What is Facial Action Coding System (FACS)?


The Facial Action Coding System (FACS) is an internationally recognised, sophisticated research tool that precisely measures the entire spectrum of human facial expressions. FACS has elucidated the physiological presence of emotion with very high levels of reliability. FACS has played a particularly important role in predicting patterns related to deception at about 80% accuracy.

Created in the 1970s by psychologists Paul Ekman and Wallace V. Friesen FACS provides a comprehensive taxonomy of human facial expressions. FACS remains the most widely used and acclaimed method for coding the minutest movements of the human face.

The system dissects observed expressions by determining how facial muscle contractions alter appearance. Each movement is categorised into specific Action Units (AUs), which represent the contraction or relaxation of one or more muscles. All facial expressions can be decomposed into their constituent AUs and described by duration, intensity, and asymmetry. Trained experts examine patterns in the changing nature of facial appearance including: movement, changes in shape and location of the features, and the gathering, pouching, bulging and wrinkling of the skin. Understanding the coordination between action units and certain expressions illuminates the implications of human body language and non verbal behaviour.

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