Getting hold of approaching objects: in search of a common control of hand-closure initiation in catching and grasping.

Both in the catching and grasping component of prehension, the hand opens and closes before hand-object contact is made. The initiation of hand closure has to be coordinated with the time course of the decrease of the distance between the hand and the target object, i.e., with the reaching component in prehension or the approach of the target in catching. The authors investigated if this initiation of hand closure could be explained by a common control. For this purpose, they fitted the dynamic timing model to data from the two tasks. In both tasks, participants were asked to get hold of an object approaching along the table top at a constant velocity. In the prehension task, participants could reach out to grasp the object; in the catching task, they were required to keep their hand stationary. In comparison with other accounts, the dynamic timing model performed best in explaining the data. The model proved adequate for the prehension task but not for the current catching task.