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A. R. Rodrigues, B. D. Gomes, G. S. Souza, I. B. Taccolini, C. A. Saito, L. C. L. Silveira; Color Adaptation: Surround Influence on Macadam Ellipses Measured With the Mollon-Reffin Test. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3835.
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Adaptation to surrounds varying in luminance has an effect on both color appearance and discrimination along different directions of the color space. We determined MacAdam color discrimination ellipses at 2 different surround conditions, using the Mollon-Reffin (1989) protocol in a psychophysical computer controlled system for IBM RISC/6000 workstations.
31 normal trichromats (22.4 ± 2.1 years old) were monocularly evaluated. The target was a Landolt C located in a surround of different chromaticity. Two reference chromaticities were used for the surround, C2 (CIE 1976: u’= 0.219; v’= 0.480) and C3 (CIE 1976: u’= 0.225; v’= 0.415). Discrimination thresholds were evaluated along 20 chromaticity axes irradiating from the reference points and the results were plotted as MacAdam ellipses. The subject was asked to indicate the C’s opening orientation as the chromatic contrast between target and reference chromaticities was varied until the discrimination threshold had been determined, using a staircase procedure. Thresholds were evaluated using two conditions: (i) the mosaic embedded on a black background; (ii) the mosaic embedded on a background with chromaticity equal to that of the reference point and luminance equal to the mosaic mean luminance.
The discrimination thresholds were plotted in the cone excitation space, fitted as MacAdams ellipses, and cone contrast values obtained with the two conditions were compared. For both conditions C3 ellipses had larger diameter (circle of equal area), larger angle of inclination, and larger ellipticity (semi-axis a / semi-axis b) than C2 ellipses. Both C2 and C3 ellipses were smaller, and C2 ellipses had smaller ellipticity when the mosaic was presented in the condition (ii) (one-way ANOVA; p < 0.05). Subjects’ improvement in chromatic discrimination when using condition (ii) occurred in all color directions except near the tritan confusion line for C2 and C3 ellipses, near the protan confusion line for the C2 ellipse, and near the deutan confusion line for the C3 ellipse.
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