1. Graduate School of Agricultural Science, Kobe University, Rokkodaicho 1-1, Nada, Kobe 657-8501, Japan
2. Graduate School of Agricultural Science, Tohoku University, Aoba 468-1, Aranaki,
Aoba, Sendai 980-0845, Japan
3. Biosignal Research Center, Kobe University, Rokkodaicho 1-1, Nada, Kobe 657-8501, Japan