Rotation direction change hastens motion sickness onset in an optokinetic drum

BACKGROUND: Many stationary subjects who view the patterned interior of a rotating cylinder (optokinetic drum) experience motion sickness (MS) symptoms. An experiment was conducted to investigate the effects of rotation direction change on MS onset and severity. It was predicted that intermittently changing rotation direction would hasten MS onset due to an increased degree of visual/vestibular sensory conflict. METHODS: There were 12 individuals who participated in the experiment (4 men, 8 women, mean age = 24.4 yr). Subjects viewed the interior of an optokinetic drum that rotated at 5 rpm (30 degrees x s(-1)). Drum rotation was either consistently in the same direction or rotation direction changed every 30 s. Eight MS symptoms were assessed at 2-min intervals using a subjective scale (0 = none, 1 = slight, 2 = moderate, 3 = severe). RESULTS: Overall, MS onset was fastest when drum rotation direction changed. Specific MS symptoms significantly affected were dizziness, stomach awareness, and nausea. CONCLUSIONS: These results suggest that a lack of correlation between the sensed and expected effects of motion alone can lead to MS. These results cannot be accounted for by a lack of correlation between sensed and expected gravitational vertical given that these were held constant across conditions.