Page 191 - Designing Sociable Robots

breazeal-79017 book March 18, 2002 14:11

172 Chapter 10

Table 10.2
A possible mapping of facial movements to affective dimensions proposed by Smith and Scott (1997). An up
arrow indicates that the facial action is hypothesized to increase with increasing levels of the affective meaning
dimension. A down arrow indicates that the facial action increases as the affective meaning dimension decreases.
For instance, the lip corners turn upwards as “pleasantness” increases, and lower with increasing “unpleasantness.”
Facial Action
Raise Raise
Eyebrow Raise upper Lower Up Turn Lip Open Tighten Raise
Meaning Frown Eyebrows Eyelid Eyelid Corners Mouth Mouth Chin
Pleasantness
Goal
Obstacle/Discrepancy
AnticipatedEffort
AttentionalActivity

Certainty
Novelty

Personal
Agency/Control

to valence here), attentional activity (maps to arousal here), and personal agency/control
(roughly maps to stance here). Table 10.2 summarizes their proposed mapping of facial
actions to these dimensions. They posit a fourth dimension that relates to the intensity of
the expression. For Kismet, the expressions become more intense as the affect state moves
to more extreme values in the affect space. As positive valence increases, Kismet’s lips turn
upward, the mouth opens, and the eyebrows relax. However, as valence decreases, the brows
furrow, the jaw closes, and the lips turn downward. Along the arousal dimension, the ears
perk, the eyes widen, brows elevate and the mouth opens as arousal increases. Along the
stance dimension, increasing positive values cause the eyebrows to arc outwards, the mouth
to open, the ears to open, and the eyes to widen. These face actions roughly correspond
to a decrease in personal agency/control in Smith and Scott’s framework. For Kismet, it
engenders an expression that looks more eager and accepting (or more uncertain for negative
emotions). Although Kismet’s dimensions do not map exactly to those hypothesized by
Smith and Scott, the idea of combining meaningful facial movements in a principled manner
to span the space of facial expressions, and to also relate them in a consistent way to emotion
categories, holds strong.