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Facial Animation and Expression 171

arousal

surprise

afraid elated

stress excitement

frustrated happy
displeasure pleasure
sad content
depression neutral
calm

bored
relaxed

sleepy
sleep
Figure 10.6
Russell’s pleasure-arousal space for facial expression.

yet reserved expressions such as a coy smile or a sly grin (which hint at a behavioral bias to
withdraw). More importantly, anger and fear reside in very close proximity to each other
despite their very different behavioral correlates. From an evolutionary perspective, the
behavioral correlate of anger is to attack (which is a very strong approaching behavior),
and the behavioral correlate for fear is to escape (which is a very strong withdrawing
behavior). These are stereotypical responses derived from cross-species studies—obviously
human behavior can vary widely. Nonetheless, from a practical engineering perspective of
generating expression, it is better to separate these two emotional responses by a greater
distance to minimize accidental activation of one instead of the other. Adding the stance
dimension addressed these issues for Kismet.
Given this three dimensional affect space, this approach resonates well with the work of
Smith and Scott (1997). They posit a three dimensional space of pleasure-displeasure (maps