Large enhancement of simultaneous color contrast by white flanking contours

Abstract

Simultaneous color contrast and assimilation are mutually opposing effects on color appearance, and their magnitude depends on spatial context. The Monnier–Shevell illusion induces a large color shift by a synergy of simultaneous assimilation and contrast using the alternating color of proximal and distant surrounds. The illusion induces a prominent effect along the blue-yellow color axis, but a subtle effect along the orthogonal color axis. In this study, we report an illusion generated by an extremely thin gray line on a cyan background that appears reddish when the line is flanked by thin white contours. We quantified the color appearance of the gray line in a color matching experiment and found that the color shift of the gray line with white contours induced large color shifts. It is also known that luminance contrast between a center and its surrounds affects the magnitude of simultaneous color contrast. However, our color contrast effects were larger for a dark line rather than for a pale line. In contrast, the perceived color shift of the line without the contours increased as the luminance of the gray line increased, supporting the known effect of Kirschmann’s third law. These results indicate that Kirschmann’s third law fails to explain the perceived color shift of our illusion, even after accounting for optical factors like aberrations. Observed color shifts could be explained by an augmented synergy theory based on intensity space, rather than chromaticity.

Influence of Stimulus Size on Simultaneous Chromatic Induction

“…We previously reported that a gray line with white flanking contours appeared reddish on a cyan background, which is similar to an L/M-cone chromaticity ( Figure 1E ; Kanematsu and Koida, 2020 ). The observed color shift was larger than the color shift of the line without contours; thus, the chromatic contrast effect was enhanced by the contours.…”

“…We previously reported that, with a decrease in the luminance of the test line, the illusionary effect increased ( Kanematsu and Koida, 2020 ). The illusory effect cannot be sufficiently explained by chromatic aberrations, as observers consistently perceived the illusory color, irrespective of its fixation near or far from the stimuli that induced different chromatic fringes by chromatic aberrations.…”

“…This experiment was performed using a monitor (UP2516D, Dell; 2,560 × 1,440 pixels, Adobe RGB monitor), equipment, script environment (Psychtoolbox 3.0.15, Brainard, 1997 on Matlab R2018a, Mathworks), and calibration with a chroma meter (CS-200, Konica Minolta, Japan), which were the same as those employed in a previous study ( Kanematsu and Koida, 2020 ).…”

“…Thus, the color appearance can be interpreted as the contrast effect from the distant rings. (E–H) The chromatic induction demos ( Kanematsu and Koida, 2020 ). The color appearance of gray rings differed among the chromaticities of the backgrounds (E–H) although the physical chromaticity of the rings was the same.…”

How much blue is turquoise? How much red is purple? Interaction of colors and backgrounds.

“…For what concerns further comparisons with other studies, our stimuli were neither lines nor spots (Kanematsu & Koida, 2020), which, in the context of simultaneous contrast, present different modalities and behavior from those of the surfaces (the rectangles of our study). We have not tested the contours but the backgrounds; we have not used methods of comparison and/or adjustment between two different pairs of targets (Ratnasingam & Anderson, 2017), the stimuli did not have the same lighting and they were not presented just for a few seconds, and so on.…”