Depth Perception

A theme running throughout the study of perception in general since the time of the ancient Greeks has been whether perceptual processes are learned (based on past experience) or innate (existent or potential at birth). In terms of depth perception, research using the visual cliff with animals and human infants too young to have had experience with depth perception indicates that humans and various species of animals are born with some innate abilities to perceive depth.

The visual cliff is one the most commonly used methods of assessing depth perception. It is an apparatus made up of a large box with a clear or see-through panel on top. One side of the box has a patterned surface placed immediately under the clear surface, and the other side has the same patterned surface placed at some distance below the clear surface. This latter side gives the appearance of a sharp drop-off or cliff. The subject of the study will be placed on the glass and consistent movement toward the shallow side is seen as an indication of depth perception ability. Newborn infants who cannot crawl commonly show much distress when placed face down over the "cliff" side.

Research with animals raised without opportunities to see (for example if reared in the dark) sustain long-lasting deficits in their perceptual abilities. Indeed, such deprivation may even affect the weight and biochemistry of their brains. This research indicates that while humans and some animal species have innate mechanisms for depth perception, these innate abilities require visual experience in order to develop and become fully functioning. This research also suggests that animals and humans may have developmentally sensitive periods in which visual experience is necessary or permanent perceptual deficits may occur.