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Review

The N400 potential could index a semantic inhibition

J. Bruno Debruille⁎

Douglas Mental Health University Institute, Montréal, Qc, CanadaDepartments of Psychiatry and of Neurological Sciences, McGill University, Montréal, Qc, Canada

A R T I C L E I N F O

⁎ DouglasMentalHealthUniversity Institute,LeE-mail address: bruno.debruille@douglas.m

0165-0173/$ – see front matter © 2007 Publisdoi:10.1016/j.brainresrev.2007.10.001

A B S T R A C T

Article history:Accepted 6 October 2007Available online 17 October 2007

In this theoretical study, I briefly review some of the first hypotheses as to the functionalsignificance of theN400 potential. I then summarize the view that the amplitude of theN400 isproportional to difficulty and indexes the efforts deployed by thebrain to integrate themeaningof a stimulus in its context.While this view accounts formany literature data, its shortcomingsarealsopointedout. Theneed for various inhibitionprocesses is thenemphasizedtogetherwiththe idea that integration difficulty may vary with the amount of inhibition to be performed.Consequently, I stress the view that N400 amplitude could index inhibition rather thanintegration. The fact that, when presented with incongruous sentence endings, subjects areaware of the meanings of both the sentence frame and the ending has an importantconsequenceon thisN400 inhibitionview. Itmeans thatdisconfirmedcontextsarenot inhibitedin some conditions, such as when incongruency is relevant in the situation. To account for thisfact, the inhibition theN400 could indexhas to start only once this relevance is coded, that is, ator after the activation of situational representations.We then show that the idea that the N400reflects sucha late inhibitionprocessmayaccount for literaturedata thataredifficult to accountfor by the integration view. Further studies are thus needed to test this inhibition idea.

© 2007 Published by Elsevier B.V.

Keywords:Event-related potentialN400DistractorKnowledgeIntegrationActivationInhibition

Contents

1. The ‘second look’ and the ‘spreading of activation’ views of the N400 potential . . . . . . . . . . . . . . . . . . . . . 4722. The integration view of N400. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4733. Introducing knowledge inhibition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4744. Assessing the N400 knowledge inhibition view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4765. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477

1. The ‘second look’ and the ‘spreading ofactivation’ views of the N400 potential

TheN400 event-relatedpotentialwasdescribed for the first timeby Kutas and Hillyard (1980) in response to incongruent

vel1,F.B.CommonPavilioncgill.ca.

hed by Elsevier B.V.

sentence endings, such as ‘He spreads the warm bread withsocks.’N400was proposed to reflect ‘the interruption of ongoingsentence processing by a semantically inappropriate word andthe “reprocessing” or “second look” that occurs when peopleseek to extract meaning from senseless sentences.’

, 6875Boul.LaSalle,Montréal,Qc,CanadaH4H1R3.Fax:+15148884099.

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This early hypothesis was soon abandoned when it wasshown that large N400s could also be evoked by congruent butunexpected sentence endings, such as ‘He was soothed by thegentle wind.’ The more expected the ending is, the smaller theamplitude of the N400 will be (Kutas and Hillyard, 1984).However, expectancy is not the only factor that was found toreduce the N400. This potential also decreases in amplitudewhen there is a semantic relationship between the unexpectedending and the ending that was expected. Thus, the N400selicited by unexpected sentence endings (e.g., ‘He liked lemonand sugar in his coffee,’where ‘coffee’ is semantically related tothe expected ending ‘tea’) were found to be smaller than theN400s elicited by unexpected endings that were not related tothe expected ending (e.g., ‘Don't touch the wet dog,’where ‘dog’is not semantically related to the expected ending ‘paint’) (Kutasand Hillyard, 1984). This reduction of N400 could be viewed asreflecting the smaller semantic activation produced by a wordthathasbeenprecededbywords thathavealready inducedmostof the relevant activations. Therefore, it was proposed that theN400 ‘reflects processes of semantic priming or activation’(Kutas and Hillyard, 1984).

