1. ATR Knowledge Science Laboratories, 2-2-2, Hikaridai, Seika-cho, Soraku-gun, Kyoto 619-0288, Japan. E-mail: ave@ultimaVI.arc.net.my
2. School of Engineering, The University of Tokyo, Tokyo, Japan
3. National Institute of Information and Communications Technology, Kyoto, Japan
4. Seinan Jo Gakuin University Fukuoka, Kyoto, Japan
5. Kyoto Institute of Technology, Kyoto, Japan