Biodynamic Hypothesis for the Frequency Tuning of Motion Sickness.

Abstract

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. 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). 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. This uncertainty in selecting the appropriate tactic for movement control around 0.2-0.3 Hz is the possible origin of 'tilt-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.