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Quanhong Wang, David P Richters, Rhea T Eskew; Interactions of S cone increments and decrements with L and M cone signals. Journal of Vision 2003;3(9):449. doi: 10.1167/3.9.449.
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Anatomical and physiological studies have revealed separate ganglion cell types carrying S-ON and S-OFF signals. Recent psychophysical findings on S-cone increment (S+) and decrement (S−) detection suggest functional distinctions between these two pathways. In past work we studied the spectral sensitivity of these mechanisms by raising S+ and S− thresholds using transient tritanopia and noise masking (“field sensitivity”-like methods). Here we use more direct, “test sensitivity” techniques. Detection contours were measured in the (M,S) and (L,S) planes of cone contrast space, in the presence of dynamic noise. The approximately equiluminant, red/green noise was used to reduce the sensitivity of the red and green detection mechanisms. For two observers, detection contours in the (M,S) and (L,S) planes are similar but not identical. S+ thresholds were nearly independent of L+ and M+ contrasts, but decreased with increasingly negative L− and M− contrasts. On the other hand, S− thresholds decreased with L+ and M+, but were nearly independent of L− and M− contrasts. The results suggest the existence of two opponent mechanisms, with S increments opposed by L and M decrements, and S decrements opposed by L and M increments. Under our conditions, the mechanisms receiving S− signals are more sensitive than those receiving S+ signals. These psychophysical results may be consistent with recent anatomical and physiological findings in primate retina.
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