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Lookup NU author(s): Professor Anya Hurlbert
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Color constancy-by which objects tend to appear the same color under changes in illumination-is most likely achieved by several mechanisms, operating at different levels in the visual system. One powerful contributory mechanism is simultaneous spatial color contrast. Under changes in natural illumination the spatial ratios of within-type cone excitations between natural surfaces tend to be preserved (Foster and Nascimento, 1994); therefore, the neural encoding of colors as spatial contrasts tends to achieve constancy. Several factors are known to influence the strength of chromatic contrast induction between surfaces, including their relative luminance, spatial scale, spatial configuration and context (Ware and Cowan, 1982; Zaidi et al., 1991). Here we test the hypothesis that color contrast is weakened by differences between surfaces which indicate that they may be under distinct illuminants. We summarize psychophysical measurements of the effects of relative motion, relative depth and texture differences on chromatic contrast induction. Of these factors, only texture differences between surfaces weaken chromatic contrast induction. We also consider neurophysiological and neuropsychological evidence and conclude that the mechanisms which mediate local chromatic contrast effects are sited at low levels in the visual system, in primary visual cortex (VI) or below, prior to image segmentation mechanisms which require computation of relative depth or motion. VI and lower areas may therefore play a larger role in color constancy than previously thought.
Author(s): Hurlbert A, Wolf K
Editor(s): Heywood, CA; Milner, D; Blakemore, C
Publication type: Book Chapter
Publication status: Published
Book Title: The roots of visual awareness: a festschrift in honour of Alan Cowey
Print publication date: 01/01/2003
Series Title: Progress in Brain Research
Place Published: London
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