Visual-vestibular conflict induced by virtual reality in humans Hironori Akiduki a , Suetaka Nishiike b, * , Hiroshi Watanabe c , Katsunori Matsuoka c , Takeshi Kubo d , Noriaki Takeda a a Department of Otolaryngology, University of Tokushima School of Medicine, Tokushima 770-0042, Japan b Department of Otolaryngology, Suita Municipal Hospital, 2-13-20 Katoyoma-cho, Saita Osaka 564-0082, Japan c Life Electronics Laboratory, National Institute of Advanced Industrial Science and Technology, Osaka 563-8577, Japan d Department of Otolaryngology and Sensory Organ Surgery, Osaka University Graduate School of Medicine Osaka 565-0871, Japan Received 16 December 2002; received in revised form 14 January 2003; accepted 15 January 2003 Abstract Conflicting inputs from visual and vestibular afferents produce motion sickness and postural instability. However, the relationship of visual and vestibular inputs to each other remains obscure. In this study, we examined the development of subjective sickness- and balance- related symptoms and objective equilibrium ataxia induced by visual – vestibular conflict (VVC) stimulation using virtual reality. The subjective symptoms evaluated by Graybiel’s and Hamilton’s criteria got gradually worse during the VVC. The objective postural instability was not observed during the VVC, but it occurred immediately after the VVC. There was a time lag between the subjective symptoms and objective ataxia induced by VVC. Our study suggests that the VVC inputs are processed in different pathways causing subjective autonomic symptoms and postural instability in humans. q 2003 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Motion sickness; Equilibrium; Ataxia; Visual-vestibular conflict; Virtual reality Abnormality of spatial orientation provokes motion sick- ness [11,15] leading to autonomic symptoms and produces postural instability [13]. Previous studies demonstrated that disparity between subjective reports of motion sickness or balance and objective postural instability [1,3,7,14]. How- ever, most studies used ready-made flight simulators, which did not ensure a suitable situation for inducing motion sickness. In these studies, subjective and objective measures were only examined before and after stimulation, because subjects were fixed in the simulator cockpit during the stimulation. In the present study, we examined the development of subjective symptoms and objective equilibrium ataxia before, during and after visual – vestibular conflict (VVC) stimulation by means of virtual reality (VR). The VR system allowed us to easily coordinate incoherent VVC to induce motion sickness and postural instability. The subjects are free to move their head and body during VR stimulation; thus the assessment of subjective symptoms and objective ataxia during the VVC were easy. Subjects were nine healthy young volunteers (eight male and one female, mean age: 28.4 years old). The VR system used in the present study was a projection-based system that surrounds the subject with four screens: three rear projection screens for walls and a down-projection screen for a floor space 9 m 2 each (CAVE; Electronic Visualization Labora- tory, University of Illinois, Chicago, IL) (Fig. 1A). Subjects wore liquid crystal stereo shutter glasses to resolve the stereoscopic imaginary. An electromagnetic tracking sys- tem attached to the glasses determined the location and angle of user’s head orientation. Subjects were immersed in two different VR conditions. The background in both conditions was made by a randomized texture pattern (Fig. 1A). One was a Mismatch condition; when subjects turned their head, the background of the VR turned to a degree double that of the head movement on a vertical axis. The other was the Control condition; an interactive computer graphics synchronizing the background image proportionally to the subject motion. The levels of the severity of motion sickness were given numerical scores according to Graybiel’s criteria: a multi symptom checklist to assess motion sickness symptomatol- 0304-3940/03/$ - see front matter q 2003 Elsevier Science Ireland Ltd. All rights reserved. doi:10.1016/S0304-3940(03)00098-3 Neuroscience Letters 340 (2003) 197–200 www.elsevier.com/locate/neulet * Corresponding author. Tel.: þ 81-6-6387-3311; fax: þ81-6-6380-5825. E-mail address: nishiike@concerto.plala.or.jp (S. Nishiike).