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Facial Action Units

Reference:
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.

Inner brow raiser
AU 1. Inner Brow Raiser: Contributes to the emotions sadness, surprise, and fear, and to the affective attitude interest. Muscular basis: frontalis (pars medialis).

Outer brow raiser
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.
Brow lowerer
AU 4. Brow Lowerer: Contributes to sadness, fear, and anger, and to confusion. Muscles: depressor glabellae, depressor supercilii, and corrugator supercilii.
Upper lid raiser
AU 5. Upper Lid Raiser: Contributes to surprise, fear, and anger, and to interest. Muscular basis: levator palpebrae superioris, and superior tarsal muscle.
Cheek raiser
AU 6. Cheek Raiser: Contributes to the emotion happiness. Orbicularis oculi (pars orbitalis) is the underlying facial muscle.
Lid tightener
AU 7. Lid Tightener: Contributes to the emotions fear and anger, and to confusion. Orbicularis oculi (pars palpebralis) is the underlying facial muscle.
Nose wrinkler
AU 9. Nose Wrinkler: Contributes to the emotion disgust. Levator labii superioris alaeque nasi are the underlying facial muscles.

Upper lip raiser
AU 10. Upper Lip Raiser: Levator labii superioris, caput infraorbitalis are the underlying facial muscles.

Lip corner puller
AU 12. Lip Corner Puller: Contributes to the emotion happiness and contempt when the action appears unilateraly. Muscular basis: zygomaticus major.

Dimpler
AU 14. Dimpler: Contributes to the emotion contempt when the action appears unilateraly, and to boredom. Buccinator is the underlying muscle.

Lip Corner Depressor
AU 15. Lip Corner Depressor: Contributes to the emotions sadness and disgust, and to confusion. Depressor anguli oris is the underlying muscle.

Chin Raiser
AU 17. Chin Raiser: This Action Unit contributes to the affective attitudes interest and confusion. The underlying facial muscle is mentalis.

Lip Pucker
AU 18. Lip Pucker: The underlying facial muscles are incisivii labii superioris and incisivii labii inferioris.

Lip Stretcher
AU 20. Lip Stretcher: Contributes to the emotion fear. The underlying facial muscle is risorius w/ platysma.

Lip Tightener
AU 23. Lip Tightener: Contributes to the emotion anger, and to the affective attitudes confusion and boredom. Muscular basis: orbicularis oris.

Lip Pressor
AU 24. Lip Pressor: Contributes to the affective attitude boredom; the underlying facial muscle is orbicularis oris.

Lips Part
AU 25. Lips Part: The muscular basis consists of depressor labii inferioris, or relaxation of mentalis or orbicularis oris.

Jaw drop
AU 26. Jaw drop: Contributes to the emotions surprise and fear. Muscular basis: masseter; relaxed temporalis and internal pterygoid.

Mouth Stretch
AU 27. Mouth Stretch: The underlying facial muscle are pterygoids and digastric.

Eyes Closed
AU 43. Eyes Closed: Contributes to the affective attitude boredom. The muscular basis consists of relaxation of Levator palpebrae superioris.

Combinations of action units

1, 2, 4
AU 1-2-4: Contributes to the emotions fear and can be recognized by the wavy pattern of the wrinkles across the forehead.

1, 2
AU 1-2: Contributes to the emotion surprise and can be recognized by a smooth line formed by the wrinkles across the forehead.

1, 4
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.

4, 5
AU 4-5: Contribute to the emotion anger.

6, 12
AU 6-12: Contributes to happiness. Notice the wrinkles around the eyes caused by cheek raising, also known as the “Duchenne Marker.”

10, 25
AU 10 – 25: Contributes to the emotion disgust. When AU10 is activated intensily, it causes the lips to part as the upper lip raises.

18, 23
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).

23, 24
AU 23 – 24: The AUs marking lip movements are often the hardest to code. The lips are being pushed together (AU24) and tightened (AU23)

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