'Two Eyes of a See-through': Impaired and Intact Semantic Knowledge in a Case of Selective Deficit for Living Things

We report a patient, RC, with a category-specific semantic deficit for living things, who shows the following pattern of behaviour: (1) he has difficulty in distinguishing among individual exemplars for living thing categories, (2) he has no impairment in grouping living things according to their shared properties and (3) in property verification and definition tasks, RC shows good knowledge of shared but not distinctive properties of living things, (especially biological functional properties) and the reverse pattern for non-living things. These findings cannot be accounted for by selective damage to a particular type or category of information. We argue that RC's deficit is predicted by a unitary model of semantic memory in which the patterns of correlation among distinctive and shared perceptual and functional properties are different for concepts in the domains of living and non-living things. These differences in conceptual structure give rise to category-specific impairments when the semantic system is damaged, even when the damage itself is not selective.