Monkeys reared in isolation with pictures as visual input: evidence for an innate releasing mechanism.

Monkeys reared in isolation from birth to 9 months received varied visual input solely from colored slides of monkeys in various activities and from nonmonkey pictures. Exploration, play, vocalization, and disturbance occurred most frequently with pictures of monkeys threatening and pictures of infants. From 2.5 to 4 months threat pictures yielded a high frequency of disturbance.Lever-touching to turn threat pictures on was very low during this period. Pictures of infants and of threat thus appear to have prepotent general activating properties, while pictures of threat appear to release a developmentally determined, inborn fear response.