Journal of Memory and Language

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1 Journal of Memory and Language 64 (2011) Contents lists available at ScienceDirect Journal of Memory and Language journal homepage: Why brother and sister are not just siblings: Repair processes in agreement computation Nicola Molinaro a,, Francesco Vespignani b, Roberto Zamparelli b, Remo Job b a BCBL, Basque Center on Cognition, Brain and Language, Donostia, Spain b Dipartimento di Scienze della Cognizione e della Formazione, University of Trento, Rovereto (TN), Italy article info abstract Article history: Received 3 March 2010 revision received 30 November 2010 Available online 8 January 2011 Keywords: Agreement Repair Reanalysis ERPs LAN P600 In the present study we analyze how the cognitive system deals on-line with number agreement mismatches and whether this on-line process influences the off-line interpretation of the sentence. In two ERP experiments we monitored the on-line processing consequences of subject-verb agreement mismatches, focusing on the integration of a following number- marked related constituent. In Experiment 1, after initial detection of a mismatch between a plural noun phrase (The siblings) and its singular verb, indexed by LAN + P600, ERP correlates of agreement processing difficulties were recorded on a following modifier when it was plural. In Experiment 2, after detection of the mismatch between two conjoined singular noun phrases in subject position (The brother and the sister) and the verb, indexed by a short-lived P600, only the singular modifier showed indexes of agreement processing difficulties. These findings support the hypothesis that when processing a morphosyntactic mismatch, the cognitive system constructs on-line a well-formed internal representation of the sentence fragment. This on-line regularization allows comprehenders to easily integrate additional incoming constituents and also influences off-line interpretation of the message (Experiment 3). Ó 2010 Elsevier Inc. All rights reserved. Introduction The phenomenon of agreement, together with fixed word order and case marking, is one of the three main ways in which languages signal grammatical relations (Nichols, 1986). Many researchers have stressed the ability and automaticity with which speakers tacitly respect and use agreement rules in the sentences they produce (for example, Berent, Pinker, Tzelgov, Bibi, & Goldfarb, 2005; Bock, Nicol, & Cutting, 1999). Many behavioral (De Vincenzi, 1991; Pearlmutter, Garnsey, & Bock, 1999; Wagers, Lau, & Phillips, 2009) and neurophysiological (Coulson, King, & Kutas, 1998; Osterhout & Mobley, 1995) studies on language comprehension have shown Corresponding author. Address: BCBL, Basque Center on Cognition, Brain and Language, Paseo Mikeletegi, 69, Donostia, Spain. Fax: address: n.molinaro@bcbl.eu (N. Molinaro). that agreement information has a rapid and measurable impact on cognition. An agreement mismatch such as The boys runs...leads to an immediate reaction by the comprehender within a few hundred milliseconds of the detection of the incongruence. Interestingly, such an error, while temporarily disrupting sentence comprehension, does not necessarily affect the ability to construct a coherent interpretation of the sentence meaning. Comprehenders are in fact able to understand nearly every utterance, not only ambiguous sentences, but also truly ungrammatical ones. As indicated by Hoftadter (1979, p. 26), one of the essential abilities for intelligence [is] certainly [...] to make sense out of ambiguous or contradictory messages. This plasticity in dealing with syntactic incongruities and recovering from erroneous analyses is an essential skill of the parser that is useful not only for communicating with non-proficient speakers (e.g. children and second language speakers) but also for language learning (Osterhout, McLaughlin, Pitkanen, Frenck-Mestre, & Molinaro, 2006) X/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi: /j.jml

2 212 N. Molinaro et al. / Journal of Memory and Language 64 (2011) In addition, native speakers can easily handle environmental noise, ambiguities, speech errors, hesitation and repetitions, which are typical of every-day language; this confirms the cognitive ability to mentally restructure a disrupted incoming input into a well-formed message. To explain the robustness of the cognitive system in dealing with formal inconsistencies during comprehension, some researchers have proposed that language processing relies on highly economical strategies (heuristics): critical semantic information would be extracted to achieve sentence interpretation (Bever, 1970; Ferreira & Patson, 2007), without necessarily performing a detailed syntactic analysis of the sentence. However, grammatical cues constrain the semantic interpretation of most utterances and could play a critical role during the on-line comprehension of a sentence. For example, when processing an decontextualized string like The boys runs... (an incongruence apparently resolved in less than a second, see Osterhout and Mobley (1995); but also De Vincenzi et al. (2003), for a direct comparison between behavioral and neurophysiological correlates of number agreement mismatches), the parser has no semantic or discourse level information available to interpret the mismatch. In these cases, two things could happen when the disagreeing constituent is detected: either (i) the opposing values of the two mismatching constituents are kept in memory until further disambiguating information arrives, or (ii) the internal mental representation of one constituent (i.e. the number of either the subject noun phrase or verb) is coerced in order to fit with the other. Both hypotheses are plausible, given the architectural properties of the cognitive system. The first hypothesis would imply that the cognitive system can process multiple alternative parses of a sentence structure at a time. Thus, in a sentence like The boys runs..., there would be no need to select either the noun or the verb number to be assigned to the incongruent sentence. The ungrammatical fragment presenting the two alternative values (plural and singular respectively) would be available to the parser until further disambiguating information arrives; at which point the different alternatives could be weighted differently, depending on the support for one interpretation or the other. For example, when all the relevant semantic and discourse level information is controlled for within the sentence, the choice of selecting singular or plural would depend on perception of another number-marked word during the unfolding sentence. A series of models of sentence comprehension (multiple constraint models: MacDonald, Pearlmutter, & Seidenberg, 1994; Trueswell, Tanenhouse, & Kello, 1993) have pointed to the ability of the cognitive system to keep in memory multiple alternatives during the processing of an ambiguous sentence structure. In this view, the short-lived processing cost elicited by a mismatching word (the verb in The boys runs...) would be due to the increased memory load of keeping the alternative representations active. The coercion hypothesis, on the other hand, is reminiscent of what in the psycholinguistic literature is termed on-line repair, i.e. the ability of the cognitive system to immediately modify the internal representation of an ungrammatical sentence fragment to build an internal well-formed syntactic representation of the sentence. The need to build such well-formed syntactic sentence representations would be for reasons of economy: it would require less cognitive resources to keep in mind an unambiguous and well structured message than a noisy one. In addition, immediate on-line repair of the number mismatch would allow easier (and faster) integration of the incoming material. A similar approach has been pursued by classical serial models of sentence processing (De Vincenzi, 1996; Frazier, 1990; Frazier & Fodor, 1978) to explain reanalysis effects in garden-path constructions. The fact that these models are implemented serially means that only a single structural interpretation can be pursed at one time, requiring a distinct monitoring system to revise and repair the initial interpretation, if need arises. In this framework, reanalysis and repair mechanisms are considered as independent and essential elements of the whole cognitive architecture, given that in the first stage the parser pursues the simplest structural choice due to economy of time and resources which sometimes turns out to be the wrong one. The parser is thus assumed to be prone to error. This implies that upon encountering inconsistent linguistic material, the first possibility to explore is that a comprehension error has occurred. If serial models assume that a choice between alternative analyses has necessarily to be performed immediately, multiple constraint models do not exclude that one interpretation could be preferred, having a higher level of activation than a competing one: repair and reanalysis can thus be described in terms of changes to the differential activation level or ranking of different alternatives operated by the same mechanism that performs the initial structuring of the incoming words, without assuming a specialized mechanism based on independent parsing principles (Grodner, Gibson, Argaman, & Babyonyshev, 2003). The aim of the present study is to analyze the processing routines by which the human parser deals on-line with an agreement mismatch: the findings will help to clarify the processes involved in the revision of ungrammaticalities and their influence on the overall interpretation of the sentence. We will also evaluate the impact that these on-line processing routines have on the off-line interpretation of the sentence. ERP evidence on syntactic resolution In a series of previous experiments (Molinaro, Kim, Vespignani & Job, 2008; Vespignani, Molinaro & Job, in press) we tried to demonstrate that after an agreement mismatch where two alternative interpretations are available for the mismatching feature, only one of them is pursued on-line and incrementally projected on for further sentence processing. We studied the electrophysiological correlates (Event Related Potentials, ERPs) of the comprehension of grammatically anomalous sentences which contained two anomalies, one early and one late. The main aim was to verify how the processing of the later anomaly was affected by the processing of the early anomaly. We developed this paradigm to evaluate the possible on-line

