The Development of Visual Perception in Man and Chimpanzee

Abstract

Two chimpanzees were reared in darkness to the age of 16 mos. The animals were then brought periodically into the light for observations. The first tests demonstrated good pupillary responses to changes in light intensity, pronounced startle reactions to sudden increases of illumination, and a turning of the eyes and head to sources of light. In the dark there was pursuit of a moving light with both eye and head movements. The eyes did not fixate steadily on a light. In all tests a resilient "spontaneous" nystagmus occurred, the quick phase usually toward the light. No fixation of any object, still or moving, could be elicited in the early tests. For a long time there was no eye blink when an object was brought quickly toward the eyes. An object brought to the face caused no response until contact was made, and then the animals reacted in a typical startle pattern. Repetitions of experience with objects presented visually were necessary before the objects were recognized. A training method using electric shock showed that the learning of avoidance responses was also a very slow and gradual process. The prompt visual learning characteristic of the normal adult primate is apparently not an innate capacity, independent of visual experience, but involves a long training in the use of the eyes. At lower phylogenetic levels the period of apprenticeship is much shorter.