Why Optical Illusions Fool the Brain

0:00Why do optical illusions fool your brain?

0:04Look at the two orange circles: which one looks bigger?

0:08Most people say the one on the right looks bigger.

0:12In fact, the two orange circles are exactly the same size.

0:17Light from the picture enters your eye.

0:22At the back of your eye, the retina turns the light into nerve signals.

0:27The optic nerve carries these signals to your brain.

0:34Your brain interprets the signals, which means it works out what you are seeing.

0:39Your brain often judges a size by comparing it with things nearby.

0:44Next to big circles, the orange circle seems smaller.

0:48Next to small circles, the same orange circle seems bigger.

0:53So your brain decides that the right one is bigger.

0:57But that is wrong, because the two orange circles are the same size.

1:02Illusions fool us because your brain interprets the signals from your eyes, and it can be wrong.