Facial Action Coding System
Facial Action Coding System (FACS) is a system to taxonomize human facial movements by their appearance on the face, based on a system originally developed by a Swedish anatomist named Carl-Herman Hjortsjö. It was later adopted by Paul Ekman and Wallace V. Friesen, and published in 1978. Ekman, Friesen, and Joseph C. Hager published a significant update to FACS in 2002. Movements of individual facial muscles are encoded by FACS from slight different instant changes in facial appearance. It is a common standard to systematically categorize the physical expression of emotions, and it has proven useful to psychologists and to animators. Due to subjectivity and time consumption issues, FACS has been established as a computed automated system that detects faces in videos, extracts the geometrical features of the faces, and then produces temporal profiles of each facial movement.
Using FACS  human coders can manually code nearly any anatomically possible facial expression, deconstructing it into the specific action units (AU) and their temporal segments that produced the expression. As AUs are independent of any interpretation, they can be used for any higher order decision making process including recognition of basic emotions, or pre-programmed commands for an ambient intelligent environment. The FACS Manual is over 500 pages in length and provides the AUs, as well as Ekman's interpretation of their meaning.
FACS defines AUs, which are a contraction or relaxation of one or more muscles. It also defines a number of Action Descriptors, which differ from AUs in that the authors of FACS have not specified the muscular basis for the action and have not distinguished specific behaviors as precisely as they have for the AUs.
- Insincere and voluntary Pan-Am smile: contraction of zygomatic major alone
- Sincere and involuntary Duchenne smile: contraction of zygomatic major and inferior part of orbicularis oculi.
Although the labeling of expressions currently requires trained experts, researchers have had some success in using computers to automatically identify FACS codes. Computer graphical face models, such as CANDIDE or Artnatomy, allow expressions to be artificially posed by setting the desired action units.
FACS is designed to be self-instructional. People can learn the technique from a number of sources including manuals and workshops, and obtain certification through testing. The original FACS has been modified to analyze facial movements in several non-human primates, namely chimpanzees, rhesus macaques, gibbons and siamangs, and orangutans. More recently, it was developed also for domestic species, including the dog, the horse and the cat. Similarly to the human FACS, the animal FACS have manuals available online for each species with the respective certification tests.
Thus, FACS can be used to compare facial repertoires across species due to its anatomical basis. A study conducted by Vick and others (2006) suggests that FACS can be modified by taking differences in underlying morphology into account. Such considerations enable a comparison of the homologous facial movements present in humans and chimpanzees, to show that the facial expressions of both species result from extremely notable appearance changes. The development of FACS tools for different species allows the objective and anatomical study of facial expressions in communicative and emotional contexts. Furthermore, a cross-species analysis of facial expressions can help to answer interesting questions, such as which emotions are uniquely human.
Codes for action units
For clarification, FACS is an index of facial expressions, but does not actually provide any bio-mechanical information about the degree of muscle activation. Though muscle activation is not part of FACS, the main muscles involved in the facial expression have been added here for the benefit of the reader.
Action units (AUs) are the fundamental actions of individual muscles or groups of muscles.
Action descriptors (ADs) are unitary movements that may involve the actions of several muscle groups (e.g., a forward‐thrusting movement of the jaw). The muscular basis for these actions hasn't been specified and specific behaviors haven't been distinguished as precisely as for the AUs.
For most accurate annotation, FACS suggests agreement from at least two independent certified FACS encoders.
Intensities of FACS are annotated by appending letters A–E (for minimal-maximal intensity) to the action unit number (e.g. AU 1A is the weakest trace of AU 1 and AU 1E is the maximum intensity possible for the individual person).
- A Trace
- B Slight
- C Marked or pronounced
- D Severe or extreme
- E Maximum
Other letter modifiers
There are other modifiers present in FACS codes for emotional expressions, such as "R" which represents an action that occurs on the right side of the face and "L" for actions which occur on the left. An action which is unilateral (occurs on only one side of the face) but has no specific side is indicated with a "U" and an action which is unilateral but has a stronger side is indicated with an "A."
