Lecture 6: Motor development

Question 1

Reflexes in newborns

Answer 1

Newborns demonstrate reflexes – innate, fixed patterns of action that occur in response to particular stimulation

Not always entirely automatic Most reflexes fade during the first few months and long persistence can used in diagnosing motor disorders

Some reflexes, such as rooting and sucking, have a clear adaptive (survival) value

Others, such as the tonic neck reflex, have no clear adaptive significance

Question 2

What are the key feeding reflexes

Answer 2

Rooting: Baby turns her head and opens her mouth when her cheek is stroked Disappears at around 3 weeks when is replaced by voluntary head turning

Sucking: when something is put in her mouth, the baby sucks repeatedly
Replaced by voluntary sucking at around 4 months

Question 3

Grasping reflexes in the hand

Answer 3

When a finger or object is pressed against the baby’s palm, the baby’s fingers close around it in a grasping action
Disappears by around 4 months when it is replaced with voluntary grasping

Question 4

Grasping reflexes in the foot

Answer 4

Appears in the foot as well as the hand (evolutionary remnant)

Human toes are too short for proper grasping

Reflex in hands and feet may once have helped baby cling on to (hairy) mother – the way nonhuman primates still do today

Question 5

Babinski Reflexes

Answer 5

When the bottom of baby’s foot is stroked, the toes fan out and then curl

Disappears around 8- 12 months

Long-term persistence might indicate neurological problems

Question 6

Stepping reflex

Answer 6

When baby is held upright over a flat surface, s/he will make rhythmic stepping movements

Disappears around 2 months

Question 7

Moro reflex

Answer 7

If baby is startled by something (e.g. sudden noise or movement) then baby throws arms out backwards and arches back before bringing arms back together as if holding something

Disappears around 6 months

Long-term persistence might indicate neurological problems

Question 8

Development of the cortex

Answer 8

Early, simple reflexes arise from the brain stem

More complex, coordinated reflexes result from the maturation of the cerebral cortex

Question 9

Primary motor cortex (M1)

Answer 9

First area of the cortex to develop

Responsible for voluntary (non-reflexive) movement

Begins with raising head (1month), control of arms and trunk (3 months); leg control is last to develop

Question 10

Why study motor processes

Answer 10

Why do we have a brain

To produce adaptable and complex movement

The only way you have to affect the world around you (with one exception)

Question 11

Motor development

Answer 11

Previously believed to be an element of neurological maturity

Current theories, however, often take a dynamic systems approach, emphasizing a confluence of many factors

Not only neural mechanisms but also increases in strength, posture control, balance, perceptual skills, and motivation

Question 12

Illustrating the dynamic systems view

Answer 12

Research by Esther Thelen and colleagues examined the stepping reflex, the infant’s performance of stepping movements when he or she is held under the arms with feet touching a surface.

The reflex was thought to disappear at about 2 months of age because of cortical maturation, but demonstrations that the reflex could be prolonged or elicited long after it was scheduled to disappear were inconsistent with this interpretation.

Question 13

Testing the dynamic systems view

Answer 13

Thelen et al., performed two experiments to test the hypothesis that rapid increases in infants’ weight made it impossible for them to execute stepping motions.

In one experiment, weights were attached to the ankles of infants who still had the stepping reflex, and the babies suddenly stopped stepping.

In the second study, infants who no longer showed the stepping reflex were found to do so when they were suspended waist-deep in a tank of water that supported their weight.

Therefore, the movement pattern and its neural basis remained but was masked by the changing ratio of leg weight to strength.

Question 14

Impact of culture on motor development

Answer 14

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

The maneuvers shown here do not harm the babies and do hasten their early motor skills (Bril & Sabatier, 1986)

Question 15

Reaching

Answer 15

For the first few months, infants are limited to prereaching movements

clumsy swiping movements by young infants toward the general vicinity of objects they see

Infants begin successfully reaching for objects at around 3 to 4 months of age

Question 16

Manual dexterity

Answer 16

At about 7 months, as infants gain the ability to sit independently, their reaching becomes quite stable

By 9-10 months of age, infants’ grasping approach to an object is affected by what they intend to do with the object (Claxton et al., 2003)

By one year old, infants show sophisticated manual dexterity

Question 17

Self-locomotion

Answer 17

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

Learning to move independently involves integrating movement from many different parts of the body

Question 18

Back-lying and locomotion

Answer 18

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

It may be that the better view of the world from their backs results in less motivation to roll over

It may also be that spending less time on their tummies causes arm strength to develop more slowly

The research is reassuring in that by 18 months of age there were no differences in the development of infant crawling

Question 19

Perception and action

Answer 19

Perceptual and motor development go hand-in-hand

As infants learn about objects, they perceive that different objects offer different affordances – properties that lend themselves to particular ways of interacting with them

Infants learn about affordances primarily through their own actions

To an adult, beans afford eating, but to a baby their pleasing texture also affords other interesting experiments and interactions

Question 20

Specificity of motor learning: walk this way

Answer 20

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

Karen Adolph and colleagues (Adolph et al., 1993) found that infants do not transfer learning from what they know about crawling down slopes to walking down them

Question 21

Specificity of motor learning: wariness of heights

Answer 21

Although we know young children can perceive depth via monocular cues, the consequences of depth are really only apparent when they start to move

The visual cliff paradigm uses a table with an apparently steep drop that is covered with a continuous transparent platform that can support the weight of an infant

A high-contrast checked pattern continues from the shallow to deep side of the “cliff”

Question 22

Gibson and walk (Visual cliff paradigm)

Answer 22

Gibson and Walk (1960) found that 6- to 14- month-old infants would not cross the deep side of the cliff, showing they perceived and understood the depth cue of relative size
Subsequent work by Campos and his colleagues (1970) showed:

1. 1½-month-old infants could perceive the difference in depth but showed no fear of the deep side (heart rate)
2. Early crawlers avoided heights earlier
   Campos (2000) – case study of 8-9m old infant who wore casts

Question 23

what does the visual cliff paradigm illustrate

Answer 23

Research with the visual cliff illustrates the interdependence of different domains of development (e.g. vision/movement)

Gibson (1979) “We must perceive in order to move, but we must also move in order to perceive”

Social referencing, the use of another’s emotional reaction to interpret an ambiguous situation, appears to be important in infants’ development of wariness of heights

What does all this tell us?

development in one domain clearly influences development in other domains

Question 24

Social referencing- Too big for their boots

Answer 24

Toddlers also make scale errors, in that they try to treat a miniature replica object as if it was a much larger real one (DeLoache et al., 2004)

One little boy is perched on top of a miniature chair, trying to sit in it just like he did with a similar-looking real chair, and the other is attempting in vain to get into a tiny car

Question 25

Why do children make scale errors

Answer 25

1. Dissociation between dorsal/ventral visual processing streams? i.e., what and where pathways some how the visual information for planning an action is not correctly integrated with the system for executing that action
2. Centration
3. Failure to inhibit an automatically afforded action? e.g. “cars are for driving”, “chairs afford sitting”

Similar behaviours are seen in patients with medial frontal lobe damage showing “utilisation behaviour” or “alien hand syndrome”