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Psychology of Human Growth and Development
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Lecture 7

Motor development

 

Lecture looks at the formation of goal oriented behaviors such as early reaching, bimanual coordination, and object manipulation.

 

Reflexes

 

1        Reflexes are involuntary responses to stimuli.

2        Several reflexes appear at birth

3        disappear with age

4        develop into gross motor skills

 

Motor-skills

 

Motor-skills can be broken down into these two-categories:

 

1)   Gross Motor Development

 

2)   Fine Motor development

 

Object manipulation

 

    refers to the control of objects in the spatial environment.

 

A. Reaching

 

Importance of skills of reaching

Provide another way in addition to seeing and hearing that infants can explore their environment

And learn about their environment / new world

 

Prereaching

    A grasping reflex in newborns and rudimentary form of reaching

-     Decline at 2 months

 

Directed reaching:

-     occurs at 3 months: more complex and efficient pattern of reaching

-     by 3 months

-     4 month olds rely more on touch to determine grip configuration

-     5 months (in normal environment) infants are able to reach in a directed way for an object and successfully grasp it.

-     6 months They can reach and grab onto an object they are concentrating on.

-     8 month use vision as a guide – more efficient as allows infant to preshape his hand as he reaches for the object

-     Up to one year: infants become highly skilled in exploring their world with their hands.

 

Return to two-handed reaching

    Despite that dramatic behavioral progression, many infants return to two-handed reaching near the end of the lst year-- particularly when objects are presented at midline

    No one has been able to offer a plausible explanation as to why infants activate two arms again when reaching for small objects toward the end of their 1st year.

 

Environmental effects of motor development of reaching and grasping

White 1967

    enriching the visual world of deprived infants advanced their abilities to attend to objects and to reach for them

    Method:

Hanging colorful toys over babies cribs

Provided them with multicolored sheets

Bumper pads

Experimental babies handled more often by their caretakers

    Results

Experimental babies exhibited visually directed reaching by just over 3 months

40% faster than controls

 

grasping

Refers to:

When and how infants begin to grasp objects of different sizes, and when object-specific grasping patterns emerge.

 

How infants grasp

 

    Infants vary their grip according to the size and shape of the object

    As well as the size of their own hands relative to the objects size

 

Developmental sequence of grasping

    16 weeks begin to use the forearm and the hand to reach with greater effectiveness

    20 weeks the use of a crude palm grasp emerges.

    16- to 24-weeks finger movements are very crude, and the hand often reaches behind the object to grasp it.

    28 weeks infants begin to use thumb-finger opposition,

    36 weeks infant's approach becomes stable and straight.

    40 weeks infants are able to extend the index finger toward the object.

 

Changes may be observed until the age of six years or later, when the features of adult grasping are established.

 

Children learn to grasp from

 

experience

program the forces on the basis of an internal model (motor memory and representations),

Rely on vision for shaping the configuration of the hand when we are about to grasp an object.

The hand receptors are also essential and come into play to update the memorized representations.

Besides the (unconscious) use of the hands in adaptive corrections of the grip, the hands are, of course, used for conscious perception of an object's properties (reaching to sense the immediate environment, a particularly important activity for normal development).

 

    The relationship of infant sleep and play positioning to motor milestone achievement.

 

Eg: Salls, Silverman, Gatty (2002)

 

METHOD:

    A cross-sectional sample of 66 infants

 

    Ages: 2.0 (n = 23), 4.1 (n = 26), and 6.0 (n = 17) months of age

 

    Caregivers identified infants' primary sleep positions and amount of awake-time in prone.

 

 RESULTS:

    The sample of 2.0-month-old supine and side sleeping infants differed significantly from the normative population on three gross motor milestones.

 

    Two-month-old infants spending 15 min or fewer of awake-time in prone passed the gross motor milestones at significantly lower percentages than the normative population.

 

    No significant differences were noted between sampled and normative populations at 4.1 and 6.0 months of age.

 

CONCLUSION:

    Results suggest that infant gross motor development may be related to sleep and play positioning.

 

Locomotion

 

One of the babies’ early achievements is the ability to reach, grasp and pick up objects

Second is ability to reach things beyond their immediate grasp by:

 

crawling

and then walking

 

Locomotor movements :

    include movements that change the child from one location to another,

o e.g.: such as crawling,

o creeping,

o walking,

o running, leaping, jumping, hopping, skipping, galloping, rolling, and climbing

 

Three phases of development of locomotion:

 

1.   Stepping Reflex

2.   Reappearance of stepping reflex

3.   walking without support

 

Development of motor-skills depends on…

 

    maturation and readiness

    all children develop physical skills in a predictable, observable sequence, there are definitely individual differences

 

Improvement of motor skills through practice:

 

    researchers held that motor behaviors emerged as a consequence of the interaction between the children's maturation and experience.

 

    Theorists in the 1980s proposed that motor skills could be improved through practice, learning, and environmental interaction,

 

    More recently, researchers have gathered evidence that appears to verify these theorists' position that motor skills are improved through intervention

 

    Researchers have reported that children receiving targeted motor intervention programs that promote the identified sequential skills make significant gains in motor development

 

Eg: Can infants between the ages of 2 months and 12 months step as long s they’re given stability and postural support necessary to stretch each leg forward and back while in an upright position?

 

Thelen (1986) and Thelen and Smith (1994)

 

    Held 7 month olds on a motorized treadmill

    Immediately they performed alternating stepping movements that were remarkably similar to more mature walking

    Were able to adjust walking speed when the treadmill moved at different rates for each leg.

 

E.g. Zelazo et al (1972)

Asked mothers of newborns to give their infants practice in the stepping reflex a few minutes a day

2 to 8 week old infants made more walking responses and walked independently at an earlier age than a control group who were given no practice.

Also practice in sitting yielded similar results

Practice is highly specific: so practice in stepping does not affect sitting

 

Development of other locomotion

 

    Running well established by the time the child is a year and a half years old

    Galloping emerges at the same time

    These skills depend on

 

improvements in balance

coordination

opportunity for practice.

 

Locomotion and other aspects of development

 

    development changes in one domain have important implications for changes in another.

E.g.: blindness retards motor development considerably

-     being blind lessens the infants ability to explore independently

    Locomotion affects the way babies understand their perceptual world

E.g. babies develop a fear of heights only after they begin crawling

 

locomotion and the role of culture

 

Effect of rearing customs on motor patterns

Cross cultural studies have provided some insights on how specific ways of caring for newborns and infants can alter motor patterns.

 

    Two related factors that may stimulate children’s early motor development  that differ among cultures are:

1)    physically handling infants

2)    giving them exercise in various motor skills

 

 

Motor development and the elderly

 

    Changes in gait

    Falls are a major contributor to the increasing morbidity rates seen in the older population.

 

 

 

TPS102