Cognitive Brain Research 17 (2003) 621–635www.elsevier.com/ locate/cogbrainres

Research report

E lectrophysiological evidence for serial sentence processing: aqcomparison between non-preferred and ungrammatical continuations

a , b*Edith Kaan , Tamara Y. SwaabaProgram in Linguistics, University of Florida, Gainesville, FL, USA

bDepartment of Psychology and Center for Mind and Brain, University of California at Davis, Davis, CA, USA

Abstract

Event-related potentials (ERPs) were used to address a much debated issue in sentence processing research, namely whether one ormultiple interpretations are pursued in case of syntactic ambiguities. For example in the syntactically ambiguous fragment ‘‘The man ispainting the house and the garage . . . ’’, ‘and’ either connects ‘the house’ and ‘the garage’, or conjoins two clauses (e.g., ‘‘The man ispainting the house and the garage is already finished’’). According to serial models, only one syntactic interpretation (the simplest) ispursued first (the first interpretation in the example). If this interpretation is incompatible with subsequently incoming words, the syntacticanalysis of the preceding sentence fragment is revised. In contrast, parallel models propose that multiple interpretations of the ambiguityare pursued simultaneously. The two models were tested by comparing ERPs to words that were either ungrammatical, or grammatical butnon-preferred continuations of the preceding sentence fragment. In a serial model, these two are not distinguished until after initialrevision; in a parallel model, a distinction can be made at an early stage. The results supported a serial model: both with an acceptabilityjudgment and a passive reading task a left lateralized negativity was found for ungrammatical and non-preferred continuations relative tounambiguous grammatical continuations, which indicates that ungrammatical and non-preferred continuations were initially processed inthe same way. However, in later time intervals, the ERPs to the ungrammatical continuation showed a posterior positivity (P600), whereasthe ERPs to the non-preferred continuation had a more anterior focus, which indicates that they were processed differently. 2003 Elsevier B.V. All rights reserved.

Theme: Neural basis of behaviour

Topic: Cognition

Keywords: Sentence processing; Serial parsing; Parallel parsing; Reanalysis; P600; LAN

1 . Introduction clauses, as in ‘‘The man is painting the house and thegarage is already finished’’). Ambiguities in sentence

Language is full of ambiguities, at the word level (e.g., structure have led to an important question in sentence‘bank’), but also at the level of sentence structure (e.g., processing research, namely how the sentence processor,‘‘The man is painting the house and the garage. . . ,’’ in or parser, deals with syntactic ambiguities such as thewhich ‘and’ either connects two noun phrases, or two above. Specifically, does the parser pursue one or more

syntactic interpretations at the point of ambiguity? Andhow does it recover from incorrect syntactic analyses? To

qDue to the personal relationship of the Editor ofCognitive Brain address these questions, two classes of models have beenResearch, Dr. G.R. Mangun, with one of the authors of this paper, the

proposed: serial models[3,4], and parallel modelsEditor-in-Chief of the Brain Research family of journals, Dr. F.E.[11,14,23,33].It has been extremely hard to empiricallyBloom, served as Editor for the paper.

*Corresponding author. Brain Imaging and Analysis Center, Room distinguish these two views[13]. Most research thus far163, Bell Building, Duke University Medical Center, Box 3918, Durham, has focused on processing in the ambiguous region itselfNC 27710, USA. Tel.:11-919-681-9345; fax:11-919-681-7033.http: [32,36]. In this paper another approach is taken, namely to/ /www.biac.duke.edu/people/staff.asp?login5kaan. Starting December,

investigate what happens if a sentence fragment is con-2003: Program in Linguistics, University of Florida, Box 115454,tinued in a way that is not compatible with the (preferred)Gainesville, FL 32611, USA.

E-mail address: kaan@duke.edu(E. Kaan). analysis of the ambiguous sentence fragment thus far

0926-6410/03/$ – see front matter 2003 Elsevier B.V. All rights reserved.doi:10.1016/S0926-6410(03)00175-7

622 E. Kaan, T.Y. Swaab / Cognitive Brain Research 17 (2003) 621–635

[26,35]. Serial and parallel models make different predic- analysis. In the unambiguous case, however, no or verytions in how the parser deals with this type of continuation, few alternative analyses of the preceding sentence frag-especially in the early stages of parsing. The aim of the ment are possible, hence the parser may decide ratherpresent study is to use the high temporal resolution of quickly that the sentence cannot yield a correct representa-event related potentials (ERPs) to investigate this early tion.parsing stage, and to help distinguish among serial and Parallel models[11,14,23,33]entail a different view ofparallel models. how incompatible input is dealt with. A parallel parser

maintains multiple analyses in memory that are compatible1 .1. Serial and parallel models with the words encountered thus far. The alternative

interpretations are often ranked on the basis of syntacticIn a serial model, the sentence processor pursues only complexity, frequency information or memory load, among

one analysis in the case of syntactic ambiguity. For other factors[11,33]. A parallel model would thereforeinstance, in the example ‘‘The man is painting the house pursue at least two readings of ‘‘The man is painting theand the garage. . . ’’ the initial reading chosen is the one in house and the garage,’’ with the reading in which ‘and’which ‘and’ connects ‘the house’ and ‘the garage’. This connects ‘the house’ and ‘the garage’ being ranked higherinitial choice is determined on the basis of parsing than the reading in which ‘and’ connects two clauses. Inprinciples (e.g., minimal attachment)[5], frequency, or contrast to the serial diagnosis model, parallel modelsother factors. Because only one reading is pursued, it predict an early processing difference between non-pre-occasionally happens that the sentence is continued in a ferred and ungrammatical continuations of the precedingway that is not compatible with the analysis chosen, e.g., sentence fragment. A non-preferred continuation, such aswhen the next word is a verb, as in ‘‘The man is painting ‘is’ in ‘‘The man is painting the house and the garage is’’

]the house and the garage is . . . .’’ How does the parser deal is compatible with at least one of the alternative analyses

]with this? According to the serial diagnosis model pro- maintained in memory. In this case, the matching alter-posed by Fodor and Inoue[3,4], the incompatible word is native analysis is activated to become the top mostcombined with the existing analysis anyway, resulting in a representation in the memory stack. However, in the casesyntactically incorrect representation. The error thus of ungrammatical continuations of either unambiguous andcreated will lead to reanalysis, that is, the analysis of the ambiguous sentence fragments, such as ‘are’ in ‘‘The manpreceding sentence fragment will be modified to see if the is painting the house but /and the garage are . . . ’’ there is

]current word can be a grammatical continuation after all. no compatible analysis available in the memory. Hence, inThe diagnosis model makes two predictions. First, the contrast to serial models, parallel models do expect an

]parser can initially not distinguish between, on the one early processing difference between non-preferred andhand, a grammatical continuation that is incompatible with ungrammatical continuations. Second, and in contrast tothe analysis pursued thus far, but that is compatible with a the serial diagnosis model, parallel models do not predictdifferent analysis of the sentence, and, on the other hand, differences between ungrammatical continuations in am-an ungrammatical continuation that is not compatible with biguous versus unambiguous contexts with respect to theany possible analysis of the preceding fragment. Only after later revision processes, because no compatible analysis isthe initial integration and revision stage will the difference maintained in working memory for either ambiguous orbecome clear. Hence, initially, no difference is expected unambiguous contexts.between non-preferred continuations such as ‘is’ in ‘‘Theman is painting the house and the garage is’’ and un- 1 .2. Event-related potentials

