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1 Priming 1055 Priming R Henson, MRC Cognition nd Brin Sciences Unit, Cmridge, UK ã 2009 Elsevier Ltd. All rights reserved. Introduction Priming refers to chnge in ehviorl response to stimulus, following prior exposure to the sme, or relted, stimulus. Exmples include fster rection times to mke decision out the stimulus, is to produce tht stimulus when generting responses, or the more ccurte identifiction of degrded version of the stimulus. From the memory perspective, the most exciting spect to priming concerns evidence tht it cn occur in the sence of conscious memory for the prior exposure (n exmple of soclled implicit or nondeclrtive memory). For instnce, mnesic ptients typiclly show intct levels of priming, despite their impirments in conscious ( explicit or declrtive ) memory. Evidence like this led to the proposl tht the rin regions supporting priming re different from the medil temporl loe (MTL) regions elieved to support declrtive memory. Indeed, it is often ssumed tht priming is the y-product of prior processing of stimulus, tht is, rising from plsticity in multiple corticl regions whose primry role is perceptul/conceptul processing. As such, priming is likely to e one of the most sic expressions of memory, influencing how we perceive nd interpret the world. A Working Exmple Priming cn e mesured using rnge of different stimuli nd tsks. To illustrte the redth of neuroscientific dt on priming, we initilly focus on one specific prdigm the word-stem completion prdigm which hs provided some of the most convincing evidence tht priming involves memory systems, nd ssocited rin regions, tht differ from those involved in declrtive memory. In the study phse of this prdigm, prticipnts perform n incidentl tsk on list of words (normlly unwre tht their memory for these words will e tested). At some time lter, they re presented with three letters tht form the strt of words (word-stems) (see Figure 1()). Some of these stems cn e completed with the words from the study phse, though in the indirect version of this tsk, prticipnts re not informed of ny reltionship etween this test phse nd the previous study phse. They re simply sked to complete the stem with the first word tht comes to mind. Priming is indexed y the incresed proility of completing stems with studied words, reltive to the seline proility of completing the stems when those words were not studied. Importntly, prticipnts normlly show this priming without reporting ny conscious reference to the prior study phse. Neuropsychologicl Evidence When this tsk is given to mnesic ptients, they typiclly show priming of equivlent mgnitude to controls. However, when the instructions t test re chnged, so tht prticipnts re sked to use the stems explicitly to recll studied words ( word-stem cued recll, direct version of the tsk), mnesic ptients typiclly perform worse thn controls (Figure 1()). This dissocition is ppeling ecuse the stimuli re kept constnt cross the indirect nd direct versions of the tsk; ll tht differs re the instructions. While mnesic ptients re lso known to hve spring of other forms of memory, such s motor skill-lerning, the intriguing spect of priming is tht it cn occur fter single stimulus presenttion ( one-shot lerning ), rther thn requiring sustined trining. Furthermore, few ptients with more posterior lesions (e.g., in occipitl cortex) hve shown the reverse pttern of impired word-stem completion for visully studied words (indirect test), despite intct performnce on recognition memory test (direct test). This doule dissocition etween the two types of memory test is strong support for different memory systems underlying priming nd declrtive memory. Further support comes from reports tht word-stem completion priming is less susceptile thn is cued recll to the effects of helthy ging, nd to some dementis like Alzheimer s disese. Psychologicl Evidence This dissocition of priming from declrtive memory following rin dmge is supported y functionl dissocitions etween direct nd indirect versions of the word-stem completion prdigm in helthy individuls. For exmple, performnce on the direct version (word-stem cued-recll) is higher when the corresponding words re generted from semntic cues t study reltive to when they re simply red, yet performnce on the indirect version (word-stem completion) is higher when the words re red reltive to eing generted from cues. Similrly, presenting words uditorily rther thn visully t study tends to impir performnce on visul word-stem completion to greter extent thn on visul word-stem cued

