Prosopagnosia

We all (except me, of course) know the uncomfortable feeling of meeting someone familiar, and have a feeling we should know them from somewhere. But where? It gets worse; this time it's someone we know, but somehow can't extract their name from the cerebral filing cabinet.

Then along comes prosopagnosia (Pros-o-pag-no-sia) or face-blindness. As I read in the paper the other day.

In one of two forms: Primary prosopagnosia, which means ya born with it and Secondary prosopagnosia, which is accquired somehow through accident. What is it? A disorder of face perception where the ability to recognize faces is impaired, although the ability to recognise objects may be relatively intact. It was thought to be rare until recently but there is evidece to suggest that up to 1 in 50 people suffer and that it runs in families.

http://home.earthlink.net/~blankface/prosopagnosia.shtml
For more info from the perspective of someone with prosopagnosia

Some think that Capgras delusion may be the reverse of prosopagnosia. In this condition people report conscious recognition of people from faces, but show no emotional response, perhaps leading to the delusional belief that their relative or spouse has been replaced by an impostor.

I'm glad I have absolutely no problem with putting names to faces.