Independent control of acceleration and direction of the hand when hitting moving targets.

Human subjects were asked to hit moving targets as quickly as they could. Nevertheless the speed with which the subjects moved toward identical stimuli differed between trials. We examined whether the subjects compensated for a lower initial acceleration by aiming further ahead of the target. We found that the initial acceleration of the hand and its initial direction were hardly correlated. Thus subjects did not aim further ahead when they hit more slowly. This supports our earlier suggestion that the acceleration of the hand and the direction in which it moves are controlled separately.