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Physical Growth and Motor Development

发布时间:2013-11-30 16:01:32  

Physical Growth and Motor

Development

Daniel Messinger

Messinger

Questions

?What is neoteny?

?What is the basic patterns of physical growth in infancy?

?How do genes and environment influence growth? ?What are the differences between individual and group growth curves?

?List some major milestones and range of age of acquisition

?What are some differences in the ordering of these milestones

?What is the sway model?

?How does mastering one milestone influence postural control in another?

Messinger

Infancy is a period of rapid, decelerating physical growth.?Rapid, decelerating growth characterizes

–Head circumference

–Body length

–Weight

Messinger

Head circumference

?An index of brain size

–but not necessarily meaningful for individuals–concernbelow 3rd percentile or above 97th

?Can be used as a predictor of early outcome in premature infants

–at birth and at one month or later corrected age?Its staying the course that its important–allowing for catch-up growth

–reach growth channel by 12 -14 months

–handout

Messinger

Babies have big heads

–Newborn head is 25% of own body length–Head length is 40% of mature length at birth–Adult head is only ~15% of body length

Messinger

Why?

?Why such large heads?

?Why such rapid, early growth in head size??Remember birth video?

Messinger

Neonteny:Mickey has a baby face?Flat with small nose

and cheekbones

?Small lower jaw

?Big cranium and

forehead

Messinger

Neoteny: Holding on to infant-like characteristics

?Neoteny characterizes human body form

–Big heads and faces

?Large eyes

?Smaller muzzle

?Spine attached at base of skull

–Brain continues growth after birth

?Essential constraint in human evolution

Messinger

Neoteny characterizes human behavior

–Late sexual reproduction

–Play and curiosity throughout life span

–Cultural flexibility

Messinger

Nervous system>Size>Sexuality

Messinger

Head growth allows brain growth?Rapid, decelerating growth

?At birth,

–1 lb.

–15% of total body birthweight

–25% of final (adult?s) brain weight

?At 6 months

–50% of final (adult?s) brain weight

Messinger

At the same time -Myelinization ?Fatty sheaths develop and insulate neurons?Dramatically speeding up neural conduction?Allowing neural control of body

–General increase in first 3 years is likely related to speedier motor and cognitive functioning

?allowing activities like standing and walking

?Endangered by prenatal lead exposure

Messinger

Infancy is a period of rapid, decelerating physical growth.?Rapid, decelerating growth characterizes

–Head circumference

–Body length

–Weight

Messinger

Genes and environment

?Body size influenced by multiple genes

–each has a small effect

–some do not function until after birth–when individual differences emerge

?Body size influenced by environment

–nutrition

–uterus can also constrain or promote growth

Messinger

Genes and environment example?Japanese-American infants

–Smaller than European-American infants

?genetics

–But larger than Japanese national infants

?dietary differences

–Higher socioeconomic status

?Taller, heavier kids who grow faster

–Professional 3 year olds: 1/2” taller

?In England

Messinger

Historical increase in body size

?Height of schoolchildren increased .7 cm per decade

–independent of race, sex, and age. Decrease in short children (<10th %ile) Most among preadolescents, blacks, boys, not seen among the 15-to 17-year-old childrenfindings may reflectan acceleration of maturation.

?24,070 5-to 17-year-oldchildren between 1973 and 1992 (Bogalusa,La)

–“Secular trend”

?David S. Freedman; Laura Kettel Khan; Mary K. Serdula; Sathanur R. Srinivasan; Gerald S. BerensonSecular Trends in Height Among Children During 2 Decades: The Bogalusa Heart StudyArch Pediatr Adolesc Med 2000 154: 155-161

Messinger

Rapid, decelerating growth: Length ?Birth length 20”

–add 10” by one year

–add 5” more by 2

yearsBoy

s

–Two year height

approximately 1/2

adult height

Messinger

Rapid, decelerating growth:Weight

?Newborn girl (7.25 lbs.)

–Gain 1.3 pounds per

month for the first 6

months

?100% bigger

–Double birth weight

–Then 1 pound per month

through 12 months

?50% bigger

–Triple birth weight

–Then less than a half a

pound per month through

36 months

MessingerGirls

Group curves

?Large samples

–Many children at a given age (e.g., 3 months)

–Find median (50th %ile), %s

?e.g. at 17 months, only 5% < 75 cm.

–Longitudinal data may have been collected

?but at monthly intervals

?What does individual growth in length look like?

