The representation of person identity in the human brain

Abstract

Every day we encounter a variety of people, and we need to recognize their identity to interact with them appropriately. The most common ways to recognize a person's identity include the recognition of a face and of a voice. Recognizing a face or a voice is effortless, but the neural mechanisms that enable us to do so are complex. The face of a same person can look very different depending on the viewpoint and it can be partly occluded. Analogously, a voice can sound very different when it is saying different words. The neural mechanisms that enable us to recognize a person's identity need to abstract away from stimulus differences that are not relevant for identity recognition. Patient studies indicate that this process is executed with the contribution of multiple brain regions (Meadows, 1974; Tranel et al., 1997). However, the localization accuracy allowed by neuropsychological studies is limited by the lack of control on the location and extent of lesions. Neuroimaging studies individuated a set of regions that show stronger responses to faces than other objects (Kanwisher et al., 1997; Rajimehr et al., 2009), and to voices than other sounds (Belin et al., 2000). These regions do not necessarily encode information about a person's identity. In this thesis, a set of regions that encode information distinguishing between different face tokens were individuated, including ventral stream regions located in occipitotemporal cortex and the anterior temporal lobes, but also parietal regions: posterior cingulate and superior IPS. Representations of face identity with invariance across different viewpoints and across different halves of a face were found in the right ATL. However, representations of face identity and of voice identity were not found to overlap in ATL, indicating that in ATL representations of identity are organized by modality. For famous people, multimodal representations of identity were found in association cortex in posterior STS.