Covert face recognition without prosopagnosia.

An experiment is reported where subjects were presented with familiar or unfamiliar faces for supraliminal durations or for durations individually assessed as being below the threshold for recognition. Their electrodermal responses to each stimulus were measured and the results showed higher peak amplitude skin conductance responses for familiar than for unfamiliar faces, regardless of whether they had been displayed supraliminally or subliminally. A parallel is drawn between elevated skin conductance responses to subliminal stimuli and findings of covert recognition of familiar faces in prosopagnosic patients, some of whom show increased electrodermal activity (EDA) to previously familiar faces. The supraliminal presentation data also served to replicate similar work by Tranel et al (1985). The results are considered alongside other data indicating the relation between non-conscious, "automatic" aspects of normal visual information processing and abilities which can be found to be preserved without awareness after brain injury.