I’m told that Square A is the exact same colour as Square B. I can’t see it really, but apparently this is a scientifically recognized principal, published by Edward H. Adelson in 1995. From the Wikipedia article,
“When interpreted as a 3-dimensional scene, our visual system immediately estimates a lighting vector and uses this to judge the property of the material.”
Fascinating, really. I’ve always known that what we see is only a rough interpolation; as it is, my eyes see certain blues differently when viewed with one or the other. This sort of thing just blows me away though. Some people say if you squint you can fool your brain into seeing them as they truly are, and I can almost make it, but there’s still some variation. See? You literally cannot trust what your eyes tell you! How’s that for paranoia inducing truth?
Adelson’s Checkerboard Illusion [bioephemera]