In the Ebbinghaus illusion, both the central circles are identical and the same size. However, the central circle that is surrounded by larger circles appears smaller than the one surrounded by smaller circles.
To appreciate the PacMan illusion (or lilac chaser), stare at the cross in the middle of the twelve lilac discs for 20 seconds. You will notice that there is a missing lilac disc.
In the Hermann grid illusion, you will perceive circular grey patches at the intersections of the white grid lines. These grey patches are not actually there, and disappear when you look directly at them.
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