Spatial and temporal distribution of face and object representation in the human brain

The research summarized here shows that cortical representations of faces and objects are both spatially and temporally distributed. Category-related neural activity that is evoked by visually presented faces and other objects appears to begin in extrastriate regions in ventral and lateral occipitotemporal cortices. These early responses appear to reflect feedforward processes that are not strongly modulated by the effects of memory and attention. Because hemodynamic imaging is insensitive to these early category-related responses, their topography is not known in detail, and, consequently, it is unknown if these early responses show the same local distribution of overlapping representations as do the later responses. In monkeys, early responses in IT cortex appear to carry more information about between category distinctions than about finer within-category distinctions. The role of early responses in human face and object processing may similarly be related more to coarser between-category discriminations. These early between-category discriminations could initiate further processing that is relevant for the identified category. After the early responses, further neural processing in extrastriate regions is in concert with neural activity in other brain areas. Thus, the extended distribution of face and object representations appears to be related to the later responses. The recruitment of the extended distribution can serve to elaborate the information contained in the representation, enable recognition of familiar faces and objects, and allow attention to modulate how the representation develops. The locally distributed representations within extrastriate visual cortical areas that are observed with neuroimaging reflect late neural responses in these areas that are modulated by the influence of the extended distribution. The relationship between the local distribution of early and late responses in extrastriate cortices is unknown, but single unit studies in monkeys and recordings with intracranial electrodes indicate that they may be closely linked.