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Rhea T. Eskew, Jr., Quanhong Wang, Franco Giulianini; Spectral asymmetries in detection mechanisms fed by S cone increments and decrements.. Journal of Vision 2002;2(10):52. doi: 10.1167/2.10.52.
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Recent anatomical and physiological findings indicate that there are separate ganglion cell types carrying S-ON and S-OFF signals. We have used several psychophysical procedures to test for spectral differences in the long-wave cone signals that interact with S cone increment and decrement (+S and −S) signals. Dynamic noise masks, presented along the S-cone, L-cone, M-cone, or a combination of L and M cone axes, were superimposed over +S and −S tests. Noise contrast power was varied to measure threshold Energy vs. Noise (EvN) functions. +S and −S thresholds were similarly affected by S cone noise. However, at least for most observers, +S thresholds were more elevated by L- and M-cone noise than were −S thresholds. These measurements are consistent with the results of McLellan and Eskew (2000), who compared S cone increment and decrement detection under conditions of transient tritanopia. In this procedure, a long wave adapting field (one that stimulates L and M cones but not S cones) is extinguished shortly before presentation of an S cone test, and in general both +S and −S thresholds are elevated. However, the spectral sensitivities of the two signals opposing the S cone signal are different for increments and decrements, with +S signals being more sensitive to the extinction of long-wave fields. Our model of these effects has a relatively greater L cone input opposing +S than −S signals.
McLellan, J.S., & Eskew, R.T. Jr. (2000) ON and OFF S-cone pathways have different long-wave cone inputs. Vision Research, 40, 2449–2465.
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