Which center circle is larger? This is a demonstration of the Titchener illusion. To most people, the center circle on the left will look smaller than the center circle on the right.

Here are the same circles again.

This is a dramatic illusion involving, among other things, local contrast. Most people find it hard to believe that the “dark gray” check outside the shadows is exactly the same color as the “light gray” check inside the shadow. On the next slide, you can see the proof of this illusion.

This revised image allows you to confirm the actual color of the two checks. Each of these little “Bs” is an exact copy of the center of the original check B.