Binocular vision and the on-line control of human prehension

The contribution of binocular visual feedback to the kinematics of human prehension was studied in two related experiments. In both experiments, the field of view of each eye was independently controlled by means of goggles fitted with liquid-crystal shutters. While wearing these goggles, which permitted either a binocular or a monocular view of the world, subjects were required to reach out and grasp a target object, which varied in size and position from trial to trial. In experiment 1, two viewing conditions were used. In one condition, binocular vision was available throughout the entire trial; in the second condition, the initial binocular view was replaced by a monocular view after the reaching movement had been initiated. When only monocular feedback was available, subjects showed a prolonged deceleration phase, although the time they spent in contact with the object was the same in both conditions. In experiment 2, monocular vision was available throughout a given trial in one condition and was replaced by binocular vision upon movement initiation in the second condition. Subjects in this experiment also displayed a prolonged deceleration phase in the monocular feedback condition relative to their performance in the binocular feedback condition. Unlike experiment 1, however, allowing only monocular feedback resulted in an increase in the amount of time subjects spent in contact with the object. Moreover, the object contact phases under the two conditions of experiment 2 were much longer than those observed in experiment 1, in which subjects received initial binocular views of the object.(ABSTRACT TRUNCATED AT 250 WORDS)