Perceptual tests of a cortical edge integration theory of lightness computation using haploscopic presentation M Rudd |
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Howard Hughes Medical Institute, University of Washington, WA, United States
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| Edge integration—the theory that lightness is computed by a cortical process that sums signed steps in log luminance across space—accounts with great precision for lightness judgments obtained with disk-annuli, Gilchrist dome, and staircase-Gelb displays (Rudd, 2010, submitted). The theory breaks with alternative lightness theories by predicting contrast effects for incremental targets, which violate the highest luminance anchoring principle (Gilchrist et al., 1999; Rudd & Zemach, 2005). Here I test the very strong prediction of cortical edge integration theory that the magnitude of such contrast effects for incremental targets will increase with haploscopic presentation: that is, when targets are presented to one eye and backgrounds having the same luminance and outer dimensions as the annular surrounds used in classical lightness induction studies are presented to the other eye. Haploscopic presentation increases the effect size dramatically, contradicting both the highest luminance principle and any theory that attempts to explain lightness based of image luminances per se, as opposed to edge-based cortical computations. The computations required by the model might be carried out in visual cortex by first encoding luminance edges in V1 and V2, then spatially integrating these edge responses at a later stage, e.g. V4 (Rudd, 2010, ECVP 2011). |
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