The dynamic time course of semantic memory impairment in Alzheimer's disease: clues from hyperpriming and hypopriming effects (original) (raw)

The nature of semantic memory de®cit in Alzheimer's disease is still a matter of controversy. To clarify this issue, we examined the evolution of semantic memory impairment in 24 Alzheimer's disease patients by means of a longitudinal study. We used two semantic tasks, one explicit and the other implicit, to evaluate the integrity of the same concepts. The explicit task was a semantic knowledge task composed of naming and questions, involving superordinate and attribute knowledge of concepts. The implicit task, a lexical decision task, assessed semantic priming and allowed a very pure measurement of semantic memory. In this task, related pairs of words had coordinate (e.g.`tiger±lion') or attribute (`tiger±stripe') relationships. In the coordinate relation between two words, the semantic priming performances were at ®rst paradoxical: they increased abnormally (hyperpriming) before falling down, whereas in the attribute condition, the priming effects were ®rst normal and then started to decrease in the ®nal sessions (hypopriming). Compared with the semantic knowledge performance, these apparently disconcerting results re¯ect a coherent pattern of semantic memory degradation in Alzheimer's disease that is a progressive deterioration starting with speci®c attribute information. The data reveal in an astonishing yet striking manner the dynamic semantic memory degradation in Alzheimer's disease through the apparently paradoxical semantic priming effects.