]grammatical continuations, such as ‘are’ in ‘‘The man ispainting the house and the garage *are.’’ Only later in the In this study we tested the above predictions using

]revision stage is a difference expected among these types ERPs. ERPs have been shown to be sensitive to syntacticof continuation: revision will yield a syntactically correct manipulations. Two components are especially relevant forsentence in case of a non-preferred continuation, but an the present study. The first is the P600 or ‘syntacticincorrect analysis in case of an ungrammatical continua- positive shift’, a positive deflection starting at around 400tion. ms. The P600 has been elicited by words that are un-

The second prediction is that it may take the parser grammatical continuations of the preceding sentence frag-longer to revise ungrammatical continuations if the preced- ment[17,40], words that are non-preferred but grammati-ing sentence fragment is ambiguous (multiple analyses cal continuations[40], or words that are complex continua-possible: e.g., ‘‘The man is painting the house and the tions[28]. The P600 component has been associated withgarage *are. . . ’’), than when it is unambiguous (only one later stages of parsing: failure of a parse[19], reanalysis

]analysis possible, e.g., ‘‘The man is painting the house but and repair[6], or syntactic integration difficulty in general

]the garage *are. . . ’’). This is because there are more ways [28].

]to revise the sentence in the ambiguous case, hence, when The second syntactic component of interest here is thethe first revision fails, the parser may try a different left anterior negativity (LAN). The typical distribution is

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left frontal (e.g., Refs.[1,8,10,37,42]), although a bilateral support of parallel parsing[8]. However, in these studiesor left central distribution has been reported as well the ambiguity can be said to involve a lexical ambiguity,[7,10,38]. In general, LAN effects have been attributed to which is known to be processes in parallel, at leastsyntax-specific processes, although some have argued that temporarily[45], and the point of disambiguation followedthese effects may reflect non-syntax specific working the onset of the ambiguity rather rapidly. A different studymemory processes[1,31,44]. Evidence in favor of the using morpho-syntactic ambiguities found an early ERPsyntax-specificity of LAN effects comes from a number of difference for non-preferred versus ungrammatical con-studies. The LAN has been observed between 100 and 500 tinuations[26], which can interpreted in support of a serialms after onset of words that are ungrammatical continua- model. However in this study, the ambiguous region maytions of the preceding sentence fragment (e.g., Refs. have been too long even for a parallel model to retain a[1,8,10,37,42]). An early LAN has been reported between non-preferred analysis[2,12].100 and 200 ms for phrase structure violations, mainlyusing auditory presentation[10,22,39]. Friederici [6] as- 1 .3. The present studysociates the early LAN with phrase structure buildingprocesses that occur at an early stage of parsing. A LAN To further test whether structural ambiguities are pro-with a later onset, typically between 300 and 500 ms, has cessed in serial (diagnosis model) or parallel we employedbeen associated with morphosyntactic processing (agree- an ambiguity that does not involve ambiguity of lexicalment) (e.g., Refs.[1,16,42]). However, a LAN in this time meaning, in particular ‘and’ conjunction ambiguities. Inwindow has also been observed for phrase structure addition, the onset of the ambiguity and the point ofviolations [8,19,20,40],suggesting that it is also sensitive disambiguation were separated by only one noun phrase toto early stages of processing. increase the likelihood that multiple structures are still

LAN effects can be used for the present purpose, since activated as predicted by parallel models. The paradigm isthey can be used to determine whether non-preferred and illustrated inTable 1.ungrammatical continuations of sentences are initially The critical word, to which we compared the ERPs, isprocessed the same (serial diagnosis model), or differently the verb in the second clause (underlined inTable 1). The(parallel models). In a serial model, the parser will initially ‘But’ grammatical condition is the baseline condition. Heretry to combine both non-preferred and ungrammatical the verb is a grammatical continuation of an unambiguouscontinuations with the preferred analysis of the preceding sentence fragment. In the ‘And’ non-preferred conditionfragment. This leads to an error, which in turn leads to the conjunct is ‘and’ rather than ‘but’. This renders therevision of the structure. Hence, in a serial model, both sentence ambiguous up to the critical verb. The preferrednon-preferred and ungrammatical continuations will elicit a interpretation is one in which ‘and’ combines the two nounLAN relative to an unambiguous, grammatical control. In a phrases ‘the house’ and ‘the garage’[5,18,24,25]. Theparallel model, ungrammatical and non-preferred continua- underlined verb is therefore a non-preferred continuationtions differ at an early stage, which will be reflected in a of an ambiguous fragment. The verb in the ‘But’ un-difference with respect to the LAN: the non-preferred grammatical condition is an ungrammatical continuation ofcontinuation is compatible with one of the analyses an unambiguous fragment, since it does not agree inretained in parallel, whereas no analyses are compatible number with the preceding subject noun phrase; the verb inwith an ungrammatical continuation. Some previous the ‘And’ ungrammatical condition is an ungrammaticalstudies that compared ungrammatical with non-preferred continuation of an ambiguous fragment.continuations have reported a negativity for ungrammatical If parsing is serial and revision proceeds according toconditions only [8,40,41], which can be interpreted in the diagnosis model, it is predicted that the critical verbs in

T able 1Examples of the experimental conditions

aCondition Examples

‘But’ grammatical The man is painting the house but the garage is already finished.]

The man borrowed the hammer but the pliers were in his toolbox.]

‘And’ non-preferred (grammatical) The man is painting the house and the garage is already finished.]

The man borrowed the hammer and the pliers were in his toolbox.]

‘But’ ungrammatical The man is painting the house but the garage are already finished.]

The man borrowed the hammer but the pliers was in his toolbox.]

‘And’ ungrammatical The man is painting the house and the garage are already finished.]

The man borrowed the hammer and the pliers was in his toolbox.]

a The critical word is underscored for the purpose of illustration.

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the ‘And’ non-preferred, ‘But’ ungrammatical and ‘And’ 1. To ensure that the ‘And’ and the ‘But’ versions did notungrammatical conditions will all show a LAN component differ significantly in terms of plausibility, we conducted arelative to the ‘But’ grammatical condition because the paper and pencil rating study on the grammatical versionverb is initially attached to the current phrase marker, of 200 potential experimental items. A comma was in-leading to first pass parsing difficulty in all three cases. serted before ‘and’ or ‘but’ to render all versions un-This LAN effect may differ slightly between the ‘And’ and ambiguous. The 200 items were split into four main lists ofthe ‘But’ ungrammatical conditions due to the nature of the 50 items, with each list having two counterbalancedviolation [1]: initial attachment of the verb will yield a sublists with 25 ‘And’ items and 25 ‘But’ items. Itemsphrase structure violation in both ‘And’ conditions, but a were randomly interspersed among 50 distracter items,subject–verb agreement violation in the ‘But’ ungrammati- which were of the same structure as the potential ex-cal condition. A parallel model, on the other hand, predicts perimental items, but were mildly implausible, for instancea difference between the ‘And’ non-preferred continuation ‘‘The team won the championship, but the fans wereand the two ungrammatical continuations: the former is thrilled’’. Participants were asked to rate each item on acompatible with one of the alternative analyses retained in scale from 1 (odd) to 5 (natural), with ‘natural’ meaningworking memory, whereas no compatible alternative parse ‘plausible, expressing a natural situation, and with ais available in the ungrammatical conditions, resulting in straightforward relation between the first and secondproblems during early stages of parsing. This would result clause.’ Each of the eight lists was rated by 14 to 16 nativein a LAN component to the verb in the ungrammatical speakers of English (121 participants in total). Participantsconditions, but not in the ‘And’ non-preferred condition. received credit for completing the questionnaire.Second, both parallel and serial models predict that these On the basis of the ratings thus obtained, 160 items werethree anomalous conditions (‘And’ non-preferred, ‘And’ selected to be used in the ERP study. Criteria for selectionungrammatical and ‘But’ ungrammatical) will show a were that both the ‘And’ and the ‘But’ versions hadP600 in the later intervals. Under the serial diagnosis plausibility scores higher than 2, and the absolute differ-model the P600 may be larger or longer lasting for the ence between the two versions was smaller than 1 [meanambiguous ‘And’ ungrammatical than for the unambiguous plausibility: ‘but’: 3.78 (S.D. 1.12); ‘and’ 3.69 (S.D. 1.18);‘But’ ungrammatical condition, because the parser may try T-testP50.21]. The 160 selected items were divided intovarious ways to revise the sentence in the ambiguous case four groups such that the four groups did not differ(as reflected by the P600), before it determines that the statistically in: (1) the mean plausibility rating for thesentence cannot be repaired. In parallel model no clear ‘And’ versions and the ‘But’ versions, (2) the difference inpredictions are made with respect to the effect of am- plausibility between the ‘But’ and the ‘And’ versions, andbiguity on the P600 for ungrammatical continuations. (3) the number of words before the critical verb. To

