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Facial Action Coding System

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The Facial Action Coding System (FACS) is the cumulative database of research and development of microexpressions within behavioral science created by The Paul Ekman Group, LLC. Seven years in the making, it was originally developed by Paul Ekman and two colleagues after many years of work discovering the universal emotions of the human face. The results have culminated in a manual that is now used by law officers, doctors, performers and is becoming increasingly popular with teachers.

FACS UsesEdit


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 1000 pages in length and provides the AUs, as well as Dr. Ekman's interpretation of their meaning. FACS defines 32 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. For example, FACS can be used to distinguish two types of smiles as follows:

  • Insincere and voluntary Pan American 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. The use of FACS has been proposed for use in the analysis of depression, and the measurement of pain in patients unable to express themselves verbally. FACS is designed to be self-instructional. People can learn the technique from a number of sources[6], including manuals and workshops, and obtain certification through testing[8]. A variant of FACS has been developed to analyze facial expressions in chimpanzees. [edit]Codes for action units

CodesEdit


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 has been added here for the benefit of the reader. 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).

For most accurate annotation, FACS suggests agreement from at least two independent certified FACS encoders. The following is a list of Action Units (AUs with underlying facial muscles). Action Descriptors (ADs) do not have specific underlying muscle action.


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