Double Dissociation between Overt and Covert Face Recognition.

Some patients with face agnosia (prosopagnosia) caused by occipitotemporal damage produce discriminatory covert responses to the familiar faces that they fail to identify overtly. For example, their average skin conductance responses (SCRs) to familiar faces are significantly larger than average SCRs to unfamiliar faces. In this study we describe the opposite dissociation in four patients with bilateral ventromedial frontal damage: The patients recognized the identity of familiar faces normally, yet failed to generate discriminatory SCRs to those same familiar faces. Taken together, the two sets of results constitute a double dissociation: bilateral occipitotemporal damage impairs recognition but allows SCR discrimination, whereas bilateral ventromedial damage causes the opposite. The findings suggest that the neural systems that process the somatic-based valence of stimuli are separate from and parallel to the neural systems that process the factual, nonsomatic information associated with the same stimuli.