Derivation of human chromatic discrimination ability from an information-theoretical notion of distance in color space

TL;DR

This paper uses information theory to show that human color discrimination ability is largely determined by photoreceptor absorption properties, explaining about 87% of the variance observed in behavioral experiments.

Contribution

It introduces an information-theoretical framework based on the Fisher metric to quantify how photoreceptor properties influence chromatic discrimination.

Findings

Photoreceptor absorption explains ~87% of variance in color discrimination.

Photoreceptor properties set the main bottleneck in chromatic information processing.

Subsequent neural encoding stages minimally alter discriminability.

Abstract

The accuracy with which humans can detect small chromatic differences varies throughout color space. For example, we are far more precise when discriminating two similar orange stimuli than two similar green stimuli. In order for two colors to be perceived as different, the neurons representing chromatic information must respond differently, and the difference must be larger than the trial-to-trial variability of the response to each separate color. Photoreceptors constitute the first stage in the processing of color information; many more stages are required before humans can consciously report whether two stimuli are perceived as chromatically distinguishable or not. Therefore, although photoreceptor absorption curves are expected to influence the accuracy of conscious discriminability, there is no reason to believe that they should suffice to explain it. Here we develop information-theoretical tools based on the Fisher metric that demonstrate that photoreceptor absorption properties explain ~87% of the variance of human color discrimination ability, as tested by previous behavioral experiments. In the context of this theory, the bottleneck in chromatic information processing is determined by photoreceptor absorption characteristics. Subsequent encoding stages modify only marginally the chromatic discriminability at the photoreceptor level.