Background: Motion sickness is a serious issue for many individuals, but the problem is particularly important among military personnel who may regularly experience unusual or extreme motion profiles as a part of their duties. As such, it is important to understand the underlying mechanisms that contribute to motion sickness, which in turn can lead to new and more effective countermeasures. The current study investigated causal etiology by examining the predictions of postural instability theory. Subjects experienced multiple motion profiles while reporting their sickness symptoms.
Methods: Postural instability was directly manipulated by including both an active and passive condition. In the active condition, subjects could actively adapt their posture to the motion profile. In the passive condition, subjects had their feet affixed in place and could not effectively adapt their posture to the motion profiles. Subjects completed both conditions to control for individual differences in motion sickness susceptibility.
Results: Active condition subjects had greater postural stability as measured by sample entropy (M = 0.179 Active, M = 0.136 Passive), and sickness symptoms increased with time. Both results provide a methodological check against our manipulation. However, there were no differences in symptoms between active or passive conditions as measured by the simulator sickness questionnaire (M = 16.56 and M = 18.25, respectively), and no relationship between our measure of postural instability and symptomology.
Discussion: These results do not support postural instability as the primary causal factor in motion sickness; however, more research is needed to elucidate the mechanisms of motion sickness etiology.Pettijohn KA, Geyer D, Gomez J, Becker WJ, Biggs AT. Postural instability and simulator seasickness. Aerosp Med Hum Perform. 2018; 89(7):634-641.