Fawcett, C., Wesevich, V., & Gredebäck, G. (2016) Pupillary contagion in infancy: Evidence for spontaneous transfer of arousal. Psychological Science, 27, 997-1003

Pupillary contagion – responding to observed pupil size with changes in one’s own pupil –has been observed in adults and suggests that arousal and other internal states could be transferred across individuals using a subtle physiological cue. Examining this phenomenon developmentally gives insight into its origins and underlying mechanisms, such as whether it is an automatic adaptation already present in infancy. In the current study, 6- and 9-month-olds viewed schematic depictions of eyes with smaller and larger pupils – pairs of circles with smaller and larger black centers - while their own pupil size was recorded. Control stimuli were comparable squares. For both age groups, infants’ pupil size was greater when viewing large-centered than small-centered circles and no differences were found for squares. The findings suggest that infants are sensitive and responsive to subtle cues to others’ internal states, a mechanism that would be beneficial for early social development.