Visual and non-visual cues in the perception of linear self motion

Surprisingly little is known of the perceptual consequences of visual or ve stibular stimulation in updating our perceived position in space as we move around. We assessed the roles of visual and vestibular cues in determining the perceived distance of passive, linear self motion. Subjects were given cues to constant-acceleration motion: either optic flow presented in a vir tual reality display, physical motion in the dark or combinations of visual and physical motions. Subjects indicated when they perceived they had trav ersed a distance that had been previously given to them either visually or physically. The perceived distance of motion evoked by optic flow was accur ate relative to a previously presented visual target but was perceptually e quivalent to about half the physical motion. The perceived distance of phys ical motion in the dark was accurate relative to a previously presented phy sical motion but was perceptually equivalent to a much longer visually pres ented distance. The perceived distance of self motion when both visual and physical cues were present was more closely perceptually equivalent to the physical motion experienced rather than the simultaneous visual motion, eve n when the target was presented visually. We discuss this dominance of the physical cues in determining the perceived distance of self motion in terms of capture by non-visual cues. These findings are related to emerging stud ies that show the importance of vestibular input to neural mechanisms that process self motion.