Sometimes only one is impaired, sometimes both. Superordinate, natural-kind categories tend to be more similar in shape than superordinate, artifact categories. So, category impairments might be due to inability to process shape information properly. Other hypothesis is perceptual-functional hypothesis. Deficit here is not at the level of shape descriptions, but is at the level of prototypical features.
Idea here is that many prototypical features are perceptual in nature.
So, brain damage affects these features, but leaves functional features intact. In addition to prototypical features and shape descriptions, concepts must include information that is not perceptually available. E.g. about internal organs, lineage, etc. Smith calls this info theoretical features.