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A. Hughes, A. Dunn; Psychphysical S-Cone Increment and Decrement Temporal Contrast Sensitivity. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2731.
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Recent physiological reports show that S-ON cells have a temporal contrast sensitivity function that is more band-pass than S-OFF cells. These studies-along with some psychophysical reports-find that the long-wavelength cone weights to S-ON and S-OFF neurons is different. The purpose of our work was to measure psychophysical temporal contrast sensitivity functions (TCSF’s) for S-cone increments and decrements. In addition to measuring s-cone increment and decrement TCSF’s under neutral adaptation conditions, we also measured it under varying states of chromatic adaptation as a way to explore L- and M-cone contributions to S-cone pathway sensitivity.
Stimulus generation and data collection were controlled using Vision Research Graphics; stimuli were presented on a ViewSonic 21’ monitor (120 Hz frame rate). Silent-substitution was used to generate test stimuli that were s-cone increments or decrements relative to a steady adapting field (of varying chromaticity). Tests were 2 deg raised cosines presented on a 20 deg white surround metameric to equal-energy white (85 cd/m2). Observers used the Method of Adjustment to determine critical flicker fusion for s-cone increments and decrements of varying frequency. We also measured s-cone increment and decrement TCSF’s under states of chromatic adaptation. In these conditions, the surround field’s chromaticity was set to one of several points along tritan, deutan, or protan confusion lines.
For tests presented on the white surround, we find S-cone increment and decrement TCSF’s to be similar, though sensitivity to s-cone increments is slightly more band-pass. As expected, for all frequencies s-cone increment and decrement sensitivity was reduced for tests presented on a surround with strong s-cone excitation. Interestingly, we find that adaptation to varying surround chromaticities along deutan and protan confusion lines result in significant asymmetries for s-cone increments and decrements.
Our findings extend several recent reports that the relative weighting of L- and M-cone input to S-ON and S-OFF cells are different. We find that chromatic adaptation reveals that the S-cone pathway’s temporal sensitivity is governed partially by factors operating at the opponent site.
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