Messinger

Common view

?Individual follows continuous growth curves

–Portrait of group is portrait of individual

?But parents report of

–growing by leaps and bounds

–growth spurts

–growing overnight

were dismissed

Messinger

One child?s growth

Messinger

Saltatory growth

?Lampl measures length/height

–3 samples of babiesevery two weeks, weekly, dailysame pattern in all groupsre-measures for reliability

Messinger

Growth jumps or spurts

?Growth occurs in spurts,

–jumps of almost a cm. (.9)

?separated by periods of no growth [stasis]

–of 2 to 15 days

?Total growth is sum of spurts

?Longer stasis continues, more likelihood of a spurt

–but spurts aperiodic

Messinger

Saltatory growth is the rule?

?

?

?prenatalinfantchildadolescent

Messinger

Prenatal growth

Messinger

Postnatal growth

Messinger

Childhood growth

Messinger

Growth occurs at the epiphyses

?growth centers in the bones where new cartilage cells are produced & gradually harden

?as growth continues, the epiphyses thin & disappear & no more growth of the bone is possible

Messinger

Practical consequences

?Fussiness and hunger during growth periods?Sleep patterns

–less before, more during?

Messinger

Developmental moral

?If you?re interested in individual growth, look at the growth of individuals!

?If change occurs between two time points

–E.g., between one month and one year

?Observe frequently during this period to describe the form development takes.

?Long-term = smooth; short-term = choppy

Messinger

What is the Shape of Developmental Change?

Adolph et al, 2008

?Developmental trajectories take many

forms

?Accurate depiction of trajectory

depends on sampling rate of

observations

?“Microgenetic method” –small time

intervals to observe developmental

process

?Overly large sampling intervals can

distort shape of change

–produce errors in estimating onset ages

–inaccurate picture of developmental

Gangitrajectory

Sampling rate can misrepresent both

form & age of development

Messinger

Motor development?Overall patterns

?Individual differences?Individual development

Messinger

Overall Motor Milestones

Messinger

Individual differences

WHO Motor Development Study: Windows of achievement for six gross motor development milestones. WHO MULTICENTRE GROWTH REFERENCE STUDY GROUP.Acta P?diatrica, 2006; Suppl 450: 86/95

Messinger

Motor learning in motor development

Messinger

Does one motor milestone help another?

?“Babies avoided reaching over risky gaps in the

sitting posture but fell into risky gaps while attempting to reach in the crawling posture…

Karen E. Adolph (2000) . Specificity of

Learning: Why Infants Fall Over a Veritable

Cliff . Psychological Science 11 (4), 290–295.

Messinger

Does sitting help crawling?

Messinger

Each postural milestone represents a different, modularly organized control system

?…infants' adaptive avoidance responses are based on information about their postural stability relative to the gap size.

?the results belie previous accounts

suggesting that avoidance of a disparity in depth of the ground surface depends on general knowledge such as fear of heights…

Messinger

Fewer errors sitting than crawling

Messinger

6 infants crawled into a .9 m gap

Messinger

Sway model: Bottom up learning?Experience with an earlier-developing skill does not transfer automatically to a later-developing skill ?Sitting, crawling, and walking postures, … involve different regions of permissible sway for different key pivots …

–the hips for sitting, the wrists for crawling, and the ankles for walk-ing).

Messinger

Extensive experience with eachpostural milestone in

development

?may be required to define the relevant control variables for the new perception-action system and to facilitate their on-line calibration.

–different muscle groups for executing movements and for generating compensatory sway; different vantage points for viewing the ground; different pat-terns of optic flow as the body sways back and forth; different cor-relations between visual, kinesthetic, and vestibular information; and so on.

Messinger

Learning can by painful

?When infants first acquired a new posture, they appeared oblivious to their limits …

?In their first weeks of crawling and walking, infants plunged straight down impossibly steep slopes.?Over weeks of locomotor experience, they became more discerning and responses became more adaptive.

?Adolph, 2008

Messinger

Learning to learn??Rather than learning cue–consequence associations (slopes are paired with falling), … infants learn to generate solutions to novel locomotor problems–perceive whether balance will be compromised and figure out an alternative position for descent). (Adolph, 2008)

Messinger

Results

?Coordination between perception and action is specific to postural control system

?Learning transfers from everyday experience with balancing to risky situations

?Learning is more specific and more flexible that previously recognizedNayfeld

Reaching (robotics video)

Messinger

References?

?

?

?LamplEdelman, Neural DarwinismHuttenlocherGreenough?Adolph?Thelen

Messinger

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