Individuals suffering from depression often have difficulty trusting others. Previous research has shown a relationship between trust formation and pupil mimicry - the synchronization of pupil... Show moreIndividuals suffering from depression often have difficulty trusting others. Previous research has shown a relationship between trust formation and pupil mimicry - the synchronization of pupil sizes between individuals. The current study therefore examined whether pupil mimicry is weaker in depressed individuals and an underlying factor of their low levels of trust. Forty-two patients with major depressive disorder (MDD) and 40 healthy control subjects played trust games with virtual partners. Images of these partners' eye regions were presented to participants before they had to make a monetary investment decision. Partners' pupils either dilated, constricted, or remained static over the course of 4-s interactions. During the task, participants' pupil sizes were recorded with eye-tracking equipment to assess mimicry. The results confirm that patients with MDD were somewhat less trusting than controls and used another's pupillary cues differently when deciding to trust. Specifically, whereas healthy controls trusted partners with dilating pupils more than partners with constricting pupils, patients with MDD particularly trusted partners whose pupils changed in size less, regardless of whether partners' pupils were dilating or constricting. This difference in investment behavior was unrelated to differences in pupil mimicry, which was equally apparent in both groups and fostered trust to the same extent. Whereas lower levels of trust observed in patients with MDD could not be explained by differences in pupil mimicry, our data show that pupil dilation mimicry might help people to trust. These findings provide further evidence for the important role of pupil size and pupil mimicry in interpersonal trust formation and shed light on the pathophysiology of clinically low trust in patients with MDD. Show less
Being observed by others fosters honest behavior. In this study, we examine a very subtle eye signal that may affect participants' tendency to behave honestly: observed pupil size. For this, we use... Show moreBeing observed by others fosters honest behavior. In this study, we examine a very subtle eye signal that may affect participants' tendency to behave honestly: observed pupil size. For this, we use an experimental task that is known to evoke dishonest behavior. Specifically, participants made private predictions for a coin toss and earned a bonus by reporting correct predictions. Before reporting the (in)correctness of their predictions, participants viewed videos of partners with dilating or constricting pupils. As dilating pupils are generally perceived positively, we expected that dishonesty would be reduced when participants look into the eyes of a partner with dilating pupils, especially when their own pupil size mimics the observed pupil size. In line with this prediction, Experiments 1 and 2 showed that, when earning a bonus meant harming the interaction partner, dishonesty occurred less frequently when the partner's pupils dilated rather than constricted. That is, when the interests of the self and the other conflict, participants use the pupil of the partner as a social cue to inform their behavior. However, pupil mimicry was not observed. In Experiment 3, we examined pupil mimicry and dishonesty in a context where there was no temptation to hurt the partner. Here, pupil mimicry between partners was observed, but there were no effects of the partner's pupil on dishonesty. Thus, when dishonesty harms the interaction partner, participants use pupillary cues from their partner to inform their behavior. Pupil mimicry, however, is bound to non-competitive contexts only. Show less