3 N. Molinaro et al. / Journal of Memory and Language 64 (2011) resolution of the disagreement between two constituents at the beginning of the sentence. Subject-verb (Molinaro, Kim, et al., 2008) and determiner-noun (Vespignani et al., in press) morphosyntactic number mismatches were presented at the beginning of the sentence; in a subsequent position, a constituent marked 3rd person was manipulated so that it could agree either with the first or with the second mismatching element. The rationale behind this manipulation was to contrast the ERP correlates of the third constituent in the two conditions (and with the fully grammatical one) in order to verify if only one of them, or both, showed signs of agreement processing difficulties. We focused on the ERP correlates as a dependent measure, given their extremely high temporal resolution. Number agreement violations have been extensively studied with this technique and show a biphasic electrophysiological pattern starting around ms and returning to the baseline around 1 s after the detection of the mismatch (Osterhout, McLaughlin, Kim, Greenwald, & Inoue, 2004). The two main components of this pattern are the Left Anterior Negativity (LAN), a left-frontal increased negativity between 300 and 450 ms, and the P600, a long-lasting positive shift between 500 and 1000 ms. The LAN has been reported in languages with both relative word order freedom and full paradigms of agreement (Italian: Angrilli et al., 2002; Finnish: Leinonen, Brattico, Jarvenpaa, & Krause, 2008; Spanish: Silva-Pereyra & Carreiras, 2007) and in more fixed word order languages with residual agreement (Dutch: Hagoort & Brown, 2000; English: Osterhout & Mobley, 1995; German: Roehm, Bornkessel, Haider, & Schlesewsky, 2005). For example, Leinonen et al. (2008) directly compared violations of inflectional and derivational morphology in Finnish: in the former violation LAN was elicited, while the latter elicited an N400 in the same time window, a component classically related to semantic processing difficulties (Kutas, Van Petten, & Kluender, 2006). The LAN is thus considered to reflect a stage of processing related to the early detection of a morphosyntactic violation (Bornkessel & Schlesewsky, 2006; Friederici, 2002; Munte, Matzke, & Johannes, 1997). LANs are also elicited by determiner-noun agreement violations at the sentence level: Barber and Carreiras (2005) reported LAN for both number ( Los chico; The (+P) kid (+S)) and gender violations ( La chico; The (+F) kid (+M)) in Spanish. Also, Molinaro, Vespignani, and Job (2008) reported the same effect for both gender and phonotactic ( Il scoiattolo; The (+IL) squirrel (+LO)) violations in Italian. The LAN component thus shows sensitivity to the target element form when it is involved in core agreement relations. Some authors have reported LAN effects during the reading of grammatical sentences that required working memory resources to be comprehended (Kluender & Kutas, 1993; Streb, Rosler, & Hennighausen, 1999). An interesting distinction has been made between the morphosyntactic LAN and the working memory LAN (Fiebach, Schlesewsky, & Friederici, 2002): the former has been termed focal LAN since its onset is around 300 ms and it returns to baseline around 450 ms; the latter is the sustained LAN, a component with similar latency that does not come back to the baseline. In the present study we focus on the focal LAN that has been consistently reported for morphosyntactic processing difficulties. The LAN is consistently reported in association with a later positive shift starting around 500 and lasting until 1000 ms. This so-called P600 has received less attention in the ERP studies on agreement processing, despite the fact that it has provided very interesting insights into the brain mechanisms involved in feature checking (Barber & Carreiras, 2005; Molinaro, Vespignani, et al., 2008; Nevins, Dillon, Malhotra, & Phillips, 2007). Initially, the P600 was generically considered a marker for syntactic processing difficulties (Osterhout & Mobley, 1995); however, a significant body of research has demonstrated that the P600 is sensitive to violations of structural-based expectancy in both linguistic (Coulson et al., 1998; Hsu, 2009; Kim & Osterhout, 2005; Osterhout, Holcomb, & Swinney, 1994) and non-linguistic materials (Patel, 2003; for reviews Kuperberg, 2007; Osterhout, Kim, & Kuperberg, in press). For the purposes of the present study, we mainly consider the literature on syntactic violations, in which the finding of earlier negative components in response to syntactic violations (as discussed by Friederici, 2002) has led to a general consensus in associating the P600 following the LAN to late reanalysis and repair processes elicited by syntactically anomalous sentences. We, among others, have proposed a particular hypothesis of the P600 to agreement violations as reflecting two processing stages (Barber & Carreiras, 2005; Carreiras, Salillas, & Barber, 2004; Hagoort & Brown, 2000; Kaan & Swaab, 2003a; Molinaro, Vespignani, et al., 2008). In the following is some of the evidence that has motivated this view. The earlier stage of the P600 would correspond to the increased positivity starting at 500 until about 700 ms. During agreement computation, this stage would be involved in building structural dependencies of the sentence, while interfacing with the available non-syntactic information (as suggested by Bornkessel & Schlesewsky, 2006; Kuperberg, 2007). Recent findings of larger early P600s for agreement violations involving person feature manipulations (assumed to involve discourse level representations, Sigurdsson, 2004; see Mancini, Vespignani, Molinaro, Laudanna, & Rizzi, 2009; Nevins et al., 2007), support the idea of a stage at which the cognitive system is accessing higher discourse level information to detect the source of the error. Interestingly, in these studies the early P600 effect is salient also in the frontal portion of the scalp (as suggested by Kaan and Swaab, 2003a, 2003b). In a later stage (after 700 ms), the P600 has a more posterior distribution and would reflect the repair of illformed sentence constructions. The finding of larger late P600s for costlier feature repair processes supports the dissociation of this subcomponent (Barber & Carreiras, 2005; Molinaro, Vespignani, et al., 2008; Silva-Pereyra & Carreiras, 2007). Interestingly, when contextual semantic information strongly biases a specific suffix for the target verb (-ed), a late P600 effect ( ms) has been reported for an unexpected suffix (-ing; Kim & Osterhout, 2005). This is possibly due to the repair process operating on the target verb inflectional morphology: as discussed above, the system would accumulate evidence in order to

4 214 N. Molinaro et al. / Journal of Memory and Language 64 (2011) map all the available information concerning the source of an error during the first P600 stage. If the ill-formedness of the sentence representation is affected by a morphological property of the target word, a repair could then be made on-line, but only at this later stage. In other words, a prolonged P600 would represent the additional effort spent in regularizing an incongruent utterance with a prominent error. Long-lasting P600s elicited by the detection of a number agreement mismatch in initial sentence positions have also been reported in previous studies of on-line resolution of number agreement violations (Molinaro, Kim, et al., 2008; Vespignani et al., in press). In both of these studies the number of a disagreeing constituent (verb in the former and noun in the latter study) influenced agreement processing on a third, number-marked, related constituent (a reflexive pronoun in the former and a verb in the latter study): we found evidence of agreement processing difficulties when the third constituent mismatched in number with the second element (while it agreed with the first), but no effect when the third constituent mismatched in number with the first element (while it agreed with the second). For example, when processing ungrammatical sentences like those in (1) (1) a. The famous dancers was nervously preparing herself... b. The famous dancers was nervously preparing themselves... We reported ERP correlates of agreement processing difficulties both at the verb and at the following plural reflexive pronoun in 1b. The singular reflexive pronouns (in 1a), on the other hand, did not differ from the grammatical control sentence. These findings are suggestive of a general, process-oriented explanation based on, for example, linear order of processing. In this framework, when encountering the number mismatch at the verb, the need for continuous processing of further incoming material would compel the comprehender to resolve the ungrammaticality online: if this is indeed the case, incoming items (following the ungrammaticality) could be integrated in a wellformed partial sentence structure, allowing an easier interpretation of the message intended by the speaker/writer. This on-line regularization would not necessarily reflect the off-line meta-linguistic analysis of the error (in which rumination and off-line conscious reprocessing could be critical), but would represent a fast and easy solution to provide the cognitive system with a well-formed internal representation of the sentence fragment (that would be stored in working memory) during the on-going processing of the sentence. The fact that an error was encountered and the nature of this error could be recorded in episodic memory, i.e. in a different storage from the one holding the sofar-parsed structure. Assuming this natural tendency towards regularization of noisy linguistic input during comprehension, once an agreement mismatch has been detected (for example, after reading the verb in 1), we assumed that the system should either modulate the internal representation of the currently-processed item (critical word) or revise the internal representation of the previous (mismatching) constituent in working memory. In other words, the cognitive system could either ignore the information provided by the currently-processed item (the verb in 1), considering it a speaker/writer misspelling/mispronunciation, or manipulate the information provided in the previous sentence fragment (the subject in 1), that is supposed to be still active in working memory. According to this hypothesis (that we termed Repair), when the mismatch at the second constituent is detected, the ungrammaticality is immediately resolved by assigning a coherent number value to the whole sentence fragment. 1 For example, in a word by word presentation of a sentence like (1a) (Molinaro, Kim, et al., 2008), the initial mismatch between the subject noun phrase and the verb would be revised on-line based on the number of the verb, i.e. singular. When processing the following reflexive pronoun, a number mismatch with its antecedent (the noun phrase in subject position) would no longer be detectable, since the internal representation of the subject has been revised to singular after detecting the mismatch with its verb. According to this account, a number mismatch is immediately re-interpreted coercing the number of the first mismatching constituent (stored in working memory) to the number of the (more recent) second constituent, rather than the opposite. This strategy would thus consist in immediately adapting the number value of the constituents that are stored in working memory when detecting a mismatch on a following constituent that is under consideration: in the example above (1), the number of the subject noun phrase would be adapted to singular because of the verb number. Interestingly, the fact that the information that is within the focus of attention (i.e. the constituent where the mismatch is detected) drives this on-line mismatch resolution by imposing its value is supported by studies on sequentially presented information (Cowan, 2001; McElree, 2001, 2006; Meng & Bader, 2000). 2 However, an alternative explanation is possible that does not exclude that multiple alternative representations are kept in memory until relevant disambiguation, a 1 With the term Repair we do not assume any theoretical approach to the type of model that our findings could explain (either serial or multiple constraints). As previously indicated, both models could support the idea that a single interpretation is pursued (or more active) after an incongruent sentence structure. 2 Using this type of paradigm, we were concerned about the possibility that in earlier experiments our participants could develop ad-hoc processing strategies due to high number of agreement violations presented both within a sentence and across the whole experiment. These strategies could have caused the pattern of results reported here. Thus, we ran a control experiment in which we presented the critical conditions of Vespignani et al. (in press) to two different groups of subjects (for example, if we consider the conditions presented in Table 1, Group 1 saw only the Plural- Singular-Plural condition, while Group 2 saw only the Plural-Singular- Singular condition of Experiment 1). Since participants of each Group saw always the same type of mismatch combination, the ad-hoc strategy hypothesis predicted no differences at the third critical constituent. However, we replicated Vespignani et al. s (in press) findings, thus supporting the idea that repair is performed on-line through a mandatory process.

