Accurate face recognition plays a critical role in developing and maintaining social relationships. Typically developing adults show expertise when processing faces, demonstrated by their ability to recognize new faces even after a single exposure. Furthermore, face recognition is superior for highly familiar faces associated with rich semantic information. Although semantic processes mediate familiar face recognition, it is unclear what processes mediate unfamiliar face recognition. The main objective of my thesis was to identify unique neural mechanisms underlying familiar versus unfamiliar face recognition and to detail how these mechanisms change as a result of learning. I used event-related potentials (ERPs) to assess the stages of face processing affected by familiarity.
In Chapter 1, I reviewed the literature contrasting familiar and unfamiliar face recognition processes from cognitive and neural perspectives.
In Chapter 2, I identified processes involved in unfamiliar face recognition by recording ERPs to repeated presentations of unfamiliar faces in upright and inverted orientations. Inverted faces portray the same structural information as upright faces but with novel orientation that disrupts identity processing. Repeated exposure to an upright face (and not an inverted face) produced repetition priming at an early perceptual stage reflected by the N170 component, suggesting that unfamiliar face recognition is mediated by early perceptual representation.
In Chapter 3, I directly tested whether semantic information modifies early perceptual face processing. I recorded ERPs to new faces that were learned over a five-day session with either person-specific or irrelevant information. N170 repetition priming was observed for all faces except those learned with person-specific information, suggesting that relevant semantic information, and not merely perceptual experience, changes early perceptual face processing.
In Chapter 4, I assessed the relationship between N170 and N400 recognition processes. Specifically, I examined whether top-down semantic processes reflected by the N400 modulate early identity processes reflected by the N170. I constructed composite faces by combining facial features from different famous individuals; the facial features conveyed incongruous identity information so that when the face was processed as a whole it was perceived to be novel. Both familiar faces and composite faces failed to elicit N170 repetition priming but did elicit a similar N400 response, suggesting that familiar face recognition can be achieved with very little facial information. Moreover, these results suggest that the retrieval of semantically relevant information during familiar face recognition occurs even in the presence of incongruous perceptual information and that such processing modulates early perceptual processes.
Together, these results demonstrate the interplay between memory and perception (which I summarize and discuss in Chapter 5), revealing different mechanisms of face recognition as a function of person-specific information. Unfamiliar face recognition takes place at the perceptual stage reflected by the N170 and is revealed through repetition priming. As an unfamiliar face becomes well known, its recognition processes shift to a later semantic stage reflected by the N400 and such semantic processes seem to modulate early perceptual processes. This knowledge has advanced our understanding of face processing at cognitive and neural levels.