Glossa Psycholinguistics

1.1 Morphological productivity and agreement processing

Questions about the role of morphological productivity in agreement processing have received little attention. However, some information can be gleaned from studies on a more widely researched question: Whether speakers whose L1 doesn’t have a specific grammatical feature – like number or gender – have difficulties using it for agreement in their L2. Answering this question is important for processing theories: While some accounts propose that the absence of a morphological feature in an L1 hinders its L2 processing (Hopp, 2022; MacWhinney, 2005) or prevents its target-like representation as a functional feature in the L2 grammar (Franceschina, 2005; Hawkins & Franceschina, 2004), other accounts don’t assume L1 influence and focus more on L2 speakers’ reliance on other types of knowledge (e.g., lexical and semantic) than on morphosyntactic knowledge during processing (Clahsen & Felser, 2018).

Processing evidence provides a nuanced answer to the question of whether L1–L2 similarity affects agreement processing in proficient L2 speakers. This evidence comes mostly from two sources: agreement violation paradigms used in event-related potential (ERP) studies, and predictive paradigms used in visual world eye-tracking studies. These previous findings often conflict. Some studies have reported that L1–L2 similarity enhances L2 speakers’ sensitivity to agreement violations (Foucart & Frenck-Mestre, 2011; Gillon Dowens et al., 2011; Sabourin & Stowe, 2008) and the predictive use of agreement (Hopp & Lemmerth, 2018). However, other studies have failed to find an effect of L1–L2 similarity on either agreement violations (Alemán Bañón et al., 2018; White et al., 2012) or agreement-based predictions (Dussias et al., 2013; Lago et al., 2023). In fact, a meta-analysis of 41 ERP studies on syntactic processing – including number and gender agreement – found that L1–L2 similarity did not significantly predict the presence or absence of any ERP component, in contrast with factors like L2 proficiency and length of immersion (Caffarra et al., 2015).

However, most previous studies used paradigms that involved explicit knowledge, such as error-detection tasks. Thus, it is unclear whether participants’ responses reflected processing mechanisms vs. task-specific strategies (Jiang, 2007). For instance, in violation-based ERP paradigms, participants were often asked to read the sentences with the goal of making grammaticality judgments (Alemán Bañón et al., 2018; Gillon Dowens et al., 2010; Sabourin & Stowe, 2008). Thus, the recorded brain responses might reflect not only participants’ sensitivity to agreement, but also specific heuristics aimed at solving the judgment task. In this regard, evidence provided by studies on morphosyntactic predictions might be more reflective of implicit processing, as participants were not asked to judge sentences, but rather to click on images on a computer screen (Dussias et al., 2013; Hopp & Lemmerth, 2018; Lago et al., 2023). However, there is growing evidence that – likely due to the simple and repetitive nature of the task – participants in visual world studies can become aware that agreement is the object of study, and that they use it strategically to perform the task (Curcic et al., 2019; Koch et al., 2021).

To complement previous studies, it is important to use more implicit tasks to diagnose the processing mechanisms underlying L2 subject-verb number agreement. The next section describes a psycholinguistic effect that fulfills this criterion: agreement attraction. Our study measured agreement attraction using a reading-for-comprehension paradigm without any judgment component. Our goal was to assess whether L1 morphological differences modulated subject-verb agreement processing in a second language.

1.2 Attraction in first language comprehension

Agreement attraction is a useful diagnostic of L2 agreement processing, because its underlying cognitive mechanisms are well-studied in L1 speakers. Attraction research on subject-verb number agreement in comprehension typically uses a 2 × 2 design manipulating the grammaticality of a sentence, i.e., whether the critical verb disagrees in number with the noun heading the subject – the key to the cabinet(s) – and whether the sentence contains a noun that mismatches the number of the subject head, typically called an attractor – bolded in example (1) below (Bock & Miller, 1991; Lago et al., 2021).

Previous studies have found that L1 speakers show processing disruptions after encountering a verb with an agreement violation in (1c–d) vs. (1a–b), which results in longer reading times and increased brain responses. Critically, ungrammatical verbs elicit smaller disruptions when the attractor noun matches the verb in number. This yields faster reading times and/or reduced brain responses – e.g., in (1d) vs. (1c) – resulting in a so-called agreement attraction effect (Jäger et al., 2020; Lago et al., 2021; Nicol et al., 1997; Pearlmutter et al., 1999; Shen et al., 2013; Tanner et al., 2014; Wagers et al., 2009).