5 N. Molinaro et al. / Journal of Memory and Language 64 (2011) strategy that we term Recency. We could hypothesize, for instance, that number agreement processing is not so critical for sentence comprehension and is checked only to evaluate local consistency between structurally related elements. What we would measure when presenting a number mismatch (i.e. LAN + P600) would not correlate with any repair process. In this proposal, linear recency is critical (for similar proposals see Tabor, Galantucci, & Richardson, 2004): the inconsistency detected at the second constituent (in 1) is left in stand-by, but the system goes on checking the agreement between the second and the third constituent. In this case there would be no need to presuppose a repair of the ungrammaticality, but the processes underlying the P600 would be sensitive only to local agreement consistency between parts of the same phrase. The value of the subject noun in initial position would not affect the processing correlates of the reflexive pronoun, and the processing of multiple alternatives would be performed and dynamically weighted based on the amount of evidence incrementally processed. In example (1) ERP correlates of processing difficulties between subject and verb emerge because of local incoherence; without considering this mismatch, similar ERP correlates would emerge at the reflexive pronoun only in 1b, because of local mismatch with the previous verb, irrespective of the subject value. The present study In the present study we aim to contrast the Repair and the Recency hypotheses by blocking the hypothesized repair strategy at work for mismatches as in (1), in which the number of the subject is revised to agree with the verb. To do this, we tested our paradigm with a structure in the first position that could not be coerced to acquire the number of the following mismatching constituent. If the plurality of the noun phrase in subject position is not expressed through morphophonological information (as in The boy-s) but through the use of multiple independent discourse entities, as in a conjoined noun phrase, it should not be possible to mentally manipulate the numerosity of the subject referents. Thus, when detecting a mismatch between a conjoined-plural subject (such as The boy and the girl) and its verb (a singular one), it should not be possible to reduce the two subject entities to singular. As in previous studies on Italian sentences, we adapt the paradigm exemplified in Table 1. We designed three experiments; the first two experiments focused on the ERP correlates of the on-line interpretation of different types of agreement mismatches. These first two experiments are aimed at disentangling the Repair and the Recency hypotheses and provide evidence of the on-line processing routines employed by the cognitive system to interpret an agreement mismatch. The third (behavioral) experiment is focused on evaluating the consequences of these on-line processes on the off-line aware interpretation of this type of ungrammatical sentences. Experiment 1: Inflectionally plural subject Experiment 1 focuses on the on-line interpretation of a mismatch between an inflectionally plural noun phrase in subject position and its verb, and the mapping of the processing consequences onto the agreement computation with a subsequent modifier. This experiment is aimed at replicating previous findings (Molinaro, Kim, et al., 2008; Vespignani et al., in press): while in previous experiments the subject number was balanced (merging plural and Table 1 Examples of the experimental sentences used in Experiments 1 3. Experiment 1: Inflectionally plural subject Condition Subject Verb phrase Modifier PPP I fratelli giunsero a casa stanchi della giornata. The siblings arrived [+P] at home tired [+P] by the day. PSP I fratelli giunse a casa stanchi della giornata. The siblings arrived [+S] at home tired [+P] by the day. PSS I fratelli giunse a casa stanco della giornata. The siblings arrived [+S] at home tired [+S] by the day. Experiment 2: Conjoined noun phrase subject Condition Subject Verb phrase Modifier CPP Il fratello e la sorella giunsero a casa stanchi della giornata. The brother and the sister arrived [+P] at home tired [+P] by the day. CSP Il fratello e la sorella giunse a casa stanchi della giornata. The brother and the sister arrived [+S] at home tired [+P] by the day. CSS Il fratello e la sorella giunse a casa stanco della giornata. The brother and the sister arrived [+S] at home tired [+S] by the day. Experiment 3: Grammatical judgement and repetition Condition Initial segment Subject Verb phrase PP Dopo una dura giornata di lavoro i fratelli giunsero a casa. After a day of hard work the siblings arrived [+P] at home. PS Dopo una dura giornata di lavoro i fratelli giunse a casa. After a day of hard work the siblings arrived [+S] at home. CP Dopo una dura giornata di lavoro il fratello e la sorella giunsero a casa. After a day of hard work the brother and the sister arrived [+P] at home. CS Dopo una dura giornata di lavoro il fratello e la sorella giunse a casa. After a day of hard work the brother and the sister arrived [+S] at home.

6 216 N. Molinaro et al. / Journal of Memory and Language 64 (2011) singular stimuli), the present study only focuses on plural subjects (with the mismatching verb always singular). First of all, we expect ERP correlates of agreement processing difficulties at the verb (a LAN followed by a P600 in line with previous studies). Crucially, differential effects are expected at the modifier position when comparing conditions PSP and PSS: the two main hypotheses under consideration, Repair and Recency, predict that the number marked modifier which refers to the subject should elicit a P600 only when it mismatches with the verb (in Table 1, the Modifier position in the PSP condition in Experiment 1): a. The Repair hypothesis states that the mismatch between the subject noun phrase and the verb is immediately interpreted according to the verb number (in line with previous findings); if the following modifier mismatches with the number of the subject noun (now revised to singular), an ERP index of agreement processing difficulties should be recorded at the plural modifier (considering the P600 amplitude on the modifier: PSP > PSS). b. In the Recency hypothesis, since the system is sensitive to the relation between constituents that are in linear proximity, the P600 would be mainly sensitive to linear local mismatches between structurally related constituents. Since in the PSP condition there is no consistency between the singular verb and the plural modifier (part of the same verb phrase), processing difficulties should be evident at the modifier position for PSP but not for PSS (considering the P600 amplitude on the modifier: PSP > PSS). Although the two hypotheses are different in nature, implying a qualitatively different model at work during the processing of syntactic incongruencies, it is interesting to note that they make the same predictions in Experiment 1. Experiment 2 is designed to contrast these alternative models. Experiment 2: Conjoined noun phrase subject In Experiment 2, we use the same design, studying the processing consequences of the on-line computation of a number mismatch between two coordinate singular noun phrases in subject position and their verb. ERP correlates of agreement mismatch are expected at the verb position. Critically, different predictions can be made for the processing of the modifier based on the alternative hypotheses we presented above: a. Following the Repair proposal, a mismatch between a coordinated subject and its verb should not be resolved on the basis of the verb number, since the plurality of the subject (extracted by the coordination of two distinct entities) cannot be reduced to singular. We thus expect the subject plurality to drive disagreement resolution and the following modifier to elicit a P600 only when it disagrees with the subject referents, despite the fact that it agrees (locally) with the verb (Table 1, the Modifier position in the CSS condition in Experiment 2, considering the P600 amplitude on the modifier: CSS > CSP). b. Following the Recency hypothesis, however, the expected outcome is the opposite. Suppose that the parser has suspended its judgment on the subjectverb mismatch and is checking the local consistency of the following number-marked elements. At the modifier, the system should be more sensitive to the local coherence between the verb and the modifier, part of the same verb phrase; so we should expect a P600 when the verb and the following modifier mismatch locally, irrespective of the type of the number feature expressed by the previous subject. Interestingly, no plural marker is expressed in the CSS condition, since all the sentence elements are singular (considering the P600 amplitude on the modifier: CSP > CSS). A summary of the predictions of these first two experiments is reported in Table 2. Experiment 3: Grammatical judgment and repetition Experiment 3 is designed to study the off-line interpretation of an ungrammatical sentence. As previously mentioned, we assume that comprehenders are aware of the ungrammaticality, but, given the need to proceed with the on-going sentence parsing when an error is encountered, a temporary repair is automatically pursued on-line (to integrate the following incoming constituents in a wellstructured partial phrase marker). We are thus interested in two types of evidence: (i) evaluating the end-ofsentence grammaticality judgment for the different conditions and (ii) determining how the on-line resolution of the ungrammaticality affects the off-line interpretation of the whole ungrammatical sentence. For this reason we asked to a group of Italian speakers for an end-of-sentence speeded grammaticality judgment on a set of items presenting the subject-verb constructions investigated in the first two experiments. These items presented the subject-verb structures studied in Experiment 1 (inflectionally plural subject-verb) and in Experiment 2 (conjoined subject-verb), that could be grammatical or not; sentences did not contain any further mismatching constituents (see Experiment 3 in Table 1). We expected high levels of accuracy in the grammaticality judgment of these items. In addition, we asked our participants to repeat the sentence after the grammaticality judgment and, in case of error detection, to correct it; this task was adapted from Meng and Bader (2000). We were interested in determining Table 2 Predictions concerning the ERPs elicited by the number marked modifier in Experiments 1 and 2. Experiment 1: Inflectionally plural subject Repair hypothesis Recency hypothesis PSP P600 P600 PSS No effect No effect Experiment 2: Conjoined noun phrase subject Repair hypothesis Recency hypothesis CSP No effect P600 CSS P600 No effect

7 N. Molinaro et al. / Journal of Memory and Language 64 (2011) the number value of the to-be-corrected sentences: this procedure permits an evaluation of the final (off-line) interpretation of the agreement mismatches. This experiment was in fact designed to verify a possible parallelism between the on-line and the off-line interpretation of subject-verb mismatches. Experiment 1: Inflectionally plural subject Method Participants Twenty-four Italian native speakers participated in the experiment. Mean age of the participants was years (SD = 4.17). All participants were right-handed and had normal or corrected to normal vision. Materials A set of 120 Italian experimental sentences was composed. All of the sentences consisted of a plural noun phrase in subject position and a verb at the beginning of the sentence. We did not use either collective nouns or very infrequent nouns in subject position. In contrast to previous experiments, the verb was not an auxiliary (see Molinaro, Kim, et al., 2008), but a lexical verb. The verb was always intransitive and was followed by a singular prepositional phrase and then a third critical constituent, which was a number marked modifier of the noun in subject position. The noun within the intervening prepositional phrase had feminine grammatical gender to avoid agreement attraction phenomena with the following critical adjective that was always masculine. In this design, the modifier could always easily refer to the noun in subject position. The prepositional phrase was used to introduce a temporal lag between the presentation of the second and third critical elements: this time lag was designed to allow the possible P600 effect elicited by the subjectverb mismatch at the verb to come back to the baseline before the presentation of the third constituent. The critical modifier was never at the end of the sentence to avoid wrap-up effects (Osterhout & Holcomb, 1995) overlapping with the critical effects of interest. From the 120 sentences plural sentences (constituting the PPP condition) we derived, as shown in Table 1 (upper section), 120 sentences belonging to the PSP condition (where both the subject noun and the modifier were plural: I fratelli [+P] giunse [+S] a casa stanchi [+P] della giornata.) and 120 sentences belonging to the PSS condition (where both the verb and the modifier were singular: I fratelli [+P] giunse [+S] a casa stanco [+S] della giornata.). Despite number incongruities (i.e. one or more participants in the message), the agreement manipulation never affected the thematic roles overall, so that the first noun phrase could always be interpreted as the subject of the sentence. The resulting 360 sentences were combined in three lists of 120 sentences with 40 sentences per condition (PPP, i.e. the control condition, PSP and PSS), so that each sentence was presented in one different condition across lists. Two hundred fillers with different syntactic structures were added in the experiment. None contained topicalized constituents. Eighty of these fillers presented agreement violations so that each participant saw an equal number of correct and incorrect sentences in the whole experiment. Procedure Each participant was seated in a dimly illuminated silent room. Words were displayed on a monitor in white letters on a dark-grey background. Each word was presented for 300 ms, followed by a 300 ms blank screen. Sentence order was randomized and every five sentences on average participants were asked to answer a YES/NO comprehension question using keyboard buttons. Comprehension questions never referred to the number of referents in the sentence, for example: Did somebody arrive home tired? The number of questions was balanced across conditions. Participants were instructed not to blink or move their eyes during sentence presentation and they were told that in some sentences there could be syntactic errors. However, they were encouraged to focus on the whole message of the sentence. To familiarize them with the procedure a practice block of 20 items was presented before the experiment, some of which had the structure used in the experiment. On average, the experiment took about 2 h per participant, including electrode montage and debriefing. Data acquisition and analysis EEG was recorded from 17 tin electrodes placed on the scalp with the aid of an elastic cap at standard positions (10 20 system): Fp1, Fp2, Fz, F3, F4, Cz, C3, C4, Pz, P3, P4, O1, O2, T7, T8, P7, and P8. Additional external electrodes were placed on mastoids and around eyes (Veog, Veog+, Heog, Heog+). All sites were referenced to the left mastoid (A1). Impedance was kept below 5 kx for mastoid and scalp electrodes, and below 10 kx for EOG electrodes. Data were acquired at a sampling rate of 250 Hz with a low-pass filter with 100 Hz cutoff frequency and a 10s time constant. EEG recordings were off-line filtered with a 30 Hz lowpass filter and re-referenced to the average activity of the two mastoids. Raw data inspection was performed independently for each subject in order to mark the artifacts (ocular activity, muscular activity and heartbeat) in the EEG recording during the whole experimental session: recordings were highly affected in five participants by heartbeat. Since this rhythmic activity would influence the final ERP results, we performed an ICA based artifact correction procedure. Following an Independent Component Analysis (ICA) on each participant recording, the independent components that explained artifactual activity were identified by visual inspection and subtracted. After the ICA correction we segmented the whole EEG recording in epochs ( 300 to 1300 ms) based on the trigger positions corresponding to the critical target word onsets. We then rejected the epochs that were marked as containing artifacts in the pre-ica raw data inspection: this resulted in the exclusion of two participants from the following analyses and 5.7% of rejections on average in the remaining 22 participants (no differences across conditions in the number of rejections F < 1). Artifact-clean shorter epochs

