Perceived emotions and AU combinations in ambiguous facial expressions

• Network analysis depicts the emotion-network and the surprise is the most repulsive to other emotions. • AU25 and related mouth-open actions are the center of the AU-network. • Matrix calculation found that AU25 weights first in contributing to perceived emotion. • AU4 and AU25 are most frequently presented in the common ambiguous facial expressions Ambiguous facial expressions are common and cannot be classified as specifically prototypical or compound in nature. We have very little understanding of the relationships connecting such expressions to perceived human emotions, such as in terms of compatibility or repulsion. This ignorance also exists with regards to their relationship to action units (AUs). This research employed network analysis to depict the network of perceived emotions and AUs in nearly 5,000 facial expressions obtained from the RAF-AU database, and calculated the centrality indices. We then used a matrix calculation to analyze the relationships between AU combinations and perceived emotions to better understand how people interpret the actions appearing on faces. The results showed that: (1) surprise was the most repulsive to other emotions in the emotion network, (2) AU25 and related open-mouth actions comprised the center of the AU network, (3) AU25 was weighted first in terms of contributing to perceived emotion, and (4) AU4 and AU25 were the most frequently presented in common ambiguous facial expressions. The results were not consistent with those of previous research, mainly due to differences in research methods and materials. The results imply that emotions perceived from ambiguous facial expressions cannot be predicted by core AUs of prototypical facial expressions. The implications and limitations of these conclusions are also discussed herein.