How to cause motion sickness: Let's hope the folks at Guantanamo don't get their hands on one of these

What in the world is this thing?

It's called an optokinetic drum, and it's one of the many implements of torture you'll find in a spatial orientation lab. In an optokinetic drum, you sit or stand inside while the entire drum rotates around you. By changing the pattern on the inside of the drum, or by changing the way the drum rotates, a researcher can easily make you lose your lunch, breakfast, or even last night's dinner.

I got the picture of the drum from the Ashton Graybill Spatial Orientation Lab, where you'll find plenty of other devices that I sincerely hope the U.S. military doesn't know about.

Optokinetic drums can be used for practical things, too, like studying animation, or motion sickness. Researchers have found that as long as the drum rotates on a vertical axis and you sit still precisely in the center of a rotating drum painted with vertical stripes, you typically won't get sick. Tilt the drum or the victim a bit to one side, and sickness will ensue quite rapidly. So what does cause motion sickness? A team led by Frederick Bonato has developed a simple experiment to try to narrow down the possibilities.

One theory about motion sickness suggests that you'll get sick any time two sensory inputs about motion conflict: when your eyes detect different motion than your sense of balance (either through your vestibular system in the inner ear, or through sensations across the rest of your body). But in response to the fact that people don't generally get sick in the vertical drum, a second theory has emerged: that only the vertical sense matters -- only when our sensations about vertical conflict will we get sick.

Bonato's team wanted to test that second theory by developing a paradigm where vertical sensations did not conflict, but participants still got sick. They did it by rotating the drum for thirty seconds in one direction, then thirty seconds in the opposite direction. While the drum changed direction, the participants were asked to close their eyes for 5 seconds, so they wouldn't see any of the wobbling while the machine got up to speed. A second group of participants closed their eyes every 30 seconds while the drum rotated in the same direction, and a control group kept their eyes open the entire time while the drum rotated in the same direction.

Every two minutes, participants were asked to report on several different symptoms of motion sickness: for example, dizziness, nausea, dry mouth, and headache. In addition, they rated their overall feeling of sickness on a scale of 0 to 10 (0 = "I feel fine," and 10 = "I feel awful as if I am about to vomit"). Once this second rating reached 5, the experiment was stopped. After 6 minutes in the changing-direction condition, a quarter of participants had dropped out, so the researchers only used the 2- and 4-minute data points. Here are their results:

Participants in the changing-direction condition experienced significantly more nausea than the group who saw the drum rotating the same direction every time. A composite score of all motion sickness symptoms showed the same result. Bonato's team argues this shows that motion sickness can occur regardless of whether the sensory conflict is in the vertical direction. In this study, the only difference between the two groups was the horizontal motion of they cylinder, and motion sickness still occurred.

Why don't people sitting in a steadily rotating drum get sick? The team suggests that the key is when a person first opens their eyes inside the drum. The expectation is to see no motion, but the motion of the drum is seen. After a while, the participant gets used to the motion, so there is less of a conflict. But when the motion reverses every 30 seconds, a new conflict between expected and actual motion occurs. Over time, this leads to sickness.

Bonato, F., Bubka, A., & Story, M. (2005). Rotation direction change hastens motion sickness onset in an optokinetic drum. Aviation, Space, and Environmental Medicine, 76(9), 823-826.