Processes of Discourse Integration: Evidence From Event-Related ...

Discourse Processes, 50:165–186, 2013 Copyright q Taylor & Francis Group, LLC ISSN: 0163-853X print/1532-6950 online DOI: 10.1080/0163853X.2013.766123

Processes of Discourse Integration: Evidence From Event-Related Brain Potentials Todd R. Ferretti Department of Psychology Wilfrid Laurier University, Waterloo, Ontario, Canada

Murray Singer Department of Psychology University of Manitoba, Winnipeg, Manitoba, Canada

Jenna Harwood Department of Psychology Wilfrid Laurier University, Waterloo, Ontario, Canada

We used ERP methodology to investigate how readers validate discourse concepts and update situation models when those concepts followed factive (e.g., knew) and nonfactive (e.g., guessed) verbs, and also when they were true, false, or indeterminate with reference to previous discourse. Following factive verbs, early (P2) and later brain components (N400 and late frontal positivity) revealed that relative to true concepts, both false and indeterminate concepts were more difficult to validate, and only indeterminate concepts were ultimately updated into the situation model. Following nonfactive verbs, there was no evidence of situational model updating for any condition. However, there was a clear N400 gradient that suggests the lower commitment of nonfactive verbs leads to less incongruence with discourse context for the indeterminate condition than the false condition. These results provide novel insight into how pragmatic constraints afforded by verbs influence discourse validation and the updating of situation models.

Correspondence concerning this article should be addressed to Todd R. Ferretti, Centre for Cognitive Neuroscience and Department of Psychology, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario N2L 3C5, Canada. E-mail: [email protected]

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Thorough comprehension of language requires the continual evaluation of discourse ideas. Coordinating the current and antecedent text units occurs at many levels of analysis. Linguistic devices signal the presence or lack of cohesion in a message (Halliday & Hasan, 1976). Definite noun phrases and anaphora must unambiguously identify their referents (Gordon, Grosz, & Gilliom, 1993; Lesgold, Roth, & Curtis, 1979; Vonk, 1985). At deeper levels of interpretation, the understander must be satisfied that the current expression is situationally coherent with the antecedent discourse. There is extensive evidence that readers are sensitive to the consistency and accuracy of text elements. For example, reading time is greater for inconsistent than consistent text constituents with reference to (a) surface representations (Klin, 1995; Long & Chong, 2001) and (b) the causal, spatial, and other dimensions of the text situation model (Albrecht & Myers, 1995; O’Brien & Albrecht, 1992; Rinck, Hahnel, & Becker, 2001). These observations indicate that comprehension requires processes of integrating the current constituent with its antecedents (Kintsch, 1988; Yang, Perfetti, & Schmalhofer, 2007). The construction-integration model (Kintsch, 1988, 1998) provides a useful framework for conceptualizing comprehension processes. During construction, a network of the explicit text ideas, closely associated concepts, and certain types of implication is derived from the current clause and from information retrieved from one’s memory for the antecedent discourse and relevant world knowledge. Integration involves the accumulation of activation in the most interconnected network elements, one impact of which is to deactivate irrelevant ideas (e.g., the associate “insect” when “bug” has been mentioned in a spying context; Swinney, 1979). Kintsch’s construction phase, of course, depends on the retrieval of relevant ideas from memory. We propose that integration encompasses both the verification or validation of discourse ideas and, depending on the outcome of verification, the updating of the situation model. Further to the retrieval processes of construction, the memory-based text processing analysis (e.g., Lorch, 1998) holds that, at the outset of encoding, the current clause provides cues for the passive retrieval of antecedent discourse ideas from memory. Those ideas are said to resonate to that clause (Ratcliff, 1978). Successful retrieval would then afford verification. Simple phrases are reconciled with candidate antecedents, such as striped animal versus skunk (O’Brien & Albrecht, 1991). Retrieval also enables the verification of complex ideas in their discourse context (Singer, 2006; see also Garrod & Terras, 2000; Kintsch, 1988; Kolodner, 1983; Traxler, Sanford, Aked, & Moxey, 1997) and with reference to world knowledge (Noordman, Vonk, & Kempf, 1992; Singer, Halldorson, Lear, & Andrusiak, 1992). Finally, depending on the outcome of verification, the understander might update the discourse situation model (e.g., Albrecht & O’Brien, 1993; O’Brien, Rizzella, Albrecht, & Halleran, 1998).

