Research Report Early electrophysiological correlates of adaptation to personally familiar and unfamiliar faces across viewpoint changes Stéphanie Caharel a, b , Corentin Jacques b, c , Olivier d'Arripe b , Meike Ramon b , Bruno Rossion b, ⁎ a Laboratoire Interpsy, psychologie de l'interaction et des relations intersubjectives, Nancy Université (Nancy 2), France b Institute of Research in Psychology and Institute of Neuroscience, Université Catholique de Louvain, Belgium c Stanford University, Department of Psychology and Neuroscience Institute, USA ARTICLE INFO ABSTRACT Article history: Accepted 19 February 2011 Available online 24 March 2011 Behavioral studies have shown that matching individual faces across depth rotation is easier and faster for familiar than unfamiliar faces. Here we used event-related potentials (ERPs) to clarify the locus of this behavioral facilitation, that is whether it reflects changes at the level of perceptual face encoding, or rather at later stages of processing. We used an identity adaptation paradigm in ERPs, during which a first (adapting) face (~3000 ms) rotated 30° in depth was followed by a second full front face (200 ms) which was either the same or a different identity as the first face. For unfamiliar faces, the early face-sensitive N170 component was reduced for immediately repeated as compared to different unfamiliar faces in the right hemisphere only. However, for personally familiar faces, the effect was absent at right hemisphere electrode sites and appeared instead over the left hemisphere at the same latency. Later effects of face identity adaptation were also present on the scalp, but from about 300 to 400 ms over fronto-central regions, and slightly later on occipito-temporal regions, there was a strong adaptation effect only for familiar faces. These observations suggest that the perceptual encoding of familiar and unfamiliar faces may be of different nature, as indicated by early (N170) hemispheric differences for identity adaptation effects depending on long-term familiarity. However, the behavioral advantage provided by familiarity to match faces across viewpoints might rather be related to processes that are closer in time to the behavioral response, such as semantic associations between the faces to match. © 2011 Elsevier B.V. All rights reserved. Keywords: Event-related potential N170 Face processing Adaptation Personal familiarity Viewpoint, rotation, identity 1. Introduction Associating two different views of the same unfamiliar person's face may be quite difficult, but familiarity with faces can make this task extremely easy (Bruce, 1982; Bruce et al., 1999; Hancock et al., 2000; Hill et al., 1997; O'Toole et al., 1998; Young et al., 1986). However, the mechanisms by which familiarity enhances the ability to match distinct face pictures of the same person (or discriminate facial pictures belonging to different persons) remain largely unclear. On the one hand, it may be that this BRAIN RESEARCH 1387 (2011) 85 – 98 ⁎ Corresponding author at: Institute of Research in Psychology, Université Catholique de Louvain, 10 Place du Cardinal Mercier, 1348 Louvain-la-Neuve, Belgium. Fax: +32 10 47 37 74. E-mail address: bruno.rossion@uclouvain.be (B. Rossion). 0006-8993/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2011.02.070 available at www.sciencedirect.com www.elsevier.com/locate/brainres