Visually guided behavior of monkeys after early binocular visual deprivation

Four infant monkeys were binocularly deprived of vision through their first year of life. After the end of the deprivation their visually guided behavior was followed for one year. Behavioral tests were performed to assess their visual functions. The performance of the deprived monkeys was compared with the performance of three normally sighted monkeys. The following functions were tested: the monkey's ability to detect a moving light spot, to track a moving object, to grasp an object, to chatter the teeth in response to a threatening face, to pick pellets from a board, to respond to a sudden visual threat and to move about in a wide space. The visually deprived monkeys remained severely visually handicapped. They were able to detect a moving light spot in a darkened room and to recognize the movement of large objects. However, they continued bumping into objects and used tactile exploration when moving about in a wide space. They never learned to respond to a threatening face, which for a normal monkey is part of the normal behavioral repertoires. The persistently poor visually guided behavior of these monkeys is in agreement with the electrophysiological findings in the posterior parietal association cortex of these monkeys; early visual deprivation permanently reduces the number of visually responsive cell groups in this association area.