this remarkable illusion, square A clearly looks darker than B. What makes it an illusion is that A and B are the exact same shade of gray. You probably don’t believe this; even we occasionally feel compelled to check again, because it seems so wrong. If you don’t want to take our word for it, take a sheet of paper and cut a couple of holes in it that show just squares A and B. You will see that the two squares are identical in color. Why are our eyes fooled so badly? Here the visual system uses background cues in the image to make sense of things. Background cues affect how items in the
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