Visual cliff experiment conducted by Eleanor Gibson and Richard Walk in 1960 is one of the classic studies in psychology. The experiment was created to test depth perception in infants and animal species by placing them on a platform that simulated a cliff providing the subjects with visual and tactile stimuli.
The experiment is usually illustrated with a picture of a baby on a checkered surface cautiously looking over the edge of the visual cliff with its mother observing from the opposite side of the apparatus. Such experimental apparatus, later adopted by many other researchers for various purposes, provided conclusive evidence that infants have an accurate perception of the environment.
The apparatus was made of a large sheet of Plexiglass covered with high-contrast checkered fabric, which is also used on the level below the glass, thus creating the illusion of a cliff. The visual cliff simulates an apparent, not real drop from one level to another, and thus, creates the visual illusion of a cliff while protecting the infant from injury.
The results of the study supported the hypothesis from the earlier research that infants are able to respond to depth cues as they are learning to crawl. Depth cues help people detect and evaluate depth in a visual environment. Relative size and overlap are the kinds of monocular cues, while retinal disparity is an example of a binocular cue.
Eleanor Gibson and Richard Walk assumed that if infants had a developed perception of depth, they would interpret the cliff as dangerous and refuse to crawl over it. Overall, the psychologists concluded that developed depth perception emerges at about the same age as when infants learn to crawl, while the fear of heights comes later in life with the experience gained through injuries from falling.