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Analysis of discourse comprehension into these subprocesses has renewed concern about the immediacy and the time-course of comprehension. Just and Carpenter (1987) advanced the principle that each successive word is immediately analyzed both at surface and gist levels. However, it has been recently noted (Stewart, Kidd, & Haigh, 2009; Yang et al., 2007) that discourse-integration evidence that stems from full-sentence reading time (e.g., Albrecht & Myers, 1995; O’Brien & Albrecht, 1992) and question answering (Singer et al., 1992) could reflect processes initiated either upon encountering a critical word or else at the end of its sentence (Haberlandt & Graesser, 1985). The immediate and stage-wise analysis of words during approximately 1250 ms following their onset has also been suggested by people’s (a) recognition of probes representing the anaphoric referents (Dell, McKoon, & Ratcliff, 1983) and (b) lexical decisions about inferential predictions (Till, Mross, & Kintsch, 1988) of those words. However, probe measures sometimes bear the disadvantages of either disrupting reading or being applied at sentence end. In this context, event-related brain potentials (ERPs) provide a powerful methodology for analyzing the chronology of discourse integration. We recently presented ERP evidence that the time-course of discourse integration is further clarified by processing signatures of complementary time regions (Ferretti, Singer, & Patterson, 2008). In the present research, we evaluate hypotheses stemming from that analysis. The introduction next provides an overview of the ERP signatures of discourse integration. Our analysis of discourse verification and the paradigm used to study it are then presented. Finally, new experiments and the hypotheses that they evaluate are described.

Electrophysiology of Discourse Processing Researchers investigating the electrophysiological correlates of discourse processing have identified ERP components that are sensitive to the integration of repeated and novel concepts into people’s situation models (see Callahan, 2008, for a recent review). The two components that have been the main focus of this research include the N400 and late positivity. The N400 is well known for indexing semantic expectancies at lexical and message levels given some context (discourse, sentence, single words; Brown, Hagoort, & Kutas, 2000). Words with a better semantic fit elicit smaller negative amplitudes in the period of 300 to 500 ms following their onset than do words that do not fit as well. The N400 is also sensitive to various constraints on coreferential processing. For example, content nouns that are repeated in a discourse yield reduced N400s relative to content nouns that are not repeated (Anderson & Holcomb, 2005; Burkhardt, 2006; Van Petten, Kutas, Kluender, Mitchiner, & McIsaac, 1991). Likewise, words that provide a better semantic match with antecedents elicit smaller N400s relative to words with a poorer semantic match (Anderson & Holcomb, 2005).

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The N400 is also sensitive to factors that increase the salience of discourse antecedents (Burkhardt, 2006; Burkhardt & Roehm, 2007; Ledoux, Gordon, Camblin, & Swaab, 2007), and the type of referential connection has been shown to influence the early and late phases of the N400 component (Burkhardt, 2006; Ferretti et al., 2008). In one study (Burkhardt, 2006), participants read target sentences in which a critical noun phrase (NP; e.g., the conductor in He said that the conductor was very impressive) bore one of three relations to the prior sentence. The noun phrase was explicit with reference to Tobias visited a conductor in Berlin; was novel but could be interpreted through a bridging relation with reference to Tobias visited a concert in Berlin; or was novel and lacked coherence and a linking anchor in the context of Tobias talked to Nina. In the early phase of the N400 (350 –450 ms), there was a gradient in amplitudes: Explicit NPs produced the smallest N400 followed by bridgable novel NPs and then novel NPs that could not be bridged. In the late phase of the N400 (450 –550), the completely novel NPs showed extended negativity relative to repeated and bridged NPs, which did not differ from each other. Burkhardt (2006) also found a late positivity that was similar for novel and bridged NPs, whereas no late positivity was observed for repeated NPs. Late positivity has been suggested to reflect elaboration of text with information from long-term memory, difficulty in conceptual integration, and increased memory demands during syntactic and semantic reanalysis (Federmeier, Wlotko, De Ochoa-Dewald, & Kutas, 2007; Kaan & Swaab, 2003; Van Petten et al., 1991). Burkhardt’s results, along with those of other researchers, suggests that late positivity also indexes integration costs associated with anaphoric complexity and situational updating (Burkhardt, 2005, 2006; Burkhardt & Roehm, 2007; Kaan, Dallas, & Barkley, 2006; Ledoux et al., 2007). Research has demonstrated that another component, a positive deflection at approximately 200– 250 ms (P2), is sometimes sensitive to (a) semantic expectancy during sentence processing (Federmeier & Kutas, 2002; Federmeier, Mai, & Kutas, 2005; Ferretti, Kutas, & McRae, 2007), (b) effects of repetition of words in discourse (Van Petten et al., 1991), and (c) pragmatic effects associated with verb factivity during discourse processing (Ferretti et al., 2008). Relatively little is known about the relationship between language processing and the P2 component, but the P2 is known to be sensitive to visual feature detection and extraction (Luck & Hillyard, 1994). P2 amplitudes that are more positive when elicited to words and pictures in linguistic contexts are generally viewed as suggesting strong top-down constraints (e.g., semantic expectancy) on the ability to process the visual features of upcoming stimuli. We will discuss P2 effects as a result of verb factivity in more detail below.

