We unconsciously pay more attention to someone who has dilated pupils

By Emma Young

How do you know when someone else is paying attention to you? If they’re staring at you intensely, that’s a pretty obvious giveaway. But there are also far subtler signals — such as the size of their pupils.

As Clara Colombatto and Brian Scholl at Yale University note in a new paper in the Journal of Experimental Psychology: General, our pupils automatically and uncontrollably dilate when we’re emotionally aroused, working something out, or just attending to something. Pupil size has been used as an objective indicator of all these things in a wealth of recent studies.

But if another person is directing their attention towards you, you need to know about it. It might be attention that you should reciprocate, to build a relationship, or it might signal a potential threat. So, Colombatto and Scholl wondered, “If the apprehension of pupil size is so helpful to scientists, might it be similarly helpful to us in everyday life?”

To investigate, they studied groups of student participants. For these screen-based studies, they manipulated the presentation of a series of images so that they only gradually became perceptible. As soon as a participant saw any part of the image emerge into their conscious awareness, they hit a key.

In each of the two main studies, the participants were repeatedly exposed to versions of face and upper torso images of two men and two women. The researchers digitally manipulated the pupils so that they were either small or large; in the first study, they also digitally cut, rotated and pasted pairs of large or small pupils to resemble shirt buttons. In the second study, instead of “buttons”, a single large or small pupil was pasted near the mouth to resemble a facial mole. Colombatto and Scholl varied the size of the pupils and the “buttons” or “moles” independently, and looked for any differences in the time it took for the images to be consciously perceived.

The team varied the size of the pupils (left) and either buttons (middle) or moles (right). Buttons and moles actually consisted of pupils digitally imposed on the shirt or face. From Colombatto and Scholl (2022)

The results showed that the participants became more rapidly consciously aware of facial close-ups with large vs small pupils — but this was not the case for large vs small “buttons” or large vs small “moles” (even though the large facial moles really stood out visually against the individuals’ skin). It seems, then, that our visual system is indeed attuned to large pupils, which carry a social meaning — but not to otherwise identical dots.

A further experiment ruled out a potential alternative explanation for the results: that a face with dilated pupils might be perceived as more attractive, and this could lead it to enter conscious awareness more rapidly. Colombatto and Scholl found, in fact, that big-pupil versions of the eye regions were considered less attractive than the small-pupil versions.

“Despite its social significance, pupil dilation is an exceptionally visually subtle signal,” the pair also notes. During debriefings after the experiments, only two of their total of 60 participants said they’d noticed any eye differences in the images. One referred to a difference in eye colour. The other said: “Some people looked more intense.” “This degree of subtlety makes the key results of the study all the more striking,” they argue — and it’s hard to disagree.

In revealing that we unconsciously pay more attention to someone who seems to be paying attention to us, the work also helps to illuminate the processes by which we come to share mutual attention. “In short, the current results suggest that the perceived attentional state of other can in turn cause us to attend to them — a novel form of ‘attentional contagion’,” the researchers conclude. 

Unconscious pupillometry: An effect of “attentional contagion” in the absence of visual awareness.

Emma Young (@EmmaELYoung) is a staff writer at BPS Research Digest

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