Continuous Use of Perceived Velocity While Hitting Running Spiders

From previous studies examining how we hit moving targets we concluded that the speed and the direction of the hand are determined independently, the former being based on the perceived velocity of the target and the latter on its perceived position. It is known that the direction in which the hand moves is continuously adjusted on the basis of the perceived target position, with a delay of about 110 ms. In the present study we examined whether the speed of the hand is also under such continuous control, or whether it is determined in advance.

Subjects were instructed to hit targets (spiders) as quickly as possible with a rod. They were presented with moving targets that appeared at unpredictable moments on a screen in front of them. Some time within 400 ms of their appearing on the screen, the velocity of the target abruptly changed. We found that this influenced the speed with which the rod hit the target as long as the change occurred at least 200 ms before the hit. Considering that the movement time of the hand was more than 200 ms, the perceived velocity must have influenced the speed of the hand during its motion. We conclude that the speed of the hand is continuously adjusted to maintain its relationship with the speed of the target.