Preliminary evidence of kinematic overlap in posed, but not spontaneous, facial expressions of fear and surprise

Recognizing facial expressions is a fundamental aspect of social communication, yet certain emotions are frequently confused, particularly fear and surprise. Across two studies, we examined the production and recognition of these expressions. Our findings indicate that fear is more often misclassified as surprise when expressions are posed rather than spontaneous. Using fine-grained three-dimensional motion capture, we analysed the dynamic features of facial movement and showed that posed expressions of fear and surprise share highly similar kinematic profiles, which may account for their frequent confusion. In contrast, spontaneous expressions of fear exhibit greater amplitude and velocity of movement in the lower part of the face. These results underscore the importance of investigating spontaneous emotional expressions and caution against overgeneralizing conclusions derived from posed expression research.