Abstract
The cooperative eye hypothesis suggests that the morphological characteristics of the human eye have evolved to facilitate following other individuals’ gaze during social interactions. For example, both the white color and larger size of the sclera—the white part of the eye—facilitate gaze identification in humans. Furthermore, while sclera color has been shown to influence social perception such as attractiveness and health, there is much less data on the potential role of sclera size on social judgments. The objective of this study was to test the effect of sclera size on social judgments by comparing perceptions about other individuals with large vs. small sclera size. 108 men and 56 women were recruited in an online within-subject experimental paradigm. Participants had to judge using a 10-level scale the sociability, trustworthiness, social rank and physical attractiveness of pictures of faces taken from a validated database. The sclera size of 50 neutral human faces (25 female models, 25 male models) were digitally modified to have a version with a large sclera (44% of the total size of the eye) and a version with a small sclera (29% of the total size of the eye) resulting in 100 faces that were pseudo-randomly presented. Effect of sclera size, sex of the model, sex of the participant and their interactions on each social judgment was tested. Results show that social judgments about sociability, trustworthiness, and physical attractiveness were significantly more positive for faces with a large sclera than small sclera size. For social rank, we found a sclera size by sex of the participant interaction where only female participants perceived faces with larger sclera as having a higher social rank than faces with smaller sclera. These preliminary results, in line with the cooperative eye hypothesis, suggest a positive social bias towards faces with larger exposed sclera.