Priming and the Brain Review minutes to several hours , subjects are given three-letter

Research in cognitive psychology, neuropsychology, words than nonstudied words. Similar kinds of tasks and neuroscience has converged recently on the idea have been developed for examining priming of numerthat memory is composed of dissociable forms and sysous different types of stimuli, including pseudowords tems (Squire, 1992; Roediger and McDermott, 1993; (Keane et al., 1995; Bowers, 1996), familiar and unfaSchacter and Tulving, 1994; Willingham, 1997). This conmiliar objects (Biederman and Cooper, 1991; Srinivas, clusion has been based on experimental and theoretical 1993; Schacter et al., 1993b), visual patterns (Musen analyses of a variety of different phenomena of learning and Squire, 1992), and environmental sounds (Chiu and and memory. One of the most intensively studied of Schacter, 1995; for extensive reviews, see Roediger such phenomena is known as priming: a change in the and McDermott, 1993; Schacter et al., 1993a). ability to identify or produce an item as a result of a Cognitive studies of healthy volunteers have provided specific prior encounter with the item (Tulving and a great deal of information about the behavioral and Schacter, 1990). psychological properties of priming (for discussion of Priming represents an example of what is often rerecent research, see Wiggs and Martin, 1998). For examferred to as implicit memory (Graf and Schacter, 1985; ple, it is known from numerous cognitive studies that Schacter, 1987; Roediger, 1990) or nondeclarative memexplicit recall and recognition of recently studied words, ory (Squire, 1992)—a nonconscious influence of past objects, or other materials is greatly affected by how experience on current performance or behavior. Priming those materials are initially encoded during the study and related types of implicit memory had been noted phase of an experiment (e.g., Craik and Tulving, 1975). occasionally since the nineteenth century in clinical and More specifically,when target items are initially encoded experimental reports but have only been studied sysin a semantic or elaborative manner (e.g., generating tematically during the past two decades (for a historical meanings of a word or rating its pleasantness), subsereview, see Schacter, 1987). Modern interest in priming quent explicit recall or recognition is much more accuwas stimulated by several developments: studies conrate than when target items are initially encoded in a cerning lexical access and representation that provided nonsemantic or shallow manner (e.g., counting the nummethods for assessing priming (e.g., Scarborough et al., ber of vowels and consonants in a word). In an early 1977), early theoretical attempts to distinguish among study of priming, Jacoby and Dallas (1981) reported different forms of memory (e.g., Tulving, 1972), and rethat priming effects on a word identification test are no ports of preserved learning in patients with amnesic greater after semantic encoding than after nonsemantic syndromes (e.g., Milner et al., 1968; Warrington and encoding—even though recognition accuracy was much Weiskrantz, 1974; see below for discussion). Based on higher after the semantic than the nonsemantic encodthese developments, a number of experiments reported ing task (although some subsequent studies have found during the early 1980’s helped to characterize the phesmall effects of semantic versus nonsemantic encodnomenon of priming and distinguish it from explicit ing manipulations on word identification and similar memory (cf. Jacoby and Dallas, 1981; Tulving et al., tasks, they are much smaller than the effects of the 1982; Graf et al., 1984). same encoding manipulations on explicit memory; for Priming is assessed with experimental tasks that do a review and discussion, see Brown and Mitchell, 1994). not require conscious recollection of particular previous Other early data established that healthy volunteers can experiences. Such tasks differ from traditional tests of show priming even when they fail to consciously recolrecall and recognition, which tap an explicit or declaralect that they have previously studied an item and that tive form of memory and require conscious, intentional priming can persist across days (Tulving et al., 1982); recollection of recently studied information. Consider, more recent data indicate that priming effects can perfor example, a prototypical experiment in which priming sist for as long as a year (e.g., Cave, 1997). is assessed with a word-stem completion test. In the Whereas the foregoing studies involved college stufirst phase of the experiment, subjects study a series dents, research on priming quickly broadened to include of words. After a delay that usually ranges from several a variety of subject populations. For example, studies