Effect of frequency and direction of horizontal oscillation on motion sickness

Background: Low frequency horizontal oscillation can cause motion sickness in some transportation systems, but the influence of the frequency, magnitude, direction, and duration of oscillation are poorly understood.Hypothesis: It was hypothesized that motion sickness was independent of the direction of horizontal oscillation (fore-and-aft or lateral) and that there was no difference in the motion sickness produced by different frequencies of horizontal oscillation (between 0.2 and 0.8 Hz) when subjects were exposed to the same peak velocity of motion at each frequency.Method: The 192 subjects were exposed within a closed cabin to sinusoidal oscillation with a velocity of ± 0.50 ms-1. Each subject experienced up to 30 min of motion while sitting with eyes open on a seat with a low backrest. The 16 conditions involved either fore-and-aft or lateral oscillation at 8 different frequencies: (i) 0.20 Hz, (ii) 0.25 Hz, (iii) 0.315 Hz, (iv) 0.40 Hz, (v) 0.50 Hz, (vi) 0.63 Hz, (vii) 0.80 Hz, or (viii) a stationary control condition. Subjects provided ratings of their motion sickness symptoms at 1-min intervals during the 30-min exposures.Results: Each frequency of oscillation produced significantly more sickness than the static control conditions. Overall, there were no significant differences in the sickness produced by the seven different frequencies or between the sickness produced by fore-and-aft or lateral oscillation. 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: With horizontal oscillation over the range 0.2 to 0.8 Hz, motion sickness is very approximately dependent on the peak velocity of oscillation. An acceleration frequency weighting having a gain inversely proportional to frequency would provide a convenient simple method of evaluating this type of motion in transport. However, the results suggest that a more complex weighting, reflecting decreased nauseogenicity at higher and lower frequencies would be more accurate. The direction of motion (i.e., fore-and-aft or lateral) had no effect on the sickness experienced