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Processes of Text Verification During Reading It was mentioned that the successful retrieval of text antecedents enables the verification of the current constituent. Suppose one has read, Norm’s house had been destroyed by a tornado and subsequently encounters, His cousin believed that Norm’s house was destroyed by a fire. Singer (2006) noted that full understanding entails the detection of the tornado-fire discrepancy. He further proposed that parsimony suggests a degree of similarity between the contributing processes and those that support intentional verification in answering a question such as Was Norm’s house destroyed by a fire? (No). It was observed, however, that processing ought to be modulated by discourse pragmatic effects. Therefore, target-sentence truth was factorially combined with the pragmatic implications of verb-complement expressions. Nonfactive verbs such as believe are noncommittal about the truth of their complements. In contrast, the factive verb knew in His cousin knew that Norm’s house was destroyed by a fire makes sense only if the cause was fire. Well-known verification models predict longer false than true answer times for affirmative sentences (e.g., Carpenter & Just, 1975; Wason & Jones, 1963). Singer (2006) suggested that if tacit verification contributes to text integration, then this trend would be observed in target sentence reading times. However, he also observed that it is infelicitous to only “believe” things that are obviously true, a state that ought to inflate nonfactivetrue reading times. Consistent with this analysis, reading times of false target sentences exceeded their true counterparts in the factive but not the nonfactive condition. In a recent extension of this analysis, Singer (2009) noted that people frequently make sensible “don’t know” replies to yes-no questions relatively quickly. For example, having learned Bill has a rifle, participants verify Bill has a pencil (“don’t know”) faster than comparable true and false items (Glucksberg & McCloskey, 1981). It has been proposed that when a preliminary memory search reveals no information relevant to a question, more prolonged memory searches are bypassed (Glucksberg & McCloskey, 1981; Klin, Guzman, & Levine, 1997; Singer, 1984). Detecting relevant information, whether consistent or inconsistent with the question focus, demands a time-consuming comparison (Carpenter & Just, 1975). By analogy, having read Norm’s house had been destroyed, the subsequent sentence, Norm’s cousin showed that Norm’s house was destroyed by a fire, has indeterminate truth. In this circumstance, one could conduct a prolonged memory search for an antecedent of fire or else simply proceed to the next sentence (e.g., van den Broek, Risden, Fletcher, & Thurlow, 1996). Consistent with answer-time studies, reading time was shorter in the don’t-know/indeterminate condition than the false condition; although this pattern was observed with the factive but not the nonfactive verb construction (Singer, 2009).

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Comparing indeterminate target sentences with consistent and inconsistent ones affords the opportunity to scrutinize the processes of access, verification, and updating that we propose to comprise discourse integration. For example, reading Norm’s cousin SHOWED that Norm’s house was destroyed by a fire in the indeterminate context might prompt the reader to update the representation with the causal agent, fire. It was suggested earlier that ERPs have the capacity to depict the detailed time-course of language processing. Study Overview Ferretti et al. (2008) extended electrophysiological investigations of discourse processing by examining the integration of concepts that were true (i.e., repeated) or false (i.e., novel and inconsistent) with reference to discourse contexts. Following Singer (2006), they also manipulated whether these target concepts were the complements of factive (e.g., know) or nonfactive verbs (e.g., believe). They found that false targets modified by a factive verb (e.g., His cousin knew that Norm’s house was destroyed by a FIRE in the context of Norm’s house had been destroyed by a tornado) generated greater N400 amplitudes than true concepts and that this difference was extended through the 1000 ms epoch. After nonfactive verbs, false target concepts also elicited a greater N400 than true concepts. However, unlike the factive condition, there were no extended N400 differences between true and false concepts. Rather, a late positivity was elicited to false target nouns. Ferretti et al. (2008) interpreted the false-factive pattern to show that readers did not update their developing situation models to include these concepts. The rationale was that the target concept was directly contradicted by the antecedent text. In contrast, they interpreted the false-nonfactive pattern to indicate the (arduous) updating of the situation model to include these concepts. This is because even if a house has been destroyed by a tornado, it is legitimate for a character to believe that the cause was different. Finally, Ferretti et al. also found that the pragmatic constraints afforded by factive and nonfactive verbs had an impact on P2 amplitudes: Following factive but not nonfactive verbs, P2 amplitudes were more positive for true than false target concepts. The authors suggested that this novel finding may indicate that the lack of a pragmatic cost for true target concepts following factive verbs leads to more efficient visual feature extraction for these concepts. The present study extends the aforementioned research by investigating the processing of information that is indeterminate although plausible in the discourse contexts. Table 1 presents a sample experimental stimulus. The critical aspect of the passage is that target sentence 5 bears the relations true, false, or indeterminate with reference to the versions of manipulated sentence 2. Like in Ferretti et al. (2008), the target concepts were the complements either of factive (Experiment 1a) or nonfactive verbs (Experiment 1b). This manipulation

