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, and thus quickly identify emotions. 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. A variant of FACS has been developed to analyze facial expressions in chimpanzees.
FACS can also be modified such that it can be used to compare facial repertoires across similar species, such as humans and chimpanzees. 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 FACS present in humans and chimpanzees, to show that the facial expressions of both species result from extremely notable appearance changes. A cross-species analysis of facial expressions can help to answer the question of 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.
Intensity Scoring 
Intensities of FACS are annotated by appending letters A–E (for minimal-maximial 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
List of Action Units and Action Descriptors (with underlying facial muscles) 
Main Codes 
|AU Number||FACS Name||Muscular Basis|
|1||Inner Brow Raiser||frontalis (pars medialis)|
|2||Outer Brow Raiser||frontalis (pars lateralis)|
|4||Brow Lowerer||depressor glabellae, depressor supercilii, corrugator supercilii|
|5||Upper Lid Raiser||orbicularis oculi|
|6||Cheek Raiser||orbicularis oculi (pars orbitalis)|
|7||Lid Tightener||orbicularis oculi (pars palpebralis)|
|8||Lips Toward Each Other||orbicularis oris|
|9||Nose Wrinkler||levator labii superioris alaeque nasi|
|10||Upper Lip Raiser||levator labii superioris, caput infraorbitalis|
|11||Nasolabial Deepener||zygomaticus minor|
|12||Lip Corner Puller||zygomaticus major|
|13||Sharp Lip Puller||levator anguli oris (also known as caninus)|
|15||Lip Corner Depressor||depressor anguli oris (also known as triangularis)|
|16||Lower Lip Depressor||depressor labii inferioris|
|18||Lip Pucker||incisivii labii superioris and incisivii labii inferioris|
|20||Lip Stretcher||risorius w/ platysma|
|22||Lip Funneler||orbicularis oris|
|23||Lip Tightener||orbicularis oris|
|24||Lip Pressor||orbicularis oris|
|25||Lips Part||depressor labii inferioris, or relaxation of mentalis or orbicularis oris|
|26||Jaw Drop||masseter; relaxed temporalis and internal pterygoid|
|27||Mouth Stretch||pterygoids, digastric|
|28||Lip Suck||orbicularis oris|
|38||Nostril Dilator||nasalis (pars alaris)|
|39||Nostril Compressor||nasalis (pars transversa) and depressor septi nasi|
|41||Glabella Lowerer||Separate Strand of AU 4: depressor glabellae (aka procerus)|
|42||Inner Eyebrow Lowerer||Separate Strand of AU 4: depressor supercilii|
|43||Eyes Closed||Relaxation of levator palpebrae superioris|
|44||Eyebrow Gatherer||Separate Strand of AU 4: corrugator supercilli|
|45||Blink||Relaxation of levator palpebrae superioris; contraction of orbicularis oculi (pars palpebralis)|
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.|
Visibility Codes 
|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|
|84||Head shake back and forth|
|85||Head nod up and down|
|98*||Fast up-down look|
See also 
- Facial feedback hypothesis
- Facial electromyography
- Computer facial animation
- Facial muscles
- Hjortsjö, CH (1969). Man's face and mimic language.
- P. Ekman and W. Friesen. Facial Action Coding System: A Technique for the Measurement of Facial Movement. Consulting Psychologists Press, Palo Alto, 1978.
- Paul Ekman, Wallace V. Friesen, and Joseph C. Hager. Facial Action Coding System: The Manual on CD ROM. A Human Face, Salt Lake City, 2002.
- Hamm, J.; Kohler, C. G.; Gur, R. C.; Verma, R. (2011). "Automated Facial Action Coding System for dynamic analysis of facial expressions in neuropsychiatric disorders". Journal of Neuroscience Methods 200 (2): 237–256. doi:10.1016/j.jneumeth.2011.06.023. PMC 3402717. PMID 21741407.
- Freitas-Magalhães, A. (2012). Microexpression and macroexpression. In V. S. Ramachandran (Ed.), Encyclopedia of Human Behavior (Vol. 2, pp.173-183). Oxford: Elsevier/Academic Press. ISBN 978-008-088-575-9x
- Del Giudice, M.; Colle, L. (2007). "Differences between children and adults in the recognition of enjoyment smiles". Developmental Psychology 43 (3): 796–803. doi:10.1037/0012-1622.214.171.1246. PMID 17484588.
- Facial Action Coding System. Retrieved July 21, 2007.
- Reed, L. I.; Sayette, M. A.; Cohn, J. F. (2007). "Impact of depression on response to comedy: A dynamic facial coding analysis". Journal of Abnormal Psychology 116 (4): 804–809. doi:10.1037/0021-843X.116.4.804. PMID 18020726.
- Lints-Martindale, A. C.; Hadjistavropoulos, T.; Barber, B.; Gibson, S. J. (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): 678–689. doi:10.1111/j.1526-4637.2007.00358.x. PMID 18028046.
- http://www.erikarosenberg.com/FACS.html Example and web site of one teaching professional: Erika L. Rosenberg, Ph.D
- Parr, L. A.; Waller, B. M.; Vick, S. J.; Bard, K. A. (2007). "Classifying chimpanzee facial expressions using muscle action". Emotion 7 (1): 172–181. doi:10.1037/1528-35126.96.36.199. PMC 2826116. PMID 17352572.
- Vick, S. J.; Waller, B. M.; Parr, L. A.; Smith Pasqualini, M. C.; Bard, K. A. (2006). "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 manual, University of California, California.
- http://www.face-and-emotion.com/dataface/facsaid/description.jsp Facial Action Coding System Affect Interpretation Dictionary (FACSAID)