The impact that prosopagnosia (face-blindness) has on the human visual system has long been hypothesized with regard to the specifics of the impairment. The leading hypothesis in the literature, the face-specificity hypothesis, proposes that prosopagnosia is specific only to human faces. Other hypotheses have offered alternative explanations for what sorts of identification tasks might be affected by damage to the fusiform face area resulting in prosopagnosia, including the biological recognition, expert recognition, and subordinate-level recognition hypotheses. An additional hypothesis, the coordinate relations hypothesis, offers a compelling explanation for the underlying process disrupted by prosopagnosia: that the brain’s ability to detect metric changes has been damaged resulting in a deficit to face recognition. This hypothesis was tested by looking for deficits in performance in a prosopagnosic when identifying non-faces, because such differences would not be explained by the face-specificity hypothesis. Therefore, sheep faces were used as a class of stimuli to explore whether prosopagnosia affects identification of sheep faces in much the same way that it affects identification of human faces. Results of two experiments showed that a prosopagnosic was impaired on identification of sheep faces, providing support for the coordinate relations hypothesis
