Optical illusions

Why do these two surfaces in the same shade of grey appear so different?

Optical illusions are more than just a bit of fun. Scientist Beau Lotto is finding out what tricking the brain reveals about how our minds work. Here he explains his findings.

Sight, hearing, taste, touch, smell. We believe what our senses tell us but most of all we trust our eyes.
But our brains are extraordinarily powerful organs.
Without us realising it, they are instantly processing the information they receive to make sense of the world around us.
And that has been crucial to our evolution.

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