A widely adopted interpretation of attraction effects is that they reflect facilitatory interference due to the partial match of the attractor with the lexical features of the verb, which are used as retrieval cues by the parser (Jäger et al., 2017). When a verb is encountered, speakers use its syntactic, semantic, and morphological features as cues to retrieve an appropriate number controller from memory. Memory chunks corresponding to preceding items are queried in parallel, and the chunk that best matches the retrieval cues is the most likely to be selected. Sentences with an attractor like (1d) elicit interference during retrieval due to partial match: While the subject head matches the syntactic cues of the verb, the plural attractor matches the number cue. Under activation-based retrieval models, this partial match increases the probability of misretrieving the attractor (Dillon et al., 2013; Engelmann et al., 2019; Nicenboim & Vasishth, 2018). Since the attractor in (1d) matches more retrieval cues than in (1c), it is also retrieved faster, which leads to a faster average retrieval time. This retrieval speedup is assumed to generate the faster processing times in the attraction condition (1d), as compared to (1c).

Attraction effects are robustly observed in ungrammatical sentences, while their existence in grammatical sentences – (1b) vs. (1a) – is unclear. In a survey of previous studies, Hammerly and colleagues (2019) reported that statistically significant number attraction effects were detected more often in ungrammatical than grammatical sentences: 91% vs. 38% of the surveyed studies. Further, work using Bayesian meta-analyses demonstrated a consistent attraction effect in ungrammatical sentences – on average, –22 ms, with a [–36, –9] ms 95% credible interval – but a negligible and task-dependent effect in grammatical sentences – on average, –7 ms, with a [–16,4] ms 95% credible interval (Jäger et al., 2020). Since more research addressing the sources of this variation is needed, our study diagnosed attraction effects only in ungrammatical sentences, in which the existence of attraction effects is uncontroversial.

1.3 Attraction in second language comprehension

Proficient L2 speakers typically show number attraction effects in comprehension, which suggests that they also use a retrieval mechanism for subject-verb agreement (Bian et al., 2021; Cheng et al., 2021; Hoshino et al., 2010; Jegerski, 2016; Lee & Phillips, 2023; Lim & Christianson, 2015; Tanner et al., 2012). But it is less clear whether attraction effects are larger in L2 speakers than in L1 speakers, with mixed results in previous studies (Jacob et al., 2017). The comparison of attraction effects in L1 vs. L2 speakers is theoretically relevant, because larger L2 attraction effects are predicted by accounts like the Interference Hypothesis (Cunnings, 2017a, 2017b). The Interference Hypothesis proposes that both L1 and L2 speakers rely on cue-based memory retrieval to process linguistic dependencies like subject-verb agreement. However, L2 speakers are more susceptible to retrieval interference during processing, which increases the likelihood of misretrievals and should result in larger attraction effects than those exhibited by L1 speakers. Our study evaluates this prediction by comparing L1 and L2 speakers of German.

Of additional interest to our study is whether morphological richness plays a role. Specifically, speakers with productive L1 agreement might be more susceptible to attraction if richer morphology affects retrieval through differential cue weighting. L1 Spanish speakers might weigh morphological cues like number more heavily at retrieval – as compared to other cues, for example, syntactic cues, which should be weighted similarly by Spanish and English speakers. A higher weighting of number cues should increase interference from number-matching elements in the attraction conditions, leading to more misretrievals and, thus, larger attraction effects in Spanish speakers than in English speakers.

To our knowledge, no previous study has evaluated this possibility by comparing attraction effects between two learner groups who differ in the richness of their L1 morphology. Therefore, inferences about these variables need to be based on comparisons across studies. These reveal an unclear pattern of results. With speakers whose L1 has subject-verb agreement, studies tend to find qualitatively similar L1–L2 attraction effects, for example, in proficient Spanish speakers of English (Tanner et al., 2012), in proficient Russian speakers of German (Lago & Felser, 2018), and in English near-native speakers of Spanish (Jegerski, 2016).

With speakers whose L1 lacks subject-verb agreement, results are more variable. Studies on proficient Korean speakers of English have shown similar L1–L2 attraction profiles, but the effects depended on the grammatical environment of the attractor noun, i.e., whether it appeared in a relative clause (e.g., The artist who made the sculpture(s) was/were…) or in a prepositional phrase (Lee & Phillips, 2023; Lim & Christianson, 2015). For example, in the study by Lee and Phillips (2023), Korean learners of L2 English showed attraction effects in relative clause constructions, but there was no evidence of attraction in prepositional phrase constructions.

