Observer and stimulus factors jointly shape perceptual similarity of static and dynamic facial emotions

Facial emotion perception is influenced by many factors (e.g. context, conceptual knowledge, facial motion), but how these factors jointly shape emotion perception remains unclear. The present study investigated how observer- and stimulus-based information interact to influence the perceived similarity of facial emotions. Participants categorised the emotion (Experiment 1) or assessed the intensity (Experiment 2) of two static or dynamic facial expressions before rating their similarity. The results showed that perceived similarity between facial expressions could be predicted by representational distances computed using stimulus properties, recognised emotions, or perceived intensity. Combining all three factors produced the best prediction performance, though the contribution of perceived intensity was more consistent for dynamic than static facial emotions. Moreover, the perception of static and dynamic facial emotions showed remarkable similarities and critical differences. All measures of similarity between facial expressions were highly correlated across dynamic and static conditions. However, dynamic facial emotions consistently elicited better categorisation performance and lower perceived intensity compared to static facial emotions. These results demonstrate novel differences in the processing of static and dynamic facial emotions and provide new insights into how perceived emotion and intensity join with stimulus properties to shape our perception of facial emotion.