Within the motion sickness literature, it is well-established that symptoms are reported by women more often than men. Despite this, very little research has aimed to understand the cause of this sex-based difference. Sensory conflict theories posit that there is an evolutionary reason behind the phenomenon, such as protection of the fetus in pregnant women, but there is little evidence to substantiate this explanation. The postural instability theory claims that motion sickness is caused by destabilized or maladaptive control of the body in nauseogenic circumstances. Therefore, the reason behind the dimorphic reports of motion sickness may be that women utilize different strategies of postural control than men during these situations. I aimed to examine this possibility by using an epidemiological approach and gathering postural data on 114 male and female students as they were exposed to nauseogenic linear oscillation created by a moving room. In addition to collecting data on the movement of the center of pressure, I also gathered anthropometric information to both ensure sexual dimorphism and to compare and analyze how biomechanical structure may play a part in postural stability. Subjective data was gathered using the Simulator Sickness Questionnaire and through a forced-choice yes/no question, “Are you motion sick now?” All participants also completed a search/inspection paradigm prior to vexing stimuli to further explore differences in how men and women control their bodies according to task. Postural data was analyzed using positional variability, detrended fluctuation analysis, and the novel multifractal detrended fluctuation analysis. Women reported motion sickness nearly four times more than men, exceeding rates seen in previous field studies. Sickness incidence also correlated with sexually dimorphic anthropometrics between the sex groups, including overall height, height of the center of mass, and foot length, while symptom severity did not differ as a function of sex. Replicating previous findings, analysis of body sway found that people in the Sick group swayed differently than those in the Well group, both prior to and during nauseogenic stimulation. Before undergoing linear visual oscillation, sway was found to be affected by an interplay of task, sex, and postural control patterns that differ between those that get sick and those that do not. Additionally, men and women differed in their postural responses to the visual motion stimulus, a novel finding in optic flow research. Analysis of movement dynamics revealed the multifractal spectrum differed between sickness groups and that this difference evolved during moving room exposure, linking subjective experience to individual differences in the multifractality of movement. These results support the hypotheses that sex differences exist in visually-induced motion sickness susceptibility, that these differences are related to sex differences in anthropometrics that are, themselves, related to the kinematics of body sway, and these differences in susceptibility have their basis in sex differences in control of body posture, both before and during exposure to potentially nauseogenic stimuli.
University of Minnesota Ph.D. dissertation. August 2016. Major: Kinesiology. Advisor: Thomas Stoffregen. 1 computer file (PDF); vii, 88 pages.
Postural stability and sex differences in visually induced motion sickness.
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