1. Faculty of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan.
2. Department of Developmental Psychology, National Children's Hospital, 3-35-31 Taisidou, Setagaya-ku, Tokyo 154, Japan.
3. Department of Neurology, National Children's Hospital 3-35-31 Taisidou, Setagaya-ku, Tokyo 154, Japan.