Recent research indicates that adults show categorical perception of facial
expressions of emotion. It is not known whether this is a basic characteri
stic of perception that is present from the earliest weeks of life, or whet
her it is one that emerges more gradually with experience in perceiving and
interpreting expressions. We report two experiments designed to investigat
e whether young infants, like adults, show categorical perception of facial
expressions. 7-month-old infants were shown photographic quality continua
of interpolated (morphed) facial expressions derived from two prototypes of
fear and happiness. In the first experiment, we used a visual-preference t
echnique to identify the infants' category boundary between happiness and f
ear. In the second experiment, we used a combined familiarisation-visual-pr
eference technique to compare infants' discrimination of pairs of expressio
ns that were equally physically different but that did or did not cross the
emotion-category boundary. The results suggest that 7-month-old infants (i
) show evidence of categorical perception of facial expressions of emotion,
and (ii) show persistent interest in looking at fearful expressions.