8 218 N. Molinaro et al. / Journal of Memory and Language 64 (2011) ( 200 to 1000 ms) were then baseline-corrected to the average activity in the 200 ms interval before target word presentation. Epochs were then averaged separately for each participant and condition: we thus extracted ERPs at the Verb and at the following Modifier for each condition (PPP, PSP, PSS). Despite the fact that the two ungrammatical conditions were identical up to the Verb position, we analyzed them separately at the Verb, in order to evaluate that in both cases ERP indexes of agreement detection were elicited and came back to the baseline before the processing of the following critical position. Single channel ERP data were averaged in different spatially homogeneous groups in order to reduce global variance and the number of levels to be interpreted in repeated measure ANOVAs (Greenhouse Geisser corrected). We planned two different clusters of electrodes. The first one was aimed at evaluating the LAN component, which is usually maximal at the left-fontal electrodes. We define this as the Quadrant analysis in which we calculated the average activity of the following clusters: left anterior (LA: F3, C3, T7), right anterior (RA: F4, C4, T8), left posterior (LP: P3, P7, O1) and right posterior (RP: P4, P8, O2). In the relative two-way ANOVA we contrasted the three conditions in a pairwise manner. Factors were Condition (two levels corresponding to the each contrast: PPP vs. PSP, PPP vs. PSS, PSP vs. PSS) and Cluster (four levels corresponding to the four quadrants). The second analysis was designed to better evaluate the P600 component, which is usually maximal along the midline electrodes with possible topographical differences in the anterior-posterior dimension. The Longitude analysis was run on three clusters: frontal (F: F3, Fz, F4), central (C: C3, Cz, C4) and parietal (P: P3, Pz, P4). In the relative two-way ANOVA we contrasted Condition (two levels for each pairwise contrast) and Cluster (three levels: F, C and P). Each analysis was performed on specific time windows of interest corresponding to the expected modulations in amplitude for each component: LAN ( ms), early P600 ( ms) and late P600 ( ms). For both analyses, in the Results section we report significant values for the Cluster factors only when they interact with the Condition. If this was the case, post-hoc analyses were performed on each Cluster; False Discovery Rate correction (Benjamini & Hochberg, 1995) was applied to the resulting p-values. Results Behavioral data Participant accuracy in the comprehension questions was 91%. This indicates that the participants were able to extract the meaning of the whole sentence even in the ungrammatical conditions. Indeed, no differences were found in the accuracy across conditions (F(2, 42) < 1). ERPs elicited at the Verb position Grand-averages elicited in the Verb position (reported in Fig. 1, negative values are plotted up) showed a left-frontal Fig. 1. Event-related potentials elicited by the Verb for the inflectionally plural subject manipulation (Experiment 1). Solid thin line represents the PPP condition; dashed line represents the PSP condition; solid thick line represents the PSS condition. Vertical bars delimit the time windows of interest in the statistical analysis. Negative values are plotted up.

9 N. Molinaro et al. / Journal of Memory and Language 64 (2011) increased negativity around 400 ms for both the PSP and the PSS conditions compared to the Control. We identified this as a focal LAN. This component was followed in both cases by a long-lasting positive effect. In the early phase ( ms), this component is evident in both the anterior and the posterior electrodes, while in the latter phase ( ms) it is mainly evident in the posterior electrodes. In the ms time window (LAN interval), the comparison between PSP and PPP condition showed an interaction between Cluster and Condition in the Quadrant analysis (F(3, 63) = 3.568, p < 0.05; 95% Confidence Interval = ±3.448). Post-hoc contrasts for each cluster of the Quadrant analysis revealed a main effect in the Left- Anterior cluster (t(21) = 2.638, p < 0.05) where the PSP condition (M = lv) was more negative than the PPP condition (M = lv). In the same time window the Quadrant ANOVA comparing the PSS with the PPP condition revealed both a main effect of Condition (F(1, 21) = 4.379, p < 0.05; 95% CI = ±1.988) and the interaction between Cluster and Condition (F(3, 63) = 4.479, p < 0.05; 95% CI = ±3.691). Post-hoc analysis showed again significant effect in the Left-anterior cluster (t(21) = 3.896, p < 0.05): compared to the PPP condition (M = lv), the PSS condition showed a more negative effect (M = lv). Finally, the comparison between PSP and PSS conditions did not reveal any significant effects at this stage. In the following time window ( ms; early P600 interval), the PSP PPP comparison showed a main effect of Condition in the Longitude analysis (F(1, 21) = 5.398, p < 0.05; 95% CI = ±2.45) thus confirming the widely distributed early P600 effect in this time window. The PSP condition was in fact more positive (M = lv) than the PPP condition (M = lv) across midline clusters. Similarly, the PSS PPP comparison showed a main effect of Condition both in the Quadrant analysis (F(1, 21) = 6.377, p < 0.05; 95% CI = ±2.002; PSS M = lv; PPP M = 1.684) and in the Longitude analysis (F(1, 21) = 8.606, p < 0.01; 95% CI = ±2.172; PSS M = lv; PPP M = 1.457). Again, no effect emerged in the PSP PSS comparison (no F > 2). In the late P600 interval ( ms) the PSP PPP comparison revealed an interaction between Condition and Cluster in the Quadrant analysis (F(3, 63) = 7.242, p < 0.01; 95% CI = ±4.715). Post-hoc comparisons showed significant differences both in the Left-Posterior cluster (t(21) = 2.081, p < 0.05; PSP M = lv; PPP M = lv) and in the Right-Posterior cluster (t(21) = 3.343, p < 0.05; PSP M = lv; PPP M = lv) confirming the posterior distribution of the effect. In the Longitude analysis the interaction between Condition and Cluster also emerged (F(2, 42) = 7.602, p < 0.01; 95% CI = ±5.3655). Following planned contrasts showed that the effect was significant in the Parietal cluster (t(21) = 2.838, p < 0.05) where the PSP conditions (M = lv) was more positive than the PPP (M = lv). The PSS PPP comparison showed an interaction between Condition and Cluster both in the Quadrant (F(3, 63) = , p < 0.001; 95% CI = ±7.725) and in the Longitude Fig. 2. Event-related potentials elicited by the modifier for the inflectionally plural subject manipulation (Experiment 1). Solid thin line represents the PPP condition; dashed line represents the PSP condition; solid thick line represents the PSS condition. Vertical bars delimit the time windows of interest in the statistical analysis. Negative values are plotted up.

10 220 N. Molinaro et al. / Journal of Memory and Language 64 (2011) (F(2, 42) = 6.674, p < 0.01; 95% CI = ±6.958) analysis. In the former analysis the interaction is due to the effect in the Left-Posterior cluster (t(21) = 2.462, p < 0.05; PSS M = 1.99 lv; PPP M = lv), while in the latter analysis only a marginal effect emerged in the Parietal cluster (t(21) = 1.834, p < 0.08) where the PSS condition (M = lv) was more positive than the PPP (M = lv). No significant effects emerged in the PSP PSS comparison (all Fs < 1). ERPs elicited at the Modifier position Grand-average waveforms (Fig. 2, negative values are plotted up) showed a larger positive effect starting around 500 ms for the PSP condition compared to the other two conditions. The PSS condition in fact does not seem to reliably dissociate from the PPP condition. No clear sign of a LAN is visually detectable in the waveforms. Statistics in the ms LAN interval did not reveal any reliable differences (all Fs < 1.5). In the early P600 time window ( ms) the comparison between PSP and PPP showed a main effect of Condition in the Quadrant analysis (F(1, 21) = 4.602, p < 0.05; 95% CI = ±1.38): the effect is due to a more positive amplitude for the PSP condition (M = lv) compared to the PPP (M = lv). A main effect of condition emerged for this comparison also in the Longitude analysis (F(1, 21) = 5.993, p < 0.05; 95% CI = ±1.439) as evidenced by the mean values across midline clusters (PSP M = lv; PPP M = lv). While the PSS PPP comparison did not show any significant effects, the PSP PSS analysis showed a main effect of Condition in the Longitude analysis (F(1, 21) = 4.369, p < 0.05; 95% CI = ±1.08) as the PSP condition (M = lv) was more positive than the PSS one (M = lv) across midline clusters. In the following time window ( ms; late P600 interval), the pattern was similar to the previous time window. The PSP PPP comparison showed main effect of Condition both the Quadrant (F(1, 21) = 6.664, p < 0.05; 95% CI = ±2.62; PSP M = lv; PPP M = lv) and in the Longitude analyses (F(1, 21) = 7.527, p < 0.05; 95% CI = ±3.22; PSP M = lv; PPP M = lv). In the same time window the PSS and the PPP did not differ. However, the PSP PSS contrast showed main effects of condition in both types of analysis (Quadrant: F(1, 21) = 4.971, p < 0.05; 95% CI = ±1.91; PSP M = lv; PSS M = lv; Longitude: F(1, 21) = 5.504, p < 0.05; 95% CI = ±3.04; PSP M = lv; PSS M = lv). Summary of results In this first experiment we replicated previous findings on subject-verb agreement violations. As consistently reported by previous studies, the morphosyntactic mismatch between the probable subject noun and the verb elicited a LAN component followed by a long-lasting P600. The P600 in the earlier time window shows a wide topographical distribution, while in the latter time window it is mainly posterior. In line with previous data (Molinaro, Kim, et al., 2008) on mismatch resolution, only when the modifier disagrees with the verb (and agrees with the subject noun phrase, PSP) do ERPs show a clear P600 effect compared to the grammatical condition (PPP). On the other hand, the condition in which the modifier disagrees with the subject noun phrase (and agrees with the verb, PSS) behaved similarly to the control condition (PPP). These findings are in line with the two main hypotheses considered in the Introduction, Repair and Recency. The fact that we did not find any LAN on the modifier could be due to the type of agreement feature processed in this position: the across-phrase relation between the subject antecedent noun and the modifier in the present experiment is not a structural agreement relation, unlike verb-subject agreement, which is triggered in a Spec-Head configuration. In terms of processing, after reading a noun phrase in initial position an active expectation would be triggered for the verb, but not for an adjunct. Experiment 2 is designed to contrast the two hypotheses: according to the Repair hypothesis, a different ERP pattern at the modifier is expected with respect to Experiment 1 (see predictions in Table 2). Since the subject is composed by two conjoined noun phrases, it cannot be reduced to singular, and the repair cannot be performed at the following mismatching verb adapting the internal representation of the subject. However, replicating the findings of Experiment 1 would support the Recency (in terms of local feature consistency) hypothesis. Experiment 2: Conjoined noun phrase subject Method Participants Twenty-two Italian native speakers (mean age years; SD = 3.69) took part in Experiment 2. All of them were right-handed and had normal or corrected to normal vision. Material We adapted the stimuli used in the previous experiment, introducing two coordinated singular noun phrases in subject position. Thus, after two coordinate noun phrases a plural verb followed in the CPP control condition and a singular verb followed in the two critical experimental conditions (see examples in Table 1). After two coordinate singular noun phrases, the following verb is a grammatical continuation only when it is plural. The choice of two singular nouns in the mismatch conditions was aimed at under-specifying the inflectional morphology that marks for plural. We tried to reduce possible local attraction effects between the conjoined noun phrase and the verb. During sentence comprehension, number attraction effects are stronger when the sentence is ungrammatical (Wagers et al., 2009). However, these effects are stronger in singular subject-plural verb configurations, while the structure we used is constituted by a plural subject-singular verb. We thus exclude possible attraction effects influencing the interpretation of the number mismatch. In addition to these experimental sentences we added 200 filler sentences with a different syntactic structure:

