Yes, You're Just Seeing Things

Think the squares marked A and B are different shades of gray?

[Loud annoying buzzer sound].

You're wrong. And MIT Professor Edward H. Adelson of the brain and cognitive sciences department, who studies perceptual sciences, can prove it. See how the illusion works.

Adelson's research focuses on topics in human and machine vision, and he also offers several interesting interactive flash demos that unravel other visual illusion mysteries, such as the Koffka Ring (shown right), in which the appearance of the half-rings depends on the overall spatial configuration, and the simultaneous contrast illusion (below).

These visualizations allow you to interact with the images' components, just in case you're still skeptical. For the simultaneous contrast illusion, in which the two smaller squares are the same color but look different because of their different backgrounds, you can drag the smaller squares around the page to judge their similarity for yourself.