The effect of lightness contrast on the colored Müller-Lyer illusion.

Two subjects estimated the length of the central line in red and blue Müller-Lyer figures that were viewed both foveally and parafoveally. The illusion figures were defined by either lightness and hue differences between figure and ground or by a hue difference alone. For both subjects, the figures defined solely by hue produced larger illusions. Since depth-cue scaling and other cognitive factors did not cause the enlargement, it was concluded that the robust, hue-produced illusions resulted from contour interactions generated within parvocellular channels that are specialized for coding color.