Vertical visual-vestibular interaction in normal human subjects

Abstract

Previous studies have described asymmetrical vertical eye movements when normal human subjects were rotated about a vertical inter-aural axis (with head rolled 90 degrees). We measured vertical eye movements induced by visual, vestibular and visual-vestibular stimuli with a magnetic scieral search coil technique while 10 normal subjects sat upright in a chair designed to rotate about the horizontal inter-aural axis at frequencies and amplitudes of natural head movements. Asymmetries in the gain of upward and downward pursuit and fixation-suppression of the VOR were found in individual subjects. However, there was no significant difference (p > 0.05) between the mean gain of up and down slow eye movements induced by vestibular, visual or visual-vestibular stimulation in the group of normal subjects. Systematic up-down asymmetries in vertical eye movements previously observed with testing about the vertical inter-aural axis were probably due to bias introduced by otolith stimulation and/or electro-oculographic eyelid artifact.