BACKGROUND: Motion sickness has afflicted the human race for thousands of years, but no one is sure what causes the telltale headaches, dizziness, and -- occasionally -- vomiting. It also seems to affect certain people more than others. A University of Minnesota professor named Thomas Stoffregen is investigating what causes motion sickness by conducting tests on a surprisingly willing batch of undergraduate students.
ABOUT MOTION SICKNESS: The most common symptoms of motion sickness are dizziness and vertigo. Motion sickness is related to balance and spatial orientation -- the way the brain informs the body where it is in space: what direction it is pointing, what direction it is moving, whether it is turning or standing still. Our sense of balance is maintained by a complex interaction among various parts of the nervous system. The inner ear monitors the directions of motion: forward, back, up, down, or side to side. The eyes monitor where the body is in space. The skin pressure receptors in the joints and spine tell the brain what parts of the body is touching the ground, while receptors in the muscles and joints indicate which parts of the body are moving. The central nervous system processes all this incoming information to make sense of it all. When the central nervous system receives conflicting information, symptoms of motion sickness may result.
ANOTHER EXPLANATION? There have been studies of how the sensations in the inner ear and eyes are different when motion sickness occurs -- such as when a person is in the car and the eyes report movement, but the body thinks it is still stationary. However, Stoffregen doesn't think the cause is perceptual differences. He thinks it can be attributed to movement. So he measures the movement of people subjected to a series of motion-sickness-inducing tests. He finds that those people who get sick start to move oddly, similar to a drunken staggering walk. Even when strapped to an upright stretcher, such people still move a little, by wriggling. People differ in their sensitivity. Only half of Stoffregen's test subjects reported feeling sick, but those were also the same students who didnýt tend to wriggle.
YOU MAKE ME SICK: Stoffregen continues to test his theory in the university's Human Factors Research Laboratory. Even though the tests are designed to cause motion sickness in participants, the subjects remain stationary while the surrounding scenery shifts. In one test, a room-like structure is mounted on metal tracks and the subject stands on a platform as the 'room' slides backward and forward on the track. Stoffregen has also computerized his tests so subjects can stand in front of a huge screen and feel the same effects. And sometimes the test subjects are asked to play games on the lab's X-Box system.