The effect of blurring on intersecting-line illusions.

It was observed by chance that illusions in patterns consisting of criss-crossing lines, such as the Orbison and Hering illusions, are markedly reduced when the patterns are blurred. In the first of two experiments the reduction with blurring was confirmed for four patterns but failed to occur in patterns lacking criss-crossing lines. In the second experiment the reduction was shown to be due mainly to the reduced luminance contrast in blurred patterns, thus confirming earlier findings on the effect of contrast of this group of illusions. Theoretical implications are discussed.