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James M Hillis, David H Brainard; Cone inputs controlling color context effects: Detection and appearance. Journal of Vision 2003;3(9):702. doi: 10.1167/3.9.702.
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© 2017 Association for Research in Vision and Ophthalmology.
Purpose. The perceptual representation of color is context dependent: both color detection thresholds and color appearance vary with background color. We pursued two related questions: 1) Do the same neural mechanisms mediate both threshold and appearance context effects? 2) What are the L, M, and S cone inputs to the mechanisms that integrate context for each task? Methods. Stimuli were presented on a calibrated RGB monitor with 14-bit intensity resolution for each channel (provided by a CRS BITS++ device). In both detection and appearance experiments, test spots (2 deg in diameter, 4 deg eccentricity) were presented for 200 ms against either uniform or bipartite backgrounds. Background colors were selected from a set that differed in L+M or S-cone intensity. In the detection experiment subjects indicated whether a single test spot appeared left or right of fixation. Multiple interleaved staircases controlled the magnitude of L+M or S-cone increments/decrements. In the appearance experiment, left and right test spots flashed simultaneously. Between flashes, subjects adjusted spot color on one side to match a fixed spot color on the other side (chosen from a set of L+M or S-cone increments/decrements). Results. Detection and matching of S-cone spots was affected by S-cone background changes but not by L+M background changes. Detection and matching of L+M tests was affected by L+M background changes but not by S-cone background changes. Conclusion. For our stimulus conditions, the same pattern of cone inputs controls the mechanisms mediating threshold and appearance context effects. Moreover, the cone inputs controlling the context effects were matched to the color direction of the test. These results are consistent with the hypotheses a) the context effects we measured are mediated by neural mechanisms common to detection and appearance and b) these mechanisms are situated at a site prior to combination of signals from S cones with signals from L and M cones.
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