2 1056 Priming Study phse MOTEL Amnesics Controls (Prime) 80 Test phse MOT-? GAR-? 50 (Primed) (Unprimed) 40 Indirect version (completion): 30 complete with the first word coming to mind Direct version (cued-recll): 0 complete with word from the study phse Completion Cued-recll Figure 1 () Schemtic of the word-stem completion prdigm. () Performnce of mnesic ptients nd mtched controls on indirect (completion) nd direct (cued-recll) versions of the tsk. () Reprinted with permission from Grf P, Squire LR, nd Mndler G (1984) The informtion tht mnesic ptients do not forget. Journl of Experimentl Psychology: Lerning, Memory nd Cognition 10: , APA pulishers. % completed recll, wheres use of study tsk tht engges semntic versus phonologicl processing of words tends to improve performnce on word-stem cued recll to greter extent thn on word-stem completion. The reduced performnce found on word-stem completion when words re generted or herd t study, rther thn red, suggests tht component of priming in this tsk reltes to the visul overlp etween words nd their stems, or more precisely, to overlp in the processes involved in visul word reding. Nonetheless, though dissocitions hve een found etween direct nd indirect tests of memory, cre must e tken when using performnce on indirect tests s pure mesure of implicit memory: even though n indirect memory test does not refer prticipnts to previous encounters with stimuli, prticipnts my voluntrily, or involuntrily, recollect such encounters. For exmple, some prticipnts my guess the reltionship etween the study nd test phse of word-stem completion tsk, nd hence ttempt to recll studied items in order to complete the stems. Moreover, even if completion comes to mind involuntrily, prticipnts my susequently recognize tht word s hving come from the study phse. Though the ltter eventulity my not ffect ehviorl mesures of priming, it is importnt when mesuring the neurl correltes of priming, s discussed in the next two sections. As consequence, considerle effort hs een devoted to developing methods tht minimize the contriution of explicit memory to priming. Neuroimging Evidence Some of the first positron emission tomogrphy (PET) nd functionl mgnetic resonnce imging (fmri) studies of priming used the word-stem completion prdigm. These studies consistently found reduced hemodynmic responses in extrstrite visul cortex for studied reltive to unstudied word-stems (often in oth direct nd indirect versions of the tsk). This reduction is ttriuted to more efficient or fcilitted visul processing of the stems corresponding to studied words, owing to the prior exposure to those words. Similr reductions hve lso een found in numer of regions including left inferior temporl nd left inferior frontl cortices. Given tht these regions re lso generlly ctivted y the tsk (e.g., vs. pssive fixtion), the reductions re consistent with fcilitted processing within lnguge-relted network tht is engged when reding words nd completing wordstems, possily including phonologicl, lexicl, nd semntic processes. Some imging studies hve lso reported hemodynmic increses in MTL cortices, even in indirect versions of the tsk. This illustrtes the prolem highlighted erlier tht explicit memory my contminte indirect tsks. In prticulr, even if this explicit memory is involuntry nd does not ffect the ehviorl response, the poor temporl resolution of hemodynmic imging techniques mens tht imging dt my include explicit memory processes rising susequent to tht response. More recent imging experiments hve therefore used vrints of the word-stem completion prdigm tht ttempt to minimize contmintion y explicit memory. For exmple, prticipnts cn e sked to complete stems with words from the study phse (i.e., word-stem cued recll), ut if they cnnot, they re sked to produce the first word coming to mind. Hving produced completion (through either pproch), they then indicte whether they rememer tht word from the study

