Before revision: The perceived color of a stimulus depends not only on its spectral properties, but also on those of its surround. For instance, a patch that looks gray on an achromatic surround appears reddish when surrounded by green, and greenish when surrounded by red. Previous studies showed that the effect of the surround is repulsive: It enhances the perceptual difference between stimulus and surround. Here, we performed psychophysical experiments to quantify the repulsion. To report the results, a notion of distance in color space was required. We therefore proposed an individually tailored metric in color space that captured the perceptual abilities of each observer.
After revision: 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 in color space that captured the perceptual abilities of each observer.