1. Department of Otorhinolaryngology, Juntendo University School of Medicine, Tokyo 113-8421, Japan.
2. Department of Otolaryngology, Keio University, Tokyo 160-0016, Japan.
3. Department of Neurology, Juntendo University School of Medicine, Tokyo 113-8421, Japan.
4. Department of Physiology, School of Allied Health Sciences, Kitasato University, Sagamihara 228-8555, Japan.