Abstract
The assumption that the smile is an evolved facial display suggests
that there may be universal features of smiling in addition to the basic
facial configuration. We show that smiles include not only a stable
configuration of features, but also temporally consistent movement patterns.
In spontaneous smiles from two social contexts, duration of lip corner
movement during the onset phase was independent of social context and
the presence of other facial movements, including dampening. These
additional movements produced variation in both peak and offset duration.
Both onsets and offsets had dynamic properties similar to automatically
controlled movements, with a consistent relation between maximum velocity
and amplitude of lip corner movement in smiles from two distinct contexts.
Despite the effects of individual and social factors on facial expression
timing overall, consistency in onset and offset phases suggests that
portions of the smile display are relatively stereotyped and may be
automatically produced.
Keywords: facial expression, nonverbal communication, emotion
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