Meanwhile, studies on Chinese speakers of English have reported similar L1–L2 attraction profiles (Cheng et al., 2021), no L2 attraction (Jiang, 2004) or similar L1–L2 attraction profiles but with a smaller size in L2 (Bian et al., 2021) or a different distribution of brain responses (Chen et al., 2007). However, several studies on Chinese learners measured attraction in grammatical sentences (Cheng et al., 2021; Jiang, 2004), where even L1 findings are inconclusive. If only studies including ungrammatical sentences are considered, then the results suggest behaviorally similar L1–L2 attraction profiles (Chen et al., 2007; Hoshino et al., 2010; Jegerski, 2016; Tanner et al., 2012).

Crucially, previous studies focused on comparing L1–L2 speakers, rather than comparing L2 learners with different L1 backgrounds. Direct comparisons between learner groups are important, because to appropriately demonstrate L1 influence, it’s not enough to show that a particular L2 behavior is consistent with speakers’ L1. Instead, one has to show that the behavior is specific to speakers’ L1, for example, by directly comparing L2 speakers whose L1s differ in the properties of the target construction (Felix, 1976; Jarvis, 2000; Pienemann et al., 2005). Otherwise, one might misattribute to L1 influence behaviors that are due to general-purpose processing mechanisms, which may be used universally by L2 learners. The current study addressed this gap by directly comparing German speakers with English or Spanish as a native language.

1.4 The present study

English and Spanish provide useful comparison points for questions about morphological richness. Morphological richness can be quantified in terms of paradigmatic richness, which describes the number of formally distinct inflected word-forms per lemma (Dressler, 2003; Xanthos et al., 2011). Based on this, English has impoverished number agreement morphology, such that only third person singular verbs mark number agreement, e.g., I/you/they/we eat vs. she/he/it eats. By contrast, Spanish verbs mark agreement in all syntactic persons, with clearly differentiable singular and plural verb forms (e.g., comió ‘ate.3SG’ vs. comieron ‘ate.3PL’). Further, English has a relatively fixed word order, but word order in Spanish is freer and grammatical subjects can be omitted – Spanish is a null-subject language – which makes sentence position less useful for subject identification. As a consequence, verb morphology is both productive and reliable as a cue for subject identification in Spanish, while English speakers might rely more on word order and syntactic information (Kail, 1989; MacWhinney, 2001; MacWhinney et al., 1984).

Our study compared L1 Spanish and English speakers in their processing of subject-verb number agreement in German – a language with productive agreement morphology, like Spanish. We tested intermediate-to-advanced L2 speakers, to ensure that any potential between-group contrasts were attributable to differences between processing mechanisms, rather than an incomplete knowledge of German. We also included speakers who had acquired German as a first language, in order to test the predictions of the Interference Hypothesis (Cunnings, 2017a, 2017b). Thus, two analyses were performed: the first compared the L1 vs. L2 groups – thus collapsing L2 speakers into one group. The second analysis focused on the L2 learners and compared English vs. Spanish native speakers, to assess whether differences in their native number systems affected their processing of subject-verb agreement in German.

We defined two experimental effects of interest. The first concerned agreement violations. This effect was diagnosed as the processing disruption elicited by a verb disagreeing with the subject in number. An example is provided by sentences (1a) vs. (1c) above: in contrast with (1a), the verb in (1c) has an agreement violation. Note that the subject and attractor noun always match in number, such that the ungrammatical verb cannot be licensed in number.

The second experimental effect concerned agreement attraction. This effect was diagnosed as the processing facilitation elicited by an ungrammatical verb in the presence of a plural attractor, as compared to an equally ungrammatical sentence without an attractor noun. An example is the comparison between (1c) and (1d).

Our study adopted an error-driven account of retrieval, which proposes that participants use memory retrieval after encountering a verb whose number does not match the number predicted on the basis of the number of the subject (Lago et al., 2015; Schlueter et al., 2019; Wagers et al., 2009). According to this account, readers first detect an agreement violation, and only afterward experience attraction due to misretrieval. Thus, agreement violations and attraction effects convey complementary information. Participants’ reactions to agreement violations provide a measure of their real-time ability to detect whether the number of the verb matches the number expectation generated by the subject. Meanwhile, reactions to attraction measure participants’ susceptibility to retrieval interference, which allows one to establish whether a retrieval mechanism is used to compute agreement.

