ILLUSORY COLOR CHANGES IN HERMANN GRIDS VARYING ONLY IN HUE

Illusory changes at the intersections of Hermann grids differing only in hue were studied in normal and color-deficient observers. The response patterns indicate that colors ranging either from red-purple to yellow (red group) or from green to purple-blue (blue-green group) can be substituted for each other without greatly changing the strength of the illusion. The same holds for green-yellow, purple and grey (neutral group). For a strong illusion, the overlying stripe and the background must belong to 1 color group and the underlying stripe to the other. The illusory patches are characterized by an increase of chroma and/or a hue shift, usually away from the color of the underlying stripe. The observed illusions may be mediated by R- and G-cones only.