11 N. Molinaro et al. / Journal of Memory and Language 64 (2011) sentences contained grammatical violations not involving number agreement mismatches. Again, no filler contained a topic structure. Procedure The same as in Experiment 1. Data acquisition and analysis We used the same strategy of acquisition and analysis as in Experiment 1. The manual rejection in this second experiment resulted in the exclusion of 6.2% of epochs on average (no differences across conditions in the number of rejections F < 1). Results Behavioral data Participants answered the comprehension questions with an overall accuracy of 93%. No accuracy difference was found across conditions (F(2, 42) < 1). ERPs elicited at the Verb position In this position, the mismatch between the plural coordinate Subject and the Verb elicited a more positive effect between 500 and 800 ms evident at frontal and parietal electrodes for both the CSP and the CSS condition. Neither a LAN nor a late P600 was evident for these two conditions compared to the CPP condition (Fig. 3, negative values are plotted up). In the ms time window (LAN interval) the analysis did not reveal any significant effects related to Condition (no F-value was associated to a probability lower than p = 0.5). In the later time interval ( ms; early P600) the CSP CPP comparison revealed a main effect of Condition in the Longitude analysis (F(1, 21) = 4.703, p < 0.05; 95% CI = ±2.23) due to the larger positivity in this time window for the CSP condition (M = lv) compared to the CPP (M = lv). Also the CSS CPP comparison revealed a main effect of Condition in the Longitude analysis (F(1, 21) = 4.982, p < 0.05; 95% CI = ±1.91), due to the positive effect for the CSS condition (M = lv). In the ms interval (late P600) no effect related to the Condition factor emerged (only in the CSP CPP comparison was the effect of Condition lower than p = 0.2 in the Longitude analysis; F(1, 21) = 3.065, p = 0.19). ERPs elicited at the Modifier position As evident in Fig. 4, ERPs in this position showed a positive shift for the CSS condition compared to the other two conditions (CPP and CSP) that did not differ between each other. Again, there is no sign of a LAN in the early time window. The statistics in the ms time interval did not show any significant effects related to Condition in the pairwise comparisons (all p-values > 0.5). In the early P600 time window ( ms) the CSS CPP comparison showed an interaction between Condition and Cluster in the Quadrant analysis (F(3, 63) = 3.773, Fig. 3. Event-related potentials elicited by the Verb for the conjoined noun phrase subject manipulation (Experiment 2). Solid thin line represents the CPP condition; dashed line represents the CSP condition; solid thick line represents the CSS condition. Vertical bars delimit the time windows of interest in the statistical analysis. Negative values are plotted up.

12 222 N. Molinaro et al. / Journal of Memory and Language 64 (2011) Fig. 4. Event-related potentials elicited by the modifier for the conjoined noun phrase subject manipulation (Experiment 2). Solid thin line represents the CPP condition; dashed line represents the CSP condition; solid thick line represents the CSS condition. Vertical bars delimit the time windows of interest in the statistical analysis. Negative values are plotted up. p < 0.05; 95% CI = ±4.63) due to the larger positive effect in the Left-Posterior cluster (t(21) = 2.471, p < 0.05) for the CSS (M = lv) compared to the CPP (M = lv). The same comparison revealed an interaction between Condition and Cluster also in the Longitude analysis (F(2, 42) = 8.39, p < 0.01; 95% CI = ±2.93): in the Parietal cluster the CSS condition (M = lv) was more positive (t(21) = 2.125, p < 0.05) than the CPP condition (M = lv). In the same time window the CSS CSP comparison also showed an interaction between Cluster and Condition in the Longitude analysis (F(2, 42) = 7.402, p < 0.01; 95% CI = ±2.21). This last interaction reflects the larger positivity for the CSS condition (M = lv) compared to the CSP condition (M = lv) in the Parietal cluster (t(21) = 2.174, p < 0.05). In this time interval CPP and CSP did not differ statistically. In the following time interval ( ms; late P600), the CSS CPP comparison showed an interaction between Condition and Cluster in the Longitude analysis (F(2, 42) = 5.503, p < 0.05; 95% CI = ±3.76). This interaction reflects the larger positive effect (t(21) = 2.588, p < 0.05) for the CSS condition (M = lv) compared to the CPP (M = lv). The CSS CSP comparison showed an effect of condition both in both analyses (Quadrant: F(1, 21) = 4.731, p < 0.05; 95% CI = ±1.98; CSS M = lv; CSP M = lv; Longitude: F(1, 21) = 4.701, p < 0.05; 95% CI = ± ; CSS M = lv; CSP M = lv). Finally, the CSP CPP comparison did not reveal any significant effects related to Condition (all p-values higher that p = 0.5). Summary of results Two main findings emerged in Experiment 2. First, in the verb position, no LAN effect was observed, and the P600 elicited by the agreement mismatch emerged only in the early ( ms) time window; this last effect was topographically distributed across the scalp (Fig. 5 shows the difference waves between the average ERPs elicited by the violation conditions and the control in both Experiments 1 and 2), as also confirmed by the lack of interaction between the Condition and the Cluster factors. Second, in the following modifier position, a P600 effect emerged only for the CSS condition, compared to both the CPP and the CSP condition that did not differ from each other. These results contrast with the findings of Experiment 1, in which we recorded the opposite pattern: the PSS condition did not differ from the PPP, while the PSP condition elicited a P600. In addition, in line with the findings of Experiment 1, in Experiment 2 we did not find any LAN at the modifier position, thus suggesting that a qualitatively similar processing mechanism (in different conditions) was elicited at the modifier position in the two experiments (see Fig. 6 where we report the difference waves between the conditions that elicited the P600 on the modifier position, PSP in Experiment 1 and CSS in Experiment 2, minus the Control condition).

13 N. Molinaro et al. / Journal of Memory and Language 64 (2011) Verb Position F3 Fz F4 Experiment 1: *I fratelli (+P) giunse Experiment (+S)... 1 Experiment 2 Experiment 2: *Il fratello e la sorella giunse (+S)... LAN T7 C3 Cz C4 T8 early & late P600 P7 P3 Pz P4 P8 4 µv 2 O1 O2 Experiment 1 Experiment 2 ms N p1 LAN early P600 Exp1 Exp2 Exp1 Exp2 Exp1 late P600 Exp2 Fig. 5. Difference waveforms between the average of the two mismatching conditions (mean of PSP and PSS for Experiment 1 and CSP and CSS for Experiment 2) and the grammatical condition (PPP in Experiment 1 and CPP in Experiment 2) at the Verb in Experiment 1 (inflectionally plural subject manipulation) and Experiment 2 (conjoined noun phrase subject manipulation). The maps referring to the critical ERP components are calculated between 350 and 450 ms for the LANs, between 500 and 800 ms for the early P600s and between 800 and 1000 ms for the late P600s. Across-experiment comparison We also compared the findings across the first two experiments. Given the high number of violations required by the experimental design and the high number of items per condition used in an ERP experiment we decided to manipulate the type of noun phrase (inflectionally plural or conjoined) in subject position as a between experiment factor. In order to avoid the development of particular strategies for processing the experimental sentences, we used a large number of fillers (200 further sentences). This technical constraint did not make it possible to play the subject type as a within subject factor. Thus, we ran further statistical analyses to evaluate the effects across the between subject manipulation of subject type. We ran the statistics used in both experiments, adding a further factor, Experiment, implemented in the ANO- VAs as a between subject factor. For each sentence position and each time window of interest we ran both the Quadrant and the Longitude analysis. In the Quadrant analysis we ran a three way ANOVA with the following factors: Condition (pairwise comparisons, where X could be both P and C: XPP XSP, XPP XSS, XSP XSS), Cluster (four levels: LA, RA, LP, RP) and Experiment (two levels: Experiment 1 and Experiment 2). In the Longitude ANOVA the same factors were used: Condition, Cluster (three levels: Frontal, Central and Parietal) and Experiment. The main effects of interest in this last analysis comprise the interaction with the Experiment factor. ERPs elicited at the Verb position In the LAN time window ( ms) the Quadrant analysis revealed the critical interactions between Condition, ClusterandExperimentforboththeXPP XSP (F(3, 126) = 2.667, p < 0.05) and the XPP XSS comparison (F(3, 126) = 2.817, p < 0.05). This interaction with the Experiment factor confirms the reliability of the LAN in Experiment 1 compared to Experiment 2. In Fig. 5 we plotted the difference waves between the average ERPs elicited by the violation conditions and the correct condition on the verb in the two experiments. It is evident that the LAN emerged only in Experiment 1.

