In the domain of interpersonal communication, the eye region has a vital role. Specifically, the pupil has an essential signalling function, reflecting different cognitive and affective states. The...Show moreIn the domain of interpersonal communication, the eye region has a vital role. Specifically, the pupil has an essential signalling function, reflecting different cognitive and affective states. The colours of the iris, surrounding the pupil, varies largely among human beings. Although studies are conducted on how the colour of the iris influences gaze perception, none have yet investigated the role of iris brightness on the perception of pupil size changes. It is furthermore known that pupil size changes affect interpersonal trust: while dilating pupils lead to a signal of trust, constricting pupils convey untrustworthiness. Nonetheless, the role of iris brightness within this process remains unknown. Moreover, there is evidence for the role of empathy within the processing of pupil size changes. Therefore, the current study explored whether iris brightness affects the perception of pupil size changes. Also, the study examined whether the brightness of the iris in dilating and constricting pupils affected the reported trustworthiness of virtual partners while controlling for the participants’ level of empathy. Fifty-one participants were included in the analysis. These participants were shown animations of a virtual partner with either dark or light irises and dilating, static or constricting pupils. In the Perception of Pupil Movement-task, they were asked: ‘Do you see movement?’. In the Trust-Game Task, they were asked: ‘Would you trust this person to donate money to a charity on behalf of you?’. The results showed that iris brightness affected the perception of pupil size changes. In stimuli with brighter irises, it was easier for participants to detect changes in the size of the pupil. Participants showed less trust when exposed to stimuli representing dilating pupils than static pupils in both light and dark irises while controlling for the individual’s level of empathy. The decreased trust in the constricting stimuli compared to the static stimuli in light and dark irises was in line with expectations. In the dark irises, there was no difference in trust scores between dilating and constricting pupils. In the stimuli representing light irises, on the other hand, there was an effect. This research found no evidence that more empathetic people perceive these subtle cues in eye contact better than less empathetic people. Our results underline the interplay of iris brightness and pupil size changes in monetary decision making and interpersonal communication, specifically regarding perceived trustworthiness.Show less
