Facial Action Coding System

Background

In 2009, a study was conducted to study spontaneous facial expressions in sighted and blind judo athletes. They discovered that many facial expressions are innate and not visually learned.

Method

Using the F.A.C.S., human coders can manually code nearly any anatomically possible facial expression, deconstructing it into the specific "action units" (A.U.) and their temporal segments that produced the expression. As A.U.s 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 F.A.C.S. manual is over five hundred pages in length and provides the A.U.s, as well as Ekman's interpretation of their meanings.

The F.A.C.S. defines A.U.s as contractions or relaxations of one or more muscles. It also defines a number of "action descriptors", which differ from A.U.s in that the authors of the F.A.C.S. have not specified the muscular basis for the action and have not distinguished specific behaviors as precisely as they have for the A.U.s.

For example, the F.A.C.S. can be used to distinguish two types of smiles as follows:

• the insincere and voluntary Pan-Am smile: contraction of zygomatic major alone
• the sincere and involuntary Duchenne smile: contraction of zygomatic major and inferior part of orbicularis oculi.

The F.A.C.S. 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.

Although the labeling of expressions currently requires trained experts, researchers have had some success in using computers to automatically identify the F.A.C.S. codes. One obstacle to automatic FACS code recognition is a shortage of manually coded ground truth data.

Uses

Baby F.A.C.S.

Baby F.A.C.S. (Facial Action Coding System for Infants and Young Children) is a behavioral coding system that adapts the adult F.A.C.S. to code facial expressions in infants aged 0–2 years. It corresponds to specific underlying facial muscles, tailored to infant facial anatomy and expression patterns.

It was created by Dr. Harriet Oster and colleagues to address the limitations of applying adult F.A.C.S. directly to infants, whose facial musculature, proportions and developmental capabilities differ significantly.

Use in medicine

The use of the F.A.C.S. has been proposed for use in the analysis of depression, and the measurement of pain in patients unable to express themselves verbally.

Interspecial applications

The original F.A.C.S. 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 domesticated species, including dogs, horses and cats. Similarly to the human F.A.C.S., the non-human F.A.C.S. has manuals available online for each species with the respective certification tests.

Thus the F.A.C.S. can be used to compare facial repertoires across species due to its anatomical basis. A study conducted by Vick and others (2006) suggests that the F.A.C.S. 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 F.A.C.S. tools for different species allows the objective and anatomical study of facial expressions in communicative and emotional contexts. Furthermore, an interspecial analysis of facial expressions can help to answer interesting questions, such as which emotions are uniquely human.

The Emotional Facial Action Coding System (E.M.F.A.C.S.) and the Facial Action Coding System Affect Interpretation Dictionary (F.A.C.S.A.I.D.) consider only emotion-related facial actions. Examples of these are:

Computer-generated imagery

F.A.C.S. coding is also used extensively in computer animation, in particular for computer facial animation, with facial expressions being expressed as vector graphics of A.Us. F.A.C.S. vectors are used as weights for blend shapes corresponding to each A.U., with the resulting face mesh then being used to render the finished face. Deep-learning techniques can be used to determine the F.A.C.S. vectors from face images obtained during motion capture acting, facial motion capture or other performances.

Codes for action units

For clarification, the F.A.C.S. is an index of facial expressions, but does not actually provide any biomechanical information about the degree of muscle activation. Though muscle activation is not part of the F.A.C.S., the main muscles involved in the facial expression have been added here.

Action units (A.U.s) are the fundamental actions of individual muscles or groups of muscles.

Action descriptors (A.D.s) 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 has not been specified and specific behaviors have not been distinguished as precisely as for the A.U.s.

For the most accurate annotation, the F.A.C.S. suggests agreement from at least two independent certified F.A.C.S. encoders.

Intensity scoring

Intensities of the F.A.C.S. are annotated by appending letters A–E (for minimal-maximal intensity) to the action unit number (e.g. A.U. 1A is the weakest trace of A.U. 1 and A.U. 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 F.A.C.S. 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 bilateral but has a stronger side is indicated with an "A" for "asymmetric".

List of A.U.s and A.D.s (with underlying facial muscles)

Main codes

Head movement codes

Eye movement codes

Visibility codes

Gross behavior codes

These codes are reserved for recording information about gross behaviors that may be relevant to the facial actions that are scored.

References

References

1. (2022-08-06). "Man's face and mimic language".
2. (1978). "Facial Action Coding System: A Technique for the Measurement of Facial Movement.". Consulting Psychologists Press.
3. (2002). "Facial Action Coding System: The Manual on CD ROM.". A Human Face.
4. Matsumoto, D., & Willingham, B. (2009). "Spontaneous facial expressions of emotion of blind individuals". ''[[Journal of Personality and Social Psychology]]'', 96(1), 1-10
5. (2012). "Encyclopedia of Human Behavior". Elsevier/Academic Press.
6. (May 2007). "Differences between children and adults in the recognition of enjoyment smiles". Developmental Psychology.
7. Rosenberg, Erika L.. "Example and web site of one teaching professional".
8. "Facial Action Coding System".
9. [http://www.cs.wpi.edu/~matt/courses/cs563/talks/face_anim/ekman.html Facial Action Coding System.] Retrieved July 21, 2007.
10. (10 Mar 2023). "Self-supervised Facial Action Unit Detection with Region and Relation Learning".
11. (2006). "Baby FACS: Facial Action Coding System for Infants and Young Children". Unpublished monograph and coding manual. New York University..
12. (November 2007). "Impact of depression on response to comedy: a dynamic facial coding analysis". Journal of Abnormal Psychology.
13. (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.
14. (February 2007). "Classifying chimpanzee facial expressions using muscle action". Emotion.
15. (December 2010). "Brief communication: MaqFACS: A muscle-based facial movement coding system for the rhesus macaque". American Journal of Physical Anthropology.
16. (2012). "GibbonFACS: A Muscle-Based Facial Movement Coding System for Hylobatids". International Journal of Primatology.
17. (2012). "OrangFACS: A Muscle-Based Facial Movement Coding System for Orangutans (''Pongo'' spp.)". International Journal of Primatology.
18. (2013). "Paedomorphic facial expressions give dogs a selective advantage". PLOS ONE.
19. (2015-08-05). "EquiFACS: The Equine Facial Action Coding System". PLOS ONE.
20. (2017-04-01). "Development and application of CatFACS: Are human cat adopters influenced by cat facial expressions?". Applied Animal Behaviour Science.
21. "Home".
22. (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.
23. (1983). "EMFACS-7: Emotional Facial Action Coding System. Unpublished manuscript". University of California at San Francisco.
24. "Facial Action Coding System Affect Interpretation Dictionary (FACSAID)".
25. Walsh, Joseph. (2016-12-16). "Rogue One: the CGI resurrection of Peter Cushing is thrilling – but is it right?". The Guardian.
26. (October 2021). "FACSHuman, a software program for creating experimental material by modeling 3D facial expressions". Behavior Research Methods.
27. "Discover how to create FACS facial blendshapes in Maya {{!}} CG Channel".
28. (2015). "2015 11th IEEE International Conference and Workshops on Automatic Face and Gesture Recognition (FG)".