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Vivianne C Smith, Joel Pokorny; Interactions of chromaticity and luminance in edge identification depend on chromaticity. Journal of Vision 2003;3(9):445. doi: https://doi.org/10.1167/3.9.445.
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Purpose: The goal of this work was to study interactions of chromaticity and luminance in edge identification. Previous studies have revealed chromaticity/luminance interactions in detection and perceptual, but not edge-related tasks.
Methods: Two horizontal spatial sawtooth patterns, one with positive and the other with negative harmonics, were compared in 2-AFC. The observer identified the pattern with the sharp upper edge. The fundamental frequency was 2 cpd, with 5 cycles presented in a 2.5 deg square field. The pattern was presented as a 1 second raised temporal cosine, replacing part of an 8 deg, 115 td background. Stimulus presentation order was random. Stimuli were specified in a cone troland (l, s, Y) chromaticity space, with correction for individual equiluminance at a nominal 115 td, and tritan direction. A preliminary set of interleaved staircases established edge identification for the six directions. (+/−l, +/−s, +/−Y). Three compound sawtooth stimuli combining two directions were chosen and included with the chosen directions in five randomly interleaved staircases, using a 3-correct/1-incorrect reversal rule.
Results: For combinations of Y with l-chromaticity, or l- with s-chromaticity, probability summation was observed. Combinations of Y with s-chromaticity revealed opponency. Data for +s, +Y and −s, −Y were sub-additive; data for +s, −Y and −s, +Y were additive. Control studies using detection rather than edge identification revealed probability summation for all combinations.
Conclusions: Luminance edges did not enhance stimuli with l-chromaticities. There was an interaction of luminance edges with s-chromaticities. Dim “blues” and bright “yellows” showed linear summation. Bright ”blues” and dim “yellows” showed opponency. This result may reflect a higher-level optimization to natural colors.
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