These predictions were tested in two experiments: in balance the number (singular /plural) of the critical verbexperiment 1 an acceptability judgment task was used; in within and across conditions, 20 items in each of the fourexperiment 2, no additional task was used. This task groups were slightly changed. No further pretesting wasmanipulation was included to make sure that the results of done. A complete list of materials can be found athttp:experiment 1 could not be attributed to possible effects of / /www.biac.duke.edu/people/staff.asp?login5kaan. Fourthe acceptability judgment task on the way in which experimental lists were created by presenting each of theparticipants processed the sentences. four item groups in a different condition within a list, and

varying the condition assignment over the four lists. In thisway, each list contained 40 sentences for each of the four

2 . Materials and methods: experiment 1 conditions, no item was seen more than once in each list,and each item appeared in a different condition across the

2 .1. Participants four lists. Within each list, the four conditions did notdiffer statistically in the plausibility ratings of the items. In

Twenty participants (six men, age 18–31 years, mean addition, 160 distracter items were created. In 80 items, the21.6 years) took part in the experiment, either paid or for conjunct ‘and’ was used to conjoin two direct object nouncredit. None had participated in the materials pretest phrases. This was to avoid that participants developed adescribed below. All were right handed, monolingual strategy that ‘and’ conjoins two clauses in the experimentalnative speakers of English and were undergraduate or items. The other 80 items contained the word ‘but’. Half ofgraduate students at Duke University. All had normal or the distracter items contained a semantic or pragmaticcorrected to normal vision, and had not suffered from anomaly. The order of experimental and distracter itemsneurological disease or trauma. Participants gave informed was pseudo randomized with the restriction that eachconsent before the experiment. experimental item was preceded by a distracter item.

The 320 sentences were divided into 10 blocks of 322 .2. Materials items, with each block containing four sentences of each

experimental condition and distracter type. The order ofQuadruplets were created of the form illustrated inTable the blocks was different for each participant.

E. Kaan, T.Y. Swaab / Cognitive Brain Research 17 (2003) 621–635 625

2 .3. Procedure

Participants were tested individually in a sound-attenuat-ing booth. Participants were seated in a comfortable chair,about 1 m in front of a computer screen. Sentences werepresented visually, word-by-word. To help the participantsfixate, two horizontal bars were presented in the center ofthe screen during the entire experiment. Words werepresented between the two horizontal bars (white lettersand bars on black background) at a rate of 300 ms perword (500 ms SOA). After the last word of a sentence, thewhite bars remained on the screen for 1500 ms, after whichthey turned blue and a question mark was presented for1000 ms with the words ‘ok’ and ‘bad’ on either side. Theblue bars remained on the screen for 5500 ms. Next thebars turned white again, and 1000 ms later the first word ofthe next sentence was presented. Participants were in-Fig. 1. Overview of the electrode positions and regions used forstructed not to blink or move their eyes while the fixation statistical analysis. Positions that do not correspond to 10-20 locationsbars were white. They were requested to judge each have an additional letter to indicate their position relative to the nearest

10-20 location (‘i’ inferior; ‘s’ superior, ‘a’ anterior, ‘p’ posterior).sentence for semantic and syntactic plausibility by pressinga button on a button box at the question mark. It waspointed out that structures that were infrequent, thoughgrammatically correct were to be regarded as acceptable2 .5. Data analysissentences of English. To familiarize the participants withthe procedure, a practice block was run with six items (two 2 .5.1. Behavioral datasemantically implausible, one syntactically implausible), Behavioral responses were considered valid if thenone of which had the structure used in the experimental response latency was between 0 and 3000 ms after onset ofmanipulation. Feedback was given after the practice block the question mark prompt, and if no other responseif the participants made any errors. No feedback was given occurred within that time window. Multivariate analyses ofduring the actual experiment. On average the experiment variance (MANOVAs) with sentence type (four levels) astook 2 h and 50 min per participant, including preparation within subject factor were carried out on the percentage ofand debriefing. correct responses, and on response latencies to correct

responses only. We conducted planned comparisons using2 .4. ERP recording Helmert contrasts to see whether the performance on the

three anomalous experimental sentence types differed fromEEG was recorded from 59 Sn scalp electrodes, the ‘But’ grammatical condition; whether the ‘And’ non-

mounted in an elastic cap. The position of the electrodes is preferred condition differed from the two ungrammaticaldisplayed in Fig. 1. Electrode positions that do not conditions, and whether there was a difference between thecorrespond to positions according to the 10-20 system have two ungrammatical conditions.an additional letter to indicate their position relative to thenearest 10-20 location (e.g., Ozi is inferior to Oz; Ozs is 2 .5.2. Event-related potentialssuperior to Oz; C1p is posterior to C1; P3a is anterior to Epochs comprised the 200 ms preceding, and 1500 msP3; T3-5i is inferior to the position midway between T3 following the onset of the critical verb. Trials withand T5; T4-6i is inferior to the position midway between excessive eye movements or drift were rejected fromT4 and T6). Horizontal EOG was recorded bipolarly from analysis. This was 7.2 to 9.8% of the data per condition.electrodes placed on the left and right outer canthus. Data were filtered off-line using a Gaussian low-pass filterVertical EOG was recorded bipolarly from two frontal with a 25 Hz half amplitude cutoff. All trials were takenelectrodes on the cap (Ep1m and Ep2m inFig. 1), and into consideration regardless of the participant’s responseelectrodes placed below the left and right eyes. An on the acceptability judgment task. However, an analysiselectrode placed on the right mastoid served as reference. on correct responses only did not qualitatively differ fromAn additional electrode was placed on the left mastoid. the analysis reported below. ERPs were quantified as theAfter off-line data averaging the signal was arithmetically mean amplitude relative to a 100 ms prestimulus baseline,re-referenced to the mean of the right and left mastoids. using the following latency windows: 100–200 ms (earlyImpedance was kept below 5 kV for mastoid and scalp LAN); 200–300 ms (P2); 300–400 ms (LAN effect),electrodes, and below 10 kV for EOG electrodes. The 500–700 ms (early P600); 700–900 ms (mid P600), andsignal was sampled at 250 Hz, and bandpass filtered 900–1100 ms (late P600), based on the literature andbetween .01 Hz and 30 Hz. visual inspection.

