Ch. 5 (Essay)

Explain dynamic systems theory of motor development.

According to dynamic systems theory of motor development, mastery of motor skills involves acquiring increasingly complex systems of action. When motor skills work as a system, separate abilities blend together, each cooperating with others to produce more effective ways of exploring and controlling the environment. For example, control of the head and upper chest combine into sitting with support. Kicking, rocking on all fours, and reaching combine to become crawling. Then crawling, standing, and stepping are united into walking. Each new skill is a joint product of the following factors: (1) central nervous system development, (2) the body's movement capacities, (3) the goals the child has in mind, and (4) environmental supports for the skill. Change in any element makes the system less stable, and the child starts to explore and select new, more effective motor patterns. The factors that induce change vary with age. The broader physical environment also profoundly influences motor skills. For example, infants with stairs in their home learn to crawl up stairs at an earlier age and also more readily master a back-descent strategy.

Describe the sex differences in body growth

In infancy, girls are slightly shorter and lighter than boys, with a higher ratio of fat to muscle. These small sex differences persist throughout early and middle childhood and are greatly magnified at adolescence. But body size is not enough to tell us how quickly a child's physical growth is moving along. The best estimate of a child's physical maturity is skeletal age, a measure of bone development. When skeletal ages are examined, girls are considerably ahead of boys. At birth, the sexes differ by about 4 to 6 weeks, a gap that widens over infancy and childhood. Girls are advanced in development of other organs as well. This greater physical maturity may contribute to girls' greater resistance to harmful environmental influences.

Using examples from the text, explain how cultural variations in infant-rearing practices affect motor development.

In some cultures, sitting, crawling, and walking are deliberately discouraged or encouraged. Japanese mothers, for example, believe that it is unnecessary to deliberately encourage motor skills. The Zinacanteco Indians of southern Mexico and the Gusii of Kenya actively discourage rapid motor progress. Babies who walk before they know enough to keep away from cooking fires and weaving looms are viewed as dangerous to themselves and disruptive to others. In contrast, among the Kipsigis of Kenya and the West Indians of Jamaica, babies hold their heads up, sit alone, and walk considerably earlier than North American infants. In both societies, parents emphasize early motor maturity, practicing formal exercises to stimulate particular skills. Walking is promoted by frequently standing babies in adults' laps, bouncing them on their feet, and exercising the stepping reflex. These infants usually skip crawling because they are rarely put on the floor. Finally, the current Western practice of having babies sleep on their backs delays gross-motor milestones of rolling, sitting, and crawling. Regularly exposing infants to the tummy-lying position during waking hours prevents these delays.

Define size and shape constancy, and explain how they contribute to infants' perception of objects.

The images that objects cast on our retina constantly change in size and shape. To perceive objects as stable and unchanging, we must translate these varying retinal images into a single representation. Size constancy—perception of an object's size as the same, despite changes in the size of its retinal image—is evident in the first week of life. Perception of an object's shape as stable, despite changes in the shape projected on the retina, is called shape constancy. Habituation research reveals that it, too, is present within the first week of life, long before babies can actively rotate objects with their hands and view them from different angles. Both size and shape constancy seem to be built-in capacities that assist babies in detecting a coherent world of objects. Yet they provide only a partial picture of young infants' object perception.

Describe some common forms of inadequate nutrition in the United States.

While severe extreme forms of malnutrition, such as kwashiorkor and marasmus, are not common in the United States, iron-deficiency anemia is common among poverty-stricken infants and children. It is a condition that interferes with many central nervous system processes. Withdrawal and listlessness reduce the nutritionally deprived child's ability to pay attention, explore, and evoke sensitive caregiving from parents, whose lives are already disrupted by poverty and stressful living conditions. Because government-supported supplementary food programs do not reach all families in need, an estimated 22 percent of U.S. children suffer from food insecurity—uncertain access to enough food for a healthy, active life. Food insecurity is especially high among single-parent families and low-income ethnic minority families. Children who suffer from food insecurity are affected in their physical growth and ability to learn.

What is lateralization of the brain, and why does it occur?

is called lateralization. Studies using fMRI reveal that the left hemisphere is better at processing information in a sequential, analytic way, a good approach for dealing with communicative information—both verbal and emotional. In contrast, the right hemisphere is specialized for processing information in a holistic, integrative manner, ideal for making sense of spatial information and regulating negative emotion. A lateralized brain may have evolved because it enabled humans to cope more successfully with changing environmental demands. It permits a wider array of functions to be carried out effectively than if both sides processed information in exactly the same way. However, the popular notion of a "right-brained" or "left-brained" person is an oversimplification. The two hemispheres communicate and work together, doing so more rapidly and effectively with age.