May 1, 2007 — The cause of motion sickness is being investigated by a researcher with a new idea: that the cause is movement, not perceptual differences. A series of motion-sickness-inducing tests shows that those people who get sick start to move oddly, similar to a drunken staggering walk.
There are plenty of treatments for motion sickness, but no one really knows what causes it. And why are some people affected, but not everybody? Human factors researchers at the University of Minnesota are conducting experiments to discover exactly what causes motion sickness. The researchers attach sensors to the test subject's head and place him in a simulated room that slowly sways back and forth. Here, they study how exaggerated or "wobbly" body motions may cause motion sickness.
Tom Stoffregen, Ph.D., a professor of human movement science at the University of Minnesota in Minneapolis told Ivanhoe about the experiments, "It's very common sense to think that that when you get motion sick you get wobbly, and what we're doing is, looking at things in exactly the opposite order that it may be that people become wobbly before they get sick. And that it's only the people that become wobbly that later get sick."
Dr. Stoffregen doesn't believe the inner-ear theory, because the inner ear isn't affected in his experiments that create visual, not physical, movement. The sophisticated sensors used in the experiments pick up subtle movements. Those who move a lot, although barely visible, are the ones that get sick. He says it's like they're subconsciously moving to compensate for the motion, but they're only making it worse.
Dr. Stoffregen says, "People who are going to get sick first become wobbly, and it's fair to say that by becoming wobbly they make themselves sick." For now, researchers can't predict who's going to get sick, but experts say the best way to prevent motion sickness is to lie down and close your eyes.
The Human Factors and Ergonomics Society contributed to the information contained in the TV portion of this report.
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.
Note: This story and accompanying video were originally produced for the American Institute of Physics series Discoveries and Breakthroughs in Science by Ivanhoe Broadcast News and are protected by copyright law. All rights reserved.
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