It is thought that various factors are involved in the process of motion sickness. Using a combination of vestibulo-ocular reflex (VOR) and a method in which the line of fixation in smooth pursuit eye movement can be freely controlled using a face a mount display (FMD), the process of motion sickness induction was studied under conditions in which phase spaces of head movement and eye movement are either synchronized or not synchronized.
Under the synchronous phase-space condition, no motion sickness was induced, when the lines of fixation controlled by VOR and FMD were in the equiphase or antiphase, while motion sickness was readily induced under the asynchronous phase-space condition. Moreover, when the head was moved under conditions in which eye movement was restricted, movement of the visual field was recognized as antiphase relative to the head movement. However, when eye movement was controlled by the subject himself/herself, motion sickness was not induced because head movement and recognition of the visual field were synchronized. On the other hand, when eye movement was controlled by the investigator, motion sickness could be induced. From the above findings based on the intrinsic model of motor command, it is assumed that asynchronous phases of head movement and eye movement generated by the inverse model and forward model of the forecast system are input information leading to motion sickness.
