Abstract
There is longstanding controversy about the relationship of the color brown to perceptually unique or elemental hues, in particular to unique yellow. We explored this perceptual relationship with a foveal 2-deg-diameter test stimulus within a dark or bright surround, which rendered the same test stimulus as yellow or brown, respectively. We show that brown and yellow share two characteristics of unique hues: Observers (1) reliably set a red/green null or balance for both brown and unique yellow and (2) can cancel all chromatic content of both R/G-balanced brown and unique yellow by adding blue. Thus, both brown and yellow are distinct from red and green and opponent to blue. We also show two differences between properties of balanced brown and unique yellow: They (1) have different red-green balances and (2) show opposite directions of rod hue bias. The chromaticity of balanced brown is shifted toward red compared to that of unique yellow, and rods exert a red bias on balanced brown but a green bias on unique yellow. Thus, the properties of yellow do not explain the properties of brown. These results stop short of establishing brown as a unique hue, separate from yellow, but do suggest differences in the neural pathways underlying brown and yellow: (1) Brown pathways have stronger M- vs. L-cone weighting compared to yellow pathways, and (2) that rods favor red vs. green for brown, the opposite to yellow, presumably by acting through S-cone pathways, which show a rod red bias.
Meeting abstract presented at OSA Fall Vision 2012