Page 193 - Designing Sociable Robots

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174 Chapter 10

Table 10.3
A summary of how FACS action units and facial muscles map to facial expressions for the primary emotions.
Adapted from Smith and Scott (1997).

Facial Action
Raise Raise Raise
Eyebrow Raise upper Lower Up Turn Down Turn Open Upper
Frown Eyebrows Eyelid Eyelid Lip Corners Lip Corners Mouth Lip
levator depressor levator
Muscular corrugator medial palpebrae orbicularis zygomaticus anguli orbicularis labii
Basis supercilii frontalis superioris oculi major oris oris superioris
Action 4 1 5 6,7 12 15 26,27 9,10
units
Emotion Expressed
Happiness X X X
Surprise X X X
Anger X X X
Disgust X X X
Fear X X X X
Sadness X X X

three muscles to map to a given action unit, since facial muscles often work in concert to
adjust the location of facial features, and to gather, pouch, bulge, or wrinkle the skin.
To analyze Kismet’s facial expressions, FACS can be used as a guideline. This must
obviously be done within reason as Kismet lacks many of the facial features of humans (most
notably, skin, teeth, and nose). The movements of Kismet’s facial mechanisms, however,
were designed to roughly mimic those changes that arise in the human face due to the
contraction of facial muscles. Kismet’s eyebrow movements are shown in figure 10.8, and
the eyelid movements in figure 10.9. Kismet’s ears are primarily used to convey arousal and
stance as shown in figure 10.10. The lip and jaw movements are shown in figure 10.11.
Using the FACS system, Smith and Scott (1997) have compiled mappings of FACS
action units to the expressions corresponding to anger, fear, happiness, surprise, disgust,
and sadness based on the observations of others (Darwin, 1872; Frijda, 1969; Scherer, 1984;
Smith, 1989). Table 10.3 associates an action unit with an expression if two or more of these
sources agreed on the association. The facial muscles employed are also listed. Note that
these are not inflexible mappings. Any emotion can be expressed by a family of expressions,
and the expressions vary in intensity. Nonetheless, this table highlights several key features.
Of the seven action units listed in the table, Kismet lacks only one (the lower eyelid).
Of the facial features it does possess, it is capable of all the independent movements listed
(given its own idiosyncratic mechanics). Kismet performs some of these movements in a
manner that is different, yet roughly analogous, to that of a human. The series of figures,