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Andrew J. Schofield, Paul B. Rock, Peng Sun, Xiaoyue Jiang, Mark A. Georgeson; What is second-order vision for? Discriminating illumination versus material changes. Journal of Vision 2010;10(9):2. doi: 10.1167/10.9.2.
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© 2015 Association for Research in Vision and Ophthalmology.
The human visual system is sensitive to second-order modulations of the local contrast (CM) or amplitude (AM) of a carrier signal. Second-order cues are detected independently of first-order luminance signals; however, it is not clear why vision should benefit from second-order sensitivity. Analysis of the first- and second-order contents of natural images suggests that these cues tend to occur together, but their phase relationship varies. We have shown that in-phase combinations of LM and AM are perceived as a shaded corrugated surface whereas the anti-phase combination can be seen as corrugated when presented alone or as a flat material change when presented in a plaid containing the in-phase cue. We now extend these findings using new stimulus types and a novel haptic matching task. We also introduce a computational model based on initially separate first- and second-order channels that are combined within orientation and subsequently across orientation to produce a shading signal. Contrast gain control allows the LM + AM cue to suppress responses to the LM − AM when presented in a plaid. Thus, the model sees LM − AM as flat in these circumstances. We conclude that second-order vision plays a key role in disambiguating the origin of luminance changes within an image.
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