Repetition priming in normal aging and Alzheimer's disease: A review of findings and theories.

Abstract

On repetition priming tasks, memory is measured indirectly as a change in performance due to recent experience. It is often functionally and neurally dissociated from performance on explicit memory tasks, which directly measure conscious recall or recognition of recent events. Repetition priming has therefore been extensively studied in normal aging and Alzheimer's disease, which feature mild to severe changes in explicit memory. Initial studies indicated that repetition priming was immune to the effects of aging and greatly reduced in Alzheimer's disease (AD). As more studies have been performed, however, these initial conclusions appear less clear than before and, in the case of AD, actually misleading. The purpose of this article is to provide a comprehensive review of this rapidly expanding literature, articulate the issues that are critical to interpreting the empirical results, and discuss what new conclusions are suggested by the overall pattern of findings.

Two aspects of impaired consciousness in Alzheimer's disease

“…One reason invoked by various authors to explain these ambiguous results is that healthy participants may use explicit retrieval strategies when performing an ostensibly implicit retrieval task (Vaidya et al, 1996). This use of explicit strategies might artificially increase the ''priming effect'' for conceptual information in normal controls but not in AD patients, considering their explicit memory deficit (Fleischman and Gabrieli, 1998). This contamination interpretation is in line with Jacoby's view that there are no ''process-pure'' memory tasks (Jacoby et al, 1992).…”

“…However, the results related to implicit (i.e., automatic) memory tasks are more controversial. Some reviews of the literature (Meiran and Jelicic, 1995;Fleischman and Gabrieli, 1998) showed that AD patients often present a preserved priming effect on implicit tasks such as word and picture identification or lexical decisions, but they are frequently impaired on priming tasks that require implicit retrieval of conceptual information such as word association, category-exemplar generation, and word-stem completion. One reason invoked by various authors to explain these ambiguous results is that healthy participants may use explicit retrieval strategies when performing an ostensibly implicit retrieval task (Vaidya et al, 1996).…”

Verb acquisition and representation in Alzheimer's disease

“…Previous work showing preserved implicit learning in AD focused largely on dot arrays, meaningless visual-perceptual material, and sensory-perceptual attributes of words. Assessments of conceptual implicit memory may not have been as successful at demonstrating learning, by comparison, because the category-exemplar test often used to assess this form of implicit memory also depends in part on substantial executive resources during the category naming component of the test phase (Fleischman et al, 1998;Fleischman et al, 2005). AD patients are impaired in their category naming (LaFleche & Albert, 1995;Mickanin, Grossman, Onishi, Auriacombe, & Clark, 1994).…”

“…It is thus possible that information acquired about the new verb may be maintained over time. Preserved implicit memory has been demonstrated with measures of sensory-perceptual priming such as word-stem completion and word identification, but conceptual priming is said to be limited in AD (Fleischman & Gabrieli, 1998;Fleischman et al, 2005). Our study thus examines the limits of the conceptual priming deficit in AD, and can begin to determine whether this approach has any therapeutic promise for learning real-world knowledge in AD.…”

Convergent behavioral and neuropsychological evidence for a distinction between identification and production forms of repetition priming.

“…AD patients often exhibit a marked deficit in word-stem completion priming (Bondi & Kaszniak, 1991;Carlesimo et al, 1995;Gabrieli et al, 1994;Heindel et al, 1989;Keane et al, 1991;Salmon et al, 1988;Shimamura et al, 1987; but see Fleischman & Gabrieli, 1998, for a review of studies reporting intact priming). The word-stem completion deficit cannot be accounted for either by explicit memory failure in AD, because such priming is intact in amnesia, or by conceptual priming failure in AD, because word-stem completion is a perceptual form of priming that is typically unaffected by conceptual encoding manipulations.…”