What do the size of your pupils say about your intelligence? Rather a lot, according to a study from last year at the Georgia Institute of Technology. Try this simple experiment and find out.
Find a room that is well-lit, but not overly bright, and don’t think about anything in particular. To recreate the conditions of the study as accurately as possible, look at a small white cross on a black background, about 70cm from your face. Now have a friend measure your pupils – carefully! – using a clear ruler. The diameter of each should be somewhere between 4mm and 8mm.
Bearing in mind that these are just averages, the larger your pupil size, the higher your fluid intelligence (as measured, for example, by tests in which participants select the next number in a sequence). The average is around 6mm, with larger or smaller pupils linked to above-average and below-average intelligence respectively.
In fairness, since measuring your pupils with a ruler is tricky, you shouldn’t worry too much about the absolute measurements. But, as the authors of the study say, a difference of about 1mm is “likely observable to the naked eye”, meaning that whether, in general, your pupils seem larger or smaller than those around you is a good rough-and-ready measure.
Why is pupil size linked to intelligence? One possibility is that the brain systems which regulate pupil size are those responsible for switching the brain out of the resting “default mode” and into action; something intelligent people are more adept at doing.
A fully referenced version of this article is available at benambridge.com. Order Psy-Q by Ben Ambridge (Profile Books, £8.99) for £6.99 at bookshop.theguardian.com
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