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L.P. Thomas, S.L. Buck; Foveal and Extra–Foveal Contributions to Rod Hue Biases . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4747.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We have previously shown green (shift of unique yellow locus), blue (shift of unique green) and short wavelength red (shift of unique blue) rod hue biases with large, dimly–mesopic, extra foveal stimuli. However, these effects disappear when stimuli are confined to a small area of the central fovea. The present study explores the interaction of these two retinal areas in determining the overall rod hue effects. Methods: We assessed rod influence by comparing spectral unique hue wavelengths (measured with 1–s duration, 1 log scot td stimuli and a staircase procedure) under cone plateau and dark adaptation conditions. We varied the spatial configuration and retinal locus of these stimuli. Results:The current results show that the magnitude of the green rod bias stays relatively constant (5–10 nm U yellow shift) once stimuli extend 1° or more from the foveal center, independent of size (1°, 2°, & 7.4°), spatial configuration (disk vs. 7.4°/2°annulus), and presence/absence of foveal stimulation (foveally centered disks vs. annuli). The blue rod bias is more variable across both conditions and observers, producing 2–40 nm shifts of U green with observer–specific variations across the conditions. However, some amount of blue rod bias is evident for all stimuli that extend 1° or more from the foveal center. The present stimulus conditions do not permit unambiguous assessment of the magnitude of the red rod hue bias. Conclusions: The present results show that the green rod hue bias is more consistent across stimulus configurations than is the blue rod hue bias. Together with past demonstrations of greater light–level independence and faster time course of the green rod bias compared to the blue rod bias, the present data support the idea that they are mediated through different pathways (LM cone vs. S cone, respectively). Although we have previously shown that these rod hue biases disappear when tiny stimuli are confined to the central fovea, stimulation of near–foveal areas is sufficient to shift the hues of foveally centered stimuli. Thus, stimulation of near–foveal rods is sufficient to induce hue shifts that dominate the perception of foveally centered stimuli.
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