Less sickness with more motion and/or mental distraction.

BACKGROUND Motion sickness may reduce passenger comfort and crew performance. Countermeasures are dominated by medication with specific and often undesirable side effects. OBJECTIVE To shown that sickness due to motion can be reduced by adding an inherent non-sickening vibration and by mental distraction. METHODS Eighteen blindfolded subjects were exposed to 20 minutes of off-vertical axis rotation (OVAR). Vibration was added by means of a head rest. Effects of OVAR and vibration were tested separately and in combination, while the subjects were performing an audio letter memorising task. This task was absent to test the effect of mental distraction. Effects were quantified by rating subjective misery and objective task performance. RESULTS Sixteen subjects completed the experiment and showed in mutual comparable conditions that head vibration reduced the amount of sickness by 25%, the mental distraction did so by 19%, and the combined effect resulted in a reduction of 39%. Their task performance decreased with increasing sickness. CONCLUSION Sickness due to low-frequency motion can be reduced by adding a high-frequency vibration and by mental distraction. The effect of vibration can be understood by assuming an internal model used by the central nervous system to optimise the control of body motion.