Adelson’s “Checker-shadow illusion”


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What to do


You will, in all likelihood, perceive the above picture as a 3-dimensional scene, where a greenish cylinder stands on a checkered plane; light comes from top left.


Now try the first button (“Question 1”) on the top right. Two patches will be indicated, and you are asked to compare their relative brightness. I think we can all agree that the top one is darker.


A second later a yellow mask will appear. Now you can compare the two patches without the 3-dimensional context. Now the brightness will be identical. The luminance is identical at all times, but the brightness (=apparent luminance) differs, depending on context.




When interpreted as a 3-dimensional scene, our visual system immediately estimates a lighting vector and uses this to judge the property of the material.


This beautiful demonstration was published by Ted Adelson 1995, the original figure is found here, his explanation here.




Adelson EH (1993) Perceptual organization and the judgment of brightness. Science 262:2042–2044

Adelson EH (2000) Lightness Perception and Lightness Illusions. In The New Cognitive Neurosciences, 2nd ed., M. Gazzaniga, ed. Cambridge, MA: MIT Press, pp. 339–351

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Created: 2002-06-13

Last update: 2013-10-04