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.

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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 .

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LO1 Physical Growth and Development

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Sequences of Physical Development

• • •

CEPHALOCAUDAL

– The head doubles in length between birth and maturity.

DEVELOPMENT – The torso, arms, and legs increase in length by ages 3, 4, 5 respectively.

PROXIMODISTAL

legs can develop.

DEVELOPMENT – Growth proceeds from trunk outward.

– Nerves must be in place before control of arms and – 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 2 nd year • Height increases by 50% during first year – Grow 4 to 6 inches during 2 nd 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 iron fortified 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

Baby needs calories and some fat for growth.

over-restrict fat and cholesterol. 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

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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

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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 visual motor coordination – 3-4 months • • Begin to make clumsy attempts to swipe at objects

Ulnar grasping

no thumbs : hold objects with fingers and palm only; – 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 areas in cortex.

differentiation

of motor – 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

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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 • 1 month – 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).

Figure 5.7 – Preferences for Visual Stimuli in 2-Month-Olds

Figure 5.8 – Eye Movement of 1- and 2 Month-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

Development in Perceptual – 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.