1. Department of Physiology and
2. Department of Orthopedic Surgery, Tokyo Medical College, Tokyo 160;
3. Department of Information and Knowledge Engineering, Faculty of Engineering, Tottori University, Tottori 680, Japan; and
4. Laboratoire de Physiologie de la Perception et de l'Action, Centre National de la Recherche Scientifique, Collège de France, Paris Cedex 05, France