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Elise W. Dees, Stuart J. Gilson, Rigmor C. Baraas; Spatio-chromatic Properties Of Human Trichromatic Vision. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6391.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the variation in spatial properties of colour vision for observers with normal trichromatic vision with a novel isochromatic stimulus.
The stimulus was a Gabor patch with the spatial structure disrupted using spatially discrete spots whose size and spacing was varied. Spot luminance was randomized around a mean level, creating luminance noise. Each spot’s chromaticity was determined by the mean colour of the region of the Gabor it covered. The space between spots was filled with a mean-luminance colour and, thus, no part of the underlying Gabor patch was visible in the stimulus, except that reconstructed by the chromatic pathway by grouping spots of similar hue. In this study, chromaticity of the Gabor patch was varied along the L- or M-cone axis in CIE 1931 (x, y) chromaticity diagram with mean chromaticity set to CIE illuminant E. Chromatic contrast sensitivity was measured for at least 12 spatial frequencies from 0.3-3.0 c/deg in most observers and up to 6 c/deg in some. Observers were classified as normal trichromats with several clinical colour vision tests including the Medmont C100 colour vision tester. Those included in the study were corrected to best logMAR letter acuity and viewed the stimuli monocularly.
L- and M-cone contrast sensitivity functions can be measured in naïve observers and are always low-pass. Sensitivity varies between observers with most observers having higher L-cone than M-cone sensitivity. The ratio of L- to M-cone sensitivity correlates highly with individual performance on the Medmont C100 test. Estimated limiting spatial frequency varies between 5-10 c/deg, again with most having higher cut-off frequency for L-cones.
The method provides a robust way of assessing spatio-chromatic processing in naïve observers and has the potential to estimate an individual’s L- to M-cone ratio. Further work is needed to understand the relationship between these behavioral measures and its link with ratios of L- and M-cone packing densities in the retina.
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