Contributions of roll and pitch to sea sickness.

The purpose of this study was to test the traditional assumption that sea sickness is uniquely provoked by heave motion characteristics, with pitch and roll movements being ineffective. In an experiment with a ship motion simulator, subjects were exposed to pitch and roll motions in combination with rather weak heave motions that have no motion sickness-inducing potential. Very high levels of motion sickness were observed (with a motion sickness rating scale) in almost 50% of our subjects. In three control experiments, it was shown that these heave motions, when presented separately, indeed have no motion sickness-inducing potential and that pitch and roll motions presented alone or in combination with each other have only a very small motion sickness-inducing potential. These results indicate that pitch and roll when combined with small heave motions, which in themselves are not sickness provoking, produce more motion sickness than claimed by the classic models. This suggests that in models on motion sickness, pitch and roll should be combined in a nonlinear fashion with heave and that such models will remain rather crude if they do not include a description of the vestibular contribution to motion sickness.