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TABLE 1 Sample Passage of Experiments 1a and 1b (Sentence 1) Ken enjoyed riding his bike to football practice in the afternoon with his brother. (Alternate Versions of Sentence 2) True: On this day, it was very hot and Ken and his brother ate oranges while they cycled. False: On this day, it was very hot and Ken and his brother ate apples while they cycled. Indeterminate: On this day, it was very hot and Ken and his brother ate while they cycled. (Sentence 3) Since it was about a five mile ride from their house to the practice field, they figured they were getting a better workout than most of the other guys on the team. (Sentence 4) By the time they got to practice, Ken was feeling sick to his stomach. (Sentence 5—Target) The coach (was certain/figured) that it was oranges that Ken ate. (Sentence 6) Everyone knew that they were sour at this time of year. Question Did Ken ride his bike to football practice? (Yes) Note. Sentence 5 used a factive verb in Experiment 1a and a nonfactive verb in Experiment 1b.

permitted the examination of the pragmatic influence of the verb on the integration of the critical concept. Based on the findings of Ferretti et al., we expected that false concepts would elicit a greater N400 than true concepts following both factive and nonfactive verbs. This difference was predicted to be more extended in time following factive than nonfactive verbs. The indeterminate concepts constituted novel information so we expected them to generate a greater N400 than true concepts following both factive and nonfactive verbs. However, it was less clear as to whether indeterminate concepts would yield N400 responses equal to or less than those of false concepts. On the one hand, Burkhardt (2006) demonstrated a N400 gradient for text targets: Negative deflection decreased monotonically from unbridgeable words, to bridgeable novel words, and finally repeated words. That result suggested an analogous N400 gradient: the least negative N400 amplitudes for true (repeated) words and the most negative amplitudes for false target words. On the other hand, the pragmatic affordances of factive and nonfactive verbs suggested a possible modulation of the N400 response. One possibility was that the N400s elicited by indeterminate and false target nouns might be more similar following factive than nonfactive verbs, at least in the early phase of the N400. This is because only factive verbs presuppose the truth of their complements and this should lead to a greater expectation that the information in their complements has been provided (or clearly true) in the preceding context. This latter constraint might be more relaxed following nonfactive verbs.

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As mentioned earlier, the late phase of the N400 should be extended for false target concepts modified by factive verbs. However, because indeterminate concepts are novel but not inconsistent with previous discourse, we expected people to successfully update their situation models to include these concepts. Successful updating should be reflected by a late positivity. Because nonfactive verbs do not presuppose the truth of their complements, we expected both false and indeterminate concepts to be successfully integrated following these verbs. Therefore, we did not expect differences between these conditions in the late component region. It is worth emphasizing that the inclusion of the indeterminate condition bears on aspects of model not reflected by the true and false conditions. Finally, we expected to replicate the P2 findings of Ferretti et al. (2008); that is, the P2 component should be more positive for true than false nouns following factive but not nonfactive verbs. Because there should also be a processing cost for indeterminate information following factive verbs, we expect that they will pattern with the false nouns in this region. To summarize, ERP methodology has the capacity to expose the chronology of discourse comprehension processing. Our prior studies offered new and incisive hypotheses about the interactive impact of text congruence and verb pragmatics on the processes in question (Ferretti et al., 2008; Singer, 2006, 2009). Those investigations suggest that discourse integration comprises stages of access, validation, and representational update. Two new experiments were designed to evaluate those hypotheses.

