The role of pupil size in communication. Is there room for learning?

The 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(5), 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 (aged 4-80 years old) and extended this work by showing that this association between large (small) pupils and a positive (negative) impression develops over age and is absent in children. Several explanations for how individuals through interactions with close others learn that large pupils mean care, interest and attention and small pupils the opposite, are discussed. To conclude, this study shows that pupil size and emotion perception are intertwined but that their relationship develops over age.