Expression Dependence in the Perception of Facial Identity

We recognise familiar faces irrespective of their expression. This ability, crucial for social interactions, is a fundamental feature of face perception. We ask whether this constancy of facial identity may be compromised by changes in expression. This, in turn, addresses the issue of whether facial identity and expression are processed separately or interact. Using an identification task, participants learned the identities of two actors from naturalistic (so-called ambient) face images taken from movies. Training was either with neutral images or their expressive counterparts, perceived expressiveness having been determined experimentally. Expressive training responses were slower and more erroneous than neutral training responses. When tested with novel images of the actors that varied in expressiveness, neutrally trained participants gave slower and less accurate responses to images of high compared with low expressiveness. These findings clearly demonstrate that facial expressions impede the processing and learning of facial identity. Because this expression dependence is consistent with a late bifurcation model of face processing, in which changeable facial aspects and identity are coded in a common framework, it suggests that expressions are a part of facial identity representation.