Pupil Size: A Measure of Trust?

Scientific American Mind:

Pupils are a rich source of social information. Although changes in pupil size are automatic and uncontrollable, they can convey interest, arousal, helpful or harmful intentions, and a variety of emotions. According to a new study published in Psychological Science, we even synchronize our pupil size with others—and doing so influences social decisions.

Mariska Kret, a psychologist now at the University of Amsterdam in the Netherlands, and her colleagues recruited 69 Dutch university students to take part in an investment game. Each participant decided whether to transfer zero or five euros to a virtual partner after viewing a video of their eyes for four seconds. The invested money is tripled, and the receiver chooses how much to give back to the donor—so subjects had to make quick decisions about how trustworthy each virtual partner seemed.

Read the whole story: Scientific American Mind