Our predictions were as follows. L1–L2 comparisons allowed us to address the question of whether intermediate-to-advanced L2 speakers could become native-like in the processing of subject-verb number agreement in German. If so, L1 and L2 speakers should show comparable reading disruptions after encountering a verb with an agreement violation. With regard to agreement attraction, if L2 speakers are more affected by interference, as posited by the Interference Hypothesis (Cunnings, 2017a, 2017b), then attraction should be larger in L2 speakers than L1 speakers. Alternatively, L1 and L2 speakers might be equally prone to interference and show similar attraction effects, consistent with native-like retrieval mechanisms.

Meanwhile, comparisons between English and Spanish speakers allowed us to address whether differences in L1 morphological productivity affect the processing of subject-verb number agreement in German. Specifically, due to the richness and reliability of number inflection in Spanish, Spanish speakers might be more fine-tuned to agreement morphology in German, resulting in stronger reading disruptions when an agreement violation is encountered. This outcome would support an extended version of the Morphological Congruency Hypothesis (Jiang et al., 2011). With regard to attraction, a higher weighting of morphological cues should give rise to stronger attraction in Spanish speakers than English speakers.

Alternatively, the morphological richness of speakers’ L1 might not affect their processing of subject-verb agreement. Specifically, intermediate-to-advanced L2 German speakers with different morphological systems might have developed similar processing mechanisms for subject-verb agreement, regardless of their first language. If so, comparable responses to agreement violations and agreement attraction should arise in the L2 groups.

2.1 Method

2.2 Results

Comprehension question accuracy in the filler trials was above 95% across all groups (L1 German mean = 98%, SD = 2%; L1 English mean = 97%, SD = 4%; L1 Spanish mean = 96%, SD = 4%). Comprehension question accuracy in the experimental trials was also high (L1 German mean = 97%, SD = 4%; L1 English mean = 94%, SD = 6%; L1 Spanish mean = 90%, SD = 8%. All L2 speakers knew German subject-verb agreement constraints, as indicated by the untimed test (mean accuracy L1 English = 98%, SD = 5%; mean accuracy L1 Spanish = 96%, SD = 6%). The statistical model did not suggest an accuracy difference between the L2 groups, and the Bayes factor showed equivalent evidence for either hypothesis, $\widehat{\beta }$ = –0.60,95% CrI [–1.45,0.31], BF₁₀ = 0.9.

Empirical reading times in the spillover region, together with the preceding and following regions, are shown in Figure 1. The results of the comparisons within and between groups are described below. For each comparison, we report the mean of the posterior probability distribution of each effect, together with a 95% credible interval (CrI), which represents the interval in which it is 95% certain that the true effect lies, given the data and the model. For easier interpretability, reading measures are backtransformed to milliseconds in the text, but statistical analyses and inferences are based on the untransformed model coefficients.

Figure 1: Empirical reading times in the critical verb+1 region, together with the preceding and following regions. Points show condition means and error bars +/–1 standard errors calculated for each condition across participants and items.

2.2.2 Group comparisons: L1 vs. L2

In addition to posterior means and credible intervals, this (and following) sections report Bayes factors, which allowed us to quantify evidence for the effects relevant to our research questions, i.e., differences in the size of grammaticality and attraction effects between groups. With regard to the effect of grammaticality, the model supported a difference between the L1 and L2 groups: compared to the L1 group, the L2 group showed less disruption in the spillover region of ungrammatical sentences, consistent with a reduced sensitivity to agreement violations, Grammaticality × Group $\widehat{\beta }$ = –27 ms, 95% CrI [–44,–10] ms (Figure 2). A Bayes factor (BF₁₀) of 23 suggested strong evidence in favor of the interaction, and the sensitivity analysis showed that a different prior would not have changed this conclusion. The model was also consistent with a main effect of grammaticality: ungrammatical sentences were read more slowly across both groups, $\widehat{\beta }$ = 27 ms, 95% CrI [19,36] ms. There was also a main effect of group, with L2 speakers reading more slowly than L1 speakers across sentence types, $\widehat{\beta }$ = 98 ms, 95% CrI [71,124] ms.