3 Priming 1057 phse. The criticl trils used to isolte the neurl correltes of priming re those stems completed with studied words ut which prticipnts indicted they did not rememer. These trils re likely to provide purer mesure of implicit memory (despite occurring in the context of direct memory tsk). When compred to seline condition (stems tht did not correspond to studied words, ut which were completed with word tht ws correctly indicted s unstudied), event-relted fmri hs replicted the reduced responses found in extrstrite, left inferior temporl, nd left inferior frontl cortices (Figure 2()). Equivlent reductions in these regions were lso found for rememered trils (stems tht were completed with studied word nd tht word ws indicted s studied), unlike in MTL cortex, where greter ctivity ws found for rememered trils reltive to primed trils (suggesting tht explicit memory hd een successfully minimized in primed trils). Furthermore, the reductions for primed nd rememered versus seline trils in these regions were lso found when using n indirect version of the tsk kin to the stndrd word-stem completion tsk. Tken together, these results suggest tht such hemodynmic reductions re not only implicit, ut lso utomtic, consistent with role for these regions in the priming oserved in helthy individuls nd in mnesic ptients. Test phse Study phse Left inferior frontl Direct Indirect Left inferior frontl Left inferior temporl fmri signl Rem Pri Bs Rem Pri Bs Direct Indirect Left inferior temporl fmri signl difference Rem-For Pri-For fmri signl Rem Pri Bs Rem Pri Bs fmri signl difference Rem-For Pri-For Occipitl Direct Indirect Medil temporl fmri signl Rem Pri Bs Rem Pri Bs fmri signl difference Rem-For Figure 2 Event-relted fmri dt from word-stem completion prdigm. In the test phse (), numer of regions including those shown in left inferior frontl, left inferior temporl nd occipitl cortices, exhiited reduced responses to primed stems (lues), nd to rememered stems (reds), reltive to seline stems (greens), regrdless of whether prticipnts performed direct (lighter colors) or indirect (drker colors) version of the prdigm. In the study phse (), numer of regions including those shown in left inferior frontl nd inferior temporl cortices showed reduced responses for susequently primed reltive to susequently forgotten words (drker r), wheres regions in medil temporl loe showed incresed responses for susequently rememered (ut not susequently primed) reltive to susequently forgotten words (lighter r). Rem, rememered; Pri, primed; Bs, seline; For, forgotten (see text). () Adpted with permission from Schott BH, Henson RN, Richrdson-Klvehn A, et l. (2005) Redefining implicit nd explicit memory: The functionl neurontomy of priming, rememering nd control of retrievl. Proceedings of the Ntionl Acdemy of Sciences of United Sttes of Americ 102: () Adpted with permission from Schott B, Richrdson-Klvehn A, Henson R, et l. (2006) Neurontomicl dissocition of encoding processes relted to priming nd explicit memory. Journl of Neuroscience 26: Copyright (2005) Ntionl Acdemy of Sciences, USA. Pri-For

4 Author's personl copy 1058 Priming One cn lso use event-relted imging methods to exmine differences t the time stimuli re encoded (i.e., during the study phse) s function of the degree to which those stimuli show lter priming (or the degree to which they show explicit memory). Using the sme prdigm s ove, for exmple, hemodynmic responses to the words t study differed for those words susequently primed (completed with the studied word ut not rememered) thn those susequently forgotten (completed with different word). Such differences were found in numer of corticl regions, including the left inferior temporl nd frontl regions tht showed priming-relted reductions t test. Agin, the pttern in these regions differed from tht in the MTL, which showed greter ctivity for words susequently rememered versus words susequently forgotten (Figure 2()). These findings suggest tht priming is ffected y how stimuli re encoded (on their initil presenttion), possily in ddition to how tht informtion is ccessed t test. Yet further work hs comined event-relted fmri with phrmcologicl interventions: for exmple, scopolmine nd lorezpm, which re elieved to modulte synptic plsticity, hve een shown to ttenute repetition suppression in the sme inferior temporl nd frontl regions during word-stem completion. Electrophysiologicl Evidence The time course of word-stem completion priming hs lso een investigting using electroencephlogrphic (EEG) nd mgnetoencephlogrphic (MEG) methods. For exmple, in stndrd indirect completion tsk, event-relted potentils (ERPs) to primed word-stems hve een reported to diverge from those to seline (unstudied) word-stems within 200 ms of the onset of the word-stem (Figure 3()). The sme ERP effect ws reported for words rememered during ms ms Priming priming seline Novel-repet 4 µv Inferior frontl gyrus Novel 2 µv 2 µv Posterior plnum temporle Repet Recll priming Ventrl occipitl Anterior temporl loe 2 µv Recll recll seline 2 µv Lterl occipitotemporl sulcus Ventrl occipitotemporl junction µv Figure 3 Electrophysiologicl dt from word-stem completion prdigm. In (), the event-relted potentils (ERPs) over right prietotemporl electrodes recorded y EEG diverge etween primed