Eye- or mouth lookers? Saccade and pupillary responses to diagnostic features of emotional facial expressions

Facial features convey important information on expressed emotions. However, the informative value of specific features differs between emotions with the eyes being more diagnostic for fear and the mouth region for happy facial expressions. Previous research has found sensitivity to the distribution of such diagnostic features in reflexive eye movements, but conflicting results have been reported for very brief viewing durations. Moreover, it is yet unknown whether autonomic activity also reflects the visual processing of these features. We briefly presented (50 or 150 ms) emotional faces (fearful, happy, and neutral) either in an upright or inverted fashion to elicit reflexive saccades. Furthermore, participants were foveated on specific facial features (i.e., eyes or mouth) by vertically shifting faces relative to the previous central fixation cross. In addition to behavioural performance, we analyzed the proportion of saccades towards facial features in the visual periphery as well as pupil size. While participants were generally very accurate and fast in classifying the emotional expressions, the initial fixation on diagnostic features did not significantly modulate their performance. However, we replicated the previously observed preferential visual orienting towards diagnostic features even for very brief presentation times. Pupil size was not modulated by the experimental manipulations. The results show that facial expression categorization can be accomplished with very restricted visual input. However, even in such conditions, first saccades were preferentially targeting diagnostic features of emotional expressions. The behavioural relevance and stability of such explorations patterns need to be examined in future studies.