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Ali Yoonessi, Frederick A. A. Kingdom; Sensitivity to color and luminance transformations in real versus phase-scrambled natural scenes. Journal of Vision 2005;5(8):277. doi: 10.1167/5.8.277.
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Traditionally, thresholds for discriminating colour and luminance differences have been measured using stimuli such as disks, gratings or gabors, and accounted for in terms of the responses of relatively low-level mechanisms in the visual pathway. On this basis we would not expect the higher-order structure of, for example, natural scenes to be a factor determining colour and luminance discrimination thresholds. We therefore decided to compare discrimination thresholds between natural scenes and phase-scrambled versions of the same scenes.
The stimuli were fifty calibrated color photographs of everyday scenes and fifty phase-scrambled images. The chromaticity and saturation of every pixel was represented as a vector in a modified version of the MacLeod-Boynton color space, and could be translated, rotated, compressed, or randomly repositioned within that color space. Thresholds for detection of each type of transformation were measured using a two-alternate forced choice method.
Thresholds for all types of transformations in color space were significantly lower in natural scenes compared to phase-scrambled images. Thresholds for detecting random changes in color, in the form of either Gaussian or fractal noise, were considerably lower in natural compared to phase-scrambled images.
The structure of natural scenes plays a significant role in our ability to discriminate colour and luminance differences.
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