METHODS Participants The participants were undergraduate students from Wilfrid Laurier University who received course credit. There were 51 participants in each of Experiments 1a and 1b, all of whom were native English speaking, had normal or corrected-tonormal visual acuity, and were right-handed. Materials The experimental materials were the 30 narrative passages of Singer (2009). Singer’s passages were based on those of Singer (2006), who in turn derived 28 of them from the materials of O’Brien, Plewes, and Albrecht (1990). Table 1, previously considered, presented a sample passage. As discussed earlier, sentence 2 always introduced a critical idea that defined the true, false, and indeterminate conditions. Sentence 5 involved a character saying or thinking something about the critical idea, and always included a factive verb (e.g., was certain)

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in Experiment 1a and a nonfactive verb (e.g., figured) in Experiment 1b. The target word that corresponded to the critical idea always followed the verb and appeared either in mid-sentence or sentence final position. Previous research suggests that sentential boundaries are areas of “wrap-up effects” that result from the integration of different sources of information that are internal and external to the sentence (Just & Carpenter, 1980; Kintsch, 1988). However, we do not believe that including target words that appeared in mid and sentence final position compromise our ability to draw generalizations from our stimuli set for at least 2 reasons. First, the location of the target words were identical across all conditions so the differences observed between our conditions could not be due to differences in sentence location. Second, the target words for all conditions were always complements of the verbs so the relationship between the target words was always the same regardless of sentence position. In both experiments, the passages were presented across three lists, such that each list contained 10 passages representing each of the three conditions (true, false, indeterminate). Note that Factivity was manipulated between experiments as opposed to a single within participant experiment because the addition of the indeterminate condition would have entailed only 5 passages per condition—too few for an ERP investigation. Thus, our approach was the best compromise between alternative designs and total number of experimental passages. The lists also included 16 filler passages that were similar to the experimental passages in length and narrative style but did not manipulate truth or factivity. A simple comprehension question was written for each experimental and filler passage, with half of the questions having each of the correct answers “yes” and “no.”

Procedure The participants sat in front of a computer monitor located in an electricallyshielded chamber. They were instructed to read each passage for comprehension and to answer a post-passage comprehension question by pressing buttons labeled “yes” and “no.” The first three sentences of every passage appeared together in full in the center of the computer screen and participants were required to press a button to signal understanding them. Participants were able to blink during the presentation of these sentences. Sentences 4 to 6 appeared in a fixed serial visual presentation (SVP) format: Each word was displayed for 300 ms plus a 200 ms interstimulus interval, with an additional 2000 ms of blank interval following each sentence. Participants were told to blink, if necessary, during the 2000 ms blank interval. The change in format between the first three and the last three sentences was necessary for the examination of evoked potentials to the target word of interest. Furthermore, allowing participants to read the first part of the passage in full helped reduced eye strain and thus eye movement artifacts.

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Recording and Analysis The electroencephalogram (EEG) was recorded from 64 electrodes (including two mastoid electrodes) distributed evenly over the scalp. See Figure 1 for a schematic diagram of the electrode array. Eye movements and blinks were monitored via electrodes placed on the outer canthus and infraorbital ridge of each eye. Electrode impedances were kept below 5 KV. EEG was processed with a bandpass of 0.05 –100 Hz and was digitized at 250 Hz. The data were re-referenced off-line to the average of the left and right mastoids. High frequency noise was removed by applying a low-pass filter set at 30 Hz. ERPs were computed in epochs that extended from 100 ms before the target words to 1000 ms after their onset. Trials contaminated by EEG artifacts and trials with incorrect answers were removed from the analysis before averaging. A total of 12.22% of trials (artifacts: 8.94%, incorrect answers: 3.28%) were removed from Experiment 1a, and a total of 17.31% of trials (artifacts: 13.20%, incorrect answers: 4.11%) were removed from Experiment 1b. One-way analyses of variance on the mean percentage of artifacts and errors for the three experimental conditions (true, false, indeterminate) demonstrated no significant effect of condition in Experiment 1a (both Fs , 1) and Experiment 1b (both Fs , 1.45).

RESULTS Four time regions of interest were inspected: 200 –300 ms (P2), 300 –500 ms (N400), 600– 1000 ms (extended N400), 800 –1000 ms (late positivity). The choice of these regions was based on visual inspection of the waveforms and on previous ERP research indicating their sensitivity to truth and factivity manipulations (Ferretti et al., 2008). We conducted two analyses of variance (ANOVA) on these data. The first ANOVA included all electrodes and examined the effect of relation (true, false, indeterminate). In this analysis, relation was a within-participants variable and list was a between-participants factor. Including the counterbalancing list variable in the ANOVA design accounted for systematic variance among the scores and so helped to expose the effects of relation. However, it was of no theoretical interest so effects involving list are not reported. In order to characterize the topographic distribution of the effect of relation over the scalp, we also conducted an additional ANOVA in which we added anteriority (anterior, central, posterior) and laterality (left hemisphere, right hemisphere) as additional within-participants variables. All electrodes except those down the midline were included in this ANOVA. Figure 1 illustrates the electrodes that made up the laterality and anteriority conditions in the distribution ANOVA.

