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CHAPTER FOUR SUMMARY During the first 2 years, body size increases dramatically—faster than at any other time after birth. Body fat is laid down quickly in the first 9 months, whereas muscle development is slow and gradual. Children of the same age differ in rate of physical growth; some make faster progress toward a mature body size than others. The best way to estimate a child’s physical maturity is by using skeletal age. Early in development, the brain grows faster than any other organ of the body. As neurons form an elaborate communication system in the brain, stimulation becomes necessary for their survival. The cerebral cortex is the largest, most complex brain structure—accounting for 85 percent of the brain’s weight, containing the greatest number of neurons and synapses. Its frontal lobes, which contain the prefrontal cortex, have the most extended period of development. At birth, the two hemispheres of the cerebral cortex have already begun to specialize, a process called lateralization. However, the brain is more plastic during the first few years than it will ever be again. Animal research and natural experiments with children who were victims of early, prolonged institutionalization provide evidence for sensitive periods in brain development. Appropriate stimulation is vital for experience-expectant brain growth—the young brain’s rapidly developing organization, which depends on ordinary experiences. Experiencedependent brain growth, in contrast, occurs throughout our lives as a result of specific learning experiences. Physical growth, like other aspects of development, results from a complex interplay between genetic and environmental factors. Heredity, nutrition, and emotional well-being all affect early physical growth. Dietary diseases caused by malnutrition affect many children in developing countries. If allowed to continue, body growth and brain development can be permanently stunted. Breastfeeding provides many benefits to infants, especially to those in poverty-stricken areas, where it protects against disease and prevents malnutrition and infant death. Babies come into the world with built-in learning capacities that permit them to profit from experience immediately. Classical and operant conditioning, habituation and recovery, and imitation are important avenues through which infants learn about their physical and social worlds. Babies’ motor achievements have a powerful effect on their social relationships. According to dynamic systems theory of motor development, each new motor skill is a joint product of central nervous system development, the body’s movement capacities, the child’s goals, and environmental supports for the skill. Cultural differences in infant-rearing practices affect the timing of motor development. Perception changes remarkably over the first year of life. Hearing and vision undergo major advances during the first 2 years as infants organize stimuli into complex patterns, improve in perception of depth, and combine information across sensory modalities. According to Eleanor and James Gibson’s differentiation theory, perceptual development is a matter of detecting invariant features in a constantly changing perceptual world, and seeking ways in which the environment affords possibilities for action. Instructor’s Resource Manual for Berk / Development Through the Lifespan, 6e Copyright © 2014, 2010, 2007 by Pearson Education, Inc. All Rights Reserved.