626 E. Kaan, T.Y. Swaab / Cognitive Brain Research 17 (2003) 621–635

Four regions were defined containing five electrodes for 3 .2. Electrophysiological dataeach hemisphere indicated inFig. 1: frontal (channelsleft / right hemisphere: F3s/F4s, FC1/FC2, F3a/F4a, F7a/

3 .2.1. Effects before 300 msF8a, F3i /F4i), central (C1a/C2a, C1p/C2p, C3a/C4a,No differences in the ERPs were found before 300 ms,C39 /C49, C5a/C6a) parietal (P19 /P29, PO1/PO2, P3a/

except for a sentence type by region interaction betweenP4a, P3i /P4i, C5p/C6p) and occipital (O19 /O29, O1i /O2i,100 and 200 ms [F(9,11)54.60;P,0.01]. This was due toTO1/TO2, T3-5i /T4-6i, Ti1 /Ti2). To assess the LANthe fact that the ‘And’ ungrammatical condition was moreeffect, we conducted an SPSS repeated measurement GLMnegative than the ‘But’ ungrammatical condition at frontalon the frontal and central regions, where the LAN is foundsites, but was more positive at occipital sites.to be maximal[1,7], with sentence type (four levels) and

hemisphere (two levels) as within-subject factors. Helmertcontrasts were used to test (1) the effect of anomaly (‘But’ 3 .2.2. LAN effectgrammatical versus the mean of the remaining three

Between 300 and 400 ms the ‘And’ non-preferred,conditions); (2) the effect of non-preferred versus un-

‘And’ ungrammatical and ‘But’ ungrammatical conditionsgrammatical continuations (‘And’ non-preferred versus the

showed a negativity relative to the ‘But’ grammaticalmean of ‘But’ ungrammatical and ‘And’ ungrammatical),

condition (Fig. 2).and (3) the effect of ambiguity on the processing of

Helmert contrasts showed that the negativity for theungrammatical continuations (‘But’ ungrammatical versus

anomalous conditions (‘And’ non-preferred, ‘But’ ungram-‘And’ ungrammatical). To investigate the P600 and effects

matical, ‘And’ ungrammatical) was significant relative topreceding 300 ms, the factor region (four levels) was

the ‘But’ grammatical condition in the central regionincluded as a within-subject factor. An additional SPSS

[F(1,19)55.96; P,0.05]. This negativity was largest inrepeated measurements GLM was carried out on midline

the left hemisphere [F(1,19)54.45, P,0.05]. Pairwiseelectrodes, with the factors sentence type (four levels) and

comparisons restricted to the left central region showed aregion (four levels: frontal electrodes Fza and Fzp; central

significant negativity for the ‘And’ non-preferredCza and Cz; parietal Pzs and Pzi; occipital Ozs and Ozi).

[F(1,19)55.49,P,0.05], ‘But’ ungrammatical [F(1,19)5When the interaction of a particular sentence type contrast

5.00, P,0.05], and ‘And’ ungrammatical conditionsand region and/or hemisphere was significant, additional

[F(1,19)55.31,P,0.05] relative to the ‘But’ grammaticalanalyses were carried out to assess the nature of the

condition. InFig. 2, the negativity extends to parietal sites,interaction. Differences in scalp distribution were assessed

but the negativity was not significant in this region. Noas described below.

differences were found for the non-preferred versus un-grammatical conditions, or between the ungrammaticalconditions (F values,1).

3 . Results

3 .2.3. P6003 .1. Behavioral data Starting at around 500 ms the ‘And’ non-preferred,

‘And’ ungrammatical and ‘But’ ungrammatical conditionThe mean latency for correct responses, and the meanshowed a positivity relative to the ‘But’ grammatical

percentage of correct responses are given inTable 2.The condition, (Fig. 3). The results of the planned comparisonsfour conditions did not differ significantly in response between the sentence types for the 500–700, 700–900 andaccuracy [F(3,17)51.42, P50.27]. Planned comparisons 900–1100 ms intervals are given inTable 3.showed that the ‘And’ non-preferred condition was re-sponded to more slowly than the two ungrammaticalconditions taken together [F(1,10)55.83, P,0.05]. No 3 .2.3.1. Effect of anomaly: ‘ But’ grammatical vs. otherother differences in accuracy or response latency wereconditions. The anomalous conditions (‘And’ non-prefer-significant. red, ‘But’ ungrammatical, ‘And’ ungrammatical) showed a

T able 2Behavioral results (experiment 1)

BUT ‘And’ BUT ANDgrammatical non-preferred ungrammatical ungrammatical

aReaction time (ms) 642 (42) 671 (48) 568 (42) 593 (26)Percentage correct (%) 87.1 (1.9) 81.8 (3.4) 89.9 (1.8) 88.4 (2.0)a Mean latencies for accurate responses only; standard error in parentheses.

E. Kaan, T.Y. Swaab / Cognitive Brain Research 17 (2003) 621–635 627

Fig. 2. Experiment 1 (acceptability judgment). ERPs to the critical verb for the C3a (left central) and C4a (right central) electrodes. (A) ‘And’non-preferred (dashed line) versus ‘But’ grammatical (solid line); (B) ‘But’ ungrammatical (dashed line) versus ‘But’ grammatical (solid line); (C) ‘And’ungrammatical (dashed line) versus ‘But’ grammatical (solid line). The LAN effect is indicated with an arrow. Negative is plotted up in this and the nextfigures. The isovoltage maps depict the mean difference for the 300–400 ms interval for each comparison.

positivity relative to the ‘But’ grammatical condition in all significant interaction of sentence type and region spanningthree intervals covering the 500 to 1100 ms time window. the 500 to 1100 ms time windows for this contrast.

Furthermore, the positivity was larger in the right than the3 .2.3.2. Effect of non-preferred vs. ungrammatical left hemisphere for the ungrammatical conditions, yieldingcontinuations. The positivity for the ungrammatical con- a sentence type by hemisphere interaction in the 700–900ditions was significantly larger compared to the non-pre- and 900–1100 ms intervals. To test whether the dis-ferred conditions at midline sites in the 500–700 ms tributional differences of the positivity between the un-interval, and at both midline and lateral sites in the 700– grammatical conditions and ‘And’ non-preferred condi-900 and 900–1100 ms intervals. Furthermore, the positivi- tions were not an artifact of amplitude differences[34] wety in the ungrammatical conditions was largest at central conducted a GLM MANOVA on thez-score scores of theand parietal sites, whereas the ‘And’ non-preferred con- difference waves (‘And’ non-preferred minus ‘But’ gram-dition was more anteriorly distributed. This yielded a matical; ‘And’ ungrammatical minus ‘But’ grammatical;

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Fig. 3. ERPs to the critical verb for a midline frontal (Fzp) and parietal (Pzi) electrode in experiment 1 (acceptability judgment). (A) ‘And’ non-preferred(dashed line) versus ‘But’ grammatical (solid line); (B) ‘But’ ungrammatical (dashed line) versus ‘But’ grammatical (solid line); (C) ‘And’ ungrammatical(dashed line) versus ‘But’ grammatical (solid line). The late positivity is indicated with an arrow. The isovoltage maps depict the mean difference for the700–900 and 900–1100 ms intervals for each comparison.

