Postural instability induced by virtual reality exposure: development of a certification protocol. 
Exposure to virtual environments often causes users to experience symptoms of motion sickness.  An accessory manifestation of motion sickness symptoms is postural disequilibrium.  If the postural disequilibrium that occurs persists beyond the time an individual is within the confines of the laboratory or system site, user safety could be compromised and products liability issues could be forthcoming.  In this study, a portable, automated postural assessment system is developed that can be employed before and after exposure to a virtual reality (VR) system in order to certify that a user's balance on exiting the system is at least demonstrably as good as it was on entering.  It is argued that if the "coming out" balance performance is sufficiently poorer than the "going in" balance, then the user should be retained until the pretest balance performance is regained.  The results from a set of normative and validation experiments on postural equilibrium identified several reliable measures of stance that could serve as a basis for certification.  Furthermore, a new automated video-based measure using only head movement showed that performance over sessions is stable and reliable.  The head movement changes that occur with stimuli, such as alcohol and simulator exposure, are well behaved, predictable, and significant even with small samples.  The implication is that the proposed objective measure of postural stability, in conjunction with procedures for obtaining self-reports of symptoms, can afford some measure of certification that exposure to a given VR system is without harm.