Spontaneous Facial Behavior Revolves around Neutral Facial Displays

Abstract

With forty-six Action Units (AUs) forming the building blocks in the Facial Action Coding System (FACS), millions of facial configurations can be formed. Most research has focused on a subset of combinations to determine the link between facial configurations and emotions. Despite the value of this research for psychological and computational reasons, it is not clear what the most common combinations of AUs are to form the most commonly expressed facial configurations. We used three diverse corpora with human coded facial action units for a computational analysis. The analysis demonstrated that the largest portion of facial behavior consists of the absence of AU activations, yielding only one specific facial configuration, that of the neutral face. These results are important for cognitive scientists, computer graphics designers and virtual human developers alike. They suggest that only a relatively small number of AU combinations are initially needed for the creation of natural facial behavior in Embodied Conversational Agents (ECAs).