1. Knowledge Creating Communication Research Center, NICT, 2-2-2 Hikaridai, Seika-cho, Soraku-gun, Kyoto 619-0288, Japan
2. Department of Humanoid Robotics and Computational Neuroscience, ATR Computational Neuroscience Laboratories, 2-2-2 Hikaridai, Seika-cho, Soraku-gun, Kyoto, 619-0288, Japan
3. Department for Automatics, Biocybernetics and Robotics, Jozef Stefan Institute, Jamova 39, 1111 Ljubljana, Slovenia
4. JST-ICORP Computational Brain Project, 4-1-8 Honcho, Kawaguchi, Saitama, Japan