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FP1

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FIGURE 1. Schematic diagram showing the electrode sites used in the analyses of Experiment 1a and 1b. Note that all electrodes down the midline (unfilled triangles) were removed for the distribution ANOVA. The different anteriority and laterality conditions are indicated as follows: Black filled circles ¼ Left Hemisphere, Anterior; Grey filled circles ¼ Left Hemisphere, Central; Unfilled circles ¼ Left Hemisphere, Posterior; Black filled squares ¼ Right Hemisphere, Anterior; Grey filled squares ¼ Right Hemisphere, Central; Unfilled squares ¼ Right Hemisphere, Posterior.

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TABLE 2 Mean Amplitudes (mV) for the Main Effect of Relation at Each Time Region of Interest in Experiments 1a and 1b Time Region (ms) Condition

200 –300

Factive (Experiment 1a) True 4.33 False 3.11 Indeterminate 3.50 Nonfactive (Experiment 1b) True 4.13 False 3.42 Indeterminate 3.58

300– 500

600–1000

800–1000

3.55 0.67 1.46

4.59 3.74 5.30

4.27 3.71 5.36

2.74 0.83 1.80

3.84 3.34 3.95

3.45 3.42 3.81

All p-values are reported after epsilon correction (Huynh-Felt) for repeated measures with greater than one degree of freedom. All F-values are significant at p , .05 unless reported otherwise.1 Experiment 1a (Factive Verbs) Table 2, top panel, shows the mean amplitudes at the four time regions. We proceed region by region. Time region 200 –300 ms (P2). Visual inspection of Figure 2 shows that P2 amplitudes were most positive over anterior locations and least positive over posterior locations. Furthermore, differences among true, false, and indeterminate target nouns began approximately 200 ms following their onset and these differences were broadly distributed over the scalp. There was a main effect of relation, F(2, 96) ¼ 3.83. Planned comparisons revealed that mean amplitudes for true nouns were more positive than false nouns, F(1, 96) ¼ 7.35, and marginally more positive than for indeterminate nouns, F(1, 96) ¼ 3.53, p ¼ .07. Mean amplitudes for false nouns and indeterminate nouns were not significantly different, F , 1. The distribution ANOVA (with the electrode sites down the midline removed) revealed a significant 3-way interaction between relation, anteriority, and

1 Note that although we present separate analysis for each experiment, we also conducted separate ANOVAs that included verb type (Factive versus Nonfactive) as a between participant variable for each time region of interest. This cross-experiment analysis did not reveal any significant verb type x relation interactions at any time region. This finding is not unexpected given the lower statistical power that results from between participant variables.

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laterality, F(4, 92) ¼ 3.81. This interaction occurred because mean amplitudes for false nouns were less positive than true and indeterminate nouns at central (bilaterally), posterior (bilaterally), and left anterior scalp locations (all p’s , .01). In contrast, at right anterior locations, amplitudes for false and indeterminate nouns were not significantly different, F , 1. No other interactions involving relation were significant in the distribution ANOVA. Time region 300– 500 ms (N400). As shown in Figure 2, the N400 was broadly distributed over the scalp and tended to be slightly more negative at central and posterior locations. The main effect of relation was significant, F(2, 96) ¼ 22.01: Amplitudes for false nouns were more negative than for true nouns, F(1, 96) ¼ 41.21, and amplitudes for indeterminate nouns were also more negative than for true nouns, F(1, 96) ¼ 21.72. The difference between false and indeterminate nouns did not reach significance, F(1, 96) ¼ 3.10, p ¼ .082. The distribution ANOVA demonstrated no significant or marginal interactions between relation and the anteriority and laterality variables. Time region 600– 1000 ms (extended N400). The main effect of relation was significant, F(2, 96) ¼ 5.82: Amplitudes for false nouns were marginally more negative than for true nouns, F(1, 96) ¼ 3.48, p ¼ .065, and significantly more negative than for indeterminate nouns, F(1, 96) ¼ 11.61. The difference between true nouns and indeterminate nouns was not significant, F(1, 96) ¼ 2.38, p . .12. Thus, unlike the N400, the extended N400 dissociated the false and indeterminate conditions. The distribution ANOVA demonstrated a significant 3-way interaction between relation, anteriority, and laterality, F(4, 192) ¼ 2.68. This interaction reflected that differences in mean amplitude between the relation conditions were relatively similar at central and anterior locations over both the left and right hemisphere; whereas at posterior locations, the difference between false nouns and both true and indeterminate nouns were larger over the right than left hemisphere. This pattern of findings is consistent with the findings of Coulson et al. (2005), who also found larger differences in the late phase of the N400 region (500 –900 ms) over right posterior head locations. Time region 800 – 1000 ms (late positivity). Visual inspection of Figure 2 indicates that between 800 and 1000 ms mean amplitudes for indeterminate nouns were considerably more positive than for true and false nouns. This late positivity was broadly distributed over the scalp. The main effect of relation was significant, F(2, 96) ¼ 5.78: Amplitudes for indeterminate nouns were significantly more positive than for true nouns, F(1, 96) ¼ 4.87, and false nouns, F(1, 96) ¼ 11.17. The difference between true and false nouns was not significant, F(1, 96) ¼ 1.29, p . .25.

