actionsunits

Actionsunits, also known as action units (AUs), are fundamental components of facial expressions, primarily used in the Facial Action Coding System (FACS) to describe and categorize facial movements. Developed by psychologists Paul Ekman and Wallace Friesen, FACS is a comprehensive system that identifies and categorizes human facial movements by their appearance on the face. Actionsunits are the basic building blocks of this system.

Each action unit corresponds to a specific muscle or group of muscles in the face. When these muscles contract, they produce distinct facial movements, which can be combined to form a wide range of expressions. For example, the contraction of the zygomatic major muscle, which raises the corners of the mouth, is designated as Action Unit 12 and is often associated with happiness or amusement. Similarly, the contraction of the corrugator supercilii muscle, which draws the eyebrows together, is designated as Action Unit 4 and is often associated with anger or concentration.

Actionsunits are typically identified and coded based on their appearance in photographs or videos. The FACS system includes a total of 46 action units, each with a unique number and description. These action units can be combined in various ways to create complex facial expressions, allowing for a detailed and nuanced analysis of emotional and communicative behaviors.

The use of actionsunits in FACS has applications in various fields, including psychology, psychiatry, and human-computer interaction. By providing a standardized and objective method for describing facial movements, actionsunits help researchers and practitioners better understand the relationship between facial expressions and underlying emotional states. Additionally, the system has been adapted for use in automated facial expression recognition systems, which have potential applications in areas such as market research, user experience design, and mental health assessment.