The role of conceptual knowledge in object use - Evidence from semantic dementia

It has been reported that patients with semantic dementia function well in everyday life and sometimes show striking preservation of the ability to us e objects, even those specific objects for which the patient has degraded c onceptual information. To explore this phenomenon in nine cases of semantic dementia, we designed a set of semantic tests regarding 20 everyday object s and compared performance on these with the patients' ability to demonstra te the correct use of the same items. We also administered a test of mechan ical problem solving utilizing novel tools, on which the patients had compl etely normal ability. All but the mildest affected patient showed significa nt deficits of naming and on the visually based semantic matching tasks. Ob ject use was markedly impaired and, most importantly, correlated strongly w ith naming and semantic knowledge. In a small number of instances, there wa s appropriate use of an object for which the patient's knowledge on the sem antic matching tasks was no better than chance; but this typically applied to objects with a rather obvious relationship between appearance and use, o r was achieved by trial and error. The results suggest that object use is h eavily dependent upon object-specific conceptual knowledge, supplemented to some degree by a combination of visual affordances and mechanical problem solving.