THE CONTROL AND COORDINATION OF ONE-HANDED CATCHING - THE EFFECT OF TEMPORAL CONSTRAINTS

The aim of the experiment was to identify the control mechanisms invol ved in a goal-directed task by manipulating the temporal constraints. Subjects were required to catch, with one hand, table tennis balls pro jected by a ball-projection machine under five temporal conditions (ba ll speed ranged from 5.7 to 9 m/s, giving rise to night times of 550-3 50 ms). By means of three-dimensional kinematics analysis the followin g results were obtained, which are some spatio-temporal adaptations of the catching movement to the increase of temporal constraints: (1) a decrease in movement time, (2) an increase in the straightness of the trajectory of the wrist, and (3) a shift backwards of the place of bal l-hand contact while (4) the grasping time was kept constant. Moreover , as a result of increasing temporal constraints, the acceleration pha se of the transportation component was kept constant while the deceler ation phase was progressively decreased and nearly suppressed. Further , an increased correlation of the initial direction of the transportat ion component with the initial direction of the ball path was found. T hese findings show some spatio-temporal adaptations of the catching mo vement when the time available is manipulated. They also support the c ontention of a shift in the control mechanisms involved in one-handed catching facing different temporal constraints.