This second hypothesis was consistent with the N400modulations that were observed when recording ERPs inresponse to words outside the context of sentences. Semanticpriming was found to reduce the N400 when words werepresented in isolation (e.g., Bentin et al., 1985). The N400selicited by target words, such as ‘doctor,’ were smaller whenthey were preceded by semantically related words, such as‘nurse,’ than when they were preceded by an unrelated word,such as ‘hat.’ Later, meaningful stimuli other than words, suchas faces, were found to elicit N400-like potentials. Moreover,whenelicited by famous faces (e.g., G.W. Bush) these potentialswere found to be smaller when these faces were preceded byfamous faces of the same semantic category (e.g., W. J. Clinton)(Barrett and Rugg, 1989). As for words, these results could beaccounted for by a semantic priminghypothesis. Indeed, as it isthe casewith lexical representations, semantic activation couldspread from the representation of a face to the representationsof semantically associated faces. Later, N400 effects were alsofound with meaningful stimuli other than words and faces,notably objects and environmental sounds (e.g., Holcomb andMcPherson, 1994; Van Petten and Rheinfelder, 1995). For theseother types of stimuli, similar networks of item representa-tions can also be hypothesized and account for these effects.Semantic activation could spread between these representa-tions within each of these networks.

2. The integration view of N400

One of the findings that challenged this view of semanticactivation spreading within a network of item representationswas the fact that the N400 evoked by one type of stimulus (e.g., aword) can be primed by a stimulus of a different type (e.g., asound from the environment; Van Petten and Rheinfelder, 1995).This implies that the spreading of semantic activation can travelfrom one network to another. Nevertheless, it can also behypothesized that the N400 indexes processes occurring at alevel higher than that of item representations, namely, the levelof ‘world knowledge.’ Indeed, this level can be activated by all

types of meaningful stimuli. According to several influentialmodels (e.g., Kintsch, 1988), comprehension of text is based onthe integration of the knowledge activated by each word into arepresentation of thewhole situation that is depicted by the text.The results of Holcomb (1993) provide support for this post-lexical N400 idea. They show that the N400 priming effect is notmodulated by the degradation of the physical aspect of thestimuluswhereas this variable has an impact at the lexical level.In addition, the same author showed that semantic strategiesknown to affect post-lexical stages of processing have an impacton theN400 effect (Holcomb, 1988). This led to the formulation ofthe ‘knowledge integration effort’ view. ‘The N400 amplitude isassumed to be directly proportional to the effort required by thisintegration process to fit each item into the representation(Holcomb, 1993). This hypothesis gained popularity for severalreasons. First, the speed atwhich people processwritten speech,as indicated by the duration of their eye fixations on each wordwhile reading (i.e., 200–300 ms; e.g., Just and Carpenter, 1987)was seen as too rapid to be reconciled with the view that a latedeflection like the N400 could reflect processes that occur asearly as the lexical ones. A second reason was probably theimpact ofwords occurring early in a paragraph. Thesewords canmodulate the N400s elicited by words occurring at the end of aparagraph if they are of critical importance for the comprehen-sion of the text and therefore for the representation of thesituation (e.g., St.George et al., 1994 and Van Berkum et al., 1999).These distant effects are difficult to understand in the context ofthe idea that theN400 indexes theautomatic spreadof activationwithin the lexicon because the effect of this spread is known tobe short-lasting.

At first sight, the semantic priming effects that have beenobserved in lexical tasks involving isolated words pairs (e.g.,Bentin et al., 1985) appear to be at odds with this post-lexicalview of the N400. Indeed, in these tasks, subjects cannot build arepresentation of the whole situation depicted by the text sincethere isno text but only isolatedwords.Nevertheless, they couldarguably attempt to do so, and knowledge integration could be a‘dumb’ process that occurs even in these tasks because, asproposed by Holcomb (1993), ‘the goal of reading or listening towords is almost always comprehension’ (see Kintsch, 1988 for amore detailed account of a model that includes a ‘dumb’automatic integration process).

However, some results cannot be easily accounted for withthe knowledge integration effort view. Words that are totallyunexpected in a particular sentence but that fit the globalcontext have been shown to elicit little or noN400. For example,very small N400s are elicited by words, such as ‘eat’ in ‘Forbreakfast theeggswouldonly eat…,’or suchas ‘mice’ in ‘Thecatfled from themice…,’ orwords suchas ‘suitcase’ in the sentence‘The woman told the suitcase…’ when this sentence follows atext that mentions a tourist, his suitcase and a woman(Kuperberg et al., 2003; Kolk et al., 2003; Nieuwland and VanBerkum, 2005, respectively). Thesewords,whichareapriori verydifficult to integrate in the representation of the situationdepicted by the sentence, should trigger maximum integrationefforts and thus largeN400s. Finally, the fact that pseudo-words(e.g., ‘toble’) elicit largerN400s than realwords in lexical decisiontasks (e.g., Rugg and Nagy, 1987 and Deacon et al., 2004) alsoseemsproblematic for theknowledge integrationeffort account.Indeed, it remains unclear as to why an item that should not

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activate knowledge to the same degree as a real word wouldtrigger greater knowledge integration efforts.