nd seline stems (upper plot), nd etween reclled nd seline stems (lower plot), within 200 ms, wheres the ERPs to primed nd reclled stems only differ from 300 ms onwrds (topogrphies lso differ). In the upper pnel of (), regions with relile differentil source-reconstructed event-relted ctivity, inferred from MEG dt, for repeted versus novel presenttion of stems re shown for two time windows. In the lower pnel, the reconstructed responses re shown for numer of regions of interest. () Dt dpted with permission from Bdgiyn RD nd Posner MI (1997) Time-course of corticl ctivtions in implicit nd explicit recll. Journl of Neuroscience 17: () Dt dpted with permission from Dhond RP, Buckner RL, Dle AL, Mrinkovic K, nd Hlgren E (2001) Sptiotemporl mps of rin ctivity underlying word genertion nd their modifiction during repetition priming. Journl of Neuroscience 10:

5 Priming 1059 direct cued-recll version of the tsk. However, when contrsting primed nd rememered wordstems directly, differences only emerged fter pproximtely 300 ms. These dt suggest tht priming occurs prior to explicit memory retrievl. Furthermore, nd consistent with fmri dt descried ove, qulittive differences hve een found in the study etween the differentil ERPs to words susequently primed versus those susequently rememered. More recently, relted experiments (in which word-stems were repetedly completed) hve used the superior sptil resolution of MEG (comined with structurl informtion from MRI) in n ttempt to loclize the evolution of repetition-relted effects over the first few hundred milliseconds from stem onset. Interestingly, n initil repetition-relted increse in electricl ctivity hs een reported erly in left inferior temporl cortex (lterl occipitotemporl sulcus), followed y lter decrese in oth this region nd left inferior frontl cortex (Figure 3()). Such sptiotemporl dt suggest rpid interctions etween rin regions, which would e invisile to hemodynmic techniques like fmri. Indeed, such dt fford greter opportunity to look t priming-relted chnges in the connectivity etween different rin regions, for exmple, s function of plsticity following initil processing of stimuli. Summry The ove studies using the word-stem completion prdigm provide convergent evidence tht priming reflects form of memory dissocile from conscious memory, nd cn rise from numer of corticl regions outside the MTL. These regions re normlly suset of those engged y the specific stimuli nd tsk (in the ove cses, numer of left inferior frontl, left inferior temporl, nd occipitl regions ssocited with word reding), suggesting tht priming reflects form of plsticity in these regions. The expression of priming is generlly ssocited with reduced neurl ctivity in these regions, possily reflecting fster nd/or more efficient processing (e.g., gresing of the trcks ). This expression ppers to occur very rpidly (round 200 ms) nd utomticlly (regrdless of precise tsk). Differences in neurl ctivity hve lso een found during the initil processing of stimuli s function of whether they re susequently primed. This implictes importnt roles for fctors such s ttention nd the type of processing in the nture of neurl/synptic chnges ssumed to underlie priming. Similr conclusions hve een reched using numer of other priming prdigms, though the specific network of corticl regions involved my differ. Indeed, the generl finding of decresed hemodynmic responses to repeted stimuli (which hs een clled repetition suppression ) hs een oserved repetedly cross rnge of stimuli nd indirect memory tsks. Interestingly, however, not ll regions ctivted y initil presenttions of stimuli show such decreses: erly sensory regions, such s V1, for exmple, do not normlly show repetition suppression. One possiility is tht not ll of the processing stges in given tsk show stimulusspecific effects of prior processing (or lterntively, such effects of prior processing hve lifetimes shorter thn is typiclly tested). An interesting theoreticl question is therefore which stges (nd ssocited rin regions) show the lrgest effects of prior processing? Are they, for exmple, stges tht involve gretest competition etween lterntive outputs/interprettions? Other Common Mesures of Priming Another common mesure of priming is the ltency to identify (e.g., nme) pictures of ojects. This mesure hs shown priming effects tht lst up to yer. In common neuropsychologicl version, in which degrded pictures re grdully clrified (the Gollin figures ), mnesic ptients show strong priming (i.e., erlier identifiction for pictures identified previously). Reserchers hve lso used such priming to investigte the