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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 (Smith et al 2004) 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 an ongoing investigation of self-motion estimation which shows that visual and vestibular information can be combined in a statistically optimal fashion. We discuss our results from the perspective that successful execution of self-motion behaviour requires the computation of one’s own spatial orientation relative to the environment.
