Professor at Leiden University

The Role of Pupil Mimicry in Social Interactions: A Real-Life Interaction Study


“I don’t really understand why it’s considered normal to stare at someone’s eyeballs”1


Although this boy suffering from autism did not see the reason for looking into each other’s eyes, the answer is clear to most other people: the eye is one of the most important regions in social interactions providing rich information about a person’s intentions and emotions. For example, the fine-grained muscles around the eyes provide us with valuable information about a person’s emotions (e.g., the Duchenne smile) and the direction a person is looking at tells us about where her attention is directed to. Another feature that has drawn a lot of attention is the pupil size. Generally, the size of your pupil relates to your level of arousal and dilates when you make a difficult decision, when you lie, or when you like someone. As a direct response of the sympathetic nervous system, it gives genuine, uncontrollable insights into your emotions and intentions. Furthermore, contrarily to other uncontrollable bodily responses such as hormonal levels the pupil size is visible to the interacting person. Intriguingly, people tend to mimic their pupil sizes, which has been suggested to form trust between people. Hence, the pupil is not only a reflection of emotions and intentions, but also communicates and responds to them in an attempt to build a social bond with another person. Recent studies substantiate this idea by showing that pupil mimicry depends on the social context only occurring within, but not across groups and species. Although these findings provide valuable first insights into the social functions of pupil mimicry, studies so far relied on computer tasks measuring participants’ responses to manipulated changes in pictures or videos. However, given the social nature of its function, experiments are needed studying pupil mimicry in real-life interactions. Moreover, previous studies have neglected the fact that the information gathered from pupil mimicry is embedded in a wide range of information from other sources. Interestingly, these responses, including facial muscle activity, eye blink and eye gaze, have also been shown to be mimicked in close interactions.

Our study addresses these shortcomings by investigating how pupil size and other psychophysiological responses and their mimicry influences our decisions in social dilemmas. Looking at several responses simultaneously allows us to investigate the integration of these signals and their unique and joint contribution to making a decision. To do so, two participants will play a social dilemma game while their facial muscle activity, pupil size, eye gaze and blinks are recorded. State-of-the-art high-tech materials are used to be able to measure these subtle responses such as the recently purchased Tobii Pro Glasses 2 (see picture). Results can enhance our understanding of what we are precisely attending to when looking in someone’s eye, how different social signals are related and integrated to reflect and communicate emotional states, to what extent different psychophysiological responses are mimicked and how this predicts our decisions in social interactions. This knowledge could be particularly used in forensic settings such as fine-tuning physiological markers of lying.

1John Elder Robison, Look Me in the Eye: My Life with Asperger’s




Eliska and Friederike testing out new lab equipment to study the value of eye contact during real life interactions. Hey, you’re supposed to look each other in the eyes! 🙂



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