Abstract
Virtual motion environments often elicit ill effects common to many actual motion environments. Immersion in such an illusory moving surround involves substantial visual, as well as postural and vestibular activity. Most provocative motion environments cause three distinct, but possibly related, responses: reflexive eye movements (EM), sensory conflict (SC), and postural instability (PS). Three current theories, concerning the cause of motion sickness (MS), emphasize one of these responses, but deny the importance of the others. Such theoretical approaches preclude the possibility of a synergistic interaction of these factors. This experiment employed a three-factor experimental design wherein each factor was manipulated alone or in combination with the others. The independent variables involved two levels of: PS (induced by having the subject stand in a posturally neutral or challenging position); SC (with or without ego vection elicited visually by whole field motion stimulation); and EM (unrestricted or controlled with fixation). Measures of PS, SC, EM, and MS were recorded under the various conditions. Analysis of measures of PS, SC, and EM confirmed the effectiveness of these manipulations. Analysis of MS measures revealed a strong effect of conditions of SC, with the greatest MS found within conditions of illusory motion. The findings lend considerable support for the SC theory of MS, but do not convincingly rule out the PS, EM, or an interactive approach to MS. Results are discussed in terms of SC eliciting visual and postural activity, which may contribute to the intensity of MS experienced within a virtual motion environment.