‘But’ ungrammatical minus ‘But’ grammatical)[43]. The grammatical difference waves (midline:P values,0.001;interaction of sentence type by region remained significant lateral sites: 500–700 ms:P,0.05; 700–900 and 900–under this correction for all three time windows for the 1100 ms:P values ,0.001). Also the interaction with‘And’ non-preferred minus ‘But’ grammatical difference hemisphere remained significant in the 900–1100 mscompared to the mean of the ‘And’ ungrammatical minus interval [sentence type by hemisphere:F(1,19)512.21,‘But’ grammatical, and ‘But’ ungrammatical minus ‘But’ P,0.01]. This suggests that processing the ‘And’ non-

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T able 3Significant Helmert contrasts for the intervals covering the late positivity, experiment 1

Contrast Region Effect 500–700 ms 700–900 ms 900–1100 ms(df51,19) F F F

‘But’ grammatical vs. Midline C 30.80** 30.57** 19.15**aother anomalous C3R 5.081 19.87** 13.04*

Lateral C 24.29** 27.04** 17.21*a bC3R 27.44** 7.901 12.25*

C3H – 17.68** 5.461

Non-preferred vs. Midline C 4.421 7.501 6.611aungrammatical C3R 17.17* 44.58** 45.14**

cLateral C 3.47 7.481 7.741aC3R 6.241 31.06** 32.83**

C3H – 6.721 20.85**

‘And’ vs. ‘But’ Lateral C3H – 4.901 –aungrammatical C3H3R 5.601 – –

1 P,0.05; * P,0.01; ** P,0.001; – N.S.; C5contrast; R5region, H5hemisphere.a Involves the contrast testing the linear differences among the regions, unless noted otherwise.b Involves the contrast testing the quadradic pattern of region.c P50.07.

preferred and the ungrammatical continuations imply ungrammatical continuations as being structurally anomal-different neural mechanisms in these later time windows. ous, regardless of whether the context is ambiguous, orHowever see Ref.[46] for a word of caution on rescaling. whether eventually a correct analysis is possible. Only the

later stages of processing are different for the conditions.3 .2.3.3. Effect of ambiguity on ungrammatical This supports the view that the ‘and’ ambiguities arecontinuations. The positivity to the ‘But’ ungrammatical processed in a serial way. However, it cannot be excludedcondition was slightly smaller at left frontal sites than to that the present results were confounded with the accep-the ‘And’ ungrammatical in the 500–700 and 700–900 ms tability judgment task, which may have caused the par-intervals. Only the sentence type by hemisphere by region ticipants to process the critical verbs in a specific way. Tointeraction in the 500–700 ms window remained signifi- test potential effects of task, we omitted an explicit task incant after rescaling [F(1,19)56.65, P,0.05]. the next study.

4 . Discussion5 . Experiment 2: materials and methods

The aim of the experiment was to directly comparenon-preferred and ungrammatical continuations of a pre- 5 .1. Participantsceding ambiguous or unambiguous sentence fragment toasses the issue of serial versus parallel parsing. As Thirty-two new participants (17 male, age 18–30 years,predicted by the serial diagnosis model, relative to the mean 21 years, all right handed) from the same subject‘But’ grammatical continuation, the non-preferred, ‘And’ pool took part in the experiment, either paid or for credit.ungrammatical and ‘But’ ungrammatical continuations Participants gave informed consent before the experiment.elicited a LAN effect, which was indistinguishable be-tween these conditions, and indicates that these threecontinuations were all initially processed as ungrammati- 5 .2. Materials, procedure and analysiscal. Only at later stages of processing was there adifference between non-preferred but grammatical, and Materials, procedure and analysis of the electrophysio-ungrammatical conditions as indexed by the positivity after logical data were the same as described for experiment 1,500 ms: the positivity had an anterior distribution for the except for the participants’ task. Participants were asked to‘And’ non-preferred condition, but was larger and had a read the sentences attentively (the question mark promptposterior maximum in the ungrammatical conditions, cf. was omitted). A practice block of six sentences, includingRef. [18]. In addition an effect of ambiguity was seen on one inplausible, was presented to familiarize the particip-the distribution of the positivity in the ungrammatical ants with the procedure. In the final averaging, 8.1–9.2%conditions in the 500–700 ms interval. These results of the data in each condition was lost due to eye move-suggest that the parser initially treats non-preferred and ments and other artifacts.

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6 . Results conditions showed an anterior negativity between 300 and400 ms, which was larger in the left hemisphere. In

6 .1. Effects before 300 ms contrast to experiment 1, no negativity was found for the‘But’ ungrammatical condition (Fig. 4).

The only difference found before 300 ms was a sentence The Helmert contrast testing the effect of anomalytype by region interaction between 200 and 300 ms (‘But’ grammatical versus ‘And’ non-preferred, ‘But’[F(9,23)54.06,P,0.01]. This was caused by the ERPs to ungrammatical and ‘And’ ungrammatical) showed a sig-the ‘But’ ungrammatical condition being more positive nificant interaction of sentence type and hemisphere in thethan to the other three conditions, especially at especially central region [F(1,31)56.43, P,0.05]. Pairwise com-at frontal sites. parisons restricted to the left hemispheric sites in the

frontal and central regions showed that the negativity6 .2. LAN effect relative to the ‘But’ grammatical condition was significant

for the ‘And’ ungrammatical condition [frontal:F(1,31)5Both the ‘And’ non-preferred and ‘And’ ungrammatical 11.19,P,0.01; central:F(1,31)58.50, P,0.01], margi-

Fig. 4. ERPs to the critical verb for the C3a (left central) and C4a (right central) electrodes in experiment 2 (passive reading). (A) ‘And’ non-preferred(dashed line) versus ‘But’ grammatical (solid line); (B) ‘But’ ungrammatical (dashed line) versus ‘But’ grammatical (solid line); (C) ‘And’ ungrammatical(dashed line) versus ‘But’ grammatical (solid line). The LAN effect is indicated with an arrow. The isovoltage maps depict the mean difference for the300–400 ms interval for each comparison.

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nally significant for the ‘And’ non-preferred condition F(1,31)512.37, P,0.001; parietal:F(1,31)56.60, P,

[frontal: F(1,31)54.00, P50.054; central:F(1,31)52.70, 0.05].P50.11], and not significant for the ‘But’ ungrammaticalcondition [frontal: F,1; central: F(1,31)51.132, P5 6 .3. Late positivity0.296]. No differences were found between the ‘And’non-preferred and ‘And’ ungrammatical continuation [F After around 500 ms, the ‘And’ non-preferred, ‘And’values ,1 for overall analysis and left central region; ungrammatical and ‘But’ ungrammatical showed aF(1,31)51.64, P50.212 for left frontal region], whereas positivity compared to the ‘But’ grammatical conditionthe ERPs did differ between the two ungrammatical (Fig. 5). The results for the planned comparisons are givenconditions [frontal: F(1,31)515.74, P,0.001; central: inTable 4.

Fig. 5. ERPs to the critical verb for a midline frontal (Fzp) and parietal (Pzi) electrode in experiment 2 (passive reading). (A) ‘And’ non-preferred (dashedline) versus ‘But’ grammatical (solid line); (B) ‘But’ ungrammatical (dashed line) versus ‘But’ grammatical (solid line); (C) ‘And’ ungrammatical(dashedline) versus ‘But’ grammatical (solid line). The late positivity is indicated with an arrow. The isovoltage maps depict the mean difference for the 700–900and 900–1100 ms intervals for each comparison.

