Monocular and binocular control of human interceptive movements.

Previous work in our laboratory has demonstrated that binocular vision makes an important contribution to skilled reaching and grasping movements directed at static targets. In the present study we examine the contribution of binocular vision to interceptive reaching movements. We monitored such movements using a high-resolution, opto-electronic recording device (WATSMART), while subjects attempted to catch balls projected at them. No differences were found between monocular and binocular viewing conditions using this paradigm - either with respect to the velocity profiles or trajectories of the reaches. Moreover, the grasp was not affected by the type of vision available. 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. In addition, the time to achieve maximum grip aperture was constant across the trials - a finding consistent with the use of a time-to-contact variable derived from optic flow information. Finally, the transport component of prehension was found to be affected by certain variables that have, in the past, been thought to exclusively affect the grasp component of prehension, whereas the grasp component of prehension was affected by factors that have traditionally been thought to affect only the transport component.