Abstract
Humans are remarkably accurate at recognizing familiar faces, even from degraded and novel pictures, while the recognition of unfamiliar faces in different pictures is often prone to error. Researchers therefore propose image-independent representations for familiar but pictorial representations for unfamiliar faces. While differences between familiar and unfamiliar face recognition are easy to demonstrate in behavioral studies, however, cognitive neuroscience has so far largely failed to show a large and robust neural correlate of image-independent familiar face recognition. Here, we examined event-related brain potentials elicited by highly personally familiar (close friends, relatives) and unfamiliar faces. We presented multiple different “ambient” images per identity, varying naturally in lighting conditions, viewing angles, emotional expressions etc., while participants responded to randomly intermixed pictures of butterflies. Familiar faces elicited more negative amplitudes than unfamiliar faces in the N250 time range (200–400 ms), which is considered to reflect the activation of stored face representations. Importantly, an increased (> 4μV) familiarity effect was observed in the subsequent 400–600 ms time range. Similar to N250, this Sustained Familiarity Effect (SFE) had a right-lateralized, occipito-temporal scalp distribution. It was reliably detected in 84% of individual participants, while it was not observed in any participant in a control experiment in which all faces were unfamiliar. Additional experiments revealed that the SFE is smaller for personally, but less familiar faces (e.g., university lecturers) and absent for pictures of celebrities. Moreover, while the N250 familiarity effect does not strongly depend on attentional resources, the SFE is substantially smaller when participants’ attention is directed away from the face stimuli. We interpret the SFE as reflecting the integration of visual with additional person-related (e.g., semantic, affective) information needed to guide potential interactions. We propose that this integrative process is at the very core of identifying a highly familiar person.