Tilted Drum Experiment

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 0degimage.jpg            5degimage.jpg         10degimage.jpg

Apparatus-The optokinetic drum consisted of a synthetic composite cylinder 122 cm in height and 107 cm in diameter. The interior of the drum was covered with 24 pairs of alternating black and white strips, all of which were equal in width (7.5 deg.). The drum was suspended from a motor attached to a beam directly above the drum by steel cables. The drum could be tilted up to 10 degrees. The participant sat in the drum such that their head was positioned in the center of the drum.  Head position was maintained throughout the experiment by means of an optical chin rest.

Procedure-The participant was seated inside the drum and familiarized with two subjective rating scales. Baseline ratings of their overall well-being were taken using a 0-10 scale (0=I feel fine, 10=I feel as if I am about to vomit). A subjective symptoms of motion sickness (SMSS) scale was used to assess spinning, dizziness, bodily warmth, headache, increased salivation, stomach awareness, nausea, and dry mouth. Participants used the following scale to rate each symptom: none=0, mild=1, moderate=2, severe=3.     The participant was instructed to position their head in the chin rest and remain stationary throughout the session. The drum was activated so that it steadily rotated at 60°/sec (10 RPM). Participants were instructed to open their eyes and overall well-being and subjective symptom data were obtained every two minutes. Participants were reminded that they could close their eyes at any time and request that the experiment be stopped, if they experienced motion sickness symptoms that were uncomfortably severe. A trial was considered finished when the subject reported a five or higher on the overall well-being or 16 minutes had elapsed. Each participant served in three tilt conditions in counterbalanced order. In one condition, the drum was perpendicular to the floor (zero degree condition). In another condition, the drum was tilted five degrees, and in a third condition the drum was tilted 10 degrees. At the conclusion of each of the three trials, the participant rested until the severity of symptoms subsided. The participant was scheduled for a subsequent trial in 48-72 hours. At the conclusion of their last trial, the participant was fully debriefed.

Results and Discussion-The mean number of minutes it took to reach the midpoint (5) of the overall well-being scale for the three experimental conditions were as follows: zero degrees, 9.7 minutes; five degrees, 7.8 minutes; ten degrees, 6.2 minutes. A repeated measures one-way ANOVA revealed a significant difference among conditions [F(2, 22)=3.68, p<.042]. A composite SSMS score was calculated for each participant by adding up the subjective ratings (0-3) for each of the eight symptoms probed (spinning, dizziness, bodily warmth, headache, increased salivation, stomach awareness, nausea, and dry mouth). Although eight symptoms were probed, realistically, the highest possible score was a “21” because, it is not possible for a participant to experience increased salivation and dry mouth at the same time. The mean number of minutes it took participants to reach the approximate midpoint of the SSMS scale (11) in each of the three conditions were as follows: zero degrees, 9.7 minutes; five degrees, 5.0 minutes; ten degrees, 4.8 minutes.  A one-way repeated measures ANOVA revealed a significant difference among conditions [F(2, 22)=4.02, p<.032].

These results clearly support the hypothesis that as sensory conflict between the visual and vestibular systems is increased, the onset latency of symptoms decreases. In the control condition (zero degrees) the onset of symptoms was the slowest. As the degree of tilt was increased, the onset of symptoms was hastened. These results offer empirical support for sensory conflict theories of motion sickness.

For a more detailed report on this study please see:

Bubka, A., & Bonato, F. (2003). Optokinetic drum tilt hastens the onset of vection-induced motion sickness symptoms. Aviation, Space, and Environmental Medicine, 74, 315-319.