Cardiac responses on the visual cliff in prelocomotor human infants.

Human infants younger than crawling age yielded reliable cardiac decelerations when placed directly atop the deep side of a visual cliff and generally nonsignificant changes when atop the shallow side. Distress was elicited less frequently on the deep side than on the shallow at these ages, in contrast to the behavior of older infants and other species. Prelocomotor infants thus can discriminate the two sides of the cliff, but not by means of distress at loss of optical support.