The Thatcher illusion: Are faces special?

By: Pete Etchells | The Thatcher illusion: Are faces special? | Neuroscience | The Guardian

Mind gamers: why was a picture of Margaret Thatcher so important for understanding the human visual system?

What’s wrong with the picture above? Obviously, the two faces are upside down, but does something seem a little odd about one of them? When you show this to most people, they can tell there’s a difference, but it’s not immediately clear what the problem is.

The Thatcher illusion was first reported by the University of York’s Professor Peter Thompson in 1980, and laid the groundwork for a new way of thinking about how we process faces. In the right-hand image, Margaret Thatcher’s eyes and mouth are inverted. Yet despite such a huge change, it’s not that easy to see – to the extent that if you present the images briefly and without alerting them to the fact that something’s different, most people won’t notice the change at all. When you look at the picture the right way round though, the difference is obvious (and slightly terrifying).

Related: Change blindness: can you spot the difference?

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