Event-related potentials elicited by the explicit and implicit processing of familiarity in faces

Brain activity underlying explicit and implicit processing of face familiarity was assessed by Event-Related Potentials (ERPs) elicited by famous and unknown faces with happy or neutral expressions. A set of faces was presented in a familiarity judgment (explicit) task and another in an expression judgment (implicit familiarity) task. After recording, these tasks were repeated exchanging the stimuli, and post-recording behavioral data from the familiarity task were used for re-averaging EEG segments from the expression task. Both explicit and implicit processing of famous faces resulted in an enhanced N250. Explicit processing of famous faces was specifically associated with earlier N400 and P600, with increased activity within brain areas involved in identity processing around 250 and 450 ms. These findings suggest different brain dynamics for explicit and implicit face processing, and that implicit processing of the identity in the context of an expression task is mainly associated with the transient activation of face representations in memory.