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D Cao, SK Shevell; Chromatic Assimilation: Results with EEW Fields . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3985.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Chromatic assimilation is the shift in color toward the appearance of nearby light. We tested possible explanations of chromatic assimilation such as spread light, spatial averaging of physical lights, and spatial integration of neural responses. Methods:Chromatic assimilation into an EEW circular field was measured as a function of the width, separation, luminance, and chromaticity of inserted concentric inducing rings. On a calibrated color CRT, a uniform circular field of diameter 3 deg was presented with inserted concentric inducing rings. Without inducing rings, the circular field appeared nearly achromatic (l, s of 0.66, 0.99). The width, spacing, luminance, and chromaticity of the inducing rings were varied systematically. The width of the rings was 1, 2, 4, 8 or 16 min with separation between rings of 1, 2, 4, 8 or 16 min (though the separation between the rings was not less than the width of the inducing rings). The luminance of the 3 deg EEW field was 4.0 cd/m2, while the luminance of the inducing rings was 2.67 or 6.0 cd/m2 (corresponding Michaelson contrast to the luminance of the EEW field of -20% or +20%). The chromaticities of the inducing rings were l, s (0.75, 0.99), (0.62, 0.99), (0.66, 2.5), (0.66, 0.25), (0.75, 2.5), (0.75,0.25), (0.62, 2.5) or (0.62, 0.25). These inducing chromaticities formed a rectangle in l, s space. Observers matched the perceived color of the 3 deg circular field by adjusting the chromaticity and luminance of a separate uniform 3 deg field presented haploscopically. Results:Stronger chromatic assimilation was observed with thinner inducing rings and narrower separations. The shifts with fixed width, separation and chromaticity of inducing rings did not depend systematically on the luminance of the inducing rings, contrary to the lawful prediction of spread light or spatial averaging of physical lights. However, the shifts with a given ring width and chromaticity were approximately linearly related to the total area covered by the inducing rings, as ring separation was varied. This is consistent with spatial integration of nonlinear neural responses. Conclusion:The measured shifts in the appearance of the circular field cannot be explained by spread light or by spatial averaging of physical lights. Spatial integration of nonlinear neural signals in chromatic pathways may account for the measured chromatic assimilation.
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