representtion of visul ojects in the rin, y exmining the extent to which primingrelted effects (e.g., in different rin regions) generlize cross different views of n oject. Another common type of priming is semntic priming, where the response to proe word (e.g., HEAVEN) is speeded when preceded y relted prime word (e.g., HELL) reltive to nonrelted word (e.g., HILL). Such priming tends to e shortlived, often not surviving more thn second etween the prime nd proe. As with visul oject priming, it hs lso een used s tool, in this cse to investigte the orgniztion of semntic memory. Yet nother type of priming tht hs een influentil on theoreticl level is ssocitive priming, where the priming of proe stimulus is modulted y whether or not it hs previously een pired with context stimulus. According to theories tht hypothesize key role for MTL in forming ssocitions, ptients with MTL dmge should not show such priming, even if such priming is shown to e implicit. At the moment, the dt pper mixed. There is lso much interest in suliminl priming, in which the prime is presented so riefly (round 50 ms; often forwrd nd ckwrd msked) tht prticipnts show little to no wreness of the prime, nd yet still show ehviorl priming to proe stimulus

6 1060 Priming presented shortly fterwrds (typiclly within few hundred milliseconds). Indeed, this type of priming hs een recommended for imging studies of implicit processing, since it is esier to rule out contmintion y explicit memory for the prime. Theories of Priming A rod distinction hs een mde etween perceptul nd conceptul priming. The min difference is tht perceptul, ut not conceptul, priming is ffected y differences in the physicl fetures of the prime nd proe stimuli, wheres conceptul, ut not perceptul, priming is ffected y differences in the degree of semntic processing of the stimuli. This distinction is supported y dissocitions in, for exmple, Alzheimer s ptients, who reportedly show intct perceptul priming ut impired conceptul priming, presumly ecuse the erly sensory res elieved to e importnt for perceptul priming re less ffected y the disese thn nterior temporl regions elieved to e importnt for conceptul priming. A relted distinction ssumes tht priming is supported y specilized perceptul representtion systems tht re distinct from the MTL memory system. In principle, this llows for dissocile forms of perceptul priming s function of modlity (e.g., visul vs. uditory). Though useful heuristics, such rod distinctions do not seem sufficient for the vrieties of priming tht hve een investigted. For exmple, the word-stem completion tsk discussed ove is difficult to fit into the perceptul/conceptul dichotomy, since it is ffected y vritions in some physicl properties, yet residul priming cn still occur cross modlities (even when voluntry explicit retrievl hs een excluded). Furthermore, word-stem completion cn e unffected y the degree of semntic processing of primes (e.g., semntic vs. phonologicl), yet e reduced following very superficil (e.g., grphemic) processing of primes. These dt re consistent with contriution from lexicl component, in ddition to perceptul components. Furthermore, other dimensions long which indirect tsks differ cn lso produce ehviorl dissocitions, such s the distinction etween competitive nd noncompetitive ccess to conceptul informtion, for exmple. An lterntive perspective is the component process view of priming, ccording to which there re typiclly severl processes involved in given tsk tht my e fcilitted y prior processing. As with the relted concept of trnsfer-pproprite processing, the mount of priming will depend on the degree of overlp etween the processes performed on the prime nd those performed on the proe (Figures 4() nd 4()). These processes my derive from interctions etween rin regions tht ecome configured ccording to the tsk demnds. Therefore, performnce will depend on the interply of components nd the processes they medite (Moscovitch, 1994: 301). A ehviorl mesure like rection time is likely to reflect the conglomertion of the times tken to perform ech component process. Only y vrying the stimuli nd tsk cn the key components in ehviorl priming e isolted (Figures 4() nd 4(c)). Alterntively, the concurrent cquisition of hemodynmic or electrophysiologicl dt llows the opportunity to exmine ctivity within the network of rin regions (nd the interctivity etween those regions) tht re configured for the current tsk. Another importnt theoreticl dimension is tht etween structurl nd episodic theories of priming. According to structurl (or strctionist ) theories, priming reflects some modifiction, such