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Colin Downey, Karen Gunther; Non-cardinal color mechanisms: Stimulus size matters. Journal of Vision 2014;14(15):49. doi: https://doi.org/10.1167/14.15.49.
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The current experiment seeks to understand the effect of stimulus size on non-cardinal color mechanisms in all three planes of color space. Multiple studies have shown subjects to perform better on cardinal colors than non-cardinal colors, especially in the RG/LUM and TRIT/LUM color planes. Solomon, Peirce, and Lennie (2004) showed neurophysiologically that stimulus size affects the strength of the luminance suppressive surround, which might make non-cardinal mechanisms in the RG/LUM and TRIT/LUM planes more sensitive to stimulus size. We therefore tested 10 color-normal subjects on visual search at four dot sizes (0.5, 1, 2, & 3°) in each of the three color planes (RG/TRIT, RG/LUM, & TRIT/LUM). A two-way ANOVA on the RG/TRIT color plane yielded a significant main effect of color axis (p=0.024, η2=0.45), a significant main effect of dot size (p=<0.001, η2=0.52), but no interaction (p=0.365). The RG/LUM color plane also yielded a significant main effect of color axis (p=0.020, η2=0.47), a significant main effect of dot size (p=<0.001, η2=0.65), but no interaction (p=0.282). Similarly, the TRIT/LUM color plane yielded a significant main effect of color axis (p=0.020, η2=0.47), a significant main effect of dot size (p=<0.001, η2=0.48), but again no interaction (p=0.424). These results suggest that non-cardinal mechanisms in the RG/LUM color plane may be more sensitive (larger effect size) to stimulus size than the isoluminant plane. Testing is underway with smaller dot sizes (0.25, 0.5, 1, & 2°), to see if we can increase the effect size of dot size within the TRIT/LUM plane.
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