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Tanner DeLawyer, Ariel Frederick, Simon Kaplan, Tracy Lin, Sophie Shonka, Steven Buck; Dependence of the color brown on the spatial configuration of high luminance surrounds. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3021. doi: https://doi.org/.
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The same long-wavelength stimuli look brown when dim and yellow-orange when bright, relative to surrounding stimuli. Earlier research showed that the stimuli directly surrounding a brown stimulus were most important in the perception of brown. We confirmed these earlier results quantitatively and then tested the dependence of brown on brighter surrounding stimuli by varying their spatial configuration, to assess necessary and sufficient conditions for perceiving brown.
Observers, under room-light adaptation, adjusted the luminance of a constant-chromaticity 4°-diameter foveal test stimulus to set both upper and lower luminance thresholds for perceiving brown under the four possible combinations of white and black near (4°x6° annulus) and far (6° and beyond) surrounds. The test stimulus appeared yellow-orange when at a high luminance and brown at a low luminance. Observers also completed a set of trials with an otherwise identical 1°, 2°, 3°, 4°, 5°, 6°, or 7°-diameter foveal test stimulus with a 2°, 4°, 6°, and 8° white near surround and black far surround.
Our results for the different combinations of near and far surrounds indicated that the perception of brown occurred at significantly higher luminance thresholds in the presence of a white near surround regardless of far surround luminance. Subjects could not perceive brown with a black near and far surround. In our spatial configuration conditions we found a general trend that as the size of the test stimulus increased, subjects had to adjust to lower luminance values in order to perceive brown. The size of the annulus did not have a significant effect on the subjects’ perception of brown.
Our replication of earlier results established quantitative light levels that are necessary for the perception of brown under normal lighting conditions both with and without the presence of a high luminance near surround. Spatial results appear to indicate that as an object covers areas of the retina outside of the fovea the perception of brownness begins to fade, requiring a higher luminance contrast in order to perceive the object as being brown. This agrees with observation that it is difficult to perceive a stimulus as brown when it is viewed extra-foveally even in the presence of a high luminance surround. This suggests the neural mechanisms for perceiving a brown object are highly dependent on foveal input.
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