Still, it is possible that knowledge integration depends on theamount of knowledge that the system is attempting to integrate.Accordingly, the relatively small N400 amplitudes generated bywords such as ‘eat,’ ‘mice’ and ‘suitcase’ in the above examplescould be due to the fact that the information activated by thesewords is indeed not incompatible with the information acti-vated by previous words. Thus, the amount of new knowledgethat they activate and that would have to be integrated remainssmall. As for pseudo-words (e.g., toble), it has been shown thatthey generate N400s in proportion to the degree that theyresemble real words. Pseudo-words that have a number of realword neighbors produce larger N400s than pseudo-words thathave relatively fewer real word neighbors (Holcomb et al., 2002).It may therefore be argued that these N400s elicited by pseudo-words index attempts at integrating the meanings of all thewords that these pseudo-words resemble. The same explana-tion can account for the increasingly large N400s elicited by realwords as a function of the number of their orthographicneighbors (Debruille, 1998; Holcomb et al., 2002).

However, this amount version of the integrationhypothesismay not be compatible with the effect of word frequency.Given that frequent contentwordsoccur in a greaternumber ofcontexts than rare contentwords, it canbe argued that they arerelated to more knowledge. Frequent content words couldtherefore activate a greater amount of knowledge. Accordingly,frequent content words should elicit larger N400s than rarecontent words, but the opposite is true, with frequent wordseliciting smaller N400s than rarewords (e.g., Smith andHalgren,1987; Rugg, 1990; Van Petten and Kutas, 1990). Meanwhile, thishighly replicated finding is easily accounted for by the effortversion of the knowledge integration hypothesis since frequentcontent words are processed faster than rare content words,indicating that they are probably easier to integrate.

Nevertheless, there are circumstances where neither the‘effort’ nor the ‘amount’ version of the knowledge integrationhypothesis seem to work. DeLong et al. (2005) have shown thatarticles such as ‘a’ or ‘an’may elicit N400s and that these N400sare larger insituationswhere expectationsareviolated (e.g., ‘Thedaywasbreezy so theboywentoutside to flya/ankite/airplane’).From the perspective of the ‘amount’ hypothesis, there is noreason to believe that ‘a’ or ‘an’ activatesworld knowledge in thesame way content words do. Accordingly, they should not elicitN400s. Yet, from the perspective of the integration ‘effort’ view,there is no reason to believe that ‘a’ or ‘an’ could cause difficultyin integration and trigger integration efforts. The ease ofintegration of these articles is likely to be at ceiling given that(a) an indefinite article could be expected at that time in thecontextof these sentences, (b) the frequencyof ‘a’and ‘an’ isveryhigh (23,523 occurrences per million for ‘a’; 3747 for ‘an’ in theKucera and Francis, 1967 count) and (c) these articles werepresented a large number of times in the experiment (more than80 times) and repetition can only ease the processing of a word.

1 Of course, this does not mean that the knowledge that otherdogs live as affectionate pet mammals may not be used at a latertime and contrasted with the ‘wild dogs’ situation depicted in thesentence.

3. Introducing knowledge inhibition

In any case, another questionneeds to be addressed: Howdoweselect the knowledge that has to be integrated? Indeed, only a

portion of the knowledge that is activated is integrated in therepresentation of the situation. This can be illustrated in severalways. For instance, the presentation of ambiguous words, suchas ‘bank,’ which has a ‘river’ and a ‘money’ meaning, has beenshown to trigger the (unconscious) activation of bothmeanings.It seems that this double activation occurs even if theambiguous word is presented within a disambiguating context(e.g., ‘The river bank…’; see for instance Gernsbacher et al.,1990).However, the inappropriatemeaning isnot used tobuild arepresentation corresponding to the situation (e.g., the repre-sentation of a river bank). An inhibition (or suppression) processis thought to occur that dampens the level of activation of themeaning incompatible with the context (see for instanceGernsbacher et al., 1990). This process would account for thefact thatwe are only consciously aware of the relevantmeaningof the ambiguousword (for a different view, seeMcNamara andMcDaniel, 2004).

