Divisive inhibition model for chromoluminance pattern equidiscrimination contours

We studied the detection of chromoluminance patterns in the presence of chromoluminance pedestals. We examined how thresholds depend on the color directions of the target and the pedestal. Both targets and pedestals were spatial Gabor patterns (horizontal, 1 cpd) .The patterns were spatially modulated in color, luminance or both. Equidiscrimination contours describe contrast thresholds for targets in different color directions on the same pedestal. We measured the equidiscrimination contours on green/red and blue/yellow pedestals. The equidiscrimination contours are asymmetrically related to the cardinal axes in isoluminant plane. The shape of the equidiscrimination contours changes with the contrast and the color directions of the pedestals. We applied a model with three pairs of mechanisms that we proposed earlier6 to these data. Each mechanism consists of a linear receptive-field like color-spatial operator followed by a nonlinear process. The nonlinear process takes two inputs: the excitation comes directly from the linear operator and the divisive inhibition is a nonlinear sum of all linear operator responses. Two linear operator pairs are color opponent while the third is non-opponent. The detection variable is computed from the outputs of the nonlinear processes combined by Quick's pooling rule.