Repetition priming of words and nonwords in Alzheimer's disease and normal aging

There has been considerable interest in repetition priming—defined as faster or more accurate processing of a repeated stimulus due to its prior processing—in elderly normal (EN) and probable Alzheimer’s disease (AD) individuals. In repetition priming paradigms, participants are generally not told about any possible relationship between the initial and later occurrences of stimulus items; thus, these paradigms are implicit tests of memory. This is in contrast to episodic memory paradigms in which specific mention is usually made of previous experience with the stimulus items, and participants are asked to recall previously seen items or to make “yes”/ “no” recognition judgments for previously seen and foil items; these paradigms are explicit tests of memory. Dissociations between repetition priming and episodic/event memory performance have often been found in AD and normal aging, with deficits on episodic memory tasks (to a much greater extent for AD than for EN groups), in the face of normal performance on repetition priming tasks (Craik & Rose, 2012; Zacks & Hasher, 2006). A particularly interesting aspect of lexical decision repetition is that nonwords can be repeated; in this case, a performance decrement is sometimes found for word-like nonwords, presumably because they become more difficult to distinguish from real words in some way (e.g., McKoon & Ratcliff, 1979, Exp. 2). Prior to describing the design features and specific rationale for the current study of repetition priming in AD, we will provide a brief overview of repetition findings in AD and normal aging, discuss the advantages of utilizing lexical decision as a repetition priming task, and review models of lexical decision and repetition priming.