Visual-Vestibular Sensory Integration During Congruent and Incongruent Self-Motion Percepts

This thesis examined the contribution of vestibular cues to self-motion perception and their integration with visual self-motion cues. The thesis is divided into five sections. In Section 1, a review of the illusory self-motion perception (i.e., 'vection') literature situates studies undertaken in this thesis. Topics reviewed include vection research, vestibular anatomy and physiology, visual-vestibular sensory integration, visual-vestibular neurophysiology and measurement methods to index vection. In Section 2, two experiments were reported. In E1, a virtual drum was displayed on a virtual reality headset. In E2, a novel measurement method consisting of a circular knob that participants rotated when experiencing vection was used to provide a direct measure of vection speed, direction, and duration. Results showed that vection strength and speed increased as visual stimuli moved faster. In Section 3, two experiments were reported in which circular vection was induced using vestibular air caloric stimulation. Participants had their eyes closed in E3 while receiving caloric vestibular stimulation. In E4 participants received caloric vestibular stimulation while viewing a stationary image in a VR headset. Participants perceived vection in the clockwise direction when cold air was applied to the left ear, and perceived counter-clockwise vection when caloric stimulation was in the right ear. Vection speed and duration measures were significantly smaller when participants viewed a stationary display (E4) than when their eyes were closed (E3). In Section 4, the goal was to determine if the visual or vestibular system prevailed in determining direction of self-motion perception during cue conflict. Participants observed an optic flow pattern that induced circular vection while receiving caloric vestibular stimulation also inducing vection. Visual and vestibular stimuli induced vection of approximately equal speeds in two conditions. In the 'congruent motion' condition, visual and vestibular stimuli signaled vection in the same direction. In the 'incongruent motion' condition, visual and vestibular stimuli signaled vection in opposite directions. Results showed that in the incongruent condition, participants experienced vection in the direction signaled by the visual stimulus and vestibular stimulus equal amounts of times. In Section 5, a general discussion on these findings as they relate to optimal cue integration hypothesis is provided.