14 224 N. Molinaro et al. / Journal of Memory and Language 64 (2011) Fig. 6. Difference waveforms at the modifier position between the condition eliciting the P600 effect and the control condition: in Experiment 1 the difference is calculated from the PSP PPP subtraction, i.e. the comparison showing the P600 effect in Experiment 1; in Experiment 2 the difference is calculated from the CSS CPP subtraction, i.e. the comparison showing the P600 effect in Experiment 2. The maps of the P600s are extracted from average activity in the whole P600 time window (i.e. both the early and the late window: ms). In the early P600 time window ( ms) no interaction with the Experiment factor emerged (all Fs < 1.5). In the following time window ( ms), statistics showed interactions between Condition, Cluster and Experiment both in the XPP XSP (Quadrant: F(3, 126) = 5.691, p < 0.01; Longitude: F(3, 126) = 6.669, p < 0.01) and the XPP XSS (Quadrant: F(3, 126) = 7.426, p < 0.01; Longitude: F(3, 126) = 4.353, p < 0.05) comparison. This means that the late stage of the P600 is different between the two experiments, larger in Experiment 1 compared to Experiment 2 in the posterior electrodes of the scalp (see late P600 effects in Fig. 5). ERPs elicited at the Modifier position As for this latter position, the pairwise comparisons in the P600 time windows confirm the differential effects across the two experiments. In fact in the ms time window the Longitude analysis showed an interaction between Condition and Experiment for the XPP XSP comparison (F(1, 42) = 4.358, p < 0.05); the same interaction emerged also for the XSP XSS (F(1, 42) = 9.797, p < 0.01) and, marginally significant, for the XPP XSS comparison (F(1, 42) = 3.36, p < 0.074). The following time window ( ms) showed a similar trend. The XPP XSP comparison showed interaction between Condition and Experiment (Longitude analysis: F(1, 42) = 7.951, p < 0.01); the XPP XSS comparison showed interaction between Condition, Cluster and Experiment (Longitude analysis: F(3, 126) = 4.491, p < 0.05); finally, also the XSP XSS comparison showed the triple interaction between Condition, Cluster and Experiment (Longitude analysis: F(3, 126) = 3.171, p < 0.07). The similar pattern of effects emerging in the two time windows (Fig. 6) robustly confirms that very similar effects are elicited in the two experiments, even if in opposite directions. In Fig. 6 we plotted the difference waves between the condition that elicited the P600 on the modifier position (PSP in Experiment 1 and CSS in Experiment 2) and the control. Since the effect was similar across time windows we plotted the maps for the whole P600 time window. Experiment 3: Grammatical judgement and repetition In the third experiment we evaluated the off-line interpretation of a number mismatch between subject and verb. We used a paradigm developed by Meng and Bader (2000) in their Experiment 4. They required participants to judge the grammaticality of German sentences and then to repeat them; in case of ungrammaticality they were required to provide a corrected version of the stimulus. These authors used sentences where wh-phrases and their finite verb disagreed in number. When required to repeat and correct those sentences, participants tended to alter the morphosyntactic case feature on the initial wh-phrase, instead of changing the morphosyntactic number feature of the following finite verb. These findings suggest that a

15 N. Molinaro et al. / Journal of Memory and Language 64 (2011) morphosyntactic mismatch is interpreted off-line based on the properties of the more recent constituent. If this is true, a mismatch between an inflectionally plural subject and a singular verb (condition PS, Experiment 3, in Table 1) should be corrected based on the verb number (singular); we however expect the opposite correction when two conjoined nouns are presented in subject position (condition CS, Experiment 3, in Table 1). This experiment is aimed at verifying three main aspects of the off-line processing of number agreement mismatches. Through this paradigm we can first evaluate the accuracy with which participants detect the subject-verb ungrammaticalities off-line, to make sure they are aware of the errors. Second, we can determine if the on-line effects we recorded on the modifier position reflect the off-line meta-linguistic interpretation of the mismatch. Experiment 1 showed that an inflectionally plural subject-singular verb mismatch is interpreted on-line as singular, while Experiment 2 showed a conjoined subject-singular verb to be interpreted as plural. It is interesting to see how participant correct off-line these number mismatches. Third, it is possible to verify if a conjoined subject is more resistant to the repair strategy, as assumed throughout the whole paper: in fact we proposed that a conjoined noun phrase cannot be revised to singular since this would imply deleting one referent, thus altering the nature of the message. Method Participants Twenty-two Italian students (12 females, mean age: years; age range: years) taking part in the Erasmus program of the University of the Basque country participated in Experiment 3 in exchange for 10. All of them were native Italian speakers visiting Spain for less than 1 month. Materials We selected a subset of 48 sentences from the dataset used in the previous two Experiments. Twenty-four sentences from Experiment 1 and 24 sentences from Experiment 2 were adapted for the purposes of the present experiment. In Experiment 3 the set adapted from Experiment 1 had the following structure: a plural noun phrase was immediately followed by the verb that was never in sentence final position; the position of the critical words varied across items. The subject and the verb were the only two number-marked elements in the sentence Dopo una dura giornata di lavoro i fratelli giunsero a casa. After a day of hard work the siblings arrived home; see PP, Plural subject Plural verb, condition in Table 1, lower panel). The set extracted from Experiment 2 had the same structure, but the subject was constituted by two conjoined singular NPs ( Dopo una dura giornata di lavoro il fratello e la sorella giunsero a casa. After a day of hard work the brother and the sister arrived home; see CP, Conjoined subject - Plural verb, condition in Table 1). We balanced the number of words per sentence in the different conditions (the average number of words was 12.5). From these 48 sentences we composed the number agreement violations modifying the number of the verb to singular (...giunsero...?...giunse...; see PS and CS conditions in Table 1, lower panel). We then created two lists with 12 sentences per condition (PP, PS, CP and CS) so that each participant did not see the same sentence in two different conditions. In order to avoid any bias toward singular or plural responses, 52 additional fillers were used. Since the experimental material was mainly constituted by plural sentences, the fillers mainly contained grammatical singular sentences and singular sentences containing gender violations in which we expected the repetition to be singular, plus some sentences with a singular subject following a plural constituent (never its verb). Each participant was presented with 100 sentences, half of them grammatically correct and half not. Procedure Participants were seated in a quiet room. The experimental sentences were presented on a notebook screen word by word at the center of the screen, similarly to the previous ERP experiments (white letters on a dark-grey background). However, rate of presentation was not fixed. In the previous experiments, the long SOA (600 ms) between subsequent words was driven by the need of avoiding overlap of the ERP components elicited by each word with the ones elicited by the following one. Since we did not record EEG in this experiment, we used a rate of presentation that better simulated speech or reading rate, with shorter words presented for a shorter interval compared to longer words. Thus, a fixation cross at the center of the screen warned the participant that a sentence was going to start. After participant s button press, each word of the sentence was presented for 187 ms plus 27 ms for each letter of that word (see Nieuwland & Kuperberg, 2008). No blanks were presented between words and the last word of the sentence was followed by a period. Immediately after sentence presentation a prompt appeared on the screen asking for a speeded grammaticality judgment of the sentence (Was the sentence grammatically correct?). Participants were required to answer as fast and as accurately as possible by pressing the corresponding YES/NO buttons on a joypad. After the participant s answer an additional prompt appeared on the screen asking the participant to repeat the sentence (Now repeat). Participants were required to repeat the sentence verbatim as accurately as possible if the sentence was grammatically correct. In case of grammatical errors participants were required to provide a corrected version of the sentence. There was no specific requirement on the type of correction to be made, participants had just to produce a grammatical version of the sentence. Participants were required to respond immediately, even if there was no explicit time limit. For each trial we reported the number assigned to the whole repeated sentence (either Singular (S) or Plural (P)), considering the repetition correct when both the subject and the verb were reported in the correct order. Five practice sentences preceded the experimental items; the whole experiment, that was divided in two blocks with a 5 min pause in the middle, lasted approximately 45 min.

16 226 N. Molinaro et al. / Journal of Memory and Language 64 (2011) Data analysis Participants whose accuracy across the whole experiment was lower than 80% in the grammatical conditions (PP and CP in Table 1) were excluded from analyses. Response time and accuracy of the speeded grammaticality judgment were analyzed grouping by both subjects (F1) and items (F2). Response times that were more than three standard deviations longer than the average response of that subject were considered outliers. Two-way analysis of variance on these data considered the following factors: Grammaticality (Correct vs. Violation) and Type of plurality (Inflectionally plural subject vs. Conjoined subject). The main analysis focused on the number of Singular and Plural repetitions for each condition that were compared through a Chi-Squared test. In this analysis we only considered the items whose grammaticality was correctly judged. Direct comparison between the proportion of corrections in different conditions was pursued using the 2- sample test for equality of proportions (Wilson, 1927); a correction of continuity was applied. We mainly compared the corrections between the two correct conditions (PP and CP) and the two ungrammatical ones (PS and CS). Results Response times Three participants were excluded from further analyses since their performance in the whole experiment was lower than the accuracy threshold in the grammatical conditions. Average RTs for each condition are reported in Table 3. Statistics did not show any significant effect; there was only a marginal effect of Type of plurality in the bysubject statistics (F1(1, 18) = 3.769, p = 0.068), suggesting a slightly more difficult judgment for the Conjoined subject conditions (M = 1772 ms, SD = 603 ms) compared to the Inflectionally plural subject conditions (M = 1669 ms, SD = 472 ms). It is possible that the higher number of words involved in the grammaticality judgment of the conjoined conditions affected reading times. Accuracy Average accuracies for each condition are reported in Table 4. A main effect of Type of plurality reflects the Table 4 Accuracy of the speeded grammaticality judgments in the four critical conditions of Experiment 3. The lower panel show the statistics calculated in the ANOVA. Condition Average accuracy levels (SD) PP (plural plural) 95.1% (6.6) CP (conjoined plural) 90.9% (7.2) PS (plural singular) 91.6% (8.8) CS (conjoined singular) 86.2% (16.3) ANOVA (2 2: Grammaticality Type of Plurality) Grammaticality F1(1, 18) = 0.05, n.s. F2(1, 92) = 0.01, n.s. Type of plurality F1(1, 18) = 5.09, p < 0.05 F2(1, 92) = 3.73, p = Grammaticality Type of Plurality F1(1, 18) = 4.73, p < 0.05 F2(1, 92) = 2.52, n.s. higher accuracy for the Inflectionally plural subject conditions (M = 93.3%, SD = 7.8%) compared to the Conjoined subject conditions (M = 88.5%, SD = 11.7%). Planned comparisons however did not show any significant difference in those contrasts (see barplots in Fig. 7). Repetitions When correctly judged, in 10.6% of the cases either the repetition did not correspond to the stimulus or was forgotten by the participant (defined as Other in Table 5). In the former case, participants forgot either subject or verb information; in many cases the thematic roles were not reported correctly. Number of Repetitions and relative percentage across all the participants is reported in Table 5. The Correct conditions were repeated correctly in the majority of cases (PP: 178 (P) vs. 13 (S), Chisquared = , df = 1, p < 0.001; CP: 152 (P) vs. 29 (S), Chi-squared = 83.58, df = 1, p < 0.001). The effect was more stable for the Inflectionally plural condition than the Conjoined subject condition (Chi-squared = 6.98, df =1, p < 0.01). Accuracy Type fo plurality, p<0.05 Table 3 Response times (RT) of the speeded grammaticality judgments in the four critical conditions of Experiment 3. The lower panel show the statistics calculated in the ANOVA. Condition Average RT (SD) PP (plural plural) 1618 ms (449) CP (conjoined plural) 1790 ms (636) PS (plural singular) 1719 ms (500) CS (conjoined singular) 1754 ms (584) ANOVA (2 2: Grammaticality Type of Plurality) Grammaticality F1(1, 18) = 0.32, n.s. F2(1, 92) = 0.41, n.s. Type of plurality F1(1, 18) = 3.76, p = F2(1, 92) = 1.27, n.s. Grammaticality Type of Plurality F1(1, 18) = 2.86, p = F2(1, 92) = 2.86, n.s. % of correct judgements CP CS PP PS Conjoined subject Inflectionally plural subject Fig. 7. Accuracy levels in the four critical conditions of Experiment 3. Dark grey bars indicate the Correct conditions (CP, conjoined subjectplural verb and PP, inflectionally plural subject-plural verb), while the light grey bars indicate the Violation conditions (CS, conjoined subjectsingular verb and PS, inflectionally plural subject-singular verb).

