Effect of magnitude and direction of horizontal oscillation on motion sickness.

Various types of motion and visual scene can cause motion sickness, but sickness in land transport seems to be often associated with variations in horizontal acceleration. If horizontal oscillation causes sickness, it seems reasonable to assume that greater amounts of motion (i.e., an increased magnitude of motion or an increased duration of motion) will increase the extent of the sickness.It was hypothesized that the magnitude, direction, and duration of horizontal oscillation would affect the sickness experienced by subjects.The 144 subjects were exposed to horizontal sinusoidal oscillation at a frequency of 0.315 Hz while seated in a closed cabin with their eyes open for up to 30 min. Subjects were exposed to one of 12 conditions with either fore-and-aft or lateral oscillation at magnitudes of either: (i) 0.28 ms(-2) rms, (ii) 0.56 ms(-2) rms, (iii) 0.70 ms(-2) rms, (iv) 0.89 ms(-2) rms, (v) 1.11 ms(-2) rms, or (vi) a stationary control condition. Subjects provided ratings of their motion sickness symptoms at 1-min intervals during the 30-min exposures.At a frequency of 0.315 Hz, an increase in either the magnitude or the duration of horizontal oscillation resulted in increases in the incidence of motion sickness. There were significant positive correlations between self-ratings of motion sickness susceptibility provided by subjects before participating in the experiment and their illness ratings during the experiment.At a frequency of 0.315 Hz, motion sickness caused by horizontal oscillation increases with increases in the magnitude and duration of horizontal oscillation. For the conditions of this study, the sickness was similar with fore-and-aft and lateral oscillation.