1. NTT Communication Science Laboratories, Atsugi, Kanagawa, Japan
2. Imperial College of Science, Technology and Medicine, London, United Kingdom
3. Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, Kawaguchi, Saitama, Japan
4. School of Information Technology and Electronic Engineering, University of Queensland, St Lucia, Queensland, Australia
5. Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, Illinois