**6. Acknowledgment**

This work is supported by Grants-in-Aid for Challenging Exploratory Research (Project # 23650202) and Priority Areas "Emergence of Adaptive Motor Function through Interaction between Body, Brain and Environment (Area #454)" from the Japanese Ministry of Education, Culture, Sports, Science and Technology to K.T. We express sincere appreciation to Ms. Mihoko Ebisawa for preparation of this manuscript.