17 N. Molinaro et al. / Journal of Memory and Language 64 (2011) Table 5 Number (and percentage) of Singular and Plural repetitions calculated over the whole set of responses given by participants in the four critical conditions of Experiment 3. Condition Singular repetitions Plural repetitions Other Total PP (plural plural) 13 (6.2%) 178 (85.2%) 18 (8.6%) 209 CP (conjoined plural) 29 (14.1%) 152 (73.4%) 26 (12.5%) 207 PS (plural singular) 124 (57.2%) 66 (30.4%) 27 (12.4%) 217 CS (conjoined singular) 34 (17.2%) 145 (73.6%) 18 (9.1%) 197 The main interest of the experiment was, however, in the repetitions involving corrections of the sentence grammaticality. The CS condition was robustly corrected to plural (CS: 145 (P) vs. 34 (S), Chi-squared = 68.83, df =1, p < 0.001); on the other hand, PS was corrected to singular the majority of the times (PS: 66 (P) vs. 124 (S), Chisquared = 17.7, df =1,p < 0.01). The selection of the singular in the PS condition (PS: = 58) appears less robust compared to the selection of the plural in the CS condition (CS: = 111). We thus compared the proportion of Singular repetitions for the PS condition to the proportion of Plural repetitions for the CS condition. The 2-sample test for equality of proportions showed a significant difference in this dimension (Chi-squared = 10.78, df =1,p < 0.01). Given that the analysis was run on proportions, we exclude a possible influence of repetitions classified as Other. Summary of results While the contrast between Experiments 1 and 2 supported the Repair hypothesis, Experiment 3 showed that the hypothesized repair process has an effect also on the off-line interpretation of an ungrammatical sentence. We thus first showed that Italian speakers had high levels of accuracy in the detection of the number mismatches (higher than 80%). Second, we showed that when the cognitive system detects a number mismatch between a conjoined noun phrase and a singular verb, the number of the subject drives the resolution of the mismatch. This effect is very strong, as evident in the amount of plural repetitions for the CS conditions (see Table 5). On the other hand, the mismatch between an inflectionally plural subject and a singular verb is corrected to singular, in line with previous findings that highlight the pivotal role of the second element in the resolution of a morphosyntactic incongruence (Meng & Bader, 2000; Molinaro, Kim, et al., 2008; Vespignani et al., in press). This is a surprising result, since it is widely assumed that number values are interpreted in the noun position and for this reason supposed to drive mismatch resolution in a subject-verb mismatch. Third, we confirmed the hypothesis that a conjoined noun phrase is more resistant to the repair strategy compared to the inflectionally plural subject. As evident in Table 5, the percentage of singular repetitions for PS is lower than the percentage of plural repetitions for CS. As previously noted, off-line meta-linguistic judgments on number mismatches should not necessarily be similar to the on-line immediate resolution of the ungrammaticality, since further variables could influence this off-line evaluation. It is worth noting that the ERP effect at the verb is more prominent for violations involving an inflectionally plural subject, while the effect observed off-line for this condition is weaker compared to the conjoined subject condition. Nonetheless, the available findings strongly support the hypothesis that a Repair process is performed on-line, and has an effect on the off-line interpretation of the ungrammatical input. An inflectionally plural subject-singular verb construction tends to be revised to singular, while a conjoined subject-singular verb tends to be corrected to plural. General discussion In the present study we analyzed the on-line resolution of subject-verb number agreement mismatch and its impact on the off-line interpretation of the sentence ungrammaticality. The Repair hypothesis An interesting dissociation was recorded at the modifier position in the first two experiments. In Experiment 1, a P600 was elicited by the PSP condition, while in Experiment 2 the same effect was elicited by the CSS condition. This ERP similarity (a P600 with a central-posterior distribution, especially in its later time window, without any LAN) indicates that a similar computation is elicited in the two cases. This mechanism is consequential to the on-line processing of the mismatch between subject and verb. Indeed, the ERP effects at the modifier position in the two experiments suggest insights into the on-line interpretation of the number mismatch at the verb position. In Experiment 1 ( I fratelli giunse The siblings arrived [+S]) we proposed that the system has to immediately select one number value to solve the incongruence (Repair hypothesis: see also Molinaro, Kim, et al., 2008; Vespignani et al., in press): as shown by some authors, the last presented element has a pivotal role in the comprehension of sequentially presented information (Cowan, 2001; McElree, 2001, 2006; Meng & Bader, 2000). In order to build a well-formed sentence fragment (thus allowing an easier integration of further incoming constituents), the internal representation of the ungrammatical sentence is repaired to be grammatical: in Experiment 1 the number of the verb is maintained as anchoring value and the internal representation of the inflectionally plural subject noun is revised to singular. This is possible since the number of the subject referent has been extracted by the inflectional morphology of the head noun (see also Meng & Bader,

18 228 N. Molinaro et al. / Journal of Memory and Language 64 (2011) ). Reanalyzing the subject numerosity to singular makes the following modifier ungrammatical when it is plural (and grammatical when it is singular). The P600 effect recorded only on the plural modifier (PSP condition) confirms our analysis. Thus, our interpretation of the phenomenon is that the sentence processor needs to operate an immediate Repair of the ungrammaticality (number disagreement) to integrate new incoming constituents with a temporarily well formed phrase marker incrementally stored in working memory. However, as we stated previously (Molinaro, Kim, et al., 2008), alternative explanations are possible for the P600 pattern at the modifier position in Experiment 1. According to the Recency analysis, agreement features could be handled by the processing routines mirrored in the P600 just as surface cues for dealing with local (short-distance) relations. This would explain the P600 at the modifier when it mismatches with the surface properties of the local verb (but not with those of the subject noun phrase). A repair mechanism would not then be needed to explain the findings in Experiment 1. Experiment 2 ( Il fratello e la sorella giunse The brother and the sister arrived [+S]) permits contrasting these alternative explanations. The Recency hypothesis predicts a P600 on the plural modifier, i.e., when it mismatches locally with the verb. This was not the case, since we recorded a P600 on the modifier when it was singular: given the P600 in this condition (CSS condition), the Recency hypothesis cannot hold, since the whole sentence does not have any constituent morphophonologically marked to plural. These findings strongly support the Repair hypothesis. The manipulation we performed in Experiment 2 was designed to block the repair strategy we observed in Experiment 1 (see also Experiment 3 repetitions for the CS condition): in fact, manipulating the representation of the coordinate subject would imply removing one of the two referent noun phrases, thus altering the nature of the whole message. In this frame, the number of the subject cannot be revised without affecting the nature of the whole message. Here, the parser selects the plurality of the coordinate subject as a referent value for interpreting the number agreement mismatch. A possible interpretation is that in Experiment 2, since the subject representation cannot be altered, it is the number of the verb which should be re-interpreted to plural. This would cause a mismatch with the following singular modifier, eliciting the P600 observed in the CSS condition. In this view, the plurality of the subject referents in a conjoined noun phrase is semantically more stable (being not re-interpretable) compared to the plurality extracted by the morphophonological properties of the subject noun phrase used in Experiment 1. This hypothesis fits well with the shorter P600 effect recorded on the verb in Experiment 2. The more prominent violation on the verb in Experiment 1 thus elicits a more complex electrophysiological pattern (LAN followed by a long-lasting P600) compared to Experiment 2. In our opinion, the additional processing in Experiment 1 reflects the additional work operated by the parser to revise the subject representation (stored in working memory) to singular (for similar explanation of the late phase of the P600 see Barber & Carreiras, 2005, and Molinaro, Vespignani, et al., 2008, who propose a reanalysis process based on Faussart, Jakubowicz, & Costes, 1999). On the other hand, in Experiment 2 the impossibility of coercing a coordinate subject to singular renders the number of the verb misleading. Consequently, the cognitive system invests less resources in the processing of the mismatching verb, without altering the information stored in working memory; this is reflected in the less prominent ERP responses recorded at the verb in Experiment 2 (lack of late P600, see Fig. 5). Experiment 3 showed that this on-line repair process has an influence also on the off-line interpretation of the sentence. When processing a subject-verb number agreement mismatch, participants are aware of the ungrammaticality of the sentence, as evidenced by the high levels of accuracy in all conditions. This good performance reflects the fact that our participants did not ignore the morphosyntactic properties of our sentences. The only significant difference we obtained was between the inflectionally plural subject conditions and the conjoined subject conditions, accuracy being slightly lower and response times longer in the latter. This difference is possibly due to the greater difficulty in processing subject-verb agreement with conjoined subject phrases that are inherently more complex. More critical for our study, the off-line correction of the number mismatch (as evidenced by the number of repetitions in the violation conditions, see Table 5) was identical to the on-line resolution, as evidenced by the P600 effects on the modifier position (see Fig. 6). This additional evidence provides further support for the reliability of the Repair hypothesis as a critical processing routine by means of which the cognitive system processes agreement irregularities. However, we are not claiming that the on-line repair directly determines the off-line interpretation of the sentence, but that it has an influence on it. If the on-line repair determined the off-line sentence interpretation, we would have expected no difference in the proportion of inflectional subject correction to singular compared to conjoined phrase subject corrections to plural. In contrast, however, the P600 recorded on the modifier in the two cases is very similar (see Across-experiment comparison ). Thus, additional factors can influence the off-line interpretation of the sentence and the on-line repair is just one relevant factor. Given the present data, it is possible to speculate about the nature of the representation on which the repair is carried out. The fact that repair could be performed only when the subject number value is morphological could mean that what is mentally modified is the feature [Number] of the initial nominal. However, according to some authors (Bornkessel & Schlesewsky, 2006; Friederici, 2002), repair should be seen as a very late stage of processing. This would support the idea that this process should target a more abstract and less linguistic-specific internal representation, one connected to semantic and discourse level information. This proposal would be supported by off-line linguistic evidence. In Italian or French, the courtesy form for a 2nd person singular subject pronoun can use a 2nd person plural form (voi/vous, respectively). The main verb agrees in

