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John Mollon, Marina Danilova; A paradox of color discrimination. Journal of Vision 2011;11(15):18. doi: https://doi.org/10.1167/11.15.18.
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© ARVO (1962-2015); The Authors (2016-present)
At early stages of the visual system, color information has been thought to be carried by two channels: one originating in the midget ganglion cells and representing the ratio of L- and M-cone excitation, the second originating in the small bistratified ganglion cells and representing the ratio of S-cone excitation to the sum of the other two. When color discrimination depends on one of the channels, are thresholds affected by the excitation of the second? Classical studies (e.g. Krauskopf & Gegenfurtner, 1992; Miyahara et al., 1993) suggest that the two channels are largely independent. In the upper-left quadrant of the MacLeod-Boynton diagram, we identify a region where the S-cone excitation affects discrimination on the L/M axis. The effect is paradoxical, in that discrimination improves when S-cone excitation is increased. Observers discriminated the two halves of a 2-deg foveal field. The luminance of each half-field was jittered, to eliminate luminance cues. Targets were presented for 150 ms on a background metameric to D65. One explanation of our results is that observers exploit a neural channel not aligned with either axis of the MacLeod-Boynton, a channel that is most sensitive near the subjective transition from reddish to greenish hues.
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