Spatiotemporal changes in neural response patterns to faces varying in visual familiarity.

Increasing experience with a previously unfamiliar face improves human ability to recognize it in challenging and novel viewing conditions. Differential neural responses to familiar versus unfamiliar faces in multiple regions of the ventral-temporal and parietal cortex have been reported in previous work, but with limited attention to how behavioral and neural measures change with increasing familiarity. We examined changes in the spatial and temporal characteristics of neural response patterns elicited by faces that vary in their degree of visual familiarity. First, we developed a behavioral paradigm to familiarize participants to low-, medium-, and high-levels of familiarity with faces. Recognition of novel, naturalistic images of the learned individuals improved with increasing familiarity with faces. Next, a new set of participants learned faces using the behavioral paradigm, outside the fMRI scanner, and subsequently viewed blocks of whole-body images of the learned and novel people, inside the scanner. We found that the face-selective FFA and OFA, and a combination of the ventral-temporal areas (e.g., fusiform gyrus) and parietal areas (e.g., precuneus) contained patterns useful for classifying highly familiar versus unfamiliar faces. Classification along the temporal-sequence of the face blocks revealed an early separation of neural patterns elicited in response to highly familiar versus unfamiliar faces in the FFA and OFA, but not in other regions of interest. This indicates the potential for a rapid assessment of the "known versus unknown" status of faces in core face-selective regions of the brain. The present study provides a first look at the perceptual and neural correlates underlying experience gains with faces as they become familiar.