1. Department of Neurology, Centre Hospitalier Emile Mayrisch, L-4005 Esch-sur-Alzette, Luxembourg
2. Vestibular Research Group Berlin, Department of Neurology, Park-Klinik Weissensee, Berlin, Germany
3. Vestibular Research Group Berlin, Department of Neurology, Schlosspark-Klinik, Berlin, Germany
4. Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA