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Dingcai Cao, Joel Pokorny, Vivianne C. Smith; Chromatic contrast with rod inducing stimuli. Journal of Vision 2004;4(11):47. doi: https://doi.org/10.1167/4.11.47.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: At mesopic light levels, rod input contributes an added chromatic signal with a higher M-cone than L-cone weighting, leading to a more greenish percept (Cao, Pokorny, & Smith, ARVO, 2004). It is of interest whether this rod hue can produce chromatic contrast. Here, the color appearance of a field altered by a rod inducing stimulus was matched with changes in cone activation.
Methods: A 2-channel photostimulator with 4 primaries per channel provided a 2° center with a 10° surround viewed at 6° in the temporal retina. The cone signals in the center and surround were maintained equal, while the rod Weber contrast in the surround was incremented 30% as a 1 Hz square-wave. Induction was measured with a temporal matching technique. The observer could toggle between stimulus and matching epochs, and adjusted cone signals of the center during the matching epoch to match the rod-induced percept seen during a stimulus epoch. Data were collected for 6 chromaticities at 3 retinal illuminances: 2, 10 and 20 photopic td.
Results: The matching luminance (L+M) was less than the stimulus luminance. The matching L/(L+M) was larger than the stimulus L/(L+M), implying the induction from rod signals caused the test appeared more reddish. The effect was largest at the lowest retinal illuminance. S/(L+M) did not require adjustment.
Conclusions: Rod hue can produce chromatic contrast. Rod inducing stimuli changed the test appearing darker and more reddish. The results indicate that the rod contribution to chromatic signals occurs before the locus of chromatic contrast.
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