Motor Development

February 7

 

Newborns – neonates – are surprisingly capable.

 

•        Which capacities are innate?

•        Which require maturation?

•        Which develop through interaction?

•        Are there discontinuities?

 

 

The Organized Newborn

 

Newborn Reflexes

 

•        A reflex is

 

•        Often used to judge neurological damage early in life

 

 

SURVIVAL REFLEXES:

 

breathing          sucking             eyeblink

rooting              swallowing        pupillary

 

 

PRIMITIVE REFLEXES:

 

moro                tonic neck         stepping

grasping            Babinski           swimming

 

 

 

Reflex

Procedure/response

Does what?

Rooting

 

 

Sucking

 

 

Moro

 

 

Palmar grasp

 

 

 

 

Adaptive Value of Reflexes

 

 

1.  Many have survival value: Sucking crucial to eating.

 

2.

 

3.

 

4.

 

 

Reflexes and motor skills

 

Disappear by 6 months as voluntary control increases.

 

Issue: Are reflexes building blocks for voluntary control?

 

      1. Babies adapt reflexes: Palmar changes depending on how palm is stimulated.

 

      1. Some reflexes disappear but return later: swimming & stepping.

 

 

How do reflexes contribute to motor control?

 

Zelazo (1983): Practice stepping increases spontaneous stepping movements.

 

Hence, exercising reflex helps develop area of cortex related to movement.

                        No exercise, reflex disappears.

 

 

Thelen (1983):  

 

So, should parents encourage walking reflex?

 

 

Motor Development

 

The organization and sequence of motor development

 

  1. Gross motor development: actions that help infant get around – crawling, standing, walking.

 

  1. Fine motor development: smaller movements – reaching & grasping.

 

 

Infancy

 

            Differentiation and integration in Postural Control,

            Locomotion, and Manual Control leads to:  

 

•        Improvements in timing, balance, and coordination

 

            Motor advances lead to: 

 

  1.            
  2. .
  3. .
  4.  

 

 

•        The developmental sequence of motor skills is quite uniform.

 

But, large individual differences in rate of development:

 

Motor skill

Average age

Range (90% infants)

Grasps cube

3 months 3 weeks

2-7 months

Crawls

 

 

Walks alone

 

 


Often, a baby is slow on some motor skills but advanced on others.

 

•        We are concerned only if slow on many skills.

 

So, what do these trends mean?

 

 

Developmental norms imply maturation:

 

•        a hard-wired sequence directed by motor development genes

 

•         Early pioneers Arnold Gesell and Myrtle McGraw believed that motor skills were determined mainly by neurological maturation of the brain.

 

 

But:

 

•        Interaction of multiple factors, each of which may be influenced by genes and experience

 

Note:    Psychologists ignored motor development for 40 years because of maturationist assumptions:

                       

                                    (Perspective = Nature, Passive Child)

 

 

 

Motor Skills as Dynamic Systems (Thelen, Pick, Smith)

 

Dynamic systems theory (DNS) views motor development as acquiring ever more complex systems of action

 

Not just development of independent skills:

 

  1. head and chest control combine into sitting with support

 

  1. crawling, standing, and stepping combine for walking.

 

So, how does DST work?

 

n      New forms emerge through processes of self-organization

n      patterns and order emerge from the interactions

n      of the multiple components of a complex system

n      without explicit instructions from organism or environment

 

Extraordinarily complex structural patterns can emerge from very simple initial conditions in dynamic systems

 

 

Evidence for DNS – Microgenetic research (Thelen, 1994)

 

•        Attach mobile to 3-month-olds’ legs.

 

            Infants’ usually kick with one leg or two in alternation.

 

•        Attach mobile so that two legged kick works best

 

Infants

 

Locomotion

 

l      At around 8 months of age, infants become capable of self-locomotion for the first time as they begin to crawl

l      Infants begin walking independently at around 13 to 14 months of age, using a toddling gait

 

Integration in locomotion

 

Adolp (1997): Strategies for moving down an incline

 

1.

2.

3.

4.

5.

 

l      Karen Adolph and her colleagues have found that infants do not  transfer what they learned about crawling down slopes to walking down them 

 

Back-Lying and Locomotion

 

l      The campaign to get parents to put babies to sleep on their backs to reduce the risk of SIDS seems to make infants less likely to roll over on schedule

 

l      It may be that the                                                     results in less motivation to roll over

l      It may also be that                                                      to develop more slowly 

 

l      By 18 months of age there were no differences in the development of infant crawling

 

Fine Motor Development: Voluntary Reaching

 

Reaching plays big role in infant cognitive development.

 

Grasping allows exploration of new things.

 

Newborns reach out for objects – prereaching – poorly coordinated.

 

Voluntary reaching begins at 3 months – infants reach in dark and light just as well.

 

Hence, does not require visual guidance – instead proprioception – allows vision to focus on other things.

 

Nature of grasp varies:

 

After reflex comes ulnar grasp – fingers close against palm.

 

By 6-7 months, use pincer grasp with thumb and index finger.

 

By 8-11 months, reaching & grasping executed smoothly.

 

 

Cultural influences

 

l      Mothers in Mali believe it is important to exercise their infants to promote their physical and motor development

l      The maneuvers shown here do not harm the babies and do hasten their early motor skills

 

 

Influences on Motor Development

 

Biological Contributions

 

1.

 

2.

 

 

Experiental Contributions

 

1.

 

2.

 

3.