visual cliff
an apparatus to investigate the development of depth perception in nonverbal human infants and in nonhuman animals, and in particular, whether depth perception is an innate ability or learned through visuomotor experience. The apparatus consists of a table with a checkerboard pattern, dropping steeply down a “cliff” to a surface with the same pattern some distance below the tabletop. The apparatus is covered with a transparent surface, and the participant is positioned on this at the border between the tabletop and the cliff. Reluctance to crawl onto the surface covering the cliff is taken as an indication that the participant can discriminate the apparent difference in depth between the two sides of the apparatus. Most infants as young as 6 months of age will not cross to the side over the cliff. [devised by Eleanor J. Gibson]