Adaptive Changes in Color Vision from Long-Term Filter Usage in Anomalous but Not Normal Trichromacy

Abstract

For over 150 years, spectrally selective filters have been proposed to improve the vision of observers with color vision deficiencies [1Maxwell J.C. XVIII. – Experiments on colour, as perceived by the eye, with remarks on colour-blindness.Trans. R. Soc. Edinb. 1855; 21: 275-298Crossref Scopus (134) Google Scholar]. About 6% of males and <1% of females have anomalies in their gene arrays coded on the X chromosome that result in significantly decreased spectral separation between their middle- (M-) and long- (L-) wave sensitive cone photoreceptors [2Nathans J. Piantanida T.P. Eddy R.L. Shows T.B. Hogness D.S. Molecular genetics of inherited variation in human color vision.Science. 1986; 232: 203-210Crossref PubMed Scopus (518) Google Scholar]. These shifts alter individuals’ color-matching and chromatic discrimination such that they are classified as anomalous trichromats [3Pokorny J. Smith V.C. Verriest G. Pinckers A.J.L.G. Congenital and Acquired Color Vision Defects. Grune & Stratton, New York1979Google Scholar, 4DeMarco P. Pokorny J. Smith V.C. Full-spectrum cone sensitivity functions for X-chromosome-linked anomalous trichromats.J. Opt. Soc. Am. A. 1992; 9: 1465-1476Crossref PubMed Scopus (157) Google Scholar]. Broad-band spectrally selective filters proposed to improve the vision of color-deficient observers principally modify the illuminant and are largely ineffective in enhancing discrimination or perception because they do not sufficiently change the relative activity of M- and L-photoreceptors [5Sharpe L.T. Jägle H. I used to be color blind.Color Res. Appl. 2001; 26: S269-S272Crossref Google Scholar, 6Moreland J.D. Westland S. Cheung V. Dain S.J. Quantitative assessment of commercial filter ‘aids’ for red-green colour defectives.Ophthalmic Physiol. Opt. 2010; 30: 685-692Crossref PubMed Scopus (11) Google Scholar]. Properly tailored notch filters, by contrast, might increase the difference of anomalous M- and L-cone signals. Here, we evaluated the effects of long-term usage of a commercial filter designed for this purpose on luminance and chromatic contrast response, estimated with a signal detection-based scaling method. We found that sustained use over two weeks was accompanied by increased chromatic contrast response in anomalous trichromats. Importantly, these improvements were observed when tested without the filters, thereby demonstrating an adaptive visual response. Normal observers and a placebo control showed no such changes in contrast response. These findings demonstrate a boosted chromatic response from exposure to enhanced chromatic contrasts in observers with reduced spectral discrimination. They invite the suggestion that modifications of photoreceptor signals activate a plastic post-receptoral substrate that could potentially be exploited for visual rehabilitation.

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