Eugena Mariska

Perceiving and correctly interpreting emotional expressions is one of the most important abilities for social animals’ communication. It determines the majority of social interactions, group dynamics, and cooperation – being highly relevant for an individual’s survival. Core mechanisms of this ability have been hypothesised to be shared across closely related species with phylogenetic similarities. This study explored homologies in human processing of species-specific facial expressions using eye-tracking. Introducing a prime-target paradigm, we tested the influences on human attention elicited by priming with differently valenced emotional stimuli depicting human and chimpanzee faces. We demonstrated an attention shift towards the conspecific (human) target picture that was congruent with the valence depicted in the primer picture. We did not find this effect with heterospecific (chimpanzee) primers and ruled out that this was due to participants interpreting them incorrectly. Implications about the involvement of related emotion-processing mechanisms for human and chimpanzee facial expressions are discussed. Systematic cross-species-investigations of emotional expressions are needed to unravel how emotion representation mechanisms can extend to process other species’ faces. Through such studies, we can better understand the implications of humans’ and apes’ shared evolutionary ancestry and better understand “Where our emotions come from”.

Despite the tight link between the visibility of the iris and pupil, the perceived effects of these two have been studied largely in isolation. We demonstrate, across two experimental studies, that the effects of perceived pupil size are dependent on the visibility of the iris. In a first study, our participants donated more and had more positive impressions of portraits of non-human primates when these were manipulated to appear having larger pupils. Post-hoc inspection of our data suggested that the difference was greater for species with more conspicuous irises. In a second study, we concomitantly manipulated iris brightness and pupil size. Brighter irises and larger pupils elicited greater donations. Participants rated photographs with brighter irises as cuter, more attractive and friendlier, but only when they had dilated pupils. Our results have methodological implications for studies manipulating eye appearance, and help interpret results from previous studies.

ABSTRACTThe eyes reveal important social messages, such as emotions and whether a person is aroused and interested or bored and fatigued. A growing body of research has also shown that individuals with large pupils are generally evaluated positively by observers, while those with small pupils are perceived negatively. Here, we examined whether observed pupil size influences approach-avoidance tendencies. Participants performed an Approach-Avoidance Task using faces with large and small pupil sizes. Results showed that pupil size influences the accuracy of arm movements. Specifically, individuals were less prone to approach a face with small pupils than a face with large pupils. Conversely, participants were less prone to avoid a face with large pupils than a face with small pupils. Collectively, these findings suggest that perceivers attend to a facial cue – pupil size – when interacting with others.

ABSTRACTThe eyes are extremely important for communication. The muscles around the eyes express emotional states and the size of the pupil signals whether a person is aroused and alert or bored and fatigued. Pupil size is an overlooked social signal, yet is readily picked up by observers. Observers mirror their own pupil sizes in response, which can influence social impressions. In a landmark study by Hess [1975. The role of pupil size in communication. Scientific American, 233, 110–119] it was shown that individuals with large pupils are perceived more positively than individuals with small pupils. In that behavioral study, participants were asked to draw pupils in line drawings of faces with empty irises and they drew large pupils in the happy face, and small ones in the angry face. The current study tested 579 participants and extended this work by showing that this association between large pupils and a positive impression develops over age and is absent in...