s lowered thresholds of, or residul ctivity in preexisting representtions. According to episodic (or instnce ) theories, ny exposure to stimulus cn, in principle, leve some residul trce of its processing. Attempts to test these theories hve used priming of novel stimuli (e.g., nonwords, or impossile ojects) or exmined the effects of context (e.g., novel ssocitions) on priming. In generl, this distinction is hrd to evlute in the sence of more detiled theories of the nture of representtion in the rin (e.g., even nonwords cn consist of fmilir igrms of letters). Nonetheless, one importnt clss of episodic theories ssumes tht ech stimulus nd response within tsk cn ecome ssocited together, or ound into single representtion (or event record ). In such cses, repetition of the stimulus cn directly cue retrievl of the ssocited response. Such stimulus response ssocitions hve een shown to influence ehvior, prticulrly in the cse of suliminl (msked) priming, ut lso in the cse of negtive priming, when the response to proe stimulus is hindered if the sme stimulus hs previously een presented in the context of different response (even if n implicit response). Such ssocitions hve lso een shown to hve drmtic effects on imging dt. Though stimulus response ssocitions cn e minimized y ensuring tht the response mde to the proe is unrelted to the response mde to the prime, it is cler tht when present, such ssocitions cn hve importnt consequences, possily y-pssing severl stges of processing tht occurred on the prime (Figure 4(d)). Future One importnt future direction tht provides strong evidence for the direct involvement of circumscried

7 Priming 1061 First presenttion (prime) Erly visul (Strite) Visul oject (Fusiform?) Semntic (Inf Front?) Living Second presenttion (proe) Erly visul (Strite) Visul oject (Fusiform?) Semntic (Inf Front?) Living Rit Erly visul (Strite) Orthogrphic (Inf Temp?) Semntic (Inf Front?) Living c Erly visul (Strite) Visul oject (Fusiform?) Semntic (Inf Front?) Living d Figure 4 Schemtic of the component process view of priming. () Initil presenttion of n oject in semntic clssifiction tsk (living vs. nonliving) involves interctions etween numer of processing stges etween the stimulus (left) nd response (right). Puttive rin regions ssocited with ech stge re shown. () Repetition of the sme oject in the sme tsk cuses fster clssifiction y virtue of fcilitted processing in some (ut not necessrily ll) of the stges (fcilittion indicted y drker lines). (c) A chnge in the stimulus involves re-processing in only one of the originl stges (in this exmple), leding to reduced priming (nd potentil isoltion of semntic component). (d) The formtion of direct stimulus response ssocition (event record) cn lso cuse priming, even though it ypsses the initil processing stges. Inf, inferior; Front, frontl cortex; Temp, temporl. rin regions in priming is the use of trnscrnil mgnetic stimultion (TMS). In the only such study to dte, either left inferior frontl cortex or control site ws stimulted pproximtely 300 ms fter the initil presenttion of visul oject. Frontl stimultion reduced the mount of priming for semntic clssifiction of tht oject when it ws repeted lter (Figure 5()). Moreover, repetition suppression for tht oject, when lter repeted, ws olished in left inferior frontl cortex, ut not in occipitl cortex (Figure 5()). This supports the existence of t lest two components to priming in this tsk: for exmple, visul component in occipitl cortex nd verl component in left inferior frontl cortex. Another importnt future direction is the comintion of multiple imging modlities, such s the comintion of sptil informtion in fmri with the temporl informtion in MEG. Once the detiled time course of ctivity cn e estimted in different rin regions, one cn go further nd explore chnges in the covrince etween these time courses, in order to infer directionlity nd possile cuslity. It will lso e useful to cquire more fmri nd EEG/MEG dt on mnesic ptients, to confirm tht primingrelted chnges in rin ctivity persist despite compromised ctivity in MTL. From theoreticl perspective, more detiled models of the cuses of priming re needed. According to the component process view mentioned ove, n importnt question is: Wht is the nture of processes tht led to fcilittion when they re re-engged, in stimulus-specific mnner, in reltion to other processes tht my not show such fcilittion? And how does this component process view incorporte other evidence suggesting role for direct stimulus response ssocitions, or episodic records? Some computtionl models hve een used to fit ehviorl priming; such