Adelson’s “Checker-shadow illusion”
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.
Comment
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.
Sources
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
Interesting comments
Created: 2002-06-13
Last update: 2013-10-04