Orientation Disparity: A Cue for 3D Orientation?

Orientation disparity, the difference in orientation that results when a texture element on a slanted surface is projected to the two eyes, has been proposed as a binocular cue for 3D orientation. Since orientation disparity is confounded with position disparity, neither behavioral nor neurophysiological experiments have successfully isolated its contribution to slant estimates or established whether the visual system uses it. Using a modified disparity energy model, we simulated a population of binocular visual cortical neurons tuned to orientation disparity and measured the amount of Fisher information contained in the activity patterns. We evaluated the potential contribution of orientation disparity to 3D orientation estimation and delimited the stimulus conditions under which it is a reliable cue. Our results suggest that orientation disparity is an efficient source of information about 3D orientation and that it is plausible that the visual system could have mechanisms that are sensitive to it. Although orientation disparity is neither necessary nor sufficient for estimating slant, it appears that it could be useful when combined with estimates from position disparity gradients and monocular perspective cues.