Representation of facial identity includes expression variability

In this study, we investigate the contribution of expression variability in the formation of face representations. We trained participants to learn new identities from face images either low or high in expressiveness, and compared their performance in a recognition test. After low expressiveness training, recognition of novel test images was modulated by image expressiveness: the more expressive the image, the slower the response. This differed from recognition after high expressiveness training, which showed little evidence of expression dependence. These findings are not readily explained by exemplar and prototype theories of face representation. However, we propose that our results can be explained by a combination of these theories, according to which average and exemplar representations co-exist – the latter of which preserve expressions and other within-person variability. We conclude that this study provides evidence that variability of expressions is, therefore, incorporated in the representation of an individual's face. Moreover, our results demonstrate that learning to recognise someone from their face entails learning how their face is changed by expressions.