Inhibition could also happen for non-ambiguous wordswhen they activate knowledge that is inappropriate to thecontext. For instance, the word ‘dog’ activates the knowledgethat dogs are affectionate pet mammals. However, this knowl-edge is not the one that has to be used to build a representationof the situation depicted in the sentence: ‘In Australia, packs ofwild dogs attack isolated sheep.’1

Other circumstances are likely to require knowledge inhibi-tion. Words (e.g., bribe) have been shown to activate not onlytheir own representations but also the representations ofwordsthey resemble (i.e., their orthographic neighbor words, e.g.,bride; see for instance Holcomb et al., 2002). Through theseinaccurate lexical activations, words can activate inappropriateknowledge. If this is the case, an inhibition mechanismmay beinvolved to prevent the integration of the inappropriateknowledge. Words that have a greater number of neighborswould then be expected to trigger more inhibition.

Knowledge inhibition could also occur when a category ofmeanings is expected. For example, the sentence frame ‘Hewas eating…’ could activate knowledge related to food in ex-pectation that the last word (e.g., bread) would most likelybelong to this category. If the sentence ending turns out to be anincongruent or a metaphorical ending, such as ‘books,’ the foodknowledgethathadbeenpre-activatedmayhave tobe inhibited.Note that, even if the last word does designate a specific type offood (e.g., bread), it could still be necessary to inhibit theknowledge related to other types of food that may have beenactivated in anticipation of other possible sentence endings.

Like integration, this preparation (or anticipation) could takeplace not only within sentences, but also every time a subject isconfronted with a series of words. The inhibition of inaccurateanticipations could therefore be required even when isolatedwords are presented sequentially, as in a lexical decision task.When such a task includes a lot of related pairs, semanticanticipation processes are ‘boosted’ (Holcomb, 1988; Koyamaet al., 1992) and knowledge corresponding to related itemsmaybe activated. If an unrelated word occurs, this knowledge has tobe inhibited.

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The greater the amount of knowledge that has to beinhibited, the more difficult the integration will be. Therefore,the reason why the amplitude of the N400 appears to vary as afunction of integration difficulty could be that the N400 isgenerated by inhibition processes. Like the integration hy-pothesis, this ‘inhibition’ hypothesis predicts graded N400amplitudes. These amplitudes would depend on the amountof knowledge that is inhibited and on the strength of itsprevious activation: the stronger the activation, the greater therequired inhibition and the greater the N400 amplitude.

However, there are situations where ‘the system decides’not to inhibit inappropriate knowledge. For instance, whenpresented with incongruent sentences, such as ‘He spread thewarm bread with socks,’ subjects are conscious of both themeaning of the incongruous endings and the meaning of thesentence context. Therefore, in this case, the knowledgeactivated by the sentence context is not inhibited despite thefact that it is incompatible with the sentence ending. This isnot so surprising given that, in these protocols, subjects arefully aware that the experimenter is studying their reactionsto congruous and incongruous sentences. To this extent,incongruous sentences also are relevant and thusmeaningful.This ‘global meaningfulness of incongruency in the experi-ment’ can be suggested as the reason for which the sentencecontext is not inhibited.

This suggestion has amajor consequence for the frameworkof reference. Since the relevance of incongruency can be codedonly at the level of the representations of situations, it meansthat at least part of the inhibition of knowledge takes place onlyafter a processing occurs at this level. For instance, in thecongruous/incongruous sentence protocols, the beginning ofthe sentence, because it is congruous, would activate arepresentation coding the occurrence of a congruous sentence.The occurrence of the incongruous sentence endingwould thenactivate the representation coding for the fact that it is anincongruous sentence that was presented. The two situationalrepresentationswould inhibit each other, possibly because theycompete for the coding of the same event. The incongruoussituational representationwould be themost strongly activatedsince it closely corresponds to the stimuli presented. Because ofthis greater level of activation, this representation would ‘win’the ‘reciprocal inhibition competition’ and dampen the level ofactivation of the congruous representation. This inhibitionwould then trigger that of the knowledge corresponding to theexpectedending (e.g., ‘butter’ in ‘Hespread thewarmbreadwithsocks') in a top–down way. All other knowledge would remainactivated since it corresponds to the representation of theincongruous sentence that occurred.

Within that framework, the large N400s that indefinitearticles, such as ‘a’ and ‘an,’ triggered in DeLong et al. (2005)suggest that the inhibition of a situational representation can beinduced not only by another situational representation but alsoby a mismatch, here, between the expected article and thearticle actually presented. That such a physical mismatch cantrigger processing at the level of situational representation isconsistent with the idea that this stage of information proces-sing receives information not only also from the network ofsemantic knowledge but also from all other sources (includingsyntactic and pragmatic sources; see for instance Kintsch,1988). Accordingly, there would be an inhibition of the

representation that codes for the situation: ‘the sentencepresentedmentions a boy flying a kite by a breezy day’, whichis activated by the sentence context ‘The day was breezy sothe boywent out to fly….’This inhibitionwould in turn lead tothe inhibition of the semantic knowledge specifically relatedto ‘kyte.’

