Sensory conflict theory and space sickness: our changing perspective.

Motion sickness is a well-known nausea and vomiting syndrome whose physical signs include vomiting and retching, pallor, cold sweating, yawning, belching, flatulence, and decreased gastric tonus. Subjective symptoms include stomach discomfort, nausea, headache, feeling of warmth, and drowsiness. The research literature has been well reviewed 0-7). Over the past hundred years, our perspective on the kinds of sensory stimulation that can cause motion sickness has broadened considerably. Originally it was assumed that motion sickness can only be caused by motion and is due to mechanical stimulation of visceral afferents or changes in cerebral blood flow caused by body motion. It was eventuaJl~ recognizee; thai people who have no inner ear halance or~an fUIlction are totally immune, indicating thai the l11alaa~ results specifically from veStibular ove;·-'lilllulation. However. by 1970 it became apparel1i that a more comprehensive etiologic frame\\ ork was needed: some forms of motion sickness were recognized in which head and body motion is normal (that is. spectacle sickness_ space sickness) or even absent (flight simulator and Cinerama sickness). We experience vigorous vestibular stimulation when we run, jump, or dance, but these activities almost never make us sick. Claremont (8) had originally suggested that mo-