FAUs

FAUs commonly refers to Facial Action Units, the building blocks of the Facial Action Coding System (FACS). Developed for systematic description of facial movements, FACS analyzes expressions in terms of muscular actions rather than inferred emotions. Each facial action unit corresponds to the contraction or relaxation of specific facial muscles, and combinations of FAUs are used to represent complex expressions. FAUs are identified by numerical codes, such as AU1 for inner brow raise and AU12 for lip corner puller.

Coding and use of FAUs involve rating the presence and intensity of each unit in a given frame or sequence. The standard scale typically ranges from 0 (not present) to 5 (maximum intensity). Versions of FACS define roughly 44–46 FAUs across regions including the eyebrows, eyes, and mouth. Analysts and automated systems generate an expression profile by summing activations across units, allowing cross-cultural and cross- individual comparisons of facial behavior.

Applications of FAUs span psychology, behavioral science, human–computer interaction, and animation. In research, FAUs enable objective analysis of facial expressions, microexpressions, and emotional perception. In technology, computer vision and machine learning systems use FAU mappings to recognize expressions, control avatars, or study social signals. Limitations include variability in anatomy, fatigue, lighting, head pose, and occlusions, all of which can affect reliability. FAUs identify movements rather than emotions themselves, so interpretations require context and often additional cues.

Other uses: the acronym FAU can also refer to unrelated terms such as Florida Atlantic University in different contexts. In those cases, FAU is not intended to denote Facial Action Units, and the plural FAUs is uncommon outside specialized discussion of FACS. This article focuses on FAUs as facial action units.