The prosopagnosic patient PS has to match one of two faces to target, while her fixation location is gaze-contingently selectively revealed. We can see that PS uses mainly the mouth to discriminate the faces.
Van Belle, G., de Graef, P., Verfaillie, K., Busigny, T., Rossion, B. (2010). Whole not hole: expert face recognition requires holistic perception. Neuropsychologia, 48, 2609-2620. [PDF]