"What Is Special about Face Recognition? Nineteen Experiments on a Person with Visual Object Agnosia and Dyslexia but Normal Face Recognition?" Journal of Cognitive Neuroscience 9:5.
This article deals with CK, a man who has visual object agnosia and dyslexia, but retains face recognition equivalent to that of a normal person. The particular type of agnosia CK suffered from was integrative agnosia, i.e. he can identify the component parts of objects but not put them together into the whole. His problems were caused by a closed-head injury following a car accident, though no significant damage revealed in MRI or CT scans.
A number of experiments testing face recognition-- upright faces, family resemblance, age-transformed faces, cariacatures, cartoons, inverted faces, face features, and others-- were conducted on CK. Researchers found that all of his face recognition skills were intact except face inversion and other configurational changes. CK could even recognize faces composed of other objects, though he didn't have any perception of the objects.
This case makes it clear that modules for object recognition and face recognition are completely separate, since this is an example of a face recognition system without an object recognition system. CK's problems with trasformations and configurations could stem from skills that involve object manipulation ability.
Note how this raises the issue of the encapsulation of face knowledge. Some studies show that visual object agnosia also has effects on face processing because both are supported by the lowest level vision.