The discoloration illusion
The discoloration illusion, a new visual phenomenon, is described. This phenomenon originates from the juxtaposition of eight chromatic parallel contours on a white background, creating a luminance gradient and enclosing a light red region. Under these conditions, the inner region appears white: the light red discolors and appears white with both surface color and luminous qualities. In two experiments, the discoloration illusion was (i) compared with the coloration effect of the watercolor illusion, obtained when the number of adjacent contours was reduced to at least two, and (ii) tested under several conditions useful for understanding the roles of the luminance gradient profile. The results suggest that discoloration is not a lightness illusion and does not depend on simultaneous contrast or on achromatic mechanisms, but more likely on chromatic mechanisms that, through the luminance chromatic gradient, provide cues about the interactions of light and surface and model the volume by depicting lights and shades. The discoloration illusion suggests a possible neural scenario where multiple juxtaposed contours may stimulate neurons, selective for different asymmetric luminance profiles and signaling not only the unilateral belongingness of the boundaries and the coloration effect but also the volumetric and the illumination effects.(Received February 13 2006)
(Accepted February 21 2006)
Key Words: Watercolor illusion; Color spreading; Simultaneous contrast; Color and luminance mechanisms; Magno-; parvo-; and konio-pathways.
c1 Address correspondence and reprint requests to: Baingio Pinna, Facoltà di Lingue e Letterature Straniere, Dipartimento di Scienze dei Linguaggi, University of Sassari, via Roma 151, I-07100 Sassari, Italy. E-mail: firstname.lastname@example.org