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Jenny Bosten, Donald MacLeod; When Red Plus Red Makes White. Journal of Vision 2011;11(15):17. doi: 10.1167/11.15.17.
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Retinal signals depend critically on contrast, or on the factor of change applied to a background stimulus; and so does perception at threshold where Weber's Law holds. We extend this principle to suprathreshold color appearance. When a colored blob fades against a grey background under steady fixation, physically different stimuli appear the same. In our experiments, such a blob is revived by a suprathreshold change of intensity. If the retina reports factors of change rather than absolute color, we make a surprising prediction: the revived blob should retain its achromatic appearance instead of emerging in its true color. A test Gaussian blob was allowed to fade, and revived by a brief (200 msec) change Subjects adjusted a briefly pulsed comparison blob in DKL space to match the revived test blob. Chromaticities of the matches to test blobs that were doubled or halved in intensity were indeed close to achromatic, though with a small shift towards the physical chromaticity of the test blob when the intensity was doubled. Results conformed to the prediction that a perceptual match is determined by equal factors of change, though with some regression towards the absolute stimulus in some subjects.
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