Motion sickness induced by periodic accelerations: Effects of motion axis, frequency, and acceleration magnitude

BackgroundCarsickness is a potential barrier to the acceptance of automated driving as it turns drivers into passengers, thus making them more susceptible to motion sickness. However, most of our current knowledge of how vehicle motion causes motion sickness comes from seasickness studies, using vertical motion only. Some more recent studies have investigated the relationship between horizontal accelerations and motion sickness, but with inconsistent methodology and sometimes conflicting results.ObjectiveTo quantify the effects of acceleration frequency and magnitude for periodic accelerations along the longitudinal, lateral, and vertical axes in a large sample of participants, using consistent methodology throughout.MethodsIn three separate experiments, in total 107 participants were exposed to sinusoidal accelerations along either the longitudinal, lateral or vertical axis with different combinations of motion frequency and peak acceleration. Motion frequency was varied between 0.03 and 3.2 Hz, with peak acceleration ranging from 0.5 to 4.0 m/s². Motion sickness was measured during motion exposure using the Motion Illness Symptoms Classification (MISC) scale, while the Simulator Sickness Questionnaire (SSQ) and a visual analogue Discomfort scale were administered after each motion exposure.ResultsMotion sickness severity due to motion exposure was similar for the three motion axes. All three outcome measures showed a clear motion frequency dependency, with motion sickness in general most severe for frequencies around 0.2 Hz. However, significant motion sickness symptoms were observed for the entire frequency range tested. The frequency dependency was less clear for lateral motion than for longitudinal and vertical motion. Higher accelerations led to more severe motion sickness, with the rate of increase decreasing when accelerations became higher.ConclusionsOur results show that motion sickness due to periodic linear accelerations occurs along all three cardinal axes and that it depends on motion frequency. This frequency dependency was less clear for lateral motion than for longitudinal and vertical motion. Our results have important implications for both predictive models of motion sickness as well as for applications in automated vehicles.