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Eli Brenner, Ruben Pastilha, Sérgio Nascimento; The neighbouring chromaticity influences the judged intensity of illumination. Journal of Vision 2018;18(10):218. doi: https://doi.org/10.1167/18.10.218.
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© ARVO (1962-2015); The Authors (2016-present)
To identify surface properties independently of the illumination the visual system must make assumptions about the statistics of scenes. Are assumptions about the intensity of the illumination independent of assumptions about its chromaticity? To find out, we asked participants to judge whether test patches within three different sets of surrounding surfaces were white or grey. Two sets were matched in terms of their mean luminance, maximal luminance, and variability in luminance, but differed in how luminance and chromaticity were associated: the highest luminance was either associated with colourful surfaces or with achromatic ones. We found that test patches had to have a higher luminance to appear white when the highest luminance in the surrounding was associated with colourful surfaces. This makes sense if one considers that a perfectly white surface reflects all of the light falling on it, while being colourful implies that a surface only reflects part of the light that falls on it, meaning that the illumination must have a higher luminance. In the third set, the highest luminance was associated with the same colourful surfaces, but the mean luminance was lower. Despite the constraints on the illumination being identical to those of the other set with high luminance chromatic surfaces, test patches did not have to have as high luminance to appear white for the third set. Considering the layout of the surfaces in the surrounding revealed that test patches did have to have the same high luminance if the high luminance colourful surfaces were adjacent to the target patch. Thus, the assumptions about the possible illumination are applied locally. A possible mechanism is relying on the contrast within each type of cone: for a surface to appear white it must stimulate each of the three kinds of cones substantially more than do any neighbouring surfaces.
Meeting abstract presented at VSS 2018
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