Vestibular Function and Eye Movements

Abstract

The vestibular (otolith and semicircular-canal) organ is important to maintain the body balance and visual stability under the earth-gravity environment. It is necessary to know further the physiological function of the otolith organ to advance understanding the mechanism of space motion sickness. Eye movement analysis is useful to study the vestibular function, though the research of the otolith organ is taking delay in comparison with the research of the semicircular canals. In this report, I briefed how early the otolith organ grows up in the fetal stages, the history and background of vestibulo-ocular researches, and the methods of eye-movement recording available for the vestibular research. In human microgravity studies, there are several episodes indicating usefulness of the eye-movement analysis. Among the sensoryconflict theories for generation of the space motion sickness, my own interest is the sensory-compensation hypothesis. Because, according to our sensory-conflict study using a large-scale linear accelerator, the visual-vestibular interaction under an unusual stimulus-combination induces motion sickness and also provokes suppression of the vestibulo-ocular reflex in the otolith system, in contrast to the canal system.