Different coupling for the reach and grasp components in bimanual prehension movements.

In this study on functional coupling in bimanual grasping movements, nine normal subjects had to reach and grasp two different objects simultaneously. Both objects could be either small or large, resulting in four different conditions of bimanual grasping. The main dependent variables were the coupling coefficients calculated either between the hand displacements or between the grip apertures of both hands, serving as variables for the coupling of the reach and the grasp component respectively. The correlation was significantly higher for the reach component than for the grasp component, with only the latter one changing significantly with variation of object size. These findings suggest different temporo-spatial coupling modes for the reach and the grasp components of bimanual grasping movements.