Perception of brown with variation in center chromaticity and surround luminance

Brown is a contrast color that depends on complex combinations of chromatic and achromatic signals. We measured brown perception with variations in chromaticity and luminance in center-surround configurations. In Experiment 1, the dominant wavelength and saturation in terms of S-cone stimulation were tested with five observers in a fixed surround luminance (60c d/m ²). A paired-comparison task required the observer to select the better exemplar of brown in one of two, simultaneously presented, stimuli (1.0° center diameter; annulus of 9.48° outer-diameter). In Experiment 2, the same task was tested with five observers in which surround luminance was varied (from 13.1 to 99.6c d/m ²) for two center chromaticities. The results were a set of win-loss ratios for each stimulus combination and converted to Z-scores. An ANOVA did not reveal a significant main effect of the observer factor but revealed a significant interaction with red/green (a ^∗) [but not with the dominant wavelength and the S-cone stimulation (or b ^∗)]. Experiment 2 revealed observer variation in interactions with surround luminance and S-cone stimulation. The averaged data plotted in 1976 L ^∗ a ^∗ b ^∗ color space indicate that high Z-score values widely distribute in the area of a ^∗ from 5 to 28 and b ^∗ over 6. The balance of the strength between yellowness and blackness differs among observers owing to the amount of induced blackness required for the best brown.