I love love love optical illusions, and it's been a while since I posted one. So here's one of the greatest and most brain-eatingly pernicious illusions of them all... and this time, via my friend Richard Wiseman's blog, it's brought to life!

[embed width="610"]http://www.youtube.com/watch?v=z9Sen1HTu5o[/embed]

Now, if you're like me, your first thought is "Baloney!" except perhaps with stronger language. However, I promise you, this is real. It's not a trick, it's not Photoshop, nothing like that*

. It's an honest to goodness optical illusion completely inside your head. I can prove it, and you can prove it for yourself. I took a screen grab from the video:

I then opened it in Photoshop and created two squares. I filled the first one with the color sampled from the "dark" square in the screengrab, the one next to the woman's right hand. I then did the same thing using the color sampled from the "light" square just to the right of the cylinder. Here is the result:

How flipping awesome is that? And you don't have to trust me: go do it yourself. Make a screen grab, or use a template

the video maker put together. Heck, just grab the screengrab I already made and look for yourself! You may note the two squares above aren't exactly the same color; getting a screen grab and compressing the file and all that mucked with the coloring a bit. But clearly, those two squares are very close in shade and color, nowhere near as different as your brain thinks they are in the checkerboard. This classic illusion

is due to the way you interpret color (or shading): it's not done independently; your brain is always comparing things. In one case, the square is surrounded by lighter squares which make it look darker, and in the other case it's surrounded by darker squares, making it look lighter. The shadow going across the squares messes with your perception as well, amplifying the effect. These kinds of illusions are maddening and overwhelming that I expect that despite my clear demo and urging of people to try this for themselves, there will be quite the spirited discussion in this post's comments (just as there was for this one

, one of my all-time favorites) . But there you go. We humans are convinced that we see the world as it really is, but that's complete rubbish. We don't. We see things filtered not just through our fallible senses, but also then interpreted by our ridiculously pliable minds. The Universe is not trying to fool us. It doesn't need to; we do an astonishingly good job of that ourselves. But as long as you're aware of it you can see through the illusion, and, if you're sufficiently willing to, you might see everything a bit more clearly.

Tip o' the Necker cube to Richard Wiseman; go subscribe to his blog. Trust me. You'll love it.

^* I noticed an edit in the video at 50 seconds in. I imagine they just had to do another take, and not work any trickery; as you'll see in my demo, it doesn't matter! The effect is real. In that it's an illusion. Um. You know what I mean.

Related posts: - The blue and the green (one of the single best illusions of all time) - The illusion will drive you mad - Why does the Moon look so huge on the horizon? - Square circle spiral