Chapter Four

Body size increases dramatically during the first 2 years of life, following organized patterns of growth called cephalocaudal and proximodistal trends. Fat increases much more rapidly than does muscle during the first year. During the first 2 years, neurons form intricate connections, and their fibers myelinate, leading to a rapid increase in brain weight. Already, the two hemispheres of the cortex have begun to specialize, although the brain retains considerable plasticity during the first year of life. Researchers have identified sensitive periods of brain development when appropriate stimulation is key to acquiring skills.

A variety of factors affect early physical growth. While heredity contributes to height, weight, and rate of physical maturation, good nutrition is essential for rapidly growing babies, and breast milk is especially well-suited to meet their needs. Malnutrition during the early years can lead to serious dietary diseases, which are associated with permanent stunting of physical growth and brain development. Finally, affection and stimulation are also vital for healthy physical growth.

Infants are marvelously equipped to learn immediately after birth. Classical and operant conditioning, habituation–dishabituation, and imitation are important mechanisms through which infants learn about their physical and social worlds.

The rapid motor development that occurs during the first 2 years follows the same organized sequences as does physical growth. The mastery of motor skills involves acquiring increasingly complex, dynamic systems of action. In this way, maturation and experience combine to influence the development of motor skills.

Perception changes remarkably over the first years of life. Hearing and vision undergo major advances during the first 2 years as infants organize stimuli into complex patterns, improve their perception of depth and objects, and combine information across sensory modalities. The Gibsons’ differentiation theory helps us understand the course of perceptual development.