Left hemispheric functional compensation in prosopagnosia? A tachistoscopic study with unilaterally lesioned patients.

Clinical observations suggest left hemispheric compensation for prosopagnosia in patients with isolated right posterior lesions. To test this hypothesis we investigated six patients with right posterior lesions, three with and three without prosopagnosia, with a series of tachistoscopic matching experiments. Faces with and without paraphernalia, shapes, objects and words were presented at different exposure durations (unlimited, 1000, 200, 50 and 20 ms). Prosopagnosia patients performed better than non-prosopagnosia patients if pure faces (eyes, nose and mouth only) were presented for an unlimited time, but performed worse than non-prosopagnosia patients if exposure duration was reduced. Patients with prosopagnosia were especially handicapped when required to match emotional expressions. Both patient groups had no difficulty in matching objects and words, even at short exposure durations. The results are discussed with respect to a possible left hemispheric compensation in prosopagnosia patients.