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What Do Pupils Tell Us?

This Moment of Science is going to report some interesting things that our pupils can reveal.

man's blue eye

Photo: feastoffools (Flickr)

Look at that pupil!

The pupils in our eyes do more than control the amount of light entering them.

What Are You Thinking?

The size of our pupils can give clues to our interest, emotions, attitudes, and thought processes.

If you’ve seen a magician tell which card someone picked from a deck, you’ve probably been amazed. Well, the pupils often open up when the magician picks the right card, so one of the tricks they use is to look at the person’s eyes.

Closing Time

The pupils tend to close in response to unpleasantness, and open in response to pleasure. For example, for those who find snakes loathsome, a picture of one will cause their pupils to close. For someone who likes snakes, the same picture will cause the pupils to open.

The same thing happens to people with strong political preferences. A conservative’s pupils will close when shown a picture of a liberal. The liberal has the same reaction when shown a picture of a conservative. Their pupils open when looking at a picture of someone of their own persuasion.


When you are concentrating hard on something like a math problem your pupils will remain open until the problem is solved.
What these and other studies have shown is that our pupils are very sensitive to our emotions and thought processes, often revealing things which we choose not to verbalize.

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