Grasping component alterations and limb transport.

The kinematic changes associated with the manipulation and transport components during a prehensile movement were examined using an experimental paradigm that required alterations in only the manipulation component. Instead of starting with the thumb and index finger naturally together (control condition), subjects began the reach-to-grasp movement with their thumb and fingers fully extended (experimental condition). In contrast to the control condition, in the experimental conditions the thumb and index finger started to close during wrist transport, then opened again prior to object grasp. In addition, there was a brief inflection in the ascending portion of the velocity profile of the wrist in over half the trials. However, all the primary features of the transport component profile remained unaltered. The results suggest that there can be substantial reorganization of the grip aperture during the first part of the reach without altering the temporal and spatial relationships between grip aperture and transport as the object to be grasped is approached.