Optokinetic motion sickness: continuous head movements attenuate the visual induction of apparent self-rotation and symptoms of motion sickness.

Symptoms of motion sickness are sometimes experienced during exposure to optokinetic stimulation. Two experimetns were performed to compare the symptoms of motion sickness elicited when subjects were exposed to incremental changes in optokinetic stimulation while sitting passively and while continuously executing shoulder-to-shoulder head movements. In the first experiment, a fixed head-movement frequency (20 cpm) was used, wheras in the second the subjects varied the frequency of their head movements in order to maintain suppression of illusory self-rotation. In both experiments, subjects in the head-moving condition had fewer and less severe symptoms of motion sickness and experienced illusory self-rotation after longer exposure times and at higher optokinetic velocities than in the head-stationary condition. Subjects in th- head-movement condition of the second experiment increased the frequency of their head movements as the velocity of optokinetic stimulation increased. The symptoms of motion sickness elicited during optokinetic stimulation tended to be dizziness, headache, eye-strain, and stomach awareness appearing in no fixed order. The pattern and constellation of symptoms are unlike those elicited by vestibular stimulation.