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8 MILLET ET AL.Downloaded By: [Millet, Xavier] At: 10:57 4 November 2009engaged by individuals during the encoding phase, weobtained a more comprehensive analysis of stemcompletion performances in AD. Indeed, our results givesupport to the assumption that word-stem completionperformances are preserved in AD patients following particularencoding conditions such as semantic generationwhereas word-stem priming seems to be highly attenuatedfollowing reading and rating encoding conditions.Following encoding instructions requiring generationprocesses—that is, providing definition and wordgeneration—several studies reported that word-stemcompletion priming was impaired while others found theopposite. Pooling the data, the present meta-analysissupports the result that word-stem completion primingin AD is similar to that exhibited by elderly controlswhen generation processes are instigated at the encodingphase: providing definition, –0.75, CI 95% [–1.52; 0.02];word generation, –0.06, CI 95% [–0.51; 0.40]). Therefore,instructions providing generation processes couldconstitute an aid to partially compensate the conceptualdeficits of the patients and allow later facilitation ofstudied information.Conceptual generation may not be the unique encodingcondition enhancing word-stem completion primingin AD patients. Even though supported by a singlestudy, our results tend to show that encoding conditionsinvolving lexical processes also facilitate AD patients’performances (–0.38, CI 95% [–1.10; 0.34]). According tothe lexical processing view of priming, word completionpriming is the result of both conceptual and lexicalprocesses (Richardson-Klavehn & Gardiner, 1998;Weldon, 1991). Because lexical priming persists at leastpartially in AD (Balota & Ferraro, 1996; Chenery,Ingram, & Murdoch, 1994; Ober & Shenaut, 1988; Ober,Shenaut, Jagust, & Stillman, 1991; Perri et al., 2003;Shenaut & Ober, 1996) processing lexical properties oftarget words at the encoding phase may have constituteda valuable aid to facilitate priming performances in ADpatients. Moreover, the results suggest that AD patientsexhibit normal priming in encoding conditionsconsisting in answering yes or no to questions (–0.32, CI95% [–1.14; 0.50]), which requires participants to processsemantic and functional attributes of concepts.The present findings suggest that reading (–0.45, CI 95%[–0.75; –0.16]) and rating pleasantness of words (–0.86, CI95% [–1.17; –0.55]) at encoding do not enhance significantword-stem completion priming in AD patients.Generating words tends to produce more conceptuallydriven processes than reading words in completionpriming tasks (Schwartz, 1989; Weldon, 1991). Likewise,making pleasantness and likeability judgments involvesa certain degree of conceptual elaboration, which is,however, probably insufficient to induce a full registrationof the meaning of the words. In other words, simplyapplying externally supplied semantic informationfollowing reading and making pleasantness and likeabilityjudgments seems less helpful to AD patients thaninternally producing semantic information in a moreelaborate operation of generation.Nonetheless, a few methodological limitations of thisstudy warrant consideration. The first and probablymain limitation refers to the number of studies includedin the conditions consisting in semantic judgment andlexical vowels counting. Indeed, the modest number ofparticipants included in these encoding conditions mayhave led to weaker statistical power. Therefore, since thepooled effect size estimated is not significant, we have tointerpret our results cautiously, and the question ofwhether word-stem completion priming in AD ispreserved in these encoding conditions can still bedebated. Second, participant numbers were noticeablyinflated because in some articles the same participantsperformed multiple encoding conditions. For thisreason, participants’ performances might be correlatedbetween the different encoding conditions considered.However, because the number of studies in some conditionswas quite modest, we chose to include these studiesto avoid further impoverishment of the statistical power.Third, our study does not allow comparing the effectsizes between the encoding conditions within eachgroup. Therefore, it is not possible to exclude that theresults observed are not biased by differential effects ofencoding condition in elderly controls. Fourth, regardingthe conditions in which AD priming performanceswere impaired, we cannot exclude the potential contaminationof implicit memory processes by explicit retrievalstrategies in normal elderly participants. Increasingstudy–test delay is known to reduce the likelihood ofexplicit contamination in implicit memory tasks (e.g.,Mitchell & Bruss, 2003). In Meiran and Jelicic’s (1995)meta-analysis, effect sizes between AD patients’ and elderlycontrols’ word-stem completion priming performanceswere not different when priming was tested with astudy delay or without any delay suggesting that theexplicit memory contamination hypothesis in this taskmay be unlikely. However, other authors showed thatAD patients’ deficits were removed by controlling forthe effects of explicit processes (e.g., Randolph, 1991).Because the data of the present meta-analysis cannotdefinitely invalidate this hypothesis, future studies arewarranted to determine whether the present results canbe attributed to the use by elderly controls of deliberaterecollection strategies.The distinctions between perceptual–conceptual andidentification–production tasks have proved useful indescribing many neuropsychological findings (e.g.,Fleischman, 2007), but as underlined in Meiran andJelicic’s (1995) meta-analytic study, it may not berelevant regarding word-stem completion primingperformances because of the componential nature of thetask. Indeed, the present meta-analysis shows that thesedistinctions failed to comprehensively predict word-stemcompletion priming performances in AD. Severalresearch studies directly led to questioning of the viabilityof such distinctions (e.g., Challis et al., 1996; Vaidyaet al., 1997) in normal aging (Geraci, 2006; Mitchell &Bruss, 2003; Prull, 2004) and AD (Lazzara et al., 2001;Maki & Knopman, 1996; Vaidya et al., 1999). Thus, thenature of the retrieval processes during the test phasedoes not probably account alone for the pattern of primingperformances in AD. While it has been frequentlyconcluded that processing manipulation at encoding did