Shape from shading

In environments where orientation is ambiguous, the visual system uses prior knowledge about lighting coming from above to recognize objects, reorient the body, and determine which way is up (where is the sun?). It has been shown that when observers are tilted to the side relative to gravity, the orientation of the light-from-above prior will change in a direction between the orientation of the body, gravity and the visual surround. Here we investigate the contribution of ocular torsion in this change of the light-from-above prior has been acknowledged but not specifically addressed.
Our initial investigation tested the hypothesis that when lighting direction is the only available visual orientation cue, change in orientation of the light-from-above prior is accounted for by ocular torsion. In this experiment observers made convex-concave judgments of a central shaded disk, flanked by three similarly- and three oppositely-shaded disks. Lighting was tested every 15° in roll in the fronto-parallel plane. Using the KUKA motion simulator to move observers into different orientations, observers were tested when upright, supine, and tilted every 30° in role relative to gravity. Our results show that change of the light-from-above prior is well predicted from a sum of two sines; one consistent with predicted ocular torsion, the other consistent with an additional component varying with twice the frequency of body tilt. The next phase of our investigations will address the nature of this second component as well as assess the relative contribution of additional lighting cues added to the surrounding environment.


Barnett-Cowan M Person, Ernst MO Person and Bülthoff HH Person (August-2010): "Where is the sun?": The sun is "up" in the eye of the beholder, 33rd European Conference on Visual Perception, Lausanne, Switzerland, Perception, 39(ECVP Abstract Supplement) 146.
CiteID: 6404

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Last updated: Friday, 05.10.2012