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Your eyes reveal the psychopath

Published: 20 Aug. 2025, 00:08

Choi Hoon

The author is a professor at Hallym University.

The word “psychopath” often comes to mind when we encounter news of a brutal crime. Such diagnoses are usually made using a tool called the Psychopathy Checklist-Revised (PCR). But researchers suggest there may be a simpler way: by looking into the eyes. More precisely, by measuring the size of the pupils. Unlike ordinary people, psychopaths show little to no dilation even when confronted with disturbing or threatening images.

The pupils serve a basic optical function — contracting in bright light and dilating in darkness. Yet, by accident, scientists discovered that pupil size is also tied to psychology. Eckhard Hess, a pioneering psychologist, once found himself engrossed in striking magazine photographs when his wife pointed out that his pupils had grown noticeably larger. Intrigued, he later tested participants by showing them both landscape scenes and photos of attractive people. As expected, the pupils dilated more in response to the latter. In other words, when we encounter someone we find appealing, our eyes portray that attraction.

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Interestingly, the effect works in reverse as well. Larger pupils tend to make a person appear more attractive. Psychologists describe this as the “reciprocity of attraction”: if pupil dilation signals interest in us, we instinctively find the other person more appealing.

This line of research laid the foundation for an entire field known as pupillometry — the study of psychological responses through pupil size. Today, scientists have found that dilation reflects not only attraction but also the intensity of emotions, both positive and negative, the degree of mental effort and even anticipation of reward.

It has long been said that the eyes are the windows to the soul. Even in the minute shift of a pupil, our inner life is on display. That is why we look each other in the eye when we talk, exchanging not just words but feelings. In an age when many shy away not only from eye contact but even from phone calls, the simple act of meeting someone’s gaze remains the irreplaceable beginning of human connection.

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.