Early temporal negativity is sensitive to perceived (rather than physical) facial identity

Increased early negativity to repeated faces over inferior temporal regions around 200-300 ms has been related to the reactivation of mental representations of individual identities of familiar faces. Since this modulation is larger for same-image (compared to different-image) repetitions of a familiar face, it is debated whether it reflects physical stimulus similarity between prime and target, or reactivation of perceived representations of identity. In Experiment 1 participants performed a four-choice identification task on famous target faces, which were always preceded by the same average face. This average face served as prime stimulus. Crucially, by adapting participants to specific anti-faces, we induced different illusory facial identities (cf. Leopold, D.A., O'Toole, A.J., Vetter, T., Blanz, V., 2001. Prototype-referenced shape encoding revealed by high-level after effects. Nature Neuroscience 4 (1), 89-94) in the same physical prime. Importantly, temporal ERPs (~ 155-235 ms) were significantly more negative for "Primed" than for "Unprimed" trials. In Experiment 2, we determined whether this effect was due to the encoding of shape information, by using anti-shape adaptors with constant average reflectance information. Priming by these anti-shape adapted average primes did not elicit a similar temporal ERP modulation. We conclude that these early temporal ERP modulations evoked by a combination of anti-face adaptation and immediate-repetition priming represent a neural correlate of the activation of mental representations of individual familiar faces. These identity specific representations can be triggered even by physically identical prime stimuli, when preceded by corresponding anti-face adaptation.