The size of your brain's visual cortex determines whether optical illusions fool you

"How we perceive the world is determined by the visual cortex, but not everybody's cortex is created equal. One person's visual cortex can be up to three times bigger than someone else's, and size matters when it comes to perception.

The primary visual cortex has a far more active role in shaping how we see the world than anyone had suspected. Researchers at University College London discovered this when they were testing a pair of optical illusions on some test subjects. Here's the first one, known as the Ebbinghaus illusion:

Which of the two circles at the center of the other circles is smaller? Most people will say the circle on the left is smaller than the circle on the right, but they're actually the exact same size."

Read more at io9 (Thanks Christopher C)