Pupil size variation in primary facial expressions–testing potential biomarker of self-criticism

There is no previous research exploring the relationship between self-criticism and pupillary reactivity. Biomarkers such as pupillary reactivity inform about the quantity of the information being processed. Potentially, they can improve predictions of self-criticism levels and identification of pathological levels of self-criticism. The goal of our study is to test whether changes in pupil size act as predictors of self-criticism in participants viewing facial emotional stimuli. This is a first study that includes all basic emotions, and allows detailed analyses of pupillary reactivity predictors. Our results show that the pathological form of self-criticism, which is Hated Self in The Forms of Self-Criticizing/Attacking and Self-Reassuring Scale (FSCRS), was significantly predicted by enlarged pupils in the presence of Anger and Disgust and by narrowed pupils in the presence of Happiness. Greater information gain for Disgust predicted higher score in Inadequate Self and Hated Self measures and lower score for Reassuring Self. The greater information gain for Anger predicted higher score in Inadequate Self and Hated Self measures, but not lower score for Reassuring Self. Pupillary reactivity seems to be a promising biomarker in diagnosing the level of self-criticism and self-reassurance by different pupilar reactions to facial emotion expression especially for Disgust. Greater information gain for Disgust predicts higher score in Inadequate Self and Hated Self measures and lower score for Reassuring Self. In the future, this finding could help create a screening tool for diagnosing pathologically self-critical people without having to rely on self-reporting instruments, which are prone to numerous biases.