Many daily decisions are made through quick evaluations of another's trustworthiness, especially when the decision involves strangers. In this process, individuals rely on a partner's tractable characteristics, such as group membership, facial expression and eye gaze. Intriguingly, my own recent research suggests that individuals also respond to their partner's pupil-size (Kret, Tomonaga & Matsuzawa, in press). Pupil-size is an interesting social signal, because it cannot be controlled or faked, in contrast to features such as eye gaze and expression. I showed that seeing someone's pupils dilate promotes trust. In addition, I showed that people synchronize their pupil-size with an observed person. 

These unprecedented findings suggest a link between autonomic pupil-synchronization and trust. Here I propose to study this relationship at the behavioural and neural level, and examine a targeted set of possible contextual moderators.

1. Objective 1 is to test whether pupil-synchronization with dilating pupils provides feedback that the interaction partner is trustworthy.
2. Objective 2 is to test the neuro-hormonal mechanisms. I predict that pupil-synchronization and subsequent development of trust shows neural overlap with empathy and is strengthened by oxytocin, a hypothalamic neuropeptide involved in social bond-formation and pro-social behavior.
3. Objective 3 is to examine possible moderators by manipulating in/out-group characteristics of the observed.

Objective 1 and 3 involve behavioural experiments that manipulate observed or, innovatively, participant's pupil-size and measures, through eye-tracking technology, the putative link between pupil-synchronization and trust. Objective 2 involves an extensive fMRI/eye-tracking study in which oxytocin (vs. placebo) is manipulated, enabling to uncover the neuro-hormonal mechanisms that engage when people synchronize with another's pupil-size. The project primarily intends to build and test new theory, but also has applied relevance for patient care.

Publications

• Kret, M.E., & de Dreu, C.K.W. (in press). Pupil-mimicry conditions trust in exchange partners: Moderation by oxytocin and group membership. The Royal Society B-Biological Sciences.
• Kret, M.E., Fischer, A.H. & de Dreu, C.K.W. (2015). Pupil-mimicry correlates with trust in in-group partners with dilating pupils. Psychological Science, 26(9), 1401-1410. I = 4.43. Download.
• Kret, M.E. (2015). Emotional expressions beyond facial muscle actions. A call for studying autonomic signals and their impact on social perception. Frontiers in Psychology, 6, 711.  I = 2.800. Download.

• emotion
• mimicry
• social decisions