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Abstract

Navigation through the environment is a naturally multisensory task involving a coordinated set of sensorimotor processes that encode and compare information from visual, vestibular,
proprioceptive, motor-corollary, and cognitive inputs. The extent to which visual information
dominates this process is no better demonstrated than by the compelling illusion of self-motion
generated in the stationary participant by a large-field visual motion stimuli. The importance
of visual inputs for estimation of self-motion direction (heading) was first recognised by Gibson
(1950) who postulated that heading could be recovered by locating the focus of expansion
(FOE) of the radially expanding optic flow field coincident with forward translation. A number
of behavioural studies have subsequently shown that humans are able to estimate their heading
to within a few degrees using optic flow and other visual cues. For simple linear translation
without eye or head rotations, Warren and Hannon (1988) report accurate discrimination of visual
heading direction of about 1.5. Despite the importance of visual information in such tasks,
self-motion also involves stimulation of the vestibular end-organs which provide information
about the angular and linear accelerations of the head. Our research has previously shown that
humans with intact vestibular function can estimate their direction of linear translation using
vestibular cues alone with as much certainty as they do using visual cues. Here we report the
results of ongoing investigation of the integration of visual and vestibular cues to self-motion.