Validity of the speed-accuracy tradeoff for prehension movements.

Subjects (n=12) grasped mirror-viewed visual targets with thumb and index finger, while prescribed movement time differed between blocks of trials. The variability of both final grip aperture (i.e. distance between thumb and index finger) and of final wrist position increased with decreasing movement time, indicating the existence of a speed-accuracy tradeoff both in the grasp and in the transport component of prehension. This tradeoff was limited to relatively short movement times (<400 ms) for the grasp component, but it extended to longer movement times for the transport component, which supports the view that the two components are controlled by separate mechanisms.