Humanity at first sight: Exploring the relationship between others' pupil size and ascriptions of humanity

Social targets' eyes are a rich source of information: partners with dilated and constricted pupils are perceived positively and negatively, respectively. Here, we tested whether observed pupil size influences the ascription of humanity. In Study 1 (n = 198) participants were asked to attribute positive uniquely human and non-uniquely human traits to ingroup (i.e., university students), derogated (i.e., homeless people) and non-derogated (i.e., Dutch) targets whose pupils varied in size. Results showed higher attribution of uniquely human traits to targets with dilated (vs. constricted) pupils, whereas no difference based on pupil size emerged on the attribution of non-uniquely human traits. The effect was stronger for non-derogated (vs. derogated and ingroup) targets. In Study 2 (n = 117) participants were asked to attribute positive uniquely human and non-uniquely human traits and emotions. Results replicated the effect of pupil size on trait attribution, especially for outgroup (vs. ingroup) members. The effect of pupil size was not qualified by emotions type (uniquely human vs. non uniquely human). Taken together, our findings show that pupil size is interpreted as a cue to attribute humanity to social targets.