Binocular Vision And The Kinematics Of Human Prehension

A series of experiments was devised to examine the contribution of binocular depth and distance cues to skilled reaching and grasping movements in humans. These movements were monitored using a high resolution opto-electronic recording device.;In the initial experiment, subjects reached out and grasped oblong blocks under conditions of either monocular or binocular vision. Kinematic analyses revealed that grasping movements made under monocular viewing conditions showed longer movement times, lower peak velocities, proportionately longer deceleration phases, and smaller grip apertures than movements made under binocular viewing. In short, subjects appeared to be underestimating the distance of objects (and as a consequence, their size) under monocular viewing.;The contribution of binocular visual feedback to the kinematics of human prehension was studied in two further experiments. In both experiments, the field of view of each eye could be independently controlled at various points during the trials by means of goggles fitted with liquid-crystal shutters. Subjects were required to reach out and grasp a target object, which varied in size and position from trial to trial. In one of these experiments, binocular vision was either available throughout the entire trial or 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. In the other experiment, monocular vision was either available throughout a given trial or was replaced by binocular vision upon movement initiation. Subjects in this experiment also displayed a prolonged deceleration phase in the monocular feedback condition relative to their performance in the binocular feedback.;The final experiment examined the role that binocular information might play in the control of reaching movements directed at moving objects. No differences were found between a monocular and binocular viewing condition using this paradigm. It appears, then, that the moving targets provide adequate monocular depth and direction information (on the basis of optic flow) for the control of skilled interceptive movements directed at them.;The nature of visual and visuomotor representations is discussed. It is argued that the representation of depth and distance in the visual domain is rather different than the representation of such attributes in the visuomotor domain. Further, it is suggested that separate neural substrates subserve these two fundamentally different processes