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Factor analysis of a large number of motion sickness self-reports from exposure to military flight simulators revealed three separate clusters of symptoms. Based on this analysis a symptom profile emerged for simulators where Oculomotor symptoms predominated, followed by Nausea and least by Disorientation-like symptoms. Current users of virtual environment (VE) systems have also begun to report varying degrees of what they are calling cybersickness, which initially appeared to be similar to simulator sickness. We have found, after examination of eight experiments using different VE systems, that the profile of cybersickness is sufficiently different from simulator sickness — with Disorientation being the predominant symptom and Oculomotor the least. The total severity of cybersickness was also found to be approximately three times greater than that of simulator sickness. Perhaps these different strains of motion sickness may provide insight into the different causes of the two maladies.

Virtual environments are envisioned as being systems that will enhance the communication between humans and computers. If virtual systems are to be effective and well received by their users, considerable human-factors research needs to be accomplished. This paper provides an overview of many of these human-factors issues, including human performance efficiency in virtual worlds (which is likely influenced by task characteristics, user characteristics, human sensory and motor physiology, multimodal interaction, and the potential need for new design metaphors); health and safety issues (of which cybersickness and deleterious physiological aftereffects may pose the most concern); and the social impact of the technology. The challenges each of these factors present to the effective design of virtual environments and systematic approaches to the resolution of each of these issues are discussed.

Although simulator sickness is known to increase with protracted exposure and to diminish with repeated sessions, limited systematic research has been performed in these areas. This study reviewed the few studies with sufficient information available to determine the effect that exposure duration and repeated exposure have on motion sickness. This evaluation confirmed that longer exposures produce more symptoms and that total sickness subsides over repeated exposures. Additional evaluation was performed to investigate the precise form of this relationship and to determine whether the same form was generalizable across varied simulator environments. The results indicated that exposure duration and repeated exposures are significantly linearly related to sickness outcomes (duration being positively related and repetition negatively related to total sickness). This was true over diverse systems and large subject pools. This result verified the generalizability of the relationships among sickness, exposure duration, and repeated exposures. Additional research is indicated to determine the optimal length of a single exposure and the optimal intersession interval to facilitate adaptation.

For those interested in using head-coupled PC-based immersive virtual environment (VE) technology to train, entertain, or inform, it is essential to understand the effects this technology has on its users. This study investigated potential adverse effects, including the sickness associated with exposure and extreme responses (emesis, flashbacks). Participants were exposed to a VE for 15 to 60 min, with either complete or streamlined navigational control and simple or complex scenes, after which time measures of sickness were obtained. More than 80% of participants experienced nausea, oculomotor disturbances, and/or disorientation, with disorientation potentially lasting > 24 hr. Of the participants, 12.9% prematurely ended their exposure because of adverse effects; of these, 9.2% experienced an emetic response, whereas only 1.2% of all participants experienced emesis. The results indicate that designers may be able to reduce these rates by limiting exposure duration and reducing the degrees of freedom of the user's navigational control. Results from gender, body mass, and past experience comparisons indicated it may be possible to identify those who will experience adverse effects attributable to exposure and warn such individuals. Applications for this research include military, entertainment, and any other interactive systems for which designers seek to avoid adverse effects associated with exposure.

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Simulator sickness has been identified as a form of motion sickness in which users of simulators exhibit symptoms characteristic of true motion sickness. In a fixed-base simulator, visual and vestibular sources of information specifying dynamic orientation are in conflict to the extent that the optical flow pattern viewed by the pilot creates a compelling illusion of self-motion, which is not corroborated by the inertial forces transmitted through the vestibular sense organs. Visually induced illusory self-motion is known as vection, and a strict interpretation of sensory conflict theory of motion sickness suggests that vection in a fixed-base simulator would be a necessary precondition for simulator sickness. Direct confirmation of this relation is reported in this article.