The Facial Action Coding System (F.A.C.S.) is the most comprehensive and objective facial coding system available to social scientists. Traditionally a time-consuming manual coding system, which quantifies all possible movements a person can make with his or her face, reliable action unit coding is automated using FaceReader.
Ekman, P.; Friesen, W. V.; Hager, J. C. (2002). Facial action coding system:
The manual on CD-ROM. Instructor’s Guide. Salt Lake City: Network Information Research Co.
Check out what Action Units look like!
Recent advances in computer vision have allowed for reliable automated facial action coding. Below you can see the 20 Action Units offered in the most recent version of FaceReader as well as some frequently occurring or difficult action unit combinations. Some images have been zoomed in on the area of interest to explicitly show what muscle movement corresponds to the specific Action Unit.
AU 1. Inner Brow Raiser: Contributes to the emotions sadness, surprise, and fear, and to the affective attitude interest. Muscular basis: frontalis (pars medialis).
AU 2. Outer Brow Raiser: Contributes to the emotions surprise and fear, and to the affective attitude interest. Frontalis (pars lateralis) is the underlying facial muscle.
AU 10. Upper Lip Raiser: Levator labii superioris, caput infraorbitalis are the underlying facial muscles.
AU 12. Lip Corner Puller: Contributes to the emotion happiness and contempt when the action appears unilateraly. Muscular basis: zygomaticus major.
AU 14. Dimpler: Contributes to the emotion contempt when the action appears unilateraly, and to boredom. Buccinator is the underlying muscle.
AU 15. Lip Corner Depressor: Contributes to the emotions sadness and disgust, and to confusion. Depressor anguli oris is the underlying muscle.
AU 17. Chin Raiser: This Action Unit contributes to the affective attitudes interest and confusion. The underlying facial muscle is mentalis.
AU 18. Lip Pucker: The underlying facial muscles are incisivii labii superioris and incisivii labii inferioris.
AU 20. Lip Stretcher: Contributes to the emotion fear. The underlying facial muscle is risorius w/ platysma.
AU 23. Lip Tightener: Contributes to the emotion anger, and to the affective attitudes confusion and boredom. Muscular basis: orbicularis oris.
AU 24. Lip Pressor: Contributes to the affective attitude boredom; the underlying facial muscle is orbicularis oris.
AU 25. Lips Part: The muscular basis consists of depressor labii inferioris, or relaxation of mentalis or orbicularis oris.
AU 26. Jaw drop: Contributes to the emotions surprise and fear. Muscular basis: masseter; relaxed temporalis and internal pterygoid.
AU 27. Mouth Stretch: The underlying facial muscle are pterygoids and digastric.
AU 43. Eyes Closed: Contributes to the affective attitude boredom. The muscular basis consists of relaxation of Levator palpebrae superioris.
Combinations of action units
AU 1-2-4: Contributes to the emotions fear and can be recognized by the wavy pattern of the wrinkles across the forehead.
AU 1-2: Contributes to the emotion surprise and can be recognized by a smooth line formed by the wrinkles across the forehead.
AU 1-4: Contributes to sadness. Recognizable by a wavy pattern of the wrinkles in the center of the forehead. Eye-brows come together and up.
AU 4-5: Contribute to the emotion anger.
AU 6-12: Contributes to happiness. Notice the wrinkles around the eyes caused by cheek raising, also known as the “Duchenne Marker.”
AU 10 – 25: Contributes to the emotion disgust. When AU10 is activated intensily, it causes the lips to part as the upper lip raises.
AU 18 – 23: Often confused as solely AU18. Notice the lips almost appear to be pulled by a single string outward (AU18) and then tightened (AU23).
AU 23 – 24: The AUs marking lip movements are often the hardest to code. The lips are being pushed together (AU24) and tightened (AU23)