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Alexandra E Boehm, John Erik Vanston, Gareth D Hastings, Austin John Roorda, William Scott Tuten; Variation in unique yellow for small foveal spots. Invest. Ophthalmol. Vis. Sci. 2021;62(8):2815.
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© ARVO (1962-2015); The Authors (2016-present)
Individuals are remarkably consistent in the color that they perceive to be uniquely yellow, despite several sources of anatomical variability. Studies using larger stimuli (≥ 1 deg) have shown that unique yellow (UY) is invariant to differences in L/M cone ratio, suggesting that color appearance is normalized to be consistent across observers. Whether this invariance is maintained at smaller spatial scales is not well understood. Otake and Cicerone (2000) showed that foveal estimates of UY shifted toward longer wavelengths when measured with small stimuli (3 arcmin), although the extent to which optical factors may have contributed to these findings, or whether this trend persists at even smaller spatial scales, is not clear.
We used an adaptive optics scanning laser ophthalmoscope (AOSLO) to correct ocular aberrations and examine how stimulus size and duration influence foveal estimates of UY. UY estimates were obtained at three stimulus sizes (1, 3, 11 arcmin diameter) and three durations (1, 4, 15 frames at 30 fps) using a multi-wavelength AOSLO, which provided simultaneous retinal imaging and aberration-corrected stimulus delivery. Stimuli were composed of varying mixtures of green (543 nm) and red (680 nm) monochromatic lights to produce metamers to intermediate wavelengths. Axial and transverse chromatic aberrations were corrected. Stimuli were viewed against a white background. Participants (n = 4) reported on each trial whether the stimulus appeared redder or greener. Primary mixtures were adjusted using an adaptive staircase procedure, and UY was defined as the mixture that was equally likely to be judged as red or green.
In the 11 arcmin/15 frame condition, the mean wavelength of UY was 585 nm (range: 580-592 nm), roughly consistent with previous estimates obtained with larger stimuli. For all subjects, UY tended toward longer wavelengths as stimulus size decreased, with an average UY at 591 nm (range: 580-602 nm) for the 1 arcmin/15 frame condition. UY was mostly constant as a function of duration, except in the case of the smallest and briefest stimuli, where UY was 3-12 nm longer.
Our results demonstrate that restricting the spatio-temporal profile of the stimulus on the retina causes UY to (1) shift to longer wavelengths and (2) exhibit more variability between observers. These findings suggest that the normalization of UY for large-field stimuli does not persist at the smallest spatial scales.
This is a 2021 ARVO Annual Meeting abstract.
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