COORDINATION IN PREHENSION - INFORMATION-BASED COUPLING OF REACHING AND GRASPING

Prehension involves the coordination of a reaching and a grasping move ment, such that the hand opens and closes in tune with the transport o f the hand to the object to be grasped. To investigate this coordinati on, we focused on the transition from hand opening to hand closing in the grasping component of prehension. Earlier research has suggested t hat the time taken to close the hand remains constant over varying rea ching amplitudes. In the present experiment, in which subjects reached for objects at six different distances and for objects that moved awa y from them at three different, constant speeds, hand-closure time was found to vary as a function of experimental conditions. Moreover, ini tiation of hand closure did not occur at a constant value of the (perc eptually available) first-order time remaining until contact with the object. However, the variations observed, occurring as a function of i nitial hand-object distance and object speed, could be accounted for b y an abstract dynamical model of perceptually driven postural changes.