1. Department of Intelligent Interaction Technologies, Faculty of Engineering, Information and Systems, University of Tsukuba, Tsukuba, Japan
2. Department of Physical Rehabilitation, National Center Hospital, National Center of Neurology and Psychiatry, Tokyo, Japan
3. Center for Innovative Medicine and Engineering and the Center for Cybernics Research, University of Tsukuba, Tsukuba, Japan
4. Institute of Systems and Information Engineering and the Center for Cybernics Research, University of Tsukuba, Tsukuba, Japan