Motion sickness with fore-and-aft and pitch oscillation: effect of the visual scene

Butler, Colleen Ann (2008) Motion sickness with fore-and-aft and pitch oscillation: effect of the visual scene. University of Southampton, Institute of Sound and Vibration Research, Doctoral Thesis, 205pp.

Abstract

Braking and acceleration expose car passengers to complex fore-and-aft and pitch motions that can cause carsickness, with the effect depending on the visual scene. Previous studies in various motion environments have suggested that external viewing reduces motion sickness relative to internal viewing or wearing a blindfold however the influences of motion and vision on motion sickness are thought to be interactive. The types of motion for which a visual scene can and cannot modify sickness are yet to be established. The aim of this research was to advance understanding of the effect of the visual scene on motion sickness caused by fore-and-aft oscillation, combinations of fore-and-aft and pitch oscillation, and pitch oscillations. The first experiment investigated the effect of the visual scene on motion sickness caused by low frequency low magnitude fore-and-aft oscillation. Six groups of 20 subjects experienced one of six visual scenes: an internal view of shapes; an external view of shapes; an external view of horizontal lines; a ‘real’ three-dimensional external view; no view (blindfolded); or an internal collimated view of shapes. Variations in the visual scene had no significant effect on motion sickness caused by 0.1 Hz fore-and-aft oscillation with an acceleration magnitude of 0.89 ms-2 r.m.s. The absence of an influence of vision differs from the effects of the visual scene on motion sickness in cars and coaches and suggested that carsickness is not solely caused by low frequency fore-and-aft acceleration. In a second experiment, six groups of 20 subjects were exposed to 0.1 Hz fore-and-aft oscillation combined with 0.1 Hz pitch oscillation with a peak pitch displacement of 3.69°. For three groups of subjects, the pitch displacement was 180° out-of-phase with the fore-and-aft displacement, such that the resultant peak acceleration acting on subjects in the fore-and-aft direction was 1.89 ms-2. The other three groups of subjects experienced the same fore-and-aft and pitch oscillations, but presented out-of-phase so that the peak fore-and-aft acceleration of ±1.26 ms-2 r.m.s. was partially offset by the pitch displacement of ±3.69°. Each subject experienced one of three viewing conditions from the first experiment: internal, blindfolded or external. The visual scene influenced the motion sickness caused by combined fore-and-aft and pitch oscillation regardless of whether pitch motion was in-phase or out-of-phase with the fore-and-aft motion: there was less sickness with an external forward view than with either an internal view or a blindfold. The effect of the phase between the fore-and-aft and pitch motion depended on the visual scene: the phase influenced motion sickness with a blindfold and with internal viewing but not with external viewing. The effect of internal, blindfold and external viewing on motion sickness caused by 0.1, 0.2 and 0.4 Hz pitch oscillation was investigated in a third experiment with 180 subjects, 20 subjects in 9 conditions. The visual scene influenced motion sickness similarly with 0.1, 0.2, and 0.4 Hz pitch oscillation: external viewing reduced motion sickness relative to internal viewing. There was no significant effect of pitch oscillation frequency. Experimental results suggest that there is no effect of the visual scene on motion sickness caused by fore-and-aft oscillation but the visual scene is influential when pitch motion is part or all of the motion stimulus. The effect of the visual scene on motion sickness cannot be predicted without specifying the motion stimulus causing sickness. Unlike previous models of motion sickness, a conceptual model is suggested in which the expected visual signal is defined for a given vestibular input. The model predicts that external viewing reduces motion sickness relative to internal or blindfolded conditions when sickness is caused by motions inclusive of pitch oscillation. Model predictions for the effect of the visual scene on motion sickness caused by other directions of oscillation are considered.

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