Purpose. We studied lateral interactions among chromoluminance patterns, meaning patterns of spatial modulation in either luminance, chromaticity, or both.

What are the rules by which these varieties of chromoluminance patterns interact?

Methods. The task of an observer was to detect a target Gabor pattern (vertical, 4 cpd) in the presence of two collinear Gabor flankers. The target and the flankers modulated along either isochromatic (“luminance”), L-M cone modulation (“red-green”) or S-cone modulation (“blue-yellow”) directions from a white background. The centers of the flankers were 1o away from the center of the target. The contrast of the chromoluminance patterns was defined as the Euclidian distance of the L-, M-, and S- cone contrast divided by the square root of 3. Flanker contrast was set at about 10 times its own detection threshold. Thresholds were measured with a 2AFC paradigm and the PSI threshold-seeking algorithm.

Result. Substantial facilitation occurred when the target and the flankers were modulated along the same color direction. However, isochromatic flankers did not facilitate either isoluminance (L-M and S cone modulation) targets. Isoluminant flankers produced slight facilitation in isochromatic targets. S cone flankers also produced facilitation in L-M targets.

Conclusion. Previous studies (Chen, Foley & Brainard, 2000) showed that an isochromatic pedestal has a large facilitation effect on isoluminance target detection while the isoluminance pedestal can only mask the isochromatic target. Here, flanking patterns have the opposite effect on the chromoluminance pattern detection than the pedestal. This result implies that lateral masking is mediated by a different chromoluminance mechanism than that for pedestal masking.

Chen, C.C. Foley, J.M. & Brainard, D.H.(2000). Detection of chromoluminance patterns on chromoluminance pedestals I: threshold measurements. Vision Research, 40, 773-88.