Facial Action Coding System

A comprehensive, anatomically based system for describing all visually discernible facial movements, originally developed by Paul Ekman and Wallace Friesen in 1977. FACS decomposes facial expressions into individual components called Action Units (AUs), each corresponding to the contraction of one or more facial muscles. The system is widely used in psychology, affective computing, and computer vision research to objectively code and classify facial expressions. In accessibility contexts, FACS provides the foundation for automated facial affect recognition systems that can help individuals with autism spectrum disorders interpret the emotional states of conversation partners.