Physiological correlates of watercolor effect.

The watercolor effect is a visual illusion that manifests itself as a combination of long-range color spreading and figure-ground organization. The current study uses behavioral and physiological measures to study the watercolor effect. We utilize a novel technique of measuring the cortical response of the illusion using the visual evoked potential (VEP). To this end, three experiments were done to investigate the contributions of luminance and hue to the magnitude of the illusion. Results of both VEP and behavior indicate a marked decrease in the -S (yellow) direction in illusion magnitude compared to the +S (blue) illusion, even though these colors were previously matched for perceptual salience.