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T able 4Significant Helmert contrasts in the intervals covering the late positivity, experiment 2

cContrast Region Effect 500–700 ms 700–900 ms 900–1100 ms(df 1,31) F F F

‘But’ grammatical Midline C 5.321 9.461 15.35**a bvs. other C3R 14.88** 16.41** 6.921

Lateral C 7.391 12.10* 14.36**a b bC3R 26.09** 9.30* 17.20**

a‘And’ non-preferred Midline C3R 4.301 18.31** 14.17**avs. ungrammatical Lateral C3R 2.85 20.48** 14.26**

aC3H3R F,1 F,1 5.871

1 P,0.05; * P,0.01; ** P,0.001; – N.S.; C5contrast; R5region, H5hemisphere.a Involves the contrast testing the linear differences among the regions, unless noted otherwise.b Involves the contrast testing the quadradic pattern of region.c The contrast testing ‘And’ ungrammatical versus ‘But’ ungrammatical yielded no significant results.

6 .3.1. Effect of anomaly: ‘ But’ grammatical vs. other reflect controlled processes (e.g., Refs.[16,21,22]). We willconditions return to this in the discussion.

The positivity for the ‘And’ non-preferred, ‘And’ gram- The positivity starting at 500 ms for the ‘And’ non-matical and ‘And’ ungrammatical was significant in all preferred, ‘And’ ungrammatical and ‘But’ ungrammaticalintervals starting from 500 ms. was replicated. The amplitude of the positivity was smaller

in experiment 2 (passive reading) compared to the experi-ment 1 (judgment task) especially for the ungrammatical6 .3.2. Effect of non-preferred vs. ungrammaticalcontinuations. This reduction of the amplitude with a taskcontinuationsthat does not draw explicit attention to the grammaticalityThe ‘And’ non-preferred condition differed in distribu-of the structure is a rather common finding, cf. Refs.tion from the ungrammatical conditions starting at 500 ms[1,15,21,42]. The anterior–posterior distribution of thefor midline sites, and at 700 ms for lateral sites. In thepositivity in the late intervals was similar to that obtained500–700 and 700–900 ms intervals the positivity for thein experiment 1: the positivity had a posterior focus for the‘And’ non-preferred condition extended to central sitesungrammatical conditions, but spread to more central sitescompared to the more posterior focus for the ungrammati-for the non-preferred condition, with a frontal focus in thecal conditions; in the 900–1100 ms interval the positivity900–1100 ms interval. In contrast to experiment 1, thefor the ‘And’ non-preferred condition had a more anteriorambiguous ‘And’ ungrammatical and unambiguous ‘But’focus. This sentence type by region interaction remainedungrammatical conditions did not differ with respect to thesignificant after rescaling in the 700–900 ms and 900–amplitude or distribution of the late positivity.1100 ms intervals for the ‘And’ non-preferred minus ‘But’

grammatical versus the difference waves involving theungrammatical conditions (P values,0.001).

8 . General discussion

6 .3.3. Effect of ambiguity on ungrammatical The aim of the present study was to test serial andcontinuations parallel models of structural ambiguity resolution by

The ‘And’ ungrammatical and ‘But’ ungrammatical comparing ERPs to (1) non-preferred and ungrammaticalconditions did not differ in the positivity after 500 ms. continuations of the preceding fragment, and (2) ungram-

matical continuations of ambiguous versus unambiguousfragments. In contrast to previous studies[8,40,41] we

7 . Discussion used ambiguities that did not involve lexical ambiguity,which is known to be processed in parallel[45]. According

Experiment 2 used the same materials as experiment 1, to a serial model of syntactic processing[3,4] non-pre-but did not have an explicit task for the participants. ferred and ungrammatical continuations are initially pro-Similarly to experiment 1, a LAN effect was observed for cessed in the same fashion, and both are expected to showthe ‘And’ ungrammatical and ‘And’ non-preferred con- early effects of processing difficulty (LAN) compared toditions versus the ‘But’ grammatical condition. However, the unambiguous control. In a parallel model, multiplein contrast to experiment 1, no such effect was seen for the analyses are retained in working memory. Non-preferred‘But’ ungrammatical condition. This indicates that the and ungrammatical continuations are expected to differ atLAN effect is sensitive to task demands, even though other an early stage, because the parser can only obtain aresearchers have claimed that it is automatic and does not compatible analysis in the non-preferred case. In general,

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the pattern of results is most consistent with a serial continue to use ‘LAN’ as a cover term for negativitiesprocessing model of structural ambiguities. Relative to the associated, directly or indirectly, with syntactic difficulty.unambiguous grammatical condition, the non-preferred and In our study, the anterior negativity was present for bothungrammatical conditions elicited a LAN between 300 and ‘And’ and ‘But’ ungrammatical conditions in the judgment400 ms, although the LAN for the unambiguous ‘But’ study (experiment 1), but only for the ‘And’ ungrammati-ungrammatical condition was present only in the judgment cal condition in the passive reading study (experiment 2).study. The non-preferred and ungrammatical conditions This suggests that the LAN is sensitive to task demandsdiffered only after 500 ms: a more frontally distributed depending on the type of violation, which is in contrast topositivity was found to the ‘And’ non-preferred continua- the idea that it is only sensitive to automatic processestion, whereas the positivity for both ‘And’ and ‘But’ [16,21,22]. Instead, the LAN also appears to reflectungrammatical continuations had a posterior maximum. processes that are at least partially controlled[48]. As we

The second prediction of the serial model is that in the mentioned in the introduction, the ‘And’ ungrammaticalcase of ungrammatical continuations, the later revision and ‘But’ ungrammatical conditions are different in termsprocesses as reflected by the P600 differ depending on of the type of incongruence. In the ‘But’ ungrammaticalwhether the preceding sentence context is ambiguous or condition ‘‘the man is painting the house but the garagenot. In an ambiguous context, more analyses are possible, are . . . ’’ the verb ‘are’ is incorrect in terms of subject–hence a serial model predicts that diagnosis and adjustment verb agreement. In the ‘And’ ungrammatical condition,processes may last longer than in the unambiguous con- ‘‘the man is painting the house and the garage are . . . ’’,texts. However, in contrast to these predictions, the the verb ‘are’ is both unexpected in terms of phraseambiguity of the preceding context did not affect the P600 structure and constitutes a violation of subject–verb agree-elicited to ungrammatical conditions between 500 and ment. Phrase structures are most likely automatically built1100 ms, except for a slight, short-lasting difference in by the parser based on word category information of thedistribution found in experiment 1, which was not repli- incoming words. In this sense, phrase structure violationscated in experiment 2. are automatically ‘noticed’ by the parser, and impervious

