Shading Fades Away Illusion
Stare at the center of the black dot for about 20 seconds. After a little while, you’ll notice that the outside of the circle – the shaded area – starts to lose definition, and even becomes a solid color. Or, your eyes may notice that the shading shrinks and isn’t even perceptible after a minute or so.
This is quite a weird optical illusion! And it only becomes more convincing the longer you stare at the black dot, so you must be patient!
Or, try it in color, it works just as well. It’s as if your brain wants to clean up the mess and focus on the object, and not the shadows.