Effects of changing object size during prehension.

The authors tested how fast the grasp component of prehension was able to adjust to a sudden change in object size. Participants grasped an object, the size of which could suddenly increase. Whereas previous researchers usually applied perturbations through a change in illumination at movement onset, the present perturbations involved a change in the object's physical size at 1 of 4 moments during the movement (125, 200, 275, and 350 ms after movement onset). The results showed that grasp adjustments came in many forms and could be as fast as 120 ms. The implications for the understanding of the coordination of reaching and grasping in prehension are discussed.