Below we will first discuss the differences that were to controlled processes and subject strategies. The check-found with respect to the early stages of parsing as ing of person and number agreement on the other handreflected in the LAN with respect to the ‘But’ ungrammati- occurs later in the parsing process, since this involvescal condition among the two experiments, the absence of phrases that have already been inserted in a phrasean effect of ambiguity on the posterior P600, and the structural configuration. Therefore the checking of persondifferences between posterior and anterior positivitites. and number agreement between a subject and a verb couldFinally we will discuss what the present results imply for be more sensitive to controlled processes[15]. In theprocessing models. judgment task, participants may have more consciously

kept track of the number of the subject noun phrase,8 .1. Early stages of parsing: the LAN effect whereas in the passive reading task they did not. In the

judgment task, this would lead to a more immediateThis study is the first to report a LAN effect for processing problem for the verbs and hence, a LAN in the

non-preferred continuations of ambiguous fragments. Pre- judgment task relative to the passive reading task.vious studies have only reported a LAN effect for con-tinuations that were genuinely ungrammatical given the 8 .2. Later stages of parsing: the posterior and frontalpreceding sentence fragment, or for difficulty related to P600syntactic complexity[30]. This suggests that the LAN isindicative of processing difficulty, whether this is caused 8 .2.1. Effect of ambiguity on ungrammaticality: theby an ungrammaticality, simply a grammatically unex- posterior P600pected continuation, or storage or retrieval from working The posterior positivity to the ungrammatical continua-memory in complex constructions. In the present experi- tion was not different in amplitude for the ambiguousments, the negativity had a left-central distribution. Al- ‘And’ ungrammatical and unambiguous ‘But’ ungrammati-though the typical distribution of LAN is left frontal (e.g., cal conditions. This suggests that the two conditions do notRefs. [1,8,10,37,42]), syntax-related negativities with a differ with respect to the later revision processes. This isbilaterial or left central distribution have been reported unexpected in a serial model, given that there are more[1,7,10,20,38].We should point out, however, that in the possibilities to restructure the analysis in the ambiguousprefrontal cortex, language regions and regions supporting ‘And’ conditions compared to the unambiguous ‘But’storage and retrieval aspects of working memory and other conditions. One possibility is that revision of a conjoinedexecutive processes are densely packed. It is therefore noun phrase into two conjoined clauses, which is triggeredlikely that the different ‘LAN’ effects reported are reflect- by the critical verb in the ‘And’ ungrammatical condition,ing at least partially different things. Further research will is relatively easy and that it hardly adds to the P600provide more insight into this. For now, however we will amplitude elicited by the revision attempts as a result of

634 E. Kaan, T.Y. Swaab / Cognitive Brain Research 17 (2003) 621–635

the subject–verb agreement violation (occurring in both processing with a reanalysis mechanism along the lines‘And’ and ‘But’ ungrammatical conditions). Support for proposed by Fodor and Inoue[3,4]. In the case of athe view that the revision from a noun phrase conjunct into structural ambiguity, such as the ‘and’ ambiguity in thea clause-conjunct is relatively easy, is provided by the present study, only one analysis is pursued. When sub-small amplitude of the P600 in the non-preferred continua- sequent words are not compatible with this analysis, suchtion. In addition, processes reflected by the P600 may not as the verbs in the ‘And’ non-preferred and ‘And’ un-be additive, that is, the P600 elicited by the revision of the grammatical conditions, this word is attached to the currentnoun phrase conjunct and by revision attempts resulting analysis anyway, leading to early processing difficulty asfrom the subject–verb agreement violation may be less reflected by the LAN, which triggers revision processesthan the effects of the individual processes combined. This (P600 component).corresponds with data from previous studies[27,28] in One potential objection to this interpretation of ourwhich none, or only a small (non-additive) increase of the results is that they could be accounted for in a parallelP600 amplitude was found when an increase in syntactic model as well. In the above, we assumed that in a parallelcomplexity (which elicits a posterior P600 in grammatical model, the critical word is simultaneously evaluatedcases)[27,28] was combined with a syntactic violation. against all analyses available in working memory. An

alternative parallel model is one in which the critical word8 .2.2. The frontal positivity is attached to each of the analyses in sequence, starting

In the present experiment, the non-preferred grammati- with the most preferred. In such a model, a non-preferredcal continuations elicited a frontal positivity between 700 continuation could yield a sense of ungrammaticality, andand 1100 ms, whereas the positivity to the ungrammatical hence, a LAN effect. However, such parallel models wouldconditions had a posterior focus. An interesting question also predict a LAN effect for lexical ambiguities, sinceconcerns the functional significance of the frontal and also in this case, the parser would start with the evaluationposterior components. A frontal positivity has been re- of the preferred interpretation. However, this is not theported in various other experiments using non-preferred pattern that has been observed: no LAN effect has been[18,40,47],or complex continuations[9,29]. Hagoort and reported for non-preferred continuations when the am-co-workers[18,19]and Friederici et al.[9] propose that the biguity involves a lexical ambiguity[8,40,41]. This dis-posterior component is indicative of a failure of a parse tinction between lexical and structural ambiguities is hardand/or the resulting repair processes, whereas the frontal to accommodate in a parallel model. The data available atcomponent reflects processing difficulty related to revision present can therefore be accounted for more easily inprocesses in the case of non-preferred continuations in models that pursue one analysis in the case of a structuralambiguous contexts. However, Kaan and Swaab[29] did ambiguity (serial model), and multiple analyses when thenot find a frontal positivity for non-preferred (where ambiguity involves different meanings of a lexical item.revision is possible) and ungrammatical continuations(where no revision is possible) of an ambiguous contextwhen directly compared to each other (viz. ‘‘The plays A cknowledgementsabout the murder that were’’, vs. ‘‘the play about the

]]murder that were. . . ’’). Instead, both continuations eli- E.K. was supported by the McDonnell-Pew Foundation

]]cited a positivity with a posterior focus. This suggests that (JSMF 2000-2044). T.Y.S. was supported by NSF grantrevision is not sufficient to elicit a frontal component. The SES-0074634. We would like to thank Elizabeth Tabonestudy by Kaan and Swaab also suggests that the dis- for her enthusiastic assistance during all stages of thetribution of the positivity is not driven by the classification study, and Joseph Kang and Henny Yeung for their help inof stimuli as ‘grammatical’ or ‘ungrammatical’: a posterior recording ERPs.P600 was found for both non-preferred and ungrammaticalcontinuations, even when only those trials were taken intoconsideration that were correctly classified as ‘grammati- R eferencescal’ and ‘ungrammatical’, respectively. One hypothesis isthat the frontal positivity reflects only a subtype of [1] S . Coulson, J.W. King, M. Kutas, Expect the unexpected: event-

related brain response to morphosyntactic violations, Lang. Cogn.revision, namely revision of the preceding phrase structure,Proc. 13 (1998) 21–58.rather than re-association of the current phrase with a

[2] F . Ferreira, J.M. Henderson, Recovery from misanalyses of garden-previous phrase, as in the Kaan and Swaab study[29]. path sentences, J. Mem. Lang. 30 (1991) 725–745.More experiments are needed to test this, and to obtain a [3] J . Fodor, A. Inoue, The diagnosis and cure of garden paths, J.better understanding of the frontal positivity and the Psycholinguist. Res. 23 (1994) 407–434.

[4] J .D. Fodor, A. Inoue, Attach anyway, in: J.D. Fodor, F. Ferreiraprocesses it is associated with.(Eds.), Reanalysis in Sentence Processing, Kluwer, Dordrecht, 1998,pp. 101–141.

8 .3. Serial and parallel processing [5] L . Frazier, Sentence processing: a tutorial review, in: M. Coltheart(Ed.), Attention and Performance XII, Lawrence Erlbaum As-

Our results are supportive of a serial model of sentence sociates, Hillsdale, NJ, 1987, pp. 559–586.

E. Kaan, T.Y. Swaab / Cognitive Brain Research 17 (2003) 621–635 635

[6] A .D. Friederici, The time course of syntactic activation during [29] E . Kaan, T.Y. Swaab, Repair, revision and complexity in syntacticlanguage processing: a model based on neuropsychological and analysis: an electrophysiological investigation, J. Cogn. Neurosci. 15neurophysiological data, Brain Lang. 50 (1995) 259–281. (2003) 98–110.

[7] A .D. Friederici, S. Frisch, Verb argument structure processing: the [30] J . King, M. Kutas, Who did what when? Using word- and clause-role of verb-specific and argument-specific information, J. Mem. related ERPs to monitor working memory usage in reading, J. Cogn.Lang. 43 (2000) 476–507. Neurosci. 7 (1995) 378–397.

