1. Department of Comparative Study of Cognitive Development (funded by Benesse Corporation), Primate Research Institute, Kyoto University, Inuyama, Aichi 484-8506, 2Brain Activity Imaging Center, Advanced Telecommunications Research Institute International, 2-2-2 Hikaridai, Seika-cho, Soraku-gun, Kyoto 619-0288, 3Department of Cognitive Psychology in Education, and 4Kokoro Research Center, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan