Visual and vestibular cues for self-orientation influence oculomotor and perceptual assessments of the internal representation of gravity and body orientation
Single Paper Presentation

Michael Barnett-Cowan
York University, Psychology, Centre for Vision Research

Laurence, R. Harris
York University, Psychology, Centre for Vision Research

     Abstract ID Number: 57
     Full text: Not available
     Last modified: March 15, 2006
     Presentation date: 06/18/2006 4:00 PM in Hamilton Building, Foyer
     (View Schedule)

Abstract
Visual and vestibular cues influence the internal representation of gravity and perceived body orientation as shown by tilting either the visual world or subjects themselves relative to gravity and aligning an unseen rod to the perceived direction of gravity. The direction of saccadic eye movements has also been used to assess the influence of vestibular, but not yet visual cues. We assessed the effects of visual and vestibular cues by independently varying body and visual orientation using the York Tumbling Room. Subjects indicated the vertical and horizontal axes of their heads (egocentric tasks), the direction of gravity and the horizon (allocentric tasks). The perceived orientation of gravity and the horizon were also measured using unseen tactile rod alignment. In the dark, body-tilt did not affect the egocentric tasks, but systematically shifted the orientations of perceived gravity as indicated by saccades and rod settings. Combinations of body-tilt and visual-tilt led to systematic shifts in the perceived direction of gravity with the perceived horizon not always orthogonal to gravity, and did not affect egocentric judgments. Thus, allocentric tasks are affected by vestibular and visual cues, whereas egocentric judgements remain robust. Oculomotor and perceptual systems may use similar representations of the direction of gravity.