Surface slant can be perceived from orientation disparities P B Hibbard1, K C Scott-Brown2 |
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1Department of Psychology, University of Essex, United Kingdom |
| We show that people can use differences in the orientation of features in the two eyes' images directly to perceive slant. We presented observers with binocular stereograms that depicted surfaces slanted in depth. These were either correlated (i.e. the luminance of corresponding features was matched across the two images) or anticorrelated (i.e. one eye's image was replaced by its photographic negative). The majority of observers were able to reliably report the direction of slant in both cases. In contrast, no observers were able to accurately make a simple 'near/far' depth judgement for our anticorrelated stimuli. We modelled the responses of cortical cells that are tuned to different orientations in the two eyes to our stimuli. Our results show that the responses of populations of these neurons provide sufficient information for the visual system to discriminate the direction of surface slant. Models of binocular processing in the visual cortex that rely purely on differences in the position of corresponding features need to be extended to account for the encoding of multiple kinds of disparity. The finding that stereopsis also makes use of orientation disparities is consistent with the orientation tuning properties of cortical binocular neurons. |
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