Semantic priming in Alzheimer's dementia

Whilst there exists general consensus in the literature that persons with dementia of the Alzheimer's type (DAT) evidence a semantic deficit, investigations to reveal the precise nature of the deficit (i.e. whether it reflects a procedural or storage deficit) have yielded equivocal results. An experimental technique used widely in the investigation of semantic processing in DAT is the semantic priming task. It has been argued that if patients with DAT are shown to perform normally on a task of automatic semantic priming, then this would argue for the structural integrity of the store of semantic memories. To date, however, the studies investigating semantic priming in DAT have described a variety of performance features with some reporting intact priming, some no priming and some exaggerated or hyperpriming. This paper reviews in detail the specific methodologies employed by the researchers investigating semantic priming in DAT in light of current theories of semantic priming. The review will outline the theoretical perspectives of semantic priming as detailed in the psycholinguistic literature on normal subjects, and then critically review the literature pertaining to semantic priming in DAT. More specifically, this paper will review the studies that have investigated attention-free semantic processing in DAT using automatic semantic priming tasks and compare their results with studies that have used, either by design or default, an attention-dependent form of semantic priming. The general weight of evidence would tend to suggest that when the experimental methodologies employed ensured only automatic activation was assessed, the DAT subjects were found to have spared semantic priming if not hyperpriming. The studies that have confounded assessment of automatic spreading activation with attention-induced priming have, without exception, demonstrated very impaired performance on the part of the DAT subjects. This pattern of results can be interpreted as reflecting significantly impaired procedural routines in DAT, with relative sparing of the structure of semantic memory