Color constancy: phenomenal or projective?

Abstract

Naive observers viewed a sequence of colored Mondrian patterns, simulated on a color monitor. Each pattern was presented twice in succession, first under one daylight illuminant with a correlated color temperature of either 16,000 or 4000 K and then under the other, to test for color constancy. The observers compared the central square of the pattern across illuminants, either rating it for sameness of material appearance or sameness of hue and saturation or judging an objective property-that is, whether its change of color originated from a change in material or only from a change in illumination. Average color constancy indices were high for material appearance ratings and binary judgments of origin and low for hue-saturation ratings. Individuals' performance varied, but judgments of material and of hue and saturation remained demarcated. Observers seem able to separate phenomenal percepts from their ontological projections of mental appearance onto physical phenomena; thus, even when a chromatic change alters perceived hue and saturation, observers can reliably infer the cause, the constancy of the underlying surface spectral reflectance.

Figure 1

An example of a pair of simulated Mondrians, depicted here in gray-scale. They consist of the same colored Munsell papers, but the pattern on the left was illuminated by a bluish light of correlated color temperature 16,000 K and that on the right by a more yellow light of 4,000 K. Although the gray-scale representation makes the patterns appear closely similar, it can be seen that some squares which are not discriminable on the left are discriminable on the right, and vice versa. Examples in color are given in Foster (2003).

Figure 2

Chromaticity coordinates of the local daylight illuminant used to simulate a change in spectral reflectance of the center square of the second of two successively presented Mondrians under global illuminants of correlated color temperature 16,000 K and 4,000 K (arrowed). Points are plotted in the CIE 1976 (u′, v′) chromaticity diagram. The smooth curve is the daylight locus (Judd, MacAdam, & Wyszecki, 1964).

Figure 3

Observers' responses as a function of change in spectral reflectance of the center square of a Mondrian for different tasks and directions of global illuminant change. (a) Proportion of binary “same-material” responses (solid symbols) and the mean material-appearance rating (open symbols) as a function of the CIE 1976 u′-coordinate of the local illuminant on the test surface. The global illuminant change was from a correlated color temperature of 16,000 K to one of 4,000 K (indicated by the gray vertical lines). The rating scale on the right ordinate has been aligned with the proportion scale on the left for maximum overlap between the two sets of data. The increments in u′ values increase because of the curvature of the daylight locus (Fig. 2). (b) Corresponding results for the opposite global illuminant change, from a correlated color temperature of 4,000 K to one of 16,000 K. (c) Mean hue–saturation rating (solid symbols) and, for comparison, the mean material-appearance rating (open symbols) from (a) as a function of the u′-coordinate of the local illuminant. (d) Corresponding results for the opposite global-illuminant change. Data based on 41 observers, 6–9 for each task and direction of global illuminant change (Experiment 1).

Figure 4

Color-constancy indices (CCIs) from hue–saturation ratings plotted against CCIs from material-appearance ratings (open symbols) and CCIs from binary “same-material” judgments plotted against CCIs from material-appearance ratings (solid symbols). Overlapping points have been shifted away from each other by 0.01.Each point is numbered by observer, from 1 to 8 (Experiment 2). The dotted line is from a logistic discriminant analysis.