Head-Mounted Displays for Clinical Virtual Reality Applications: Pitfalls in Understanding User Behavior while Using Technology LISA K. SIMONE, PH.D., 1,3 MARIA T. SCHULTHEIS, PH.D., 2,3 JOSE REBIMBAS, B.S., 3 and SCOTT R. MILLIS, PH.D. 3,4 ABSTRACT The use of virtual environments with head-mounted displays (HMDs) offers unique assets to the evaluation and therapy of clinical populations. However, research examining the effects of this technology on clinical populations is sparse. Understanding how wearers interact with the HMD is vital. Discomfort leads to altered use of the HMD that could confound per- formance measures; the very measures which might be used as tools for clinical decision making. The current study is a post-hoc analysis of the relationship between HMD use and HMD comfort. The analysis was conducted to examine contributing factors for a high inci- dence of simulator sickness observed in an HMD-based driving simulator. Pearson correla- tion analysis was used to evaluate objective and subjective measures of HMD performance and self-reported user comfort ratings. The results indicated weak correlations between these variables, indicating the complexity of quantifying user discomfort and HMD performance. Comparison of two case studies detailing user behavior in the virtual environment demon- strates that selected variables may not capture how individuals use the HMD. The validity and usefulness of the HMD-based virtual environments must be understood to fully reap the benefits of virtual reality (VR) in rehabilitation medicine. 591 CYBERPSYCHOLOGY & BEHAVIOR Volume 9, Number 5, 2006 © Mary Ann Liebert, Inc. INTRODUCTION W ITH THE ADVENT of faster and affordable hard- ware and accessories, virtual reality (VR) sys- tems are being explored for a wider range of applications beyond flight simulation and three- dimensional (3D) gaming. One area where this trend can be seen is in medicine. Recent applica- tions of virtual reality in medicine have included surgical 1 and dental training 2 and clinical perfor- mance assessment. 3–5 Findings indicated that sup- plemental VR training improved skills and shortened surgical procedure time, making VR a good training tool. VR has also expanded into broader areas including the use of the technology for treatment and for clinical decision-making. For example, VR has been used in conjunction with ex- posure therapy for fear or anxiety conditioning, such as fear of heights and fear of driving. 6–8 VR has also been successfully applied for distraction of pain during various medical procedures. 9 In rehabilitation medicine, VR can offer several unique assets to both assessment and treatment of physical, cognitive and behavioral disabilities. 10 1 Department of Biomedical Engineering, New Jersey Institute of Technology, Newark, New Jersey. 2 Department of Psychology, Drexel University, Philadelphia, Pennsylvania. 3 Kessler Medical Rehabilitation Research and Education Corporation, West Orange, New Jersey. 4 Rehabilitation Institute of Michigan, Detroit, Michigan.