The effects of luminance surrounds on the perception of the color brown

Abstract

Past research has indicated that in order to perceive brown, a high luminance surround (HLS) must be present in the visual field such that brown is lower luminance than the HLS. However these experiments did not determine the range of light levels across which brown could be seen and how these vary depending on the characteristics of the HLS. Our observers adjusted the luminance of a constant-chromaticity, 2-deg-diameter, foveal test stimulus to set both upper and lower luminance thresholds for perceiving brown under four surround conditions: the four possible surround combinations of a white (high luminance) and black (low luminance) near (3-deg outside diameter) and far (full screen outside of the 3-deg-diameter near surround) surround. We found that when there was a white near surround (NS) brown was perceived over the highest range of luminance values regardless of the far surround's (FS) luminance. The luminance values in these conditions were significantly higher at both the upper and lower threshold than all other conditions. With a white FS and a black NS, both the upper and lower luminance thresholds for perceiving brown shifted significantly downward. Surprisingly, even when both the NS and FS were black, some subjects still perceived brown (at significantly lower luminance values than in all other conditions). This suggests that even when there is no higher luminance surround, some people are still capable of perceiving brown at very low luminance. This raises questions about the conventional conception of brown and the role of surround luminance.

Meeting abstract presented at OSA Fall Vision 2012