What is second-order vision for? Discriminating illumination versus material changes

• Published in: Journal of vision (Charlottesville, Va.) Vol. 10; no. 9; p. 2
• Main Authors: Schofield, Andrew J, Rock, Paul B, Sun, Peng, Jiang, Xiaoyue, Georgeson, Mark A
• Format: Journal Article
• Language: English
• Published: United States 16.07.2010
• Subjects: Contrast Sensitivity - physiology; Cues; Depth Perception - physiology; Discrimination (Psychology) - physiology; Humans; Lighting; Models, Neurological; Orientation - physiology; Photic Stimulation - methods; Surface Properties
• ISSN: 1534-7362; 1534-7362
• DOI: 10.1167/10.9.2

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.