models now need to e extended to the neurl level, to mke contct with the imging nd electrophysiologicl dt descried ove. One importnt question for these models is: Is there single neurl mechnism underlying priming, or multiple mechnisms operting on different sptil nd temporl scles (e.g., long-term potentition/depression, or synptic depression, or even firing-rte dpttion)? A finl importnt question is how priming nd explicit memory, if truly dissocile, nonetheless interct in mny circumstnces. Some hve suggested tht the cuse of priming (often descried s incresed fluency of processing) cn, under some conditions, e utilized y people in order to mke n explicit memory judgment. In other words, people cn

8 1062 Priming LIFG MOG Behviorl priming (ms) Frontl Control Frontl stimultion Neurl priming Neurl priming LIFG MOG TMS loction Control stimultion Figure 5 A trnscrnil mgnetic stimultion (TMS) study of priming. () Using semntic clssifiction tsk like in Figure 4, TMS of left inferior frontl cortex (ut not of control region in left motor cortex) shortly fter initil presenttion of visul ojects reduced susequent ehviorl priming. () TMS of the frontl region olished fmri repetition suppression in tht region when the oject ws susequently repeted ut did not olish repetition suppression in occipitl cortex. LIFG, left inferior frontl gyrus; MOG, middle occipitl gyrus. Adpted y permission of Mcmilln Pulishers Ltd: Nture Neuroscience. (Wig GS, Grfton ST, Demos, nd Kelley WM (2005) Reductions in neurl ctivity underlie ehviorl components of repetition priming. Nture Neuroscience 9: ), copyright (2005) ttriute the feeling of fster/esier processing of stimulus to pst encounter with tht stimulus. A current controversy is whether mnesic ptients cn e encourged or even tught to use such fluency cues to improve their memory judgments. See lso: Cognition: An Overview of Neuroimging Techniques; Declrtive Memory System: Antomy; Electroencephlogrphy (EEG); Memory Representtion; Memory Disorders; Multiple Memory Systems. Further Reding Bdgiyn RD nd Posner MI (1997) Time course of corticl ctivtions in implicit nd explicit recll. Journl of Neuroscience 17: Bowers JS nd Mrsolek CJ (2003) Rethinking Implicit Memory. Oxford: Oxford University Press. Buckner RL, Petersen SE, Ojemnn JG, et l. (1995) Functionl ntomicl studies of explicit nd implicit memory retrievl tsks. Journl of Neuroscience 15: Dhond RP, Buckner RL, Dle AL, Mrinkovic K, nd Hlgren E (2001) Sptiotemporl mps of rin ctivity underlying word genertion nd their modifiction during repetition priming. Journl of Neuroscience 10: Grieli JDE (1998) Cognitive neuroscience of humn memory. Annul Review of Psychology 49: Grf P, Squire LR, nd Mndler G (1984) The informtion tht mnesic ptients do not forget. Journl of Experimentl Psychology: Lerning, Memory nd Cognition 10: Grill-Spector K, Henson R, nd Mrtin A (2006) Repetition nd the rin: Neurl models of stimulus-specific effects. Trends in Cognitive Science 10: Henson RNA (2003) Neuroimging studies of priming. Progress in Neuroiology 70: Jcoy LL (1983) Perceptul enhncement: Persistent effects of n experience. Journl of Experimentl Psychology: Lerning, Memory nd Cognition 9: Logn GD (1990) Repetition priming nd utomticity: Common underlying mechnisms? Cognitive Psychology 22: Moscovitch M (1994) Memory nd working with memory: Evlution of component process model nd comprisons with other models. In: Schcter DL nd Tulving E (eds.) Memory Systems, pp Cmridge: MIT Press. Roediger HL nd McDermott KB (1993) Implicit memory in norml humn sujects. In: Boller F nd Grfmn J (eds.) Hndook of Neuropsychology, vol. 8, pp Amsterdm: Elsevier. Schcter DL (1987) Implicit memory: History nd current sttus. Journl of Experimentl Psychology: Lerning, Memory nd Cognition 13: Schott BH, Henson RN, Richrdson-Klvehn A, et l. (2005) Redefining implicit nd explicit memory: The functionl neurontomy of priming, rememering nd control of retrievl. Proceedings of the Ntionl Acdemy of Sciences of United Sttes of Americ 102: Schott B, Richrdson-Klvehn A, Henson R, et l. (2006) Neurontomicl dissocitionof encoding processes relted to priming nd explicit memory. Journl of Neuroscience 26:

9 Priming 1063 Squire LR (1987) Memory nd Brin. New York: Oxford University Press. Tenpenny PL (1995) Astrctionist versus episodic theories of repetition priming nd word identifiction. Psychonomic Bulletin nd Review 2: Wig GS, Grfton ST, Demos K, nd Kelley WM (2005) Reductions in neurl ctivity underlie ehviorl components of repetition priming. Nture Neuroscience 9: Relevnt Wesite Memory. In Wikipedi: The Free Encyclopedi.