19 N. Molinaro et al. / Journal of Memory and Language 64 (2011) the plural with this pronominal subject, but any subsequent participle or adjective appears in the singular, agreeing in gender and number with the logical subject (i.e. the singular addressee), not with the verb (see (2) for Italian): (2) Voi siete stato felice you[+p] have[+p] been[+s] happy[+s] you sing-formal have been happy Similarly, a sentence that begins with I ragazzi pensa... the boys thinks[+s]... could continue with a perfectly grammatical post-verbal subject, as in (4) 3 : (4) I ragazzi pensa Carlo a prenderli the boys thinks Carlo to collect them as for the boys, Carlo intends to collect them This strongly suggests that the number of the first nominal does not directly interact with the modifier, which would be mainly sensitive to the logical number of the subject. In sum, the findings on the modifier in Experiments 1 and 2 confirm the strategy of the cognitive system to immediately repair an incongruent sentence on-line: an agreement mismatch triggers an immediate repair through which the system, after integrating all the available information, selects a unique number value for the grammatical disagreement. If the mismatch is based on the pluralization of a discourse entity based on morphophonological information extracted from the noun s inflection, the value of the last processed constituent coerces the internal representation of the subject; otherwise, when relevant information dominates the value of the processed mismatching constituent, this regularization strategy (mirrored in the prolonged P600 effect recorded in Experiment 1) is blocked and the system relies on the number of the sentence fragment already stored in memory, somehow ignoring following number values. This on-line process influences the interpretation of the whole message, in that it constrains the build-up of the internal restructured representation of the message intended by the source. Repair vs. Reanalysis One important aspect of the present study is that it was carried out in Italian, a language with greater word order freedom than English (the language investigated in Molinaro, Kim, et al., 2008). Working on the agreement between subject and main verb in a null-subject language like Italian leaves open the theoretical possibility of a local structural ambiguity. The problem is that in the presence of a number mismatch between the sentence-initial nominal and the main verb, the parser might no longer interpret this nominal as the subject, but as a topicalized element whose gap is expected to appear later in the sentence. The ill-formed English sentences in (1) begin just like the perfectly well-formed Italian (3) (where pro indicates the presence of an unpronounced singular subject, and i famosi danzatori is a left topic, picked up by the -li pronoun, object of aspettando). (3) I famosi danzatori stava nervosamente aspettandoli dalle 9 the famous dancers[3p+p] pro was[3p+s] nervously waiting-for-them since 9 as for the famous dancers, he was nervously waiting for them since 9 o clock Structures of this sort, though very common in spoken language, are not present in the experimental stimuli of our experiment, but the word by word presentation modality gives the participants ample time to consider them. Thus, the existence of such structures might support the development of an alternative (topic) interpretation of the sentence to the initially preferred first-nominal-as-subject. In other words, after encountering a mismatching verb after an initial nominal, the system could revise its initial preference to a topic one (either a pro or a post-verbal construction). This additional strategy (at work in null-subject languages), that we can call Reanalysis, predicts that the system either re-interprets completely the sentence structure or activates parses additional to the first-nominal-as-subject one. The discovery of a gap and/or a sentential subject in the continuation of the sentence would constrain the type of structure to be assigned to the sentence. We think this is an important aspect of the present study, since many sentence processing models state that when faced with a syntactic irregularity, the system exploits all the possible grammatical alternatives before considering the sentence as ungrammatical (Garden-Path model, Frazier, 1987; but also MacDonald et al., 1994; Tabor et al., 2004). For example, when reading the verb in Experiment 1 the parser could postulate the existence of a null singular subject that agrees with the verb. Here, the ERP effects recorded on the verb could represent the additional activation of a topic construction. Whether the topic is coordinated or not should make no difference at all, so we can hypothesize that a similar reanalysis is operated after reading the verb also in Experiment 2. However, the findings on the modifier are critical, since we would have expected the same results in both Experiments 1 and 2: in fact, if the following modifier is singular, it would simply agree with this subject, while if it is plural we would expect processing difficulties due to the fact that the system realizes that the topic interpretation is not the correct parse (considering the P600 amplitude on the modifier we would have expected the following ERP pattern: Experiment 1: PSP > PSS, Experiment 2: CSP > CSS). Critically, this was not the case, indicating that the Repair explanation is the only possible interpretation of the findings emerging in the present study. These findings have interesting implication for the type of parsing involved in Italian subject-verb mismatches. In 3 Note that by marking pro in (3) in the canonical position for overt subjects we are not committing ourselves to a specific linguistic structure for null or post-verbal subjects, nor to a particular mental realization of these constructions. Evidently, the parser must be able to handle these cases without hesitations. The way this is performed is an interesting research topic, but one which is orthogonal to our present argument.

20 230 N. Molinaro et al. / Journal of Memory and Language 64 (2011) fact, when faced with a mismatch between the number of the initial nominal and a following verb, the system could possibly reanalyze the sentence as a topic structure (Reanalysis hypothesis, see examples 3 and 4). This type of structure is less frequent in Italian than that in which the first nominal is the subject; however, it is syntactically acceptable and it could be a viable alternative interpretation (for an Italian speaker). Many theoretical proposals (Frazier, 1987; MacDonald et al., 1994; but see also Fodor & Ferreira, 1998) have stressed the ability of the parser to pursue any alternative grammatical parse (that is faithful to the input), once it is compelled to perform reanalysis of an ongoing interpretation. Our findings seem to be at odds with this, since we find evidence that the system continues with its initial choice (first-nominal-as-subject) even if it is not faithful to the input, instead of assuming a less preferred (but more faithful to the input) interpretation of the sentence, at least in the experimental setting of our study. This would confirm the ability of the processing system to easily deal with local mismatches and repair them on-line, before accessing further possible disambiguating information. ERPs effects at the Verb position Distinct ERP effects emerged at the mismatching verb in the first two experiments (see Fig. 5 for a direct comparison of the difference waves). Even if this distinction was not the main focus of our study, we think that this dissociation is worthy of comment, since it could stimulate further research on the processing of subject-verb agreement. While the mismatch in Experiment 1 is detected after processing the inflectional morphology of the noun phrase in subject position ( I fratelli giunse The [+P] siblings arrived [+S]), in Experiment 2 the mismatching verb follows a coordinate noun phrase ( Il fratello e la sorella giunse The [+S] brother and the [+S] sister arrived [+S]). The main finding is that a LAN emerges in this position in the former case but not in the latter. We are not committed to how the initial computation happens here, but the qualitative difference observed at the verb position across experiments suggests that somehow the mismatch between the coordinated subject and its verb is recognized more slowly than the more prominent inflectional mismatch in Experiment 1. From a linguistic point of view, this is not surprising. There is considerable evidence that the coordination morpheme and (and its equivalent in other languages), unlike number inflection, does not insert a plural feature value. (5), for instance, shows that conjunction of singular quantificational nominals only marginally triggers plural agreement, in Italian as in English; (6) shows that the conjunction of certain mass nouns inside a noun phrase does not license a plural determiner in Italian, though it can trigger plural verb agreement (Heycock & Zamparelli, 2005; the phenomenon is even more visible in English in the contrast between the acceptable this boy and girl are dancing together and these (two) boy and girl are dancing together); finally (7) shows that the conjunction of sentential subjects, which arguably carry no number feature, triggers singular verb agreement (Zamparelli, 2008). (5a) Nessun linguista e nessun filosofo pensa/ pensano che il linguaggio sia facile No linguist and no philosopher thinks [+S]/think [+P] that the language is easy (5b) Ogni genitore ed ogni insegnante voleva/volevano parlare Every parent and every teacher wanted [+S]/ wanted [+P] speak [+INF] (6) La/ Le tua pazienza e determinazione sono ben note a tutti The [+S]/the [+P] your patience and determination are well-known [+P] to everybody (7) [Che Marco sia qui] e [che Maria sia partita] sembra strano/ sembrano strani [that Marco is here] and [that Maria has left] seems strange [+S]/seem strange [+P] Some authors (Osterhout et al., 2004) have questioned the reliability of the LAN effect as an index of morphosyntactic processing. This is due to the fact that while some agreement relations elicit a LAN (subject-verb agreement), others do not (e.g. anaphoric agreement, for a comparison see Osterhout & Mobley, 1995). In our opinion, this dissociation is not accidental but could reflect distinct processing difficulties related to the structural properties involved in the resolution of the agreement relation in most cases. Unfortunately, the agreement structures implemented in our two experiments vary on a number of dimensions. First of all, the inflectional mismatch in Experiment 1 is less complex and easier to detect compared to that of Experiment 2. Syntactic complexity has been shown to elicit only a P600 component more evident in its earlier stage (Kaan, Harris, Gibson, & Holcomb, 2000; Osterhout & Holcomb, 1992); this component is morphologically very similar to the one reported for the mismatch between a conjoined noun phrase and its verb in Experiment 2. Secondly, while the subject-verb mismatch in Experiment 1 is determined only by the inflectional morphology of the noun phrase in subject position, this type of morphological information is underspecified on the subject in Experiment 2 (see examples 5 7): it could be that the operation that controls for the consistency between subject and verb features does not have as a target inflectional information, but information that directly maps onto the referent information. Consequently, the plurality of a conjoined noun phrase would be notionally more complex (Heycock & Zamparelli, 2005), since the number value has to be computed from the semantics of the two singular referents (much as in Marc i told Anna j that they i+j should leave). The processing stage indexed by the LAN could then be sensitive to the formal vs. notional nature of the agreement relation. Thirdly, the local relation between the verb and the preceding noun in our structures is different: while the noun preceding the singular verb in Experiment 1 is plural (...fratelli giunse... siblings arrived [+S]), in Experiment 2 it is singular (...sorella giunse... sister arrived [+S]). It should be noted that attraction phenomena are stronger with singular subjectplural verb configurations (see Pearlmutter et al., 1999;