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Jean-Jacques Orban de Xivry, Meike Ramon, Philippe Lefèvre, Bruno Rossion; Abnormal eye fixations on personally familiar faces following acquired prosopagnosia reveal a lack of individual holistic face perception. Journal of Vision 2008;8(6):885. doi: https://doi.org/10.1167/8.6.885.
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Selective impairment of face recognition following brain damage, as in acquired prosopagnosia, may cause a dramatic loss of diagnosticity of the eyes area of the face and an increased reliance on the mouth for identification (Caldara et al., 2005). To clarify this phenomenon, we measured eye fixation patterns in a pure case of prosopagnosia (PS, Rossion et al., 2003) during her identification of personally familiar faces (27 children of her kindergarten). Consistent with previous evidence, the normal control (her colleague) identified the faces within two fixations located centrally, just below the eyes. This pattern of fixations remained unchanged even by increasing difficulty by presenting anti-caricatures. In contrast, the great majority of the patient's fixations were located on the mouth, confirming the abnormally reduced processing of the upper area of the face in acquired prosopagnosia. Most importantly, the prosopagnosic patient also fixated each eye spontaneously in between the first and last fixation, making more eye movements than the normal control. This spontaneous fixation on the eyes also rules out a behavior of avoidance of the eyes, as observed in autistic or bilateral amygdala patients. Rather, these results support a high-level perceptual account according to which acquired prosopagnosic patients have lost the ability to represent multiple elements of an individual face as a perceptual unit (holistic face perception). To identify a given face they focus very precisely on each local feature rather than seeing the whole of a face from its diagnostic center (i.e. the “center of mass” of the face, just below the eyes). The upper area of the face is particularly less attended to and less relevant for the prosopagnosic patient because it contains multiple features that require normal holistic perception in order to be the most diagnostic region. Consequently, prosopagnosic patients develop a more robust representation of the mouth, a relatively isolated feature in the face that may contain more information than any single element of the upper area of the face.
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