[8] A .D. Friederici, A. Hahne, A. Mecklinger, Temporal structure of [31] R . Kluender, M. Kutas, Bridging the gap: evidence from ERPs onsyntactic parsing: early and late event-related brain potential effects, the processing of unbounded dependencies, J. Cogn. Neurosci. 5J. Exp. Psychol. Learn. Mem. Cogn. 22 (1996) 1219–1248. (1993) 196–214.

[9] A .D. Friederici, A. Hahne, D. Saddy, Distinct neurophysiological [32] M .C. MacDonald, M.A. Just, P.A. Carpenter, Working memorypatterns reflecting aspects of syntactic complexity and syntactic constraints on the processing of syntactic ambiguity, Cognit. Psy-repair, J. Psycholinguist. Res. 31 (2002) 45–63. chol. 24 (1992) 56–98.

[10] A .D. Friederici, E. Pfeifer, A. Hahne, Event-related brain potentials [33] M .C. MacDonald, N.J. Pearlmutter, M.S. Seidenberg, The lexicalduring natural speech processing: effects of semantic, morphological nature of syntactic ambiguity resolution, Psychol. Rev. 101 (1994)and syntactic violations, Cogn. Brain Res. 1 (1993) 183–192. 676–703.

[11] E . Gibson, A Computational Theory of Human Linguistic Process- [34] G . McCarthy, C.C. Wood, Scalp distributions of event-relateding: Memory Limitations and Processing Breakdown, Carnegie potentials: an ambiguity associated with analysis of varianceMellon University, Pittsburg, PA, 1991. models, Electroencephalogr. Clin. Neurophysiol. 62 (1985) 203–

[12] E . Gibson, Linguistic complexity: locality of syntactic dependencies, 208.Cognition 68 (1998) 1–76. [35] M . Meng, M. Bader, Ungrammaticality detection and garden path

[13] E . Gibson, N.J. Pearlmutter, Distinguishing serial and parallel strength: evidence for serial parsing, Lang. Cogn. Proc. 15 (2000)parsing, J. Psycholinguist. Res. 29 (2000) 231–240. 615–666.

[14] P . Gorrell, Establishing loci of serial and parallel effects in syntactic [36] D . Mitchell, Sentence parsing, in: M. Gernsbacher (Ed.), Handbookprocessing, J. Psycholinguist. Res. 18 (1989) 61–73. of Psycholinguistics, Academic Press, San Diego, CA, 1994, pp.

[15] T .C. Gunter, A.D. Friederici, Concerning the automaticity of 375–410.¨syntactic processing, Psychophysiology 36 (1999) 126–137. [37] T .F. Munte, H.-J. Heinze, G.R. Mangun, Dissociation of brain

[16] T .C. Gunter, L.A. Stowe, G. Mulder, When syntax meets semantics, activity related to syntactic and semantic aspects of language, J.Psychophysiology 34 (1997) 660–676. Cogn. Neurosci. 5 (1993) 335–344.

¨[17] P . Hagoort, C. Brown, J. Groothusen, The syntactic positive shift [38] T .F. Munte, M. Matzke, S. Johannes, Brain activity associated with(SPS) as an ERP measure of syntactic processing, Lang. Cogn. Proc. syntactic incongruencies in words and pseudo-words, J. Cogn.8 (1993) 439–483. Neurosci. 9 (1997) 318–329.

[18] P . Hagoort, C. Brown, L. Osterhout, The neurocognition of syntactic [39] H .J. Neville, J.L. Nicol, A. Barss, K.I. Forster et al., Syntacticallyprocessing, in: C. Brown, P. Hagoort (Eds.), Neurocognition of based sentence processing classes: evidence from event-related brainLanguage, Oxford University Press, Oxford, 1999, pp. 273–316. potentials, J. Cogn. Neurosci. 3 (1991) 151–165.

[19] P . Hagoort, C.M. Brown, ERP effects of listening to speech [40] L . Osterhout, P.J. Holcomb, Event-related brain potentials elicited bycompared to reading: the P600/SPS to syntactic violations in spoken syntactic anomaly, J. Mem. Lang. 31 (1992) 785–806.sentences and rapid serial visual presentation, Neuropsychologia 38 [41] L . Osterhout, P.J. Holcomb, D.A. Swinney, Brain potentials elicited(2000) 1531–1549. by garden-path sentences: evidence of the application of verb

[20] P . Hagoort, M. Wassenaar, C.M. Brown, Syntax-related ERP-effects information during parsing, J. Exp. Psychol. Learn. Mem. Cogn. 20in Dutch, Cogn. Brain Res. 16 (2003) 38–50. (1994) 786–803.

[21] A . Hahne, A. Friederici, Differential task effects on semantic and [42] L . Osterhout, L.A. Mobley, Event-related brain potentials elicited bysyntactic processes as revealed by ERPs, Cogn. Brain Res. 13 failure to agree, J. Mem. Lang. 34 (1995) 739–773.

¨(2002) 339–356. [43] F . Rosler, M. Heil, U. Glowalla, Monitoring retrieval from long-[22] A . Hahne, A.D. Friederici, Electrophysiological evidence for two term memory by slow event-related brain potentials, Psycho-

steps in syntactic analysis: early automatic and late controlled physiology 30 (1993) 170–182.¨ ¨processes, J. Cogn. Neurosci. 11 (1999) 194–205. [44] F . Rosler, T. Pechmann, J. Streb, B. Roder, E. Hennighausen,

[23] G . Hickok, Parallel parsing: evidence from reactivation in garden- Parsing of sentences with varying word order: word-by-wordpath sentences, J. Psycholinguist. Res. 22 (1993) 239–250. variations of processing demands are revealed by event-related brain

[24] J . Hoeks, The Processing of Coordination, University of Nijmegen, potentials, J. Mem. Lang. 38 (1998) 150–176.Nijmegen, 1999. [45] D .A. Swinney, Lexical access during sentence comprehension: (Re)

[25] J .C.J. Hoeks, W. Vonk, H. Schriefers, Processing coordinated struc- consideration of context effects, J. Verb. Learn. Verb. Behav. 18tures in context: the effect of topic-structure on ambiguity res- (1979) 645–659.olution, J. Mem. Lang. 46 (2002) 99–119. [46] T .P. Urbach, M. Kutas, The intractability of scaling scalp dis-

[26] J .-M. Hopf, M. Bader, M. Meng, J. Bayer, Is human sentence tributions to infer neuroelectic sources, Psychophysiology 39 (2002)parsing serial or parallel? Evidence from event-related potentials, 791–808.Cogn. Brain Res. 15 (2003) 165–177. [47] J .J.A. Van Berkum, C.M. Brown, P. Hagoort, Early referential

[27] E . Kaan, Investigating the effects of distance and number interfer- context effects in sentence processing: evidence from event-relatedence in agreement processing: an ERP study, J. Psycholinguist. Res. brain potentials, J. Mem. Lang. 41 (1999) 147–182.31 (2002) 165–193. [48] S .H. Vos, T.C. Gunter, H.H.J. Kolk, G. Mulder, Working memory

[28] E . Kaan, A. Harris, E. Gibson, P. Holcomb, The P600 as an index of constraints on syntactic processing: an electrophysiological inves-syntactic integration difficulty, Lang. Cogn. Proc. 15 (2000) 159– tigation, Psychophysiology 38 (2001) 41–63.201.