List of action units and action descriptors (with underlying facial muscles)
Head movement codes
|AU number||FACS name||Action|
|51||Head turn left|
|52||Head turn right|
|55||Head tilt left|
|M55||Head tilt left||The onset of the symmetrical 14 is immediately preceded or accompanied by a head tilt to the left.|
|56||Head tilt right|
|M56||Head tilt right||The onset of the symmetrical 14 is immediately preceded or accompanied by a head tilt to the right.|
|M57||Head thrust forward||The onset of 17+24 is immediately preceded, accompanied, or followed by a head thrust forward.|
|M59||Head shake up and down||The onset of 17+24 is immediately preceded, accompanied, or followed by an up-down head shake (nod).|
|M60||Head shake side to side||The onset of 17+24 is immediately preceded, accompanied, or followed by a side to side head shake.|
|M83||Head upward and to the side||The onset of the symmetrical 14 is immediately preceded or accompanied by a movement of the head, upward and turned and/or tilted to either the left or right.|
Eye movement codes
|AU number||FACS name||Action|
|61||Eyes turn left|
|M61||Eyes left||The onset of the symmetrical 14 is immediately preceded or accompanied by eye movement to the left.|
|62||Eyes turn right|
|M62||Eyes right||The onset of the symmetrical 14 is immediately preceded or accompanied by eye movement to the right.|
|M68||Upward rolling of eyes||The onset of the symmetrical 14 is immediately preceded or accompanied by an upward rolling of the eyes.|
|69||Eyes positioned to look at other person||The 4, 5, or 7, alone or in combination, occurs while the eye position is fixed on the other person in the conversation.|
|M69||Head and/or eyes look at other person||The onset of the symmetrical 14 or AUs 4, 5, and 7, alone or in combination, is immediately preceded or accompanied by a movement of the eyes or of the head and eyes to look at the other person in the conversation.|
|AU number||FACS name|
|70||Brows and forehead not visible|
|71||Eyes not visible|
|72||Lower face not visible|
|73||Entire face not visible|
Gross behavior codes
These codes are reserved for recording information about gross behaviors that may be relevant to the facial actions that are scored.
|AU number||FACS name||Muscular basis|
|38||Nostril dilator||nasalis (pars alaris)|
|39||Nostril compressor||nasalis (pars transversa) and depressor septi nasi|
|41||Lid droop||Levator palpebrae superioris (relaxation)|
|42||Slit||Orbicularis oculi muscle|
|43||Eyes closed||Relaxation of Levator palpebrae superioris|
|44||Squint||Corrugator supercilii and orbicularis oculi muscle|
|45||Blink||Relaxation of Levator palpebrae superioris; contraction of orbicularis oculi (pars palpebralis)|
|84||Head shake back and forth|
|85||Head nod up and down|
|98*||Fast up-down look|
- Computer facial animation
- Computer processing of body language
- Facial electromyography
- Facial feedback hypothesis
- Facial muscles
- Hjortsjö CH (1969). Man's face and mimic language. free download: Carl-Herman Hjortsjö, Man's face and mimic language"
- Ekman P, Friesen W (1978). Facial Action Coding System: A Technique for the Measurement of Facial Movement. Palo Alto: Consulting Psychologists Press.
- Ekman P, Friesen WV, Hager JC (2002). Facial Action Coding System: The Manual on CD ROM. Salt Lake City: A Human Face.
- Hamm J, Kohler CG, Gur RC, Verma R (September 2011). "Automated Facial Action Coding System for dynamic analysis of facial expressions in neuropsychiatric disorders". Journal of Neuroscience Methods. 200 (2): 237–56. doi:10.1016/j.jneumeth.2011.06.023. PMC 3402717. PMID 21741407.
- Ramachandran VS (2012). "Microexpression and macroexpression". In Ramachandran VS (ed.). Encyclopedia of Human Behavior. 2. Oxford: Elsevier/Academic Press. pp. 173–183. ISBN 978-0-12-375000-6.
- Del Giudice M, Colle L (May 2007). "Differences between children and adults in the recognition of enjoyment smiles". Developmental Psychology. 43 (3): 796–803. doi:10.1037/0012-16220.127.116.116. PMID 17484588.
- Facial Action Coding System. Retrieved July 21, 2007.
