Luminance dependency of perceived color shift after color contrast adaptation caused by higher-order color channels

Abstract

Color adaptation is a phenomenon in which, after prolonged exposure to a specific color (i.e. adaptation color), the perceived color shifts to approximately the opposite color direction of the adaptation color. Color adaptation is strongly related to sensitivity changes in photoreceptors, such as von Kries adaptation and cone-opponent mechanisms. On the other hand, the perceptual contrast of colors (e.g. perceptual saturation of the red-green direction) decreases after adaptation to a stimulus with spatial and/or temporal color modulation along the color direction. This phenomenon is referred to as color contrast adaptation. Color contrast adaptation has been used to investigate the representation of colors in the visual system. In the present study, we measured color perception after color contrast adaptation to stimuli with temporal color modulations along complicated color loci in a luminance-chromaticity plane. We found that, after the observers adapted to color modulations with different chromaticities at higher, medium, and lower luminance (e.g. temporal alternations among red, green, and red, each at a different luminance level), the chromaticity corresponding to perceptual achromaticity (the achromatic point) shifted to the same color direction as the adaptation chromaticity in each test stimulus luminance. In contrast, this luminance dependence of the achromatic point shift was not observed after adaptation to color modulations with more complex luminance-chromaticity correspondences (e.g. alternating red, green, red, green, and red, at five luminance levels, respectively). In addition, the occurrence or nonoccurrence of the luminance-dependent achromatic point shift was qualitatively predicted using a noncardinal model composed of channels preferring intermediate color directions between the cardinal chromaticity and luminance axes. These results suggest that the noncardinal channels are involved in the luminance-dependent perceived color shift after adaptation.

Figure 1.

L–M colors used in the experiment in the CIE 2006 xy chromaticity diagram. The red and blue lines indicate the colors on the L–M axis from -1 to 1 and the color gamut of the monitor used in the experiment, respectively.

Figure 2.

Properties of adaptation color. (a) Loci of adaptation color on the chromaticity-luminance plane in Experiment 1. The red and blue lines represent “<” and “>” adaptation loci, respectively. (b) Luminance (black line) and L–M (red line) of “<” adaptation color as a function of time. (c) Loci of adaptation color on L- and M-cone contrast plane. No log transform is applied to the axes. Although S-cone contrast was modulated along the luminance axis, it is ignored in this figure.

Figure 3.

(a) Achromatic points after adaptation in Experiment 1. The thin lines show individual observers’ results, and the bold lines show the results averaged across the observers. The line colors indicate the adaptation conditions. (b) Differences between the “<” or “>” adaptation and the control condition averaged across the observers. The shaded zones show 95% confidence intervals calculated using a parametric bootstrap method with 10,000 repetitions.

Figure 4.

Differences in achromatic points between “<” and “>” adaptation conditions averaged across observers. The shaded zone shows 95% confidence intervals calculated using a parametric bootstrap procedure with 10,000 repetitions.

Figure 5.

Relative sensitivities of channels to different color directions before and after “<” adaptation in our 8-channel model. Each line color corresponds to the sensitivity of each channel, and the distance between the origin and the line indicates the relative sensitivity to different color directions. Dotted and bold lines show the sensitivities before and after adaptation, respectively.

Figure 6.

Achromatic points predicted by color representation models. (a) Noncardinal (8-channel) model. (b) Cardinal (4-channel) model.

Figure 7.

Achromatic points predicted by color representation model with eight channels and linear luminance representation.

Figure 8.

Loci of adaptation color in the chromaticity-luminance plane with linear luminance scale for (a) the additional experiment and (b) Experiment 1.

Figure 9.

(a) Achromatic points after adaptation in the additional experiment. (b) Differences between the “<” or “>” adaptation and the control condition averaged across the observers. The formats are identical to those in Figure 3, except that the luminance axis is depicted on a linear scale.

Figure 10.

Properties of adaptation color in Experiment 2. The formats are the same as Figure 2.

Figure 11.

Achromatic points after the double “<” and “>” adaptation predicted by the noncardinal model.

Figure 12.

(a) Achromatic points after adaptation in Experiment 2. The thin lines show individual observers’ results, and the bold lines show the results averaged across the observers. The line colors show the adaptation conditions. The results of the control conditions are the same as Figure 3a. (b) Differences between the “<” or “>” adaptation and the control condition averaged across the observers. The shaded zones show 95% confidence intervals calculated using a parametric bootstrap method with 10,000 repetitions.

Figure 13.

Differences in achromatic points between “double <” and “double >” adaptation conditions averaged across observers. The shaded zone shows 95% confidence intervals calculated using a parametric bootstrap procedure with 10,000 repetitions.