Background: Stationary subjects who view the interior of an optokinetic drum often experience motion sickness (MS) symptoms, perhaps because visual and vestibular sensory inputs are in conflict. It was predicted that intermittently changing drum rotation velocity would cause an increase in sensory conflict, and subsequently lead to more MS. Visual input indicating frequent changes in self-motion would not be consistent with vestibular input indicating no self-motion. When drum rotation is steady, visual and vestibular inputs are more likely to agree given that the vestibular organs only respond to change.
Methods: There were 12 individuals who participated in the experiment (7 men, 5 women, mean age = 24.0 yr). In two conditions subjects viewed the interior of an optokinetic drum that steadily rotated at either 5 RPM or 10 RPM. In a third condition drum velocity alternated every 30 s between 5 RPM and 10 RPM (5/10 RPM condition). In all conditions the subject's head was immobilized in the center of the drum that rotated on an Earth-vertical axis. Subjects completed the Simulator Sickness Questionnaire (SSQ) designed by Kennedy and colleagues both before a trial and after 4 min of drum viewing. A total SSQ score and three SSQ sub-scores (nausea, oculomotor, and disorientation) were obtained.
Results: Mean post-treatment total SSQ scores (mean = 41) were significantly the highest in the 5/10 RPM condition followed by the conditions of steady rotation velocity at 10 RPM (mean = 36) and 5 RPM (mean = 24). Likewise, mean nausea sub-scores were also the highest (mean = 24) in the 5/10 RPM condition followed by the 10 RPM condition (mean = 19) and the 5 RPM condition (mean = 11).
Conclusions: These results support the hypothesis that a conflict between sensed and expected effects of self-motion alone can lead to MS. Changing rotation velocity increases sensory conflict that in turn leads to more MS.