The presentation of facial expressions in real life is a dynamic process. Previous research has found that people may exhibit either representational momentum or averaging effects when evaluating social traits from changing expressions, and these effects can compete with each other. This study aims to investigate how individuals make social trait evaluations of the final facial expression following a sequence of expression transitions. In Experiment 1, we manipulated both the presentation mode (static vs. dynamic) and the final frame (high-intensity vs. low-intensity smiles) to examine judgments of warmth, trustworthiness, dominance, competence, and emotional valence. Results revealed representational momentum in judgments of warmth, trustworthiness, and dominance, with ratings biased in the direction of expression change. Emotional valence partially mediated the relationship between the expression presentation mode and social trait evaluation ratings. Experiment 2 further explored the mechanism by manipulating the type of transition (smooth, disrupted, frozen, or static). Notably, representational momentum persisted even in the absence of transitional continuity, indicating a high degree of robustness. These findings suggest that the dynamic information of facial expressions is crucial in social trait evaluation.
