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Simultaneous contrast stimulus. (A) Illustration of a reflectance edge and (B) an illumination edge simultaneous brightness/lightness contrast stimulus. In (A, B) all of the test patches have the same luminance. The low luminance and high luminance backgrounds are also equivalent in the two stimuli. Stimulus (A, B) differ only in the addition of a far surround to three sides of the high luminance background in (B) to simulate an illumination edge.