Figure 2: A. Model-estimated means and 95% credible intervals of grammaticality and attraction effects in L1 and L2 at the critical verb+1 region. B. Bayes factor sensitivity analyses for the interaction between grammaticality and group, and attraction and group. Bayes factors were computed at a range of prior standard deviations representing different ranges of a priori assumed plausible effect sizes. Triangles indicate the a priori prior standard deviations used in the main analysis and the Bayes factors reported in the text.

With regard to the effect of attraction, we focused on ungrammatical sentences, which is where we predicted attraction to arise. There was inconclusive evidence against an Attraction × Group interaction, suggesting similar effects in the L1 and L2 groups, $\widehat{\beta }$ = 8 ms, 95% CrI [–15,30] ms. The sensitivity analysis indicated that priors assuming a wider range of plausible effect sizes would have provided more conclusive evidence against an interaction, but that the evidence was inconclusive for more constraining priors. The model was consistent with a main effect of attraction, $\widehat{\beta }$ = –10 ms, 95% CrI [–17,–2] ms. The model was also consistent with slower reading times in L2 speakers than L1 speakers, $\widehat{\beta }$ = 93 ms, 95% CrI [67,121] ms.

2.2.3 Learner comparisons: L1 English vs. L1 Spanish

With regard to grammaticality, there was moderate evidence against a Grammaticality × L1 interaction, suggesting that Spanish and English speakers did not differ in their sensitivity to agreement violations, $\widehat{\beta }$ = 4 ms, 95% CrI [–24,31] ms, BF₁₀ = 0.27 (Figure 3). The sensitivity analysis indicated that a different choice of prior would not have changed our conclusions. By contrast, the model was consistent with a main effect of grammaticality, with ungrammatical sentences being read more slowly than grammatical sentences across L2 speakers, $\widehat{\beta }$ = 17 ms, 95% CrI [2,32] ms. There was also a main effect of L1, with Spanish speakers reading more slowly than English speakers, $\widehat{\beta }$ = 47 ms, 95% CrI [14,80] ms. The model was not consistent with an effect of proficiency, $\widehat{\beta }$ = –7 ms, 95% CrI [–95,78] ms.

Figure 3: A. Model-estimated means and 95% credible intervals of grammaticality and attraction effects for L2 speakers at the critical verb+1 region. B. Bayes factor sensitivity analyses for the interaction between grammaticality and L1, and attraction and L1. Bayes factors were computed at a range of prior standard deviations representing different ranges of a priori assumed plausible effect sizes. Triangles indicate the a priori prior standard deviations used in the main analysis and the Bayes factors reported in the text.

With regard to attraction in ungrammatical sentences, the results were inconclusive about an Attraction × L1 interaction: while Spanish speakers had a numerically larger attraction effect than English speakers, the Bayes factor was inconclusive, $\widehat{\beta }$ = –27 ms, 95% CrI [–56,1] ms, BF₁₀ = 1.56. The sensitivity analysis indicated that a different choice of prior would not have yielded a more conclusive Bayes factor. Additionally, the model was not consistent with a main effect of attraction, $\widehat{\beta }$ = –5 ms, 95% CrI [–22,11] ms, but it was suggestive of a facilitatory effect in the Spanish group, $\widehat{\beta }$ = –19 ms, 95% CrI [–42,4] ms. The model was consistent with slower reading times in Spanish speakers than English speakers, $\widehat{\beta }$ = 37 ms, 95% CrI [5,71] ms. The model was not consistent with an effect of proficiency, $\widehat{\beta }$ = 0 ms, 95% CrI [–90,88] ms.

3.1 Agreement violations: Sensitivity decreases in a second language, but it is not modulated by L1 morphological richness

Compared to L1 speakers, L2 speakers were less sensitive to agreement violations. This may be surprising, given that we tested constructions in which the subject and verb were linearly close – separated only by an adverb – and that we focused on intermediate-to-advanced German learners: Most of our participants had spent years living in Germany, they rated themselves as proficient, and they were fully aware of German subject-verb agreement constraints, as attested by their accurate untimed test performance – 98% and 96% mean accuracy in L1 English and L1 Spanish, respectively. We also made sure that agreement processing was not confounded with lexical problems: participants’ knowledge of the plural form of the critical nouns was separately assessed, and our analyses only included trials with appropriately identified plural forms.

