Proficiency and working memory based explanations for nonnative speakers’ sensitivity to agreement in sentence processing

This study examines the roles of proficiency and working memory (WM) capacity in second-/foreignlanguage (L2) learners’ processing of agreement morphology. It investigates the processing of grammatical and ungrammatical shortand long-distance number agreement dependencies by native English speakers at two proficiencies in French, and the relationship between their proficiency and WM capacity in French and their sensitivity to agreement violations. Native English speakers at midand high proficiencies in French and native French speakers completed an acceptability judgment task, a self-paced reading task, and a WM task in French, and the English speakers also completed a WM task in English. The results showed that whereas all participants performed at ceiling on the acceptability judgment tasks, only the high-level L2 learners and native speakers showed some sensitivity to number agreement violations. For L2 learners, this sensitivity did not vary as a function of the length of the agreement dependency. The results also indicated that L2 learners tended to be more sensitive to agreement violations as their WM memory capacity in French increased. The implications of these results for theories of L2 morphological processing are discussed. Agreement morphology such as plural marking (e.g., the cats) is known to be difficult for second-/foreign-language (L2) learners, who commonly make agreement errors in production (e.g., Lardiere, 2006; White, Valenzuela, & KozlowskaMacGregor, 2004) and do not process agreement as efficiently as native speakers do (e.g., Jiang, 2004, 2007; Keating, 2009). Even at high proficiencies, attainment in this domain is highly variable, especially when L2 learning began after the onset of puberty (e.g., Birdsong & Molis, 2001; Johnson & Newport, 1989). This can be so even if the morphological feature to be learned is instantiated in the native language (e.g., Hopp, 2010). Focusing on the processing of agreement morphology, three types of accounts have sought to explain L2 learners’ variable sensitivity to agreement: storage accounts (e.g., Ullman, 2001, 2004), which © Cambridge University Press 2012 0142-7164/12 $15.00 Applied Psycholinguistics 34:3 616 Coughlin & Tremblay: Nonnative speakers’ sensitivity to agreement propose that L2 learners fail to decompose morphologically complex words; structural accounts (e.g., Clahsen & Felser, 2006; Jiang, 2004, 2007; Keating, 2009; Sato & Felser, 2010), which claim that L2 learners lack or cannot deploy the structure necessary to process agreement dependencies; and computational accounts (e.g., Hopp, 2010; McDonald, 2000, 2006), which attribute L2 learners’ difficulty with agreement dependencies to reduced processing efficiency due to L2 learners’ limited decoding abilities and working memory (WM) capacity. In this study, we review each of these accounts, with particular attention to the role of WM capacity in L2 processing, and we assess their predictive power for understanding inter-L2-learner variability in the processing of agreement morphology. We will present the results of an (offline) acceptability judgment task and an (online) selfpaced reading task examining the effects of proficiency and WM capacity on the processing of shortand long-distance agreement dependencies between object clitics and their antecedents in French. We will then discuss the implications of our findings for theories of L2 morphological processing. THEORIES OF L2 MORPHOLOGICAL PROCESSING Ullman (2001, 2004; see also Pinker, 1999; Pinker & Ullman, 2002) proposed that native speakers’ lexical and grammatical processing depend on two different memory systems: respectively, declarative memory and procedural memory. Declarative memory is used for the learning and knowledge of facts and events, and it can be recollected consciously; for language, it is the memory system that allows native speakers to associate meanings to word forms. In contrast, procedural memory is used for the learning and control of skills and habits, and it cannot be recollected consciously; for language, it is the memory system that enables native speakers to compute grammatical structures (e.g., phonology, morphology, syntax, and semantics). To explain L2 learners’ poorer ability to compute grammatical structures (compared to native speakers) but their relatively intact ability to learn lexical words, Ullman (2001) proposed that L2 learners increasingly rely on declarative memory as their age of first exposure to the target language increases, and that their reliance on declarative memory should decrease as their exposure to and use of the target language increases (Ullman, 2004). This does not imply that multimorphemic words in the lexicon are not analyzed but that the lexical analyses are not procedural computations: they are instead derived from pattern recognition or from rules learned during pedagogical instruction. Thus, according to Ullman’s model, the processing of grammatical structure, including agreement morphology, is qualitatively different for native and nonnative speakers, at least nonnative speakers at lower levels of proficiency.1 One prediction that the declarative-procedural (DP) model makes is that L2 learners should process regularly and irregularly inflected words somewhat similarly. That