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

John S Werner,Brennan Marsh-Armstrong,Kenneth Knoblauch

doi:10.1016/j.cub.2020.05.054

Abstract

For over 150 years, spectrally selective filters have been proposed to improve the vision of observers with color vision deficiencies [1]. 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 [2]. These shifts alter individuals' color-matching and chromatic discrimination such that they are classified as anomalous trichromats [3, 4]. 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 [5, 6]. 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.

Highlights

Maxwell [1] proposed the possibility of improving color discrimination with red and green filters placed over the eyes of a dichromat who entirely lacked M or L cones, but this approach has been shown to be of limited efficacy [19]. Even though such methods cannot lead to normal color vision, it might be thought that anomalous trichromacy would be more amenable to improvements with filtering by spectral reshaping of the three present classes of cone sensitivities
The results cannot be attributed to practice because the protanomalous observer wearing neutral density filters showed no changes over days and reported no changes in his color vision (Figure 3, green points, and Figure S3)
Normal observers sometimes report an effect of the filters on color appearance, but the two normal trichromats who wore the filters displayed no change in their chromatic contrast response relative to their achromatic contrast response (Figure 3, blue points, and Figure S3)

Summary

Introduction

Even though such methods cannot lead to normal color vision, it might be thought that anomalous trichromacy would be more amenable to improvements with filtering by spectral reshaping of the three present classes of cone sensitivities. Participants (classified as described in STAR Methods) were male volunteers (8 anomalous and 2 normal trichromats) invited to wear glasses with either of the two notch filters shown.

Results

Conclusion