1. Center for Evolutionary Cognitive Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Meguro, Tokyo 153-8902, Japan
2. Emotional Information Joint Research Laboratory, RIKEN Brain Science Institute, Wako, Saitama, Japan
3. ERATO, Okanoya Emotional Information Project, Japan Science Technology Agency, Wako, Saitama, Japan
4. Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Meguro, Tokyo 153-8902, Japan