The time it takes to truly know someone: Neurophysiological correlates of face and identity learning during the first two years.

How long does it take to truly know a person? To answer this question, we investigated how event-related brain potential (ERP) correlates of facial familiarity (N250) and the integration of identity-specific knowledge (Sustained Familiarity Effect, SFE) develop over time. Sixty undergraduate students from three year groups were tested with images of a university friend (with two, 14, and 26 months of familiarity for Year 1, Year 2, and Year 3 students), a highly familiar friend from home, and an unfamiliar identity. While clear ERP familiarity effects for home friends were observed in all groups, university friends yielded a clear N250 effect but only a small SFE in Year 1. Importantly, both effects significantly increased for university friends from Year 1 to Year 2, but not afterwards. Our results demonstrate that neural representations of visual familiarity and identity-specific knowledge build up over time and are fully developed by 14 months of familiarity