Although the mechanics of how the eye works are well understood, debate still exists as to how the complex machinery of the brain interprets neural impulses supplied by the eye. In an attempt to understand the evolutionary origins and functions of the visual system, the authors pose the question "What is the function of vision?" Topics covered include: visual processing in the primate, disorders of visual recognition, spatial perception and the visual control of action, dissociations between perception and action, attention, consciousness, and the coordination of behavior. The issues raised will be of interest to psychologists, vision scientists, neuroscientists, and ophthalmologists.