1. G. Wang, Laboratory for Neural Information Processing, Frontier Research Program, Institute of Physical and Chemical Research (RIKEN), and Department of Physiology II, Faculty of Medicine, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima-shi, Kagoshima, 890, Japan.
2. K. Tanaka, Laboratory for Neural Information Processing, Frontier Research Program, and Information Science Laboratory, RIKEN, 2-1 Hirosawa, Wako-shi, Saitama, 351-01, Japan.
3. M. Tanifuji, Department of Information Science, Fukui University, and Precursory Research for Embryonic Science and Technology (PRESTO), Research Development Corporation of Japan, 3-9-1 Bunkyo, Fukui, 910, Japan.