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Caterina Ripamonti, Gordon Henning, Andrew Stockman; S-cone pathways. Journal of Vision 2012;12(9):109. doi: 10.1167/12.9.109.
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In the presence of a background that excites M- and L-cones, there is clear evidence for an unusual S-cone luminance contribution that is delayed and inverted with respect to the usual M- and L-cone signals (Stockman et al., 1991; Ripamonti et al. 2009). This S-cone contribution, however, disappears in the absence of any background, which suggests that it may be some form of gain control acting on existing L- and M-cone signals (rather than being a direct contribution). Here, we continue our investigation of S-cone pathways by looking at S-cone signals in observers with unusual syndromes: some with only S-cones (S-cone monochromatism or Blue-cone monochromatism BCM), and others with an excess of S-cones in whom S-cones have replaced rods during development (enhanced S-cone syndrome or ESCS). We measured their temporal modulation transfer functions at three time-averaged 440-nm target radiances of 7.40, 8.73 and 9.61 log10 quanta s-1 deg-2. Each flickering 4°-diameter target was superimposed in the centre of a steady 9°, 620-nm background of 11.41 log10 quanta s-1 deg-2 to isolate the S-cone response. At all target levels, we found evidence for increased S-cone temporal sensitivity in the BCM and ESCS observers, but with unexpected and abrupt sensitivity peaks. These peaks are consistent with constructive and destructive interference between fast non-inverted, and slow inverted signals, suggesting the existence of multiple S-cone signals. We suspect that the slow, inverted signal is comparable to the sluggish gain control found in normals, but in these syndromes acting on an existing S-cone signal. In the ESCS observers, we were able to measure the S-cone luminance contribution (relative to M- and L-cone signals). Remarkably, the S-cone contribution is also slow and inverted as it was in normals. Apparently, even in ESCS observers, any S-cone luminance contribution is still indirect.
Meeting abstract presented at VSS 2012
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