The Facial Action Coding System (FACS) was first described by Paul Ekman and colleague Wallace V. Friesen in their article entitled Measuring Facial Movement for Environmental Psychology and Nonverbal Behavior 1(1) fall 1976.
The authors’ goal “… was to develop a comprehensive system which could distinguish all possible visually distinguishable facial movements.” The system presents a series of Action Units (or ‘AU’s in the FACS terminology) which can be used to taxonomize human expressions.
See, for example, a video of : AU2 the Outer Brow Raiser. (For copyright reasons Improbable is not permitted to reproduce the video here, but you can access it (AU2s.mpg) via this page)
Researchers can purchase the entire FACS system on CD-ROM here for US$260 (plus shipping).
• Although the authors are confident that FACS is complete for scoring the visible, reliably distinguishable actions of the brows, forehead, and eyelids, they do note that : “FACS probably does not include all of the visible, reliably distinguishable actions in the lower part of the face. The hinged jaw and rubbery lips allow a nearly infinite number of actions.”
• To develop FACS, the authors spent the better part of a year with a mirror, anatomy texts, and cameras learning to fire separately the muscles in their own faces – with the exception of the Tarsalis muscle which cannot be fired voluntarily (though its effect on appearance are not different from those of one of the voluntarily controlled muscles, levator palpebrae.)
• According to a recent article in Nature 465, 412-415 (2010) Professor Eckman “ …no longer publishes all of the details of his work in the peer-reviewed literature because, he says, those papers are closely followed by scientists in countries such as Syria, Iran and China, which the United States views as a potential threat.”