Due to this, our results suggest that L2 speakers are less able than L1 speakers to apply knowledge about L2 inflectional morphology when reading sentences in real time (Jiang, 2007). Specifically, while knowledge about L2 morphology may be represented in the L2 grammar, its application during sentence processing might be effortful and require more attentional resources, as opposed to other types of knowledge that can be applied automatically and/or without conscious awareness. In this sense, our results echo findings in single-word studies, which suggest variable effects in the priming of inflectional morphemes (Ciaccio & Veríssimo, 2022; Feldman et al., 2010; Veríssimo et al., 2018).

Further, English and Spanish speakers showed comparable sensitivity to agreement violations, with moderate evidence against a between-group difference. Thus, having productive L1 agreement morphology does not automatically confer an advantage in real-time L2 use, at least at high proficiency levels. This speaks against an extended version of the Morphological Congruency Hypothesis, according to which morphology can only be fully processed if a morpheme is congruent between a speaker’s L1 and L2 (Jiang et al., 2011). We entertained an extended version of the Morphological Congruency Hypothesis based on a reading eye-tracking study in the domain of tense processing (Sagarra & Ellis, 2013). This study found that learners whose L1 had productive tense morphology – Romanian – were more sensitive to L2 verb tense violations than learners whose L1 had poorer morphology – English.

We can think of two explanations for the different findings across studies. The first is methodological: the eye-tracking method used by Sagarra and Ellis (2013) has a better temporal resolution than self-paced reading. For example, if our study had used eye-tracking, evidence of between-group differences could have emerged in measures related to the re-reading of the verb+1 region and/or regressions to preceding sentence regions. Such measures are not available in a self-paced reading study.

Alternatively, the contrast between studies might be due to inherent differences between tense and number. Both are grammatical properties, but tense has stronger semantic consequences: a tense violation like Yesterday the boy cooks leaves comprehenders uncertain about the temporal dimension of the event, as it is unclear how to resolve the conflict between inflectional and lexical information. By contrast, number agreement, especially in languages with overt (non pro-drop) subjects, like English and German, is a process with reduced semantic import – the number of the subject is always available to comprehenders, because it is marked independently from the verb. As a result, verb agreement might not be salient – regardless of L1 status – which might further explain why reactions to agreement violations were reduced in L2 learners.

Finally, while our results do not support an extended version of the Morphological Congruency Hypothesis, they are consistent with the original version of this hypothesis, which concerns the congruency of a morpheme between a speaker’s L1 and L2 – a morpheme is congruent if it conveys the same meaning across languages. Under this criterion, German plural agreement morphology is congruent for both Spanish and English speakers, as both languages have corresponding morphemes to express a number distinction in the third person. Therefore, the original Morphological Congruency Hypothesis would not predict differences between English and Spanish learners of German, which is consistent with our results.

3.2 Attraction effects do not increase in a second language, and the role of L1 morphological productivity is unclear

All between-group comparisons regarding agreement attraction yielded inconclusive results. Thus, we keep their discussion short, in order to avoid overinterpretation. Nonetheless, the observed patterns are informative for current discussions in the L2 literature. The first finding concerns the comparison of attraction effects between L1 and L2 speakers: Attraction effects were numerically smaller in L2 speakers than in L1 speakers. Although the Bayes factor for this effect was inconclusive, the effect’s direction was the opposite than predicted by the Interference Hypothesis (Cunnings, 2017a, 2017b). The Interference Hypothesis proposes that cue-based memory retrieval is used to compute syntactic dependencies, like subject-verb agreement. According to this hypothesis, L2 speakers are more prone to interference than L1 speakers; thus, attraction effects – which are due to interference – should be larger in L2 than L1. But our results suggest that agreement attraction, if anything, is smaller in L2 German than in L1 German. While the inconclusiveness of the analysis prevents us from claiming that L2 effects were conclusively smaller, they were clearly not larger.

We suggest that our results demonstrate reduced sensitivity to inflectional morphology in L2, i.e., difficulties with morphological processing, rather than increased interference during syntactic licensing. According to an error-driven view of attraction, comprehenders only initiate a retrieval process when they detect that the number of the verb does not match the number predicted by the parser on the basis of the number of the subject (Lago et al., 2015; Schlueter et al., 2019; Wagers et al., 2009). But in order to notice an error, L2 speakers need to have successfully implemented at least two processes: (i) they have to generate a number prediction after reading the subject (e.g., a projected memory chunk for the verb with 3rd person plural features); (ii) they have to map the morphological information on the verb to syntactic features, in order to compare them directly against the original number prediction (i.e., map -eten in unterzeichneten to ‘3rd person plural’). There is evidence that both these processes are compromised in L2 speakers (for an overview of L2 predictive skills, see Schlenter, 2023; for evidence of processing difficulties with inflection, see Veríssimo et al., 2018). Under this explanation, the numerically smaller attraction effect in L2 was a downstream consequence of L2 speakers’ reduced ability to perform processes (i) and/or (ii).

