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Patients with congenital face blindness outperform controls on
face perception test

Outcome: Individuals born with face-blindness (congenital prosopagnosia), while impaired at recognizing familiar faces and even making perceptual judgments about whether two unknown faces are the same or different, are better than matched controls at detecting similarities/differences between parts of two faces in a composite face comparison task.

Impact/benefits: This interesting scenario is one in which a neuropsychological group performs more accurately than the control sample. Moreover, the specificity of the performance profile sheds light on the potential mechanism underlying this interesting neurodevelopmental disorder.

Background/explanation: In the ‘composite face task’ (see image below), individuals view two consecutively presented composite faces, and make same/different decisions based only on the top part of the face. The bottom part of the face is to be ignored. The two faces are created such that the two top parts could either be the same or different while the bottom part is always different. Additionally, the top and bottom parts of a single face can be either aligned or misaligned. Due to the holistic nature of face processing, even when instructed to judge only the top halves of aligned faces and to ignore the bottom parts, normal observers exhibit significant interference induced by the presence of the task-irrelevant bottom half of the composite face (which is always different). Thus, erroneously, they tend to judge two faces with identical tops as ‘different’ rather than ‘same’ (i.e. make false alarms). This interference from the task-irrelevant bottom of the face is substantially reduced when configural information is disrupted, as in the misaligned condition (Figure 1, bottom row) (Young et al., 1987) and also when the faces are inverted. In contrast with normal individuals, the prosopagnosic individuals perform equivalently with aligned and misaligned faces and are impervious to (the normal) interference from the task-irrelevant bottom part of faces. Interestingly, the extent of the local bias evident in the composite task is correlated with the abnormality of performance on diagnostic face processing tasks.

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Credit: Avidan, Tanzer & Behrmann, manuscript under review, Neuropsychologia.
Images kindly provided by Isabel Gauthier, Vanderbilt University (PEN network).