The cognitive approach to familiar face processing in human subjects

Effect of familiarity on the processing of human faces

Most brain imaging studies on face perception have investigated the processing of unknown faces and addressed mainly the question of specific face processing in the human brain. The goal of this study was to highlight the effects of familiarity on the visual processing of faces. Using [15O]water 3D Positron Emission Tomography, regional cerebral blood flow distribution was measured in 11 human subjects performing an identical task (gender categorization) on both unknown and known faces. Subjects also performed two control tasks (a face recognition task and a visual pattern discrimination task). They were scanned after a training phase using videotapes during which they had been familiarized with and learned to recognize a set of faces. Two major results were obtained. On the one hand, we found bilateral activations of the fusiform gyri in the three face conditions, including the so-called fusiform-face area, a region in the right fusiform gyrus specifically devoted to face processing. This common activation suggests that different cognitive tasks performed on known and unknown faces require the involvement of this fusiform region. On the other hand, specific regional cerebral blood flow changes were related to the processing of known and unknown faces. The left amygdala, a structure involved in implicit learning of visual representations, was activated by the categorization task on unknown faces. The same task on known faces induced a relative decrease of activity in early visual areas. These differences between the two categorization tasks reveal that the human brain processes known and unknown faces differently.

Task modulation of brain activity related to familiar and unfamiliar face processing: an ERP study

In order to investigate stimulus-related and task-related electrophysiological activity relevant for face processing, event-related potentials (ERPs) from 58 electrodes at standard EEG sites were recorded while subjects performed a simple visual discrimination (control) task, in addition to various face processing tasks: recognition of previously learned faces and gender decision on familiar and unfamiliar faces. Three electrophysiological components or dipolar complex were recorded in all subjects: an occipital early component (P1, around 110 ms); a vertex positive potential (VPP; around 158 ms) which appeared to be specific to faces; and a negative central component, N2 (around 230 ms). Parametric analysis and source localization were applied to these components by means of a single-subject analysis methodology. No effect of familiarity was observed on any of these early component. While the VPP appears to be independent of the kind of processing performed, face task modulations of the early P1 and the N2 were observed, with a higher amplitude for the recognition than for the gender discrimination task. An attentional modulation of early visual areas is proposed for the first effect (P1 modulation), while the N2 seems to be related to general visual memory processing. This study strongly suggests that the VPP reflects an early visual stage of face processing in the fusiform gyrus that is strictly stimulus-related and independent of familiarity. It also shows that source localization algorithms may give reliable solutions on single subject averages for early visual components despite high inter-subject variability of the surface characteristics of ERPs.

Can we learn from the clinically significant face processing deficits, prosopagnosia and Capgras delusion?

This review describes two clinically significant face processing deficits, prosopagnosia and Capgras delusion, and provides new knowledge about the face recognition process by a convergence of empirical findings. These empirical findings are structured around two questions that are reviewed from the perspectives of the two deficits. First is the question of hemispheric specificity, which inquires into the degree of each hemisphere's contribution to the face recognition process. Second is the question of dual neural pathways, which addresses the possibility that the face recognition process proceeds along two parallel pathways in the brain. Findings from the hemispheric specificity studies reinforce the current view that right hemispheric involvement is necessary for face recognition while left hemispheric involvement is minimal. Findings from the dual neural pathways studies reinforce the plausible but yet unproven hypothesis that two neural pathways pass information from the visual association cortex in the occipital lobe toward the temporal lobes and limbic system when faces are seen and recognized. These findings, which also indicate that each of the dual neural pathways carries different, nonredundant information, could be instrumental in showing that the pathways play different roles in the manifestations of the clinically significant face processing deficits, prosopagnosia and Capgras delusion.