FIGURE 2. Experiment 1a mean amplitudes for true, false, and indeterminate target nouns following factive verbs at selected head locations (color figure available online).

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FIGURE 3. Experiment 1b mean amplitudes for true, false, and indeterminate target nouns following nonfactive verbs at selected head locations (color figure available online).

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The distribution ANOVA demonstrated a significant 3-way interaction between relation, anteriority, and laterality, F(4, 192) ¼ 3.25. Similar to the 600– 1000 ms region, this interaction occurred because the mean amplitude differences between the relation conditions were relatively similar over the left and right hemispheres at central and anterior locations. At posterior locations, the difference between false nouns and both true and indeterminate nouns was again larger over the right than left hemisphere. Experiment 1b (Nonfactive Verbs) Table 2, bottom panel, shows the mean amplitudes for Experiment 1b (see also Figure 3). Time region 300 –500 ms (N400) exhibited a main effect of relation, F(1, 96) ¼ 11.24: Amplitudes for false nouns were more negative than both true nouns, F(1, 96) ¼ 22.48, and indeterminate nouns, F(1, 96) ¼ 5.80. Amplitudes for indeterminate nouns were also more negative than for true nouns, F(1, 96) ¼ 5.44. The distribution ANOVA did not reveal any interactions between relation and the anteriority and laterality variables. None of the other time regions yielded any significant or marginal main effects and interactions.

DISCUSSION This study applied ERP methodology to the scrutiny of discourse integration processes. In particular, we propose that discourse comprehension requires, among other processes, the access of relevant ideas from memory; verifying the current clause in the context of the accessed information; and, depending on the former processes, possibly updating the discourse situation model. There is accumulating evidence that ERP profiles distinguish among those processes (Burkhardt, 2006; Ferretti et al., 2008; van Berkum et al., 1999; Yang et al., 2007). To clarify these issues, we inspected people’s comprehension of assertions that were embedded in the complements of factive and nonfactive verbs. In so doing, it was possible to modulate, in subtle ways, the reader’s perception of the congruence between the assertions and their text antecedents. Furthermore, concepts of indeterminate accuracy were examined in addition to the usual true and false ones. This provided the opportunity to evaluate readers’ comprehension of ideas that, while not strictly asserted, are strongly suggested by the narrative. That is, having previously learned that Norm’s house was destroyed, what is the reader’s reaction to Norm’s cousin showed/said that Norm’s house was destroyed by a fire? Across Experiments 1a and 1b, the results were strikingly orderly. We interpret the standard N400 region as reflecting the semantic congruence of the text element in its discourse context, the extended N400 region as reflecting continued integration costs associated with semantic incongruency (Burkhardt,

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2006; Ferretti et al., 2008), and the late positivity as an index of situational updating (Burkhardt, 2006; Ferretti et al., 2008). In the standard N400 region, the indeterminate condition produced (a) a response similar to false concepts in factive complements and (b) deflections intermediate between false and true items in nonfactive complements. This suggests that the previously unsanctioned factive construction, Norm’s cousin showed that Norm’s house was destroyed by a fire, is initially considered inconsistent with existing information. With the lower commitment of a nonfactive expression, in contrast, the standard N400 region suggests a lesser degree of incongruence of the indeterminate condition. The extended N400 region then clarifies readers’ resolution of the various conditions. In the factive condition (Experiment 1a), having grappled with the tentative mismatch of indeterminate expressions and their antecedents, the reader has little reason to dispute the accuracy of fire. As a result, indeterminate items do not produce an extended N400, unlike the false items. In the nonfactive condition (Experiment 1b), in contrast, there was no effect of relation. This may reflect the fact that, in the discourse model, the cousin may legitimately say whatever he wishes, regardless of its accuracy. In what circumstances does the reader update the situational model to incorporate new text information? Region 800– 1000 ms, interpreted to reflect updating, bears on this question. With factive complements, a distinct positivity distinguished the indeterminate conditions from the others. Without reasons to doubt the truthfulness of the character or the cooperation of the author (Grice, 1975), the reader is justified in adding the new information to the situation model. In contrast, there is no need to update in the true condition and no rationale for doing so in the false condition—the late positivity is similar in those conditions.2 Nonfactive expressions such as The cousin said . . . , in contrast, strongly sanction updating in none of the relation conditions. Although nonfactive verbs do not strongly sanction situational updating, the results of Ferretti et al. (2008) suggested that the false condition and possibly the indeterminate condition would elicit greater positivity in the late region, relative to the true condition. Although we did find this pattern in mean amplitudes, the main effect of relation did not reach significance. There were two main differences between the present study and that of Ferretti et al. (2008) that may have contributed to this null effect. First, the present study included an indeterminate condition whereas in Ferretti et al. readers never received passages with indeterminate information. Second, Ferretti et al. manipulated verb factivity 2 Although the false factive condition did not produce a late positivity exhibited by the indeterminate condition, we are not suggesting that readers recognized the incongruity in the false factive condition and then did not engage in further processing. Rather, we interpret the extended N400 in the false factive condition as evidence of continued integration processing that occurs for at least 1000 ms following the onset of the false information.