Before discussing between-group differences in L2, one limitation of the current study should be acknowledged: the observed attraction effects were always small, which could have created a floor effect and prevented the detection of between-group modulations: even the L1 German group showed a modest processing facilitation of –9 [–17,–2] ms. A smaller attraction effect might be expected, since we used comprehension questions (as opposed to acceptability judgment questions), which focused participants’ attention on the meaning of the sentence, as opposed to its grammatical status. A second potential reason for the small attraction effects might be our choice of relative clause materials. In relative clauses, the attractor is not linearly adjacent to the verb, as is the case in prepositional constructions (e.g., the key to the cabinets). However, it has been shown that the linear distance between the attractor noun and the verb is not critical. Rather, it is the linear and syntactic distance between the target and attractor nouns that matters. For example, in double prepositional constructions (e.g., the smell of the stable of the farmer), attraction rates increase when the second – rather than the third – noun is plural (Franck et al., 2002; Lago & Felser, 2018). Since the second noun is farther from the verb, but closer to the head noun, this suggests that linear and/or syntactic closeness to the agreement controller (rather than the verb) modulates attraction effects.

The increased distance between the target and attractor noun could explain the reduced attraction in our relative clause constructions, since the attractor noun was syntactically more distant from the subject noun. But this would be surprising, given previous findings with Korean speakers of English, who were more prone to attraction with relative clauses than prepositional phrases (Lee & Phillips, 2023; Lim & Christianson, 2015). At present, the role of the grammatical environment of the attractor and its potentially different role in L1 and L2 processing is unclear: more research will be necessary to resolve this issue. A final reason for our small attraction effects could be the animacy difference between the (inanimate) attractor and the (animate) target noun. Since the target verbs always required animate licensors (e.g., the verb sign), the use of animacy as a retrieval cue could have reduced interference and boosted the retrieval of the target noun.

Our second finding was that attraction effects were numerically larger in Spanish speakers than English speakers. The Bayes factor was inconclusive, but its direction supports an extended version of the Morphological Congruency Hypothesis, according to which the productivity of a L1 morpheme affects its L2 processing. With regard to attraction, an extended version of the Morphological Congruency Hypothesis might predict that Spanish speakers would weigh number features more highly at retrieval (due to their productive L1 agreement morphology). This should result in increased interference – and, thus, more attraction – in Spanish speakers than English speakers. Interestingly, since there was evidence against an extended Morphological Congruency Hypothesis with regard to agreement violations (see 3.1), proponents of this hypothesis might need to restrict it by assigning it a more selective role in L2 processing. For example, it could be proposed that L1 morphological productivity affects the weighting of shared L1–L2 features during syntactic retrieval (thus, yielding different attraction effects across L2 speakers), but not the initial detection of an agreement error (thus, yielding similar violation effects across L2 speakers).

As English-Spanish differences in attraction were inconclusive, more research is necessary to assess the hypothesis above. And it is also possible that the apparent difference arose due to a confound. Recall that Spanish speakers consistently showed longer reading times than English speakers, as evidenced by the main effect of L1 in all statistical comparisons. It is possible that the longer reading times in the verb+1 region allowed the more successful detection of attraction effects in the Spanish group. By contrast, the attraction effect in English speakers might have been distributed across regions, thus preventing its reliable measurement.

Alternatively, differences in attraction effects between English and Spanish speakers might be real, but we may have lacked the statistical power to detect them. Recent work suggests that samples of more than 300 participants are needed to detect a 2 × 2 medium-size interaction in between-subject designs (Brysbaert, 2019). Crucially, attraction effects are small: on average –22 ms [–36, –9] ms in ungrammatical sentences (Jäger et al., 2017). Because it is logistically challenging to recruit hundreds of L2 speakers – matched in demographic properties – we think that multi-laboratory collaborations will be crucial to properly assessing whether attraction is modulated by L1 morphological productivity.