Greebles!

http://www.sciencenews.org/view/generic/id/336982/title/Face_deficit_holds_object_lesson

A man who is brain-damaged and can't remembered faces is also having trouble memorizing the computer generated "Greebles" in a study at the University of Richmond, VA. Four healthy volunteers struggled at first, but can now tell them apart while the brain damaged man still cannot discern one Greeble from another. This study may lend some new insight into the study of facial recognition.