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Marianne Maertens, Robert Shapley; When increments match decrements. Journal of Vision 2014;14(15):40. doi: https://doi.org/10.1167/14.15.40.
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An important theme in lightness research has been the perceptual separation between increments and decrements. Some authors have reported that increments are never matched in lightness with decrements (e.g. Heinemann, 1955; Whittle and Challands, 1969; Gilchrist, 2006). And in fact, if lightness depended only on edge contrast, then increments, which have positive contrast, should always appear relatively lighter than decrements, which have negative contrast. This is indeed what is often found when geometrically and photometrically simple displays are used as stimuli. The perceptual increment/decrement split is supported by neurophysiological data pointing to a fundamental separation between neurons driven by darks (OFF neurons) and neurons driven by lights (ON neurons) in primary visual cortex (e.g. Yeh et al., 2009; Kremkow et al., 2014). Here, we present results from an experiment on lightness judgments in which we used customized checkerboards as stimuli. The checkerboards appeared more realistic with respect to their organization in depth as well as their photometric properties. We found that, for lightness judgments involving comparisons between regions that differed in illumination, observers matched increments with decrements without difficulty and were satisfied with their matches. These results indicate that there is a processing mechanism which transforms a lightness signal that is only dependent on local edge contrast into a representation that depends on edge contrast and context.
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