Motion sickness susceptibility and the utilisation of visual and otolithic information for orientation.

Movement of large portions of the visual field can induce a static observer to experience illusory self-motion, changes in perceived orientation and motion sickness. Two experiments were performed to determine whether susceptibility to motion sickness might be related to an inability to ignore misleading visual information for orientation, measured here in terms of the magnitude of the apparent tilt of the vertical induced by rotation of the visual field about the line of sight. Significant and additive effects of sex and motion sickness susceptibility were demonstrated. Females susceptible to motion sickness proved highly inaccurate when attempting to set a line to the vertical with rotation of the background, while males resistant to motion sickness were the most accurate at this task. Two possible explanations are discussed, the first suggesting subclinical intersubject differences in otolithic sensitivity, and the second postulating deficiencies in intersensory integration. Parallels are drawn with the patterns of multisensory coordination for postural orientation seen in children and in patients with benign paroxysmal positional vertigo.