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Is seeing believing? Study helps explain optical illusions

Which of the surrounding circles labelled 1-8 is the same size as the circle in the middle of the image?

The answer is 3. This shows how much the illusion strength varies. Sam Schwarzkopf's results suggest that in people who perceive stronger illusions, ie. those who say a higher number, the primary visual cortex is smaller.

Reveal image

Everybody falls for optical illusions, but some people see the illusion more than others.

How strongly someone falls for the illusion may depend on the size of the brain's visual cortex, the part of the brain that processes vision, according to research published in Nature Neuroscience.

It suggests that people do not all see the same world in the same way; different brains see different worlds.

The research was carried out by Sam Schwarzkopf of University College London.

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First broadcast 6 December 2010

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