A two-process probabilistic theory of emotion perception based on a nonline
ar combination of facial features is presented. Assuming that the upper and
the lower part of the face function as the building blocks at the basis of
emotion perception, an empirical test is provided with fear and happiness
as target emotions. Subjects were presented with prototypical fearful and h
appy faces and with computer-generated chimerical expressions that were a c
ombination of happy and fearful. Subjects were asked to indicate the emotio
ns they perceive using an extensive list of emotions. We show that some emo
tions require a conjunction of the two halves of a face to be perceived, wh
ereas for some other emotions only one half is sufficient. We demonstrate t
hat chimerical faces give rise to the perception of genuine emotions. The f
indings provide evidence that different combinations of the two halves of a
fearful and a happy face, either congruent or not, do generate the percept
ion of emotions other than fear and happiness. (C) Academie des Sciences/El
sevier, Paris.