Biodynamic Hypothesis for the Frequency Tuning of Motion Sickness

INTRODUCTION: Motion sickness is often provoked by oscillatory translational (linear) acceleration. For humans, motion frequencies around 0.2-0.3 Hz are the most provocative.A current explanation for this frequency band is that it spans a region of maximum ambiguity concerning the interpretation of vestibular signals. Below 0.2-0.3 Hz, linear accelerations are interpreted as 'tilt; whereas at higher frequencies accelerations are interpreted as 'translation', i.e., linear motion through space. This is termed the 'tilt-translation' hypothesis. However, the origin of this particular frequency range is unclear. We investigated whether the differential perceptions of oscillations at different frequencies derives from the biodynamics of active self-initiated whole body motion. METHODS: Video-films were taken of subjects running slaloms of various combinations of lengths/amplitudes to provoke a range of temporal frequencies of slalom (reciprocal of time to run a cycle). RESULTS: The usual tactic for cornering at frequencies <0.25 Hz was whole-body tilt, whereas >0.4 Hz lateropulsion of the legs with torso erect was observed. Between these frequencies subjects showed variable tactics, mixing components of both tilt and lateropulsion. CONCLUSIONS: This uncertainty in selecting the appropriate tactic for movement control around 0.2-0.3 Hz is the possible origin of lilt-translation' ambiguity. It also follows that externally imposed motion around these frequencies would challenge both perception and motor control, with the consequence of motion sickness.