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Perception

Perception is the set of processes by which organisms use information provided by the environment to build representations of objects and events and to plan actions. A life-span approach to understanding perception necessarily involves understanding perceptual development because there are significant changes in perceptual processing particularly early in life, due to maturation and experience in infancy and childhood. How much do infants know about their environment? How do they discover the sensory information that surrounds them in determining the fundamental facts of the world?

Remarkable advances in methods, coupled with the ingenuity and curiosity of dedicated researchers, have begun to provide answers to these important questions. Even newborn infants are well equipped to make sense of their world. This early start accompanies and contributes to later abstract reasoning and other higher level cognitive operations. This entry reviews research on basic and more complex visual and auditory functions, including visual attention and speech perception, as well as other sensory systems and intermodal perception, when two or more systems work in tandem. Most of what follows is focused on the early years. Elsewhere in this volume there are entries dedicated to perceptual limitations in older age groups (e.g., visual disorders, deafness).

Visual Perception

Basic Visual Functions

To see objects and events, infants must discern detail, see motion, distinguish brightness and color, and detect depth differences—relative distance—among objects in the visual field. In addition, they must direct their visual attention appropriately to selected targets. Studies of newborns have revealed rudiments of these abilities, and there is rapid improvement across the next several months. Acuity is initially poor, estimated between 20/200 and 20/400 for most newborns, but improves quickly, along with contrast and color sensitivity. Development of motion perception is more complex, due in part to the diverse nature of motion information itself. Sensitivity to different types of motion develops at different rates, suggesting maturation of separate processing mechanisms in the brain, but these differences are not large, and full motion sensitivity is probably nearly complete by 6 months. Together, research on fundamental visual functions indicates that vision is near adult levels by 6–8 months after birth, though other visual capacities, discussed below, develop well beyond this time.

Depth perception, likewise, develops piecemeal. The first depth cues to which infants are sensitive are based on movement, as when one object moves in front of another, and sensitivity emerges around 2 months. A few months later infants develop binocular disparity, when the two eyes receive slightly different views of close objects, useful for fine-grained depth discriminations in near space (e.g., grasping a small object). Finally, pictorial depth cues, information that can be depicted in pictures, are used between 4 and 7 months. By 7 months, therefore, infants have nearly fully developed depth perception abilities.

Visual Attention

There are four major kinds of eye movement: optokinetic and vestibulo–ocular responses, saccades, and smooth pursuit. Optokinetic eye movements occur in response to whole-scale movement of the visual field, as when looking out of a moving train. Vestibulo–ocular eye movements compensate for head and body motion when the observer’s goal is to fixate a stationary (or moving) target. Both eye movement patterns can be observed at birth, along with saccades, a series of scans from one object to another. Scanning patterns undergo improvements, as attention becomes increasingly guided by cognitive control. Finally, smooth pursuit, the ability to track small moving targets with smooth eye movements, emerges within a few months after birth. The timing is similar to that of motion discrimination, suggesting some direct or indirect relation between the two.

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