Lecture 6: Motor development Flashcards
Reflexes in newborns
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
What are the key feeding reflexes
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
Grasping reflexes in the hand
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
Grasping reflexes in the foot
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
Babinski Reflexes
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
Stepping reflex
When baby is held upright over a flat surface, s/he will make rhythmic stepping movements
Disappears around 2 months
Moro reflex
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
Development of the cortex
Early, simple reflexes arise from the brain stem
More complex, coordinated reflexes result from the maturation of the cerebral cortex
Primary motor cortex (M1)
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
Why study motor processes
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)
Motor development
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
Illustrating the dynamic systems view
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.
Testing the dynamic systems view
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.
Impact of culture on motor development
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)
Reaching
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
Manual dexterity
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
Self-locomotion
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
Back-lying and locomotion
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
Perception and action
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
Specificity of motor learning: walk this way
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
Specificity of motor learning: wariness of heights
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”
Gibson and walk (Visual cliff paradigm)
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:
- 1½-month-old infants could perceive the difference in depth but showed no fear of the deep side (heart rate)
- Early crawlers avoided heights earlier
Campos (2000) – case study of 8-9m old infant who wore casts
what does the visual cliff paradigm illustrate
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
Social referencing- Too big for their boots
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
Why do children make scale errors
- 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
- Centration
- 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”
