touch).
– Studies show infants transfer information
from one sense to another.
• This has been demonstrated in infants as young
as one month of age.
Sensory and Perceptual Development
• The Active/Passive Controversy in Perceptual
Development
– Children develop from passive, mechanical
reactors to the world around them into
active, purposeful seekers and organizers
of sensory information. As they mature:
• Intentional action replaces automatic
“capture” responses to stimuli
• Systematic search replaces
unsystematic; they progressively pay
more attention to details and people
• Attention becomes selective
• Irrelevant information becomes ignored
Sensory and Perceptual Development
• Nature and Nurture in Perceptual Development
– Evidence for Role of Nature
• Newborns come into the world with many
perceptual skills.
• Vision for close objects and can track moving
objects and scan for preferred stimuli
• Hearing is good.
• Sensory changes as with motor changes appear
linked to maturation of nervous system
Sensory and Perceptual Development
• Nature and Nurture in Perceptual Development
– Evidence for Role of Nurture
• Children and lower animals have critical periods
in perceptual development.
• Failure to receive adequate sensory stimulation
during these periods can result in permanent
sensory deficits.
– The final verdict
• Most developmentalists agree Nature AND
Nurture interact to shape perceptual
development.