- Reed LI, Sayette MA, Cohn JF (November 2007). "Impact of depression on response to comedy: a dynamic facial coding analysis". Journal of Abnormal Psychology. 116 (4): 804–9. CiteSeerX 10.1.1.307.6950. doi:10.1037/0021-843X.116.4.804. PMID 18020726.
- Lints-Martindale AC, Hadjistavropoulos T, Barber B, Gibson SJ (2007). "A psychophysical investigation of the facial action coding system as an index of pain variability among older adults with and without Alzheimer's disease". Pain Medicine. 8 (8): 678–89. doi:10.1111/j.1526-4637.2007.00358.x. PMID 18028046.
- Rosenberg EL. "Example and web site of one teaching professional". Archived from the original on 2009-02-06. Retrieved 2009-02-04.
- "Facial Action Coding System". Paul Ekman Group. Retrieved 2019-10-23.
- Parr LA, Waller BM, Vick SJ, Bard KA (February 2007). "Classifying chimpanzee facial expressions using muscle action". Emotion. 7 (1): 172–81. doi:10.1037/1528-3518.104.22.168. PMC 2826116. PMID 17352572.
- Parr LA, Waller BM, Burrows AM, Gothard KM, Vick SJ (December 2010). "Brief communication: MaqFACS: A muscle-based facial movement coding system for the rhesus macaque". American Journal of Physical Anthropology. 143 (4): 625–30. doi:10.1002/ajpa.21401. PMC 2988871. PMID 20872742.
- Waller BM, Lembeck M, Kuchenbuch P, Burrows AM, Liebal K (2012). "GibbonFACS: A Muscle-Based Facial Movement Coding System for Hylobatids". International Journal of Primatology. 33 (4): 809–821. doi:10.1007/s10764-012-9611-6. S2CID 18321096.
- Caeiro CC, Waller BM, Zimmermann E, Burrows AM, Davila-Ross M (2012). "OrangFACS: A Muscle-Based Facial Movement Coding System for Orangutans (Pongo spp.)". International Journal of Primatology. 34: 115–129. doi:10.1007/s10764-012-9652-x. S2CID 17612028.
- Waller BM, Peirce K, Caeiro CC, Scheider L, Burrows AM, McCune S, Kaminski J (2013). "Paedomorphic facial expressions give dogs a selective advantage". PLOS ONE. 8 (12): e82686. Bibcode:2013PLoSO...882686W. doi:10.1371/journal.pone.0082686. PMC 3873274. PMID 24386109.
- Wathan J, Burrows AM, Waller BM, McComb K (2015-08-05). "EquiFACS: The Equine Facial Action Coding System". PLOS ONE. 10 (8): e0131738. Bibcode:2015PLoSO..1031738W. doi:10.1371/journal.pone.0131738. PMC 4526551. PMID 26244573.
- Caeiro CC, Burrows AM, Waller BM (2017-04-01). "Development and application of CatFACS: Are human cat adopters influenced by cat facial expressions?" (PDF). Applied Animal Behaviour Science. 189: 66–78. doi:10.1016/j.applanim.2017.01.005. ISSN 0168-1591.
- "Home". animalfacs.com. Retrieved 2019-10-23.
- Vick SJ, Waller BM, Parr LA, Smith Pasqualini MC, Bard KA (March 2007). "A Cross-species Comparison of Facial Morphology and Movement in Humans and Chimpanzees Using the Facial Action Coding System (FACS)". Journal of Nonverbal Behavior. 31 (1): 1–20. doi:10.1007/s10919-006-0017-z. PMC 3008553. PMID 21188285.
- Friesen W, Ekman P (1983), EMFACS-7: Emotional Facial Action Coding System. Unpublished manuscript, 2, University of California at San Francisco, p. 1
- "Facial Action Coding System Affect Interpretation Dictionary (FACSAID)". Archived from the original on 2011-05-20. Retrieved 2011-02-23.
- Paul Ekman's articles relating to FACS
- Paul Ekman's Facial Action Coding System (FACS)
- More information on the different animal FACS projects
- New Yorker article discussing FACS
- Details from 1978 edition of FACS
- Site at WPI
- download of Carl-Herman Hjortsjö, Man's face and mimic language" (the original Swedish title of the book is: "Människans ansikte och mimiska språket". The correct translation would be: "Man's face and facial language")