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Brad Duchaine, Galit Yovel, Edward Butterworth, Ken Nakayama; Elimination of all domain-general hypotheses of prosopagnosia in a single individual: Evidence for an isolated deficit in 2nd order configural face processing. Journal of Vision 2004;4(8):214. doi: 10.1167/4.8.214.
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Five hypotheses have been proposed to account for the information-processing deficit that causes prosopagnosia. To support one of these explanations, it is necessary to rule out all of the alternative hypotheses. Last year, we presented the results of testing with Edward, a developmental prosopagnosic, who performed poorly on all face tasks, but normally with five of six tests of non-face discrimination. Those results ruled out the within-class hypothesis. Since then we have run him with tests addressing the configural processing hypothesis, the non-decomposable hypothesis, and the curvature hypothesis. Edward performed normally with all of these tests so his results are inconsistent with these explanations. The only remaining hypothesis, the face-specific hypothesis, proposes that prosopagnosia results from an impairment to the holistic processes which operate on upright faces. To test this explanation, we tested Edward in a same-different discrimination test with faces differing either in the spacing of the features or the features themselves. Consistent with the face-specific hypothesis, Edward was out of the normal range with the spacing items but normal with the feature items. Taken together, these results indicate that normal adults have mechanisms specialized for face-specific configural processing.
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