Conceptual priming in semantic dementia: A window into the cognitive and neural basis of conceptual implicit memory.

The present study examined the impact of impairment in semantic memory on conceptual repetition priming by means of the longitudinal study of a patient with semantic dementia. ST was tested in four consecutive years, during which his semantic memory progressively deteriorated. On each occasion, he performed an abstract/concrete verification task and a verb generation task. In both of these tasks, performance during a test phase was compared for stimuli previously processed in a study phase and stimuli first seen in the test phase. Control subjects showed priming, as indicated by faster responses to studied than to baseline stimuli. ST showed intact priming that was of normal magnitude in the first two years of testing, but failed to show priming in the subsequent two years of testing. This pattern of results is interpreted with reference to the differential decline of item-specific and superordinate knowledge. The implications of these findings for the neural basis of conceptual priming are also discussed.