In a number of studies, we have demonstrated that the spatial-temporal coupling of eye and hand movements is optimal for the pickup of visual information about the position of the hand and the target late in the handís trajectory. Several experiments designed to examine temporal coupling show the eye arriving to the target area concurrently with the hand achieving peak acceleration. Between the time the hand reached peak velocity and the end of the movement, increased variability in the position of the shoulder and the elbow was accompanied by a decreased spatial variability in the hand. Presumably, this reduction in variability was due the use of retinal and extra-retinal information about the relative positions of the eye, hand and target. The hand does not appear to be a slave to the eye however. For example, we have been able to decouple the eye movement and hand movement using Muller-Lyer configurations as targets. Predictable bias, found in primary and corrective saccadic eye movements, was not found for hand movements, if on-line visual information was available during aiming. That is, the hand remained accurate even when the eye had a tendency to undershoot or overshoot the target position. However, biases of the hand paralleled those of the eye when vision of the target was removed during the aiming movement, even though vision of the hand remained. These findings accent the versatility of human motor control and have implications for current models of limb control.
This research was supported by the Natural Sciences and Engineering Research Council of Canada, and the National Fund for Scientific Research in Belgium.