Why Do We Confuse Fear with Surprise? A Preliminary Kinematic Investigation of Dynamic Facial Expressions of Spontaneous and Posed Fear and Surprise

Recognizing facial expressions of emotion is a fundamental social skill, yet certain emotions are frequently confused. We investigated the recognition accuracy and kinematic characteristics of posed versus spontaneous dynamic expressions of fear and surprise. First, we tested whether posed fear is more often misrecognized as surprise than spontaneous fear. Results confirmed this hypothesis. Second, we employed 3D motion capture to analyze facial kinematics during the expression of these emotions (both spontaneous and posed). The kinematic analysis provided an intriguing explanation for this phenomenon, revealing that the kinematic profiles of posed fear and posed surprise were highly similar, suggesting that misrecognition may stem from overlapping dynamics. Contrarily, spontaneous expressions of fear are characterized by significantly greater movement, amplitude and velocity in the lower face, in line with evolutionary models of fear contagion. These findings support the role of distinct neural pathways—the Involuntary Pathway for spontaneous expressions and the Voluntary Pathway for posed expressions —in shaping the spatiotemporal dynamics of emotional displays. Our results emphasize the importance of studying the facial movement during the expressions of spontaneous emotions and caution against overgeneralizing results from posed emotional expression research.