With the most commonly used Action Units (AU’s) from the Facial Action Coding System (FACS) illustrated, I could now use all these AU’s to combine them into full expressions. I’ve attempted to make combinations that can be interpreted as expressions of 6 big emotions: anger, disgust, happiness, sadness, surprise and fear. I say attempted, as there is not really a standard for what the different emotions look like. Also, because the illustrations of the AU’s show a strong form of the movements, the full expressions can look a bit extreme and could be much more subtle.
Starting of with anger. Mostly characterized by the brow moving down and in (AU 4). The expression can be accompanied by ‘thinning’ (AU 23) and tightening (AU 24) of the lips, as well as flaring of the nostrils and tightening of the eyelids.
Then there is the expression of disgust. The most important parts of this expression are the pulling up, and wrinkling of the nose (AU 9) and the raising of the upper lip (AU 10) (which does not necessarily part the lips, although it does here, as it makes the expression stronger (or exaggerated)). Here the expression is also accompanied by the eye lid tightener.
Next is happiness. The smile is mainly a combination of the lip corner puller (AU 12) and the cheek raiser (AU 6). Fake smiles often only show the corners of the mouth movement, missing the ‘smiling eyes’ movement (AU 6 is difficult for most people to do voluntarily).
The expression of sadness is made by the raising (AU 1) and tightening (AU 4) of the inner brow, as well as raising the cheeks (AU 6) (which is, interestingly, just as important here as in the smile expression) and, maybe the most recognizable, the corners of the lips pulling down (AU 15).
Next on the list is surprise. The expression of surprise is characterized by an overall lengthening and opening up of the face. Both the inner (AU 1) and outer (AU 2) parts of the brow are raised, the upper eyelid is raised (AU 5), the lips are parted (AU 25) and the jaw drops down (AU 26).
Last on the list is the expression of fear. This expression looks quite tense overall, tightening outward: the inner (AU 1) and outer (AU 2) brow raise and tighten (AU 4), here the eye lids are also raised (AU 5) and tightened (AU 7), then finally there’s the lateral stretching of the lips and the pulling of the platysma (AU 20).