The larger N400s elicited by pseudo-words (e.g., toble) thanby real words (e.g., table) could also be accounted for in thesame framework. A pseudo-word would first activate thelexical representation of the word(s) it resembles and, hence,its corresponding knowledge and the situational representa-tion corresponding to the event defined by the occurrence ofthe word ‘table’ in the context of the experiment. Thedetection of the physical mismatch between the representa-tion of the real word and the pseudo-word actually presentedwould trigger the activation of another situational represen-tation: that of the event defined by the occurrence of amisspelled word. The two situational representations wouldcompete and the accurate one would win this competition.The inaccurate one would be inhibited and the inhibition ofthe semantic knowledge corresponding to the real wordwouldensue. Incidentally, it is not possible to specify whether theN400 would reflect the inhibition process itself or its effects onthe areas that code for the knowledge at stake. Both ideasmake the N400 inhibition idea capable of accounting forvarious scalp distributions found across N400 studies.

On the other hand, note that the N400, could, in thetheoretical framework developed, also index the inhibition ofinappropriate situational representations. However, in thepresent study, we will continue naming the hypothesis: theN400 knowledge inhibition hypothesis since the present workis a continuation of Debruille et al. (1996) and Debruille (1998).Nevertheless there are data that can be used to support theidea that the N400 also indexes the inhibition of situationalrepresentations and to support the above idea that thisinhibition would be followed by top–down processes. Whenstudying the N400 elicited by the last word of a paragraph, theglobal situation depicted by the text seems to have an impacton the N400 that is earlier than that of the content word thatimmediately precedes (Camblin et al., 2007; Polse et al., 2007).On the one hand, it may seem exaggerated to propose thatbrain processes would already be at that stage during the firstpart of the N400. But, on the other hand, ERPs seem to dependon the semantic category of the word as early as 200 ms afterthe onset of the word (Hauk and Pulvermuller, 2004; Moscosodel Prado et al., 2006). This suggests that the semanticknowledge corresponding to a word is activated no laterthan 200 ms post onset. There would thus be enough time forthe activation of situational representations.

It can be hypothesized that top-down activations startingfrom the ‘winning’ situational representation would lead toadditional amount of activation of the lower level representa-tions it subsumes: the semantic knowledge and the itemrepresentations. This would ‘help’ these representations toinhibit concurrent representations at their level. Once con-current representations are no longer activated, theywould nolonger be capable of reciprocally inhibiting appropriaterepresentations. These latter representations would thenreach their peak level of activation, which could correspondto consciousness.

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4. Assessing the N400 knowledgeinhibition view

Recently, some consideration has been given to the possibilitythat the N400 potential indexes not only activation but alsoinhibition processes (Barber et al., 2004; Barber and Kutas,2007). However, to the best of our knowledge, only threestudies (Debruille et al., 1996, in press; Debruille, 1998) havebeen specifically built to test the hypothesis that the N400indexes inhibition. Nevertheless, the N400 knowledge inhibi-tion hypothesis could account for the N400 data that weredifficult to reconcile with the knowledge integration effortview. This inhibitionmay provide a reason for the small N400selicited by words that are unexpected but that fit the generalcontext of a sentence (as in Kuperberg et al., 2003; Kolk et al.,2003; Nieuwland and Van Berkum, 2005). The knowledge thesewords activate is compatible with what is activated by thecontext. Therefore, they should not trigger knowledge inhibi-tion. For instance, in the sentence ‘The cat fled from themice…’ (Kolk et al., 2003), the word ‘mice’ is unexpected but itactivates knowledge that is compatible with the knowledgeactivated by ‘fled’ and ‘cat.’

