This perplexing optical illusion has my brain in check mate

We love a good trick of the eye here at Creative Bloq. Our pick of the best optical illusions includes everything from Super Mario confusing us on a staircase to a spinning horse. But some mind benders still just leave me stumped, and this is one of them.

The checker shadow illusion is a famous optical illusion that's been intriguing scientists for years. But I have to admit that I suspected a fast one when I first came across it. We're told that Square A and square B in the illustration below are exactly the same shade of grey. How can that be?

I'm familiar with the effect of contrast illusions, and we've covered lots of them before. They cause areas of identical colour to look different depending on the surrounding context. In this example, we presume that square B will be lighter than A because we know what chequerboards and chessboards look like, and we see that B is lighter than the squares immediately beside it vertically and horizontally. The illustration below proves that the two squares are indeed the same colour by linking them together.

But I still had doubts because when I tried to isolate the two individual squares by covering the rest of the composition, square B still looks lighter than square A to me. So I pulled the image into Photoshop (yes, I was that determined to prove the illusion wrong). But a quick check with the eye dropper tool proved that the two squares are indeed identical in hue. So I surrender. Check and mate. The optical illusion is real.

You can learn more about the illusion in this 2020 scientific paper from Masahiro Yamamoto and Shinsuke Shimojo. In the meantime, don't miss the weird AI optical illusions that are amazing the internet.