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Abstract

The human face is an important and complex communication channel.
Humans can, however, easily read in a face not only identity
information, but also facial expressions with high accuracy. Here, we
present the results of four psychophysical experiments in which we
systematically manipulated certain facial areas in video sequences of
nine conversational expressions to investigate recognition performance
and its dependency on the motions of different facial parts. These
studies allowed us to determine what information is it necessary}
and {it sufficient to recognize the different facial
expressions. Subsequent analyses of the face movements and correlation
with recognition performance show that, for some expressions, one
individual facial region can represent the whole expression. In other
cases, the interaction of more than one facial area is needed to
clarify the expression. The full set of results is used to develop a
systematic description of the roles of different facial parts in the
visual perception of conversational facial expressions.