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Kathy T. Mullen, Alison Y. Leung, Alyssa Baxter; Changes in S-cone increment and decrement sensitivity as a function of age and eccentricity. Journal of Vision 2008;8(17):71. doi: 10.1167/8.17.71.
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Introduction: There is emerging evidence that the “blue” and “yellow” responses of S-cone opponent color vision are mediated by distinct neural cell types in the subcortical visual pathway, but so far there is little psychophysical evidence for any functional distinctions between them. Here we explore the effects of visual eccentricity on the sensitivity on the two types of S-cone opponent response across a range of different ages. Methods: We measured cone contrast sensitivity of human vision to S-cone increments (S+, blue) and decrements (S−, yellow) for calibrated S-cone isolating stimuli presented in the fovea or at 11 degrees of eccentricity (nasal field, horizontal meridian) with corrections for the presence of macular pigment in the fovea but not periphery. Stimuli were Gaussian blobs (sigma=1deg) in a temporal Gaussian envelope (sigma=125ms). Thresholds were obtained for 55 subjects ranging from 20–79 years. Results: Contrast detection thresholds to blue (S-cone increments) and yellow (S-cone decrements) remain stable with age until subjects reach their 50s, when both types of threshold show a significant and progressive increase with age. Comparing across age groups, we find significantly higher thresholds for S+ (blue) than for S− (yellow) in the periphery, whereas in the fovea these thresholds are no different. Thus the blue thresholds (S+) show a greater rise between fovea and periphery than yellow (S−). Conclusions: 1. The progressive deterioration with age in lens and optic media has little impact on blue-yellow color vision until around 50 years of age. 2. Our results indicate that there is an intrinsically poorer sensitivity to S-cone increments than decrements in the periphery thus supporting the idea that these two processes are physiologically distinct. 3. We speculate that this may reflect a chromatic normalization that compensates for the disappearance of macular pigment in the periphery by selectively reducing blue sensitivity over yellow.
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