A kinematic investigation of the dynamic characteristics of fear and surprise

This study investigates the kinematic characteristics of facial expressions in response to two basic emotions—fear and surprise—in both posed and spontaneous contexts, with a specific focus on posed expressions. Nineteen participants (11 expressing fear, 8 expressing surprise) were recorded while displaying these emotions, with facial dynamics measured using a threedimensional motion analysis system to capture temporal, spatial, and velocity-based parameters. A 2x2 ANOVA examined the main effects and interactions between condition (posed, spontaneous) and expression (fear, surprise) on kinematic variables. The results revealed significant main effects of expression, suggesting that posed surprise requires greater motor coordination and cognitive resources than posed fear. Additionally, interactions between condition and expression highlighted unique kinematic profiles for each emotion, with spontaneous fear showing the highest acceleration and velocity. Empathy, as assessed by the Interpersonal Reactivity Index (IRI), positively correlated with specific kinematic variables in posed expressions, emphasizing individual differences in emotional simulation. These findings enhance understanding of the cognitive and motor demands involved in posing fear and surprise, highlighting the distinct kinematic signatures of each emotion.