The control and coordination of one-handed catching: the effect of temporal constraints.

The aim of the experiment was to identify the control mechanisms involved in a goal-directed task by manipulating the temporal constraints. Subjects were required to catch, with one hand, table tennis balls projected by a ball-projection machine under five temporal conditions (ball speed ranged from 5.7 to 9 m/s, giving rise to flight times of 550-350 ms). By means of three-dimensional kinematics analysis the following 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 ball-hand contact while (4) the grasping time was kept constant. Moreover, as a result of increasing temporal constraints, the acceleration phase of the transportation component was kept constant while the deceleration phase was progressively decreased and nearly suppressed. Further, an increased correlation of the initial direction of the transportation component with the initial direction of the ball path was found. These findings show some spatio-temporal adaptations of the catching movement when the time available is manipulated. They also support the contention of a shift in the control mechanisms involved in one-handed catching facing different temporal constraints.