Analysis of Dynamic Characteristics of Spontaneous Facial Expressions

The relationship between emotions elicited by film clips and spontaneous dynamic facial expressions was investigated. Participants (n = 10) watched 13 emotional film clips, and their facial responses were recorded using a motion capture system. We extracted 3-sec length intervals in which facial events occurred from motion sequences. The participants were asked to self-assess their felt emotional arousal and positive and negative affect for each interval. To find the spatiotemporal components of dynamic facial expressions, we employed the multiway decomposition method, PARAFAC, on a time sequence of facial landmark coordinates standardized via methodologies of geometric morphometrics. The second component was related to facial movement that appears slowly and then maintains a stable state over a long term. Finally, the third component was linked to movement that appears and rapidly returns to the initial state. Local regression analysis was performed to obtain the distribution of the component scores on a two-dimensional plane: pleasure–displeasure and arousal–sleepiness. The third component was negatively correlated with arousal level.