MAR 15, 2013
This experimental study found that some individuals with developmental prosopagnosia can covertly recognize faces and suggests that this phenomenon results from disconnected links between intact identity-specific visual memory traces and later semantic face processing stages.
The study included 12 participants with developmental prosopagnosia. They performed a task that required them to judge the familiarity of successively presented famous or nonfamous faces. Electroencephalography (EEG) was recorded during task performance.
An event-related potential (ERP) is a stereotyped electrophysiological response to a stimulus that is measured with EEG. In six of the 12 subjects, famous faces that were not recognized triggered an occipito-temporal ERP N250 component, which is thought to reflect the activation of stored visual memory traces of known individual faces. In contrast, the P600f ERP component, which is linked to late semantic stages of face identity processing, was not triggered by nonrecognized famous faces.
However, ERP correlates of explicit face recognition obtained during those few trials when participants with developmental prosopagnosia classified famous faces as known or familiar were similar to the effects the authors found in a previous study in participants with intact face recognition abilities. This suggests that face recognition mechanisms in individuals with developmental prosopagnosia are not qualitatively different from that of unimpaired individuals.
The authors conclude that these ERP results provide the first neurophysiological evidence for covert face recognition in developmental prosopagnosia. They say the results also indicate that the activation of stored visual representations of familiar faces is not sufficient for conscious explicit face recognition.