抄録
Jeannerod (1981) proposed that prehension movements consist of two components; the transport component and the manipulation component. These two components are independent each other. The transport component is based on extrinsic properties of the object (e.g. location), whereas the manipulation component is based on intrinsic properties (e.g. size). While many studies about the effects of location and size of the object on prehension were investigated, the influence of object orientation has been examined in a few papers. To investigate how orientation of the object is processed, we made two experiments with virtual reality (VR) technique. In experiment 1, we studied the properties of prehension movements to a computer-generated target (a virtual cylinder), comparing it with prehension movements to a real object (a wooden cylinder) and pantomimed movements (subjects were required to pretend to grasp the same cylinder). Results showed that the kinematic pattern of prehension movements to a 3-dimensional virtual image is similar to that of actual performance using a real object. Therefore, VR technique is valid for investigating the kinematics of prehension movements, although there is no tactile feedback when grasping. In experiment 2, we used a visual perturbation paradigm by which the location, size (width) and orientation (in this case, inclination) of the object to be reached and grasped could be changed 150ms after the beginning of movement. Participants could smoothly modify their arm movement (transport), distance of fingers (manipulation) and rotation of wrist to visual perturbation, but the latencies of the modifications for these three movements differed from each other. This result suggests that the orientation of a target is processed in a different system from that for the size or location on prehension movements. That is, hand transport, wrist rotation, and grasping could each be processed by independent visuomotor channels.