is, they should store morphologically simple and complex words in declarative memory as single units, whether or not morphological, nonprocedural generalizations have taken place within the lexicon. In the psycholinguistic research on this topic, three main methods have been used to determine how L2 learners (and native speakers) process regularly and irregularly inflected words. The first one examines whether the processing of inflected words is subject to Applied Psycholinguistics 34:3 617 Coughlin & Tremblay: Nonnative speakers’ sensitivity to agreement frequency effects; because frequency effects have been associated with lexical storage (i.e., the more frequently a word is encountered, the stronger the memory traces), the DP model predicts that L2 learners should show token frequency effects for both regularly and irregularly inflected words, whereas native speakers should show such effects only for irregularly inflected words. The second method aims to determine whether regularly inflected words prime their stem; if inflected words and their stem have separate lexical entries, as would be predicted by the DP model, then L2 learners’ processing of stems should not be primed by their inflected form, unlike that of native speakers. Finally, the third method examines the electrophysiological brain responses evoked by regular words that were irregularly inflected and irregular words that were regularly inflected; the DP model predicts that both word forms should elicit similar electrophysiological responses for L2 learners but different electrophysiological responses for native speakers. Using these methods, the existing L2 research on this topic has revealed mixed findings. On the one hand, in a multiple-choice task where participants chose the correctly inflected verb form, Birdsong and Flege (2001) found that advanced Korean and Spanish L2 learners of English show stronger frequency effects for irregular verbs (e.g., swam) than for regular ones (e.g., helped). Similarly, in an event-related potential (ERP) study, Hahne, Mueller, and Clahsen (2006) report that both native German speakers and Russian L2 learners of German showed a P600 effect (typically associated with grammatical violations) for regular verbs that were incorrectly inflected (e.g., getanzen “danced”; correct form: getanzt) and an N400 effect (typically associated with lexical/semantic violations) for irregular verbs that were regularly inflected (e.g., gelauft “run”; correct form: gelaufen), consistent with a dual route for processing regularly and irregularly inflected words and unlike what the DP model would predict for L2 learners. In contrast, in a masked priming study, Silva and Clahsen (2008) found that regularly inflected verbs (e.g., prayed) do not prime their stem (e.g., pray) for advanced Chinese, German, and Japanese L2 learners of English (unlike native speakers). In line with these findings, using lexical decision and masked priming experiments, Neubauer and Clahsen (2009) found that advanced Polish L2 learners of German showed frequency effects for both regularly (e.g., gespielt “played”) and irregularly (e.g., gelaufen “run”) inflected words, whereas native German speakers showed frequency effects only for irregularly inflected ones. Similarly, Bowden, Gelfand, Sanz, and Ullman (2010) found frequency effects for both regular (e.g., pesco “(I) fish”) and irregular (e.g., pienso “I think”) present-tense verbs in the production latencies of intermediate to advanced English L2 learners of Spanish, but not for regular verbs in the production latencies of native Spanish speakers. These results suggest that L2 learners store morphologically complex words as single units in declarative memory, consistent with the predictions of the DP model. One possibility, which is also consistent with the DP model, is that L2 learners rely more on declarative memory in earlier stages of development. The findings of Osterhout, McLaughlin, Pitkamen, Frenck-Mesitre, and Molinaro (2006) and Osterhout et al.’s (2008) ERP study are consistent with this hypothesis: for novice English L2 learners of French, morphological anomalies that yield an N400 effect shortly after the onset of instruction eventually yield a P600 effect after several months of instruction (for a proposed development, see Steinhauer, White, & Drury, 2009). Applied Psycholinguistics 34:3 618 Coughlin & Tremblay: Nonnative speakers’ sensitivity to agreement A different approach to L2 learners’ processing of agreement morphology is Clahsen and Felser’s (2006a) shallow structure hypothesis (SSH), according to which late L2 learners compute shallower and less detailed syntactic structures, and rely more on lexical, semantic, and pragmatic information than native speakers. SSH claims that the processing of grammatical structure is qualitatively different for native and nonnative speakers, regardless of proficiency in the target language. This hypothesis was proposed to explain reduced or absent structure-based effects in L2 learners’ processing of temporary syntactic ambiguities and filler-gap dependencies (e.g., Felser & Roberts, 2007; Felser, Roberts, Marinis, & Gross, 2003; Marinis, Roberts, Felser, & Clahsen, 2005; Papadopoulou & Clahsen, 2003). Whereas Clahsen and Felser (2006a) originally claimed that highly proficient L2 learners may process agreement morphology in a similar manner as native speakers (unlike syntax), