While they tell us a story, our pupils dilate and contract following a pattern that varies according to the interest we put in the speech and is synchronized with our interlocutor.

The pupils are responsible for regulating the amount of light that reaches the retina.

When we have a conversation we often unconsciously imitate some of the facial expressions and gestures of our interlocutor. Although the behavior is avoidable, as long as we pay a little attention, there is another phenomenon that we cannot control: our pupils begin to dilate and shrink in the same pattern as the other person’s.

This is a totally involuntary reaction. As Mariska Kret, a researcher at the University of Amsterdam, stated, “we can force a smile, but not change the size of the pupils“. This expert in psychology is the co-author of several studies on the synchronization of this structure of the eyeball that occurs in both humans and chimpanzees and that reveals a lot of information about its owner.

Now, another team of scientists has observed a new peculiarity of the phenomenon associated with interactions between people: while listening to a speech, the constriction and dilation of our pupils are synchronized with those of the speaker if we are really attentive. These moments of maximum concentration coincide with the most interesting parts of the story that they are telling us.

The findings, collected in the latest issue of Journal of Experimental Psychology, are the result of the work of two researchers from the American University of Dartmouth who have analyzed the changes that occur in the central part of the eye during a dialogue. We tend to think that the pupils widen only in response to changes in light, but they also modify their size while the brain processes information.

Generally, in attention and communication studies, participants are asked what they remember after someone else has told them a fact. This method forces volunteers to exercise their memory and identify their thoughts and feelings themselves, so the result may be biased and reflect possible forgetfulness or erroneous memories. That is why the authors of the recent work have chosen to monitor concentration in real time, measuring a physiological response that cannot be controlled consciously.

A sincere indicator of interest

“The eyes are the mirror of the soul” is a popular saying “accredited by many scientific works that relate the dilation of the pupils and the movement of the eyes with mental states such as attention and intention ”, explains Thalia Wheatley, one of the signatories of the research and head of the Social Intelligence Laboratory at the University of Darmouth.

For the test, Wheatley and his colleague had the collaboration of students from the same university, all of legal age without visual or hearing problems that could interfere with their ocular response. Some of the volunteers were recorded while telling an autobiographical story, while the dilation of his pupils was measured with an infrared detector. This instrument emits light that is reflected in the eyes and is captured later with optical sensors.

The experts selected among the recordings four videos whose protagonists were very expressive and another four that were not so expressive. Later, another group of people, unrelated to the previous process, listened only to the audios to evaluate how captivating the stories were. The data obtained from their responses was used to create a time series that represented the change in interest aroused for each narrative in time.

In the dark some pupils can reach 9mm in diameter.

In the dark some pupils can reach 9mm in diameter.
Raniel DiazFlickr

In the last part of the trial, the volunteers were able to see the images that accompanied the sound, while the detectors measured the change in the size of their pupils. What dilation reflects a state of conscious attention, the researchers analyzed the variation patterns of those who told the story and of the spectators in search of moments of synchronization.

Thus, the activity of the pupils revealed that the listeners they concentrated on the speech when the narratives got more interesting, well at those points matched the enlargement and contraction patterns of both interlocutors.

The results also demonstrated the influence of two personality traits on this concordance. On the one hand, those more empathetic people showed a greater involvement in listening and their pupils imitated those of the narrator earlier. On the other, the more expressive rapporteurs more often caused the pupils to synchronize with their audience.

It is not the first time that Wheatley and his partner study this curious phenomenon. The new work is based on the conclusions of a previous one with which showed that changes in the size of the central part of the eye reflect the state of consciousness and the degree of attention we pay to information. The next step for the researchers will be to use the same infrared technique to simultaneously measure the ocular response of both interlocutors.

But, in addition to reflecting interest, the involuntary reaction influences the formation of bonds of trust between two people, according to one of Kret’s works. “The results confirm the relevant role of human eyes in the expression of what we love and hate“, Explains the text. Specifically, “the synchrony of the pupils It is useful in social relationships in which trust is transmitted and falsehood is detected; it is beneficial for interactions within a group, survival and prosperity ”, concludes the study.