Life Wellbeing The truth about intelligence? It’s in your eyes, controversial research suggests
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The truth about intelligence? It’s in your eyes, controversial research suggests

Close up of a human eye
The larger the pupils, the higher the intelligence a new study finds. Photo: Getty
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Researchers love a black hole, and not just in the far reaches of the universe.

In the last 20 years, interest has cranked up in the behaviour and function of the pupil, the hole in the middle of the eye that serves as the aperture – pupil dilations as an indicator of effort, opening and closing to let more light in when it’s dark, and less light when it’s bright.

The iris, the circle of colour surrounding the pupil, controls the size of the hole.

Simple, right? Except the pupil is also as messenger.

When a person is lying the pupils are significantly larger. Why? Probably because lying takes up much more mental energy than telling the truth.

The pupils also indicate when we’re getting sleepy or have become sleep deprived. When you’re well rested, your pupils will maintain the same size for 15 minutes in darkness. If you’re sleep deprived, the pupil loses stability, and subtly fluctuates in size.

Controversial research now suggests that the size of our pupils at rest might serve as a proxy measure of intelligence. The bigger the pupil baseline, the smarter you are. The differences are so great between people of high and low cognitive ability, they’re visible to the naked eye.

First evidence came by accident

There was speculation for decades about this possible link because pupil dilation was associated with cognitive processes such as perception, attention, learning and memory.

A group of psychologists – from the Georgia Institute of Technology –first saw evidence for the link by accident.

They were conducting an experiment that measured “the amount of mental effort people used to complete memory tasks”.

They used pupil size as their measuring stick.

To standardise the test, the Georgia researchers established the baseline of each participant’s pupil size – by having them stare at a blank screen and take in an equal amount of glare.

When the results indicated a link between baseline size and intelligence, they weren’t sure if it was a fluke.

The controversial 2016 experiments

In 2016, in a series of experiments, these same researchers recruited 512 people, established their pupil-size baseline – and then had them engage in tasks that measured working memory (the short-term memory used when processing the here and now) capacity and fluid intelligence (associated with abstract thinking and solving problems).

Pupils were measured by eye-tracking units whilst participants carried out these tests.

Sure enough, their results established a strong association between cognitive ability and baseline pupil size.

Not too bright

This week, the Georgia team published a new paper that explains what went wrong.

The short version: the studies that seemed to shoot down their theory “only measured working memory capacity and not fluid intelligence” – and it turns out that working memory doesn’t exhibit as strong an association with pupil size.

But where the other studies fatally stumbled was in their methodology. It seems the screens they used for establishing baseline pupil size were … too bright.

The Georgia Institute authors conducted two large-scale studies to investigate how different lighting conditions affected baseline pupil size values and the correlation with cognitive abilities.

“We found that fluid intelligence, working memory capacity, and attention control did correlate with baseline pupil size except in the brightest lighting conditions.

“We showed that a reduced variability in baseline pupil size values is due to the monitor settings being too bright.”

They’ve titled their new paper: Is baseline pupil size related to cognitive ability? Yes (under proper lighting conditions).

Next step? Independent studies will support the new findings … or not.