Timing a one-handed catch I. Effects of telestereoscopic viewing

The aim of this study was to examine the role of binocular and monocular in formation sources in specifying time-to-contact. More specifically, it was investigated whether the timing of the one-handed catch is consistent with a binocular tau-function strategy. Subjects (n=8) were required to time the ir grasp to catch a ball approaching with a constant spatial trajectory. Th e ball approached at three different constant velocities (1.5, 2.0 and 2.5 m/s). Vergence and disparity were manipulated through subjects wearing a te lestereoscope to increase the effective interocular separation, under both binocular and monocular viewing. Subjects performed 24 trials in each of th e four conditions. Subjects' started the opening of the hand earlier in the binocular telestereoscope condition when a ball approached with velocity o f 1.5 m/s. They then closed the hand earlier in the binocular telestereosco pe condition at all ball approach velocities. There were no effects of tele stereoscope on the timing of hand opening and closing under monocular viewi ng. This finding suggests the use of the binocular information in timing th e grasp. However, there were effects of approach velocity under all conditi ons of monocular and binocular viewing. Subjects' closed the hand earlier a s a function of increasing approach velocity. Together, the effects of the telestereoscope and approach velocity indicate that timing of the one-hande d catch is not consistent with the use of a binocular "tau-function" variab le. Rather, it is concluded that multiple sources of monocular and binocula r information contribute to the regulation of timing.