The inhibition view can account for the fact that words thatare more frequently used elicit smaller N400s than words thatare less frequently used (Smith and Halgren, 1987; Rugg, 1990;Van Petten and Kutas, 1990). Similarly, it can account for thesmaller N400s elicited by words that are repeated in anexperiment vs. words that are presented only once (Smith andHalgren, 1987; Rugg, 1990; Van Petten et al., 1991). The brainmakes fewer errors when it is processing stimuli that it is welltrained to process. Inaccurate representations of neighborwords would be less often and/or less strongly activated, andconsequently, less inaccurate knowledge would be activatedor inaccurate knowledge would be less activated. Therefore,there would be less knowledge inhibition for frequent and forrepeated words. Another factor may come into play: the factthat frequent words occur in a greater number of contextsthan rare words. As such, the representation(s) of theknowledge that frequent words activate may be compatiblewith a greater number of situations and knowledge represen-tations. Less inhibition would be necessary for these repre-sentations. As for words that are repeated in an experiment,they may, with each successive presentation, activate lessinappropriate knowledge related to contexts different fromthat of the experiment andmore of the appropriate knowledgeneeded to perform the task at hand. Less and less knowledgeinhibition may be required with each repetition, reflected insmaller N400s.

The greater N400s obtained for the first content words of asentence versus the last words appear, at first sight, less easyto explain within the inhibition perspective. However, it ispossible that a sentence produces anticipations about thenext sentence. For instance, the DeLong et al. (2005) sentence:‘The day was breezy.’ leads to expectations that the nextsentence will have something to do with the wind. If the firstcontent words of the next sentence disconfirm this anticipa-tion, the anticipated knowledge will have to be inhibited.Generally, the beginning of a sentence provides a greateramount of information specifying what the sentence is about

than the end of the sentence. Therefore, the content words atthe beginning of sentences may trigger greater inhibition ofwhat was anticipated than the end of sentences.

In a previous study (Debruille, 1998), we tested one of theaccounts of the knowledge inhibition hypothesis, namely theinhibition of knowledge activated by the eliciting stimulusitself, via inaccurate lexical representations. To achieve thisgoal, we capitalized on the idea that real words activate notonly their own representation but also those of words thatresemble them (for a discussion of the effects of suchactivations, see, for instance, Holcombet al., 2002). Two criticaltypes of infrequent words were used. First, look-alike words,such as ‘BRIBE,’ that have a more frequent word (e.g., ‘BRIDE’)in their orthographic neighborhood (this neighborhood isdefined as all the words that can be created by changing asingle letter of a word). Second, eccentric words, such as‘SIGNAL,’ that do not resemble a more frequent word. Thepresentation of look-alikes was assumed to lead to theactivation of inaccurate knowledge via the activation of therepresentation of the neighbor word. Therefore, look-alikeswere expected to necessitate more knowledge inhibition thaneccentrics. Consistent with the N400 knowledge inhibitionhypothesis, greater N400s were obtained for look-alikes thanfor eccentrics. It was also found that despite the additionalN400 activity they generated look-alike words, such as ‘BRIBE,’did not trigger the perception of the meaning of the neighborword, e.g., BRIDE,’ and did not prime words related to theirneighbor, suchas ‘GROOM,’ thatwereplaced immediately afterthem. This was consistent with the idea that the additionalN400 activity is not indexing the integration of the neighborword.

Nevertheless, the abovementioned results do not allowfor rejection of the integration hypothesis. It could be arguedthat the additional N400 activity generated by look-alikesindexes unsuccessful attempts at integrating the neighborwords. On the other hand, the absence of priming of thewords related to the neighbor, such as ‘GROOM,’ that wereplaced immediately after look-alikes, could be due to the longtime interval (i. e., 2's) that existed between the onset of thelook-alike and the onset of this latter word. Finally, theaforementioned N400 differences obtained between look-alikes and eccentrics were small. This could be due in partto the lexical decision task used in the experiment, a taskknown to produce N400s of intermediate size. Tasks thatfocus on semantic properties, such as a semantic categoriza-tion task, are known to induce larger N400s (e.g., Chwillaet al., 1995; Kounios and Holcomb, 1994; West and Holcomb,2000). Debruille et al. (in press) used task induced modula-tions to test the integration vs. inhibition alternative. Theresults obtained support the inhibition view.

5. Conclusion

This brief theoretical study shows that it may be interesting togive further consideration to the hypothesis that the N400indexes an inhibition that starts at, or after, the activation ofsituational representations. While several theoretical pointsremain to be specified, as mentioned, it is hoped that this studywill triggerexperimentalworksdevoted to the testingof the idea.

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Acknowledgments

The author is supported by scholarship MSH-40304 from theCanadian Institutes for Health Research. This study wasmadepossible by grant 194517-02 from the National Science andEngineering Council of Canada (NSERC) allocated to theauthor who thanks Natalie Phillips and Phil Holcomb fortheir invaluable input.

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