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Motion Sickness
Motion sickness symptoms, although temporary, can be extremely unpleasant. Millions of travelers are affected by motion sickness each year. Although the constellation of symptoms varies, they can include dizziness, headache, bodily warmth, increased salivation, stomach awareness, diarrhea, dry mouth, pallor, nausea, retching and vomiting. Safety is a concern because symptoms can adversely affect human performance in addition to comfort. Even though motion sickness has affected humans for over 25 centuries, no cure exists. Common remedies include drugs that can sometimes cause side effects such as drowsiness, and questionable devices that may only provide relief by producing a placebo effect. Motion sickness is unique among sicknesses. It is not caused by factors that are typically associated with other illnesses (e.g., bacteria, viruses, parasites, poisons, etc). Instead, motion sickness seems to be result simply when a person (or animal) experiences self-motion either in a vehicle, such as an automobile or boat, or in an environment that causes the perception of self-motion (simulator or virtual environment).
Motion sickness has several variants. Typical forms of motion sickness include airsickness, seasickness, and carsickness, and their names are self-explanatory. Other less common variants are nonetheless disruptive in their respective environments. Space sickness, a form of motion sickness that occurs in zero gravity environments, can (and often does) affect the comfort and effectiveness of astronauts living and working in space. Simulator sickness, or cybersickness, affects civilians and military personnel who use vehicle simulators or virtual reality environments as part of their training regime. Those who play video games can even experience these forms of motion sickness. The games however usually include a first person perspective.
There are currently several theories of motion sickness. The most widely known class of theories is based on sensory conflict (Kennedy & Frank, 1986; Oman, 1990; Reason & Brand, 1975). These theories treat uncorrelated sensory inputs as the cause of symptoms. Conflict occurs when input from two sensory modalities (e.g., visual and vestibular) send signals to the central nervous system that do not correlate, or agree. The subjective vertical mismatch theory of motion sickness (Bles, Bos, de Graaf, Groen, Wertheim, 1998) specifically asserts that conflicts regarding sensed and expected vertical as the responsible conditions for MS onset. According to this theory other types of sensory conflict should not lead to symptoms.
Not all MS theories are based on sensory conflict. Stoffregen and colleagues (Riccio & Stoffregen, 1991; Smart, Stoffregen, & Bardy, 2002; Stoffregen & Riccio, 1991) have formed a theory based on postural instability. The postural instability theory asserts that MS is related to sub-optimal perception-action coupling that can lead to unstable control of body posture in novel motion environments. Ebenholtz and colleagues (Ebenholtz, et al., 1994) have proposed that eye muscle traction associated with nystagmus eye movements can elicit afferent signals that stimulate the vagus nerve and ultimately lead to motion sickness symptoms. However, although it has been shown that nystagmus eye movements are correlated with MS symptoms in some situations, the idea that such eye movements cause MS has not been experimentally tested.
Recent Motion Sickness Experiments Conducted on Motion Sickness in our Laboratory
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