Detection of chromoluminance patterns on chromoluminance pedestals I: threshold measurements

Measurement of the detection thresholds of patterns on pedestals: of variou s kinds has the potential of providing insight into the mechanisms that med iate pattern vision. This study is concerned with chromoluminance patterns, that is, patterns that vary over space in luminance, chromaticity, or both . Contrast thresholds for 1 c/deg Gabor patterns (targets) were measured as a function of the contrast of Gabor pedestal patterns (TvC functions),: wh ere the pedestals paired with each target were modulated in a wide range of directions in color space. For most target-pedestal pairs, the TvC functio n decreased (facilitation) and then increased as pedestal contrast increase d. The increase went above the absolute contrast threshold (masking) for al l target-pedestal pairs except in cases where facilitation occurred at the upper end of the pedestal contrast range. The specific form of the TvC func tion varied greatly with the target and pedestal, consistent with a general , model of pedestal effects proposed by Foley [Journal of the Optical Socie ty of America A, 1994, 11(6)]. There were two sets of target-pedestal pairs for which facilitation did not occur, but masking did occur: pairs in whic h the target was a luminance modulation:and the pedestals were individually isoluminant and pairs in which the pedestal was blue/yellow and the target was in any-of our directions except blue/yellow. (C) 2000 Elsevier Science Ltd. All rights reserved.