Perceptual spaces and their symmetries: The geometry of color space

TL;DR

This paper characterizes the geometry of color space through behavioral experiments, revealing perceptual symmetries and proposing an individualized metric that captures how humans perceive color differences and similarities.

Contribution

It introduces an individualized perceptual metric based on discrimination thresholds, uncovering natural symmetries in perceptual computations of color space.

Findings

Perceptual metric accurately describes discrimination thresholds.

Perceptual coordinates reveal symmetry in surround effects.

Color matching follows a simple symmetric law in perceptual space.

Abstract

Our sensory systems transform external signals into neural activity, thereby producing percepts. We are endowed with an intuitive notion of similarity between percepts, that need not reflect the proximity of the physical properties of the corresponding external stimuli. The quantitative characterization of the geometry of percepts is therefore an endeavour that must be accomplished behaviorally. Here we characterized the geometry of color space using discrimination and matching experiments. We proposed an individually tailored metric defined in terms of the minimal chromatic difference required for each observer to differentiate a stimulus from its surround. Next, we showed that this perceptual metric was particularly adequate to describe two additional experiments, since it revealed the natural symmetry of perceptual computations. In one of the experiments, observers were required to discriminate two stimuli surrounded by a chromaticity that differed from that of the tested stimuli. In the perceptual coordinates, the change in discrimination thresholds induced by the surround followed a simple law that only depended on the perceptual distance between the surround and each of the two compared stimuli. In the other experiment, subjects were asked to match the color of two stimuli surrounded by two different chromaticities. Again, in the perceptual coordinates the induction effect produced by surrounds followed a simple, symmetric law. We conclude that the individually-tailored notion of perceptual distance reveals the symmetry of the laws governing perceptual computations.