Differences in pupil size during self-reported experiences of disgust, sadness, fear, anger, and happiness.

Previous research has found pupil dilation associated with stimuli pre-assigned as positive and negative in their emotional valence; however, it is not yet clear how self-rated experiences of specific emotions may correlate with differences in pupil size. Using a novel methodology across two studies, 200 participants were presented with emotionally engaging images and sounds and then rated the extent to which they felt happy, sad, angry, fearful, and disgusted in response to these. Data were analyzed using linear mixed effects models to examine whether the participant's own emotion ratings predict pupil size. In 2 studies using standardized images and sounds, and varied 30-s audio clips, in trials with higher self-reported disgust and sadness there was a consistent relationship with pupil dilation. Disgust was most often the strongest predictor of pupil dilation. This effect emerged ∼2 s after stimulus onset and remained present throughout stimulus presentation. Happiness had a weaker effect on pupil dilation and fear was associated with a late pupillary response. Anger was associated with pupil constriction, but only in Study 2. The present approach finds the most consistent relationship between pupil dilation and self-rated disgust and sadness, compared to other negative emotions. The findings thus suggest that measures of pupil size warrant further investigation as a potential indicative psychophysiological correlate of self-reported emotions, with implications for distinguishing negative emotions, such as disgust from anger.