Effect of seating, vision and direction of horizontal oscillation on motion sickness

Background: Low frequency horizontal oscillation can cause motion sickness in some forms of transport but the influence of the characteristics of the motion and the visual and postural conditions of the body on sickness are not known. Hypotheses: It was hypothesised that body position, vision and direction of motion will have an effect on motion sickness. Method: There were 72 seated subjects who were exposed to horizontal oscillation at 0.25 Hz, 0.7 ms(-2) r.m.s. (peak-to-peak displacement of 0.8 m) for up to 30 min while in 1 of 6 conditions. Three conditions involved fore-and-afr motion and three involved lateral motion. For motion in each axis, subjects sat within a dosed cabin with either: a) a high backrest with their eyes open; b) a low backrest with their eyes open; or c) a low backrest with their eyes closed and blindfolded. Subjects provided ratings of their motion sickness symptoms at I-min intervals during the 30-min exposures. Results: The most nauseogenic stimulus was fore-and-aft motion with a low backrest and the eyes open. Self-ratings of motion sickness susceptibility provided by subjects before participating in the experiment were positively correlated with their illness ratings during the experiment. Conclusions: Restraint to the upper body during exposure to horizontal acceleration may reduce the susceptibility to motion sickness caused by horizontal oscillation. The relative nauseogenicity of fore-and-aft and lateral oscillation depends on the support given to the upper body. In the conditions of the experiment the effects of the postural support given to the subjects and their prior susceptibility to motion sickness were greater than any effect of the visual conditions.