Abstract
Binocular information is considered paramount in the planning of prehensile movements. Here we investigate its contribution to the online control stage. Subjects reached for objects following an initial monocular view and binocular information was introduced at predetermined intervals during the reach. If, during the reach, the addition of relative disparities between the hand and target is important then reach profiles should approximate those manifest under full binocular conditions. Subjects reached for and picked up objects of three different depths (3, 4.5 and 7 cm) at three different positions (14.5, 25 and 36.7 cm) along the midline. Vision was controlled using a pair of LCD goggles which could alternate between a binocular and monocular view depending on the experimental condition. Six viewing conditions were employed of which the first two were a fully monocular reach and a fully binocular reach. The final four conditions consisted of a monocular initial view followed by the introduction of binocular information 0%, 25%, 50% or 75% into the temporal duration of the reach following movement onset. Movements were recorded using a ProReflex motion analysis system. The expected differences between overall binocular and monocular reaches were present along with normal scaling of the transport and grasp components for object distance and object size respectively. Differences between the reach kinematics of the four ‘partial binocular’ conditions were found when compared to monocular-only conditions. When binocular information was introduced later in the reach, the benefits were much reduced. Therefore these results suggest that the improvement afforded by binocular cues in on-line control of prehensile movements is only observed when the information is present through at least 75% of the reaches duration.