Abstract
When the environment changes color, for example after putting on tinted glasses, the visual system adapts, and the world regains ‘normal’ appearance. For strong shifts, adaptation may progress over hours, but little work has measured its long-term time course. We studied this adaptation by reconstructing subjective color space using multidimensional scaling (MDS), to characterize its perceptual consequences for a large range of colors. Seven observers wore bright red glasses for 1.5 hr. Color perception was measured before and immediately after observers put the glasses on, after 45 min, and 1.5 hr of wear. Observers viewed pairs of filled color circles, 1.5 degrees in diameter, centered within a 6-degree black square on a naturalistic background image. Thirteen colors were chosen from two concentric circles in LAB space comprising unique and intermediate hues at two saturation levels, and one gray. Observers rated the difference between each possible color pair on a scale of 0 (identical) to 9 (largest difference). Metric MDS was used to reconstruct perceptual spaces from measured dissimilarity matrices. We delivered glasses and color-calibrated laptops to observers, who participated at home. Wearing red glasses caused the world to subjectively appear very reddish, and all pairs of colors were rated as relatively similar. As observers adapted, colors subjectively regained more normal appearances, and the dissimilarity between color pairs gradually increased. In the MDS solutions, the mean pair-wise Euclidean distance between all color pairs increased significantly during the first 45 min, from 3.03 to 3.68 (p < 0.01), and further increased to 4.20 by the end of 1.5 hr (p < 0.1). The results indicate that hour-long color adaptation expands the perceptual color space, in addition to recalibrating the perceived neutral point (shown in past work). Future work can model the mechanisms underlying the time courses of these effects.