This study examines the effects of pupil dilation and iris brightness on the prosocial behavior of people and their attitudes toward primates. We hypothesize that these factors influence...Show moreThis study examines the effects of pupil dilation and iris brightness on the prosocial behavior of people and their attitudes toward primates. We hypothesize that these factors influence perceptions of primates and have an impact on monetary donations as well as ratings of attractiveness, friendliness, and cuteness. The study used a modified dictator game as the primary methodology, with 81 participants completing an online survey and meeting the criteria. Participants were randomly assigned to different iris brightness conditions, either dark or light. During the survey, participants were presented with a total of 64 image pairs, each containing facial portraits of 32 different primate species. We manipulated iris brightness and pupil size of the portraits. Analysis of the data, conducted using mixed repeated measures ANOVA, revealed that pupil dilation significantly influenced several variables. Primates with dilated pupils received higher donation amounts. Although the effects of iris brightness did not reach statistical significance, there was a notable trend indicating increased generosity toward primates with lighter irises. Interestingly, when the pupil was more visible, as shown in the light iris condition, the effects of pupil dilation tended to be more pronounced, although they did not reach the threshold for statistical significance. This research contributes to our understanding of the complex mechanisms behind prosocial behavior when exposed to specific facial features and provides insight into how humans perceive and interact with non-human species, particularly in the context of eye appearance.Show less