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as a within variable whereas the present research varied factivity presented across two separate experiments. Encountering only the nonfactive construction, and sometimes in conjunction with indeterminate information, may have created greater uncertainty for the readers to accept any of the information provided in the complements and, as a result, dampen differences between conditions in the late region. It is noteworthy that the orderliness of these data further substantiates the relevance of the late positivity for exposing the updating of the discourse representation. The circumstances and constraints of updating are a central focus of contemporary discourse research (e.g., Dutke & Rinck, 2006; O’Brien, Cook, & Peracchi, 2004; Radvansky & Copeland, 2001), so measures that distinctly reflect the contributing processes of updating will prove informative to researchers. Finally, the early positivity (P2; 200– 300 ms) was consistent with Ferretti et al.’s (2008) finding of more positive amplitudes for true than false nouns following factive but not nonfactive verbs. The present finding that indeterminate concepts patterned with the true and false nouns following nonfactive verbs and with false nouns following factive verbs at anterior locations is consistent with the fact that there is a processing cost associated with encountering novel information that does not appear earlier in the discourse. Researchers have suggested that more positive P2 amplitudes indicate strong top down constraints (e.g., semantic expectancy) on the ability to process the visual features of upcoming stimuli (Federmeier & Kutas, 2002; Federmeier et al., 2005; Ferretti et al., 2007; Ferretti et al., 2008). The results of the present study and Ferretti et al. (2008) suggest that the pragmatic constraints of factive and nonfactive verbs can influence the ability of readers to process the visual features associated with their complements. An alternative explanation to the P2 findings is that they reflect differences in the leading edge of the N400 component. The distribution ANOVA for the P2 region demonstrated that amplitudes for indeterminate and false nouns patterned together following factive verbs at right anterior scalp locations. At all other head regions, the mean amplitudes more closely matched the pattern of N400 results that showed a trend for false nouns to be more negative than indeterminate nouns. The similarity between the P2 amplitudes and the standard N400 region at most head regions does suggest that the leading edge of the N400 overlaps with the P2 region. However, the presence of the 3-way interaction between relation, anteriority, and laterality in the P2 data and the lack of a similar interaction in the standard N400 region suggest that the P2 data are not simply mirroring the N400 data. Finally, the distribution of the present P2 effects were relatively similar to the anterior P2 effects reported in Ferretti et al. (2008). Their P2 amplitudes were largest at anterior locations and slightly larger over the midline and right

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hemisphere. Past research has also shown the difference in P2 amplitudes to repeated versus nonrepeated content words in discourse to be largest over the right hemisphere (Van Petten et al., 1991), and larger P2 effects over the right hemisphere has been found to words presented in isolated sentences (Kutas, Van Petten, & Besson, 1988).

CONCLUSION Since the earliest chronometric studies of anaphoric resolution (e.g., Carpenter & Just, 1977) and bridging inference (Haviland & Clark, 1974), it has been apparent that detecting the relations among discourse ideas is central to comprehension. ERP methodology provides an informative window upon the component processes of discourse integration. In the present study, we used ERP profiles to advance the understanding of the tacit verification of text ideas and the resultant updating of the situation model. The results reveal remarkable dissociations among the truth conditions across the time regions of interest. They serve to refine our conceptualization of discourse integration to include stages of retrieving antecedent information, verifying discourse ideas, and model updating. We consider information retrieval to align with the construction phase of construction-integration (Kintsch, 1988, 1998) and verification and updating to correspond to Kintsch’s integration processes.

ACKNOWLEDGMENTS This research was supported by separate Discovery Grants awarded to the first and second authors by the Natural Sciences and Engineering Research Council (Canada).

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