Professor at Leiden University

Pupil mimicry: a bonding mechanism

Eliska: “Did your mother ever ask: “Did you steal a cookie? Look at me!” – and you had to look away. Eyes are important social signals. Eye contact increases with familiarity and liking and seems to promote trust. What underlies this trust-enhancing effect of eye contact?”


Humans often make inferences about someone else’s mental state: what the other person believes, how he or she feels, and whether he or she can be trusted. Other people’s eyes, and especially their pupils, are particularly important physical features when it comes to decisions about trust. A new study from Leiden University provides surprising clues about how pupillary changes may influence the observer’s behavior.


In the study, we tested subjects in the MRI scanner while they were looking into the eyes of others. In these other eyes, the pupil changed size. Not only did the subjects unconsciously subjects matched their own pupil size to the pupils of the other, (this process was measured with an eye tracker), but this mirroring behavior also led to increased trust (which we measured via an economic game). When we looked at the brain data the situation immediately became clear: the mirroring of pupil size is a social, emotional process. The networks involved in mirroring pupil size turned out to be the same ones that are active when we try to understand someone’s state of mind. In consequence, participants who mimicked the dilated pupils of a partner were more likely to trust that partner.


Latest news
Latest blog