作者单位:Department of Computational Intelligence and Systems Science,Tokyo Institute of Technology, G3-46, 4259 Nagatsuta-cho,Midori-ku, Yokohama 226-8502, Japan[1]Sony Computer Science Laboratories, Inc., Takanawa Muse Bldg, 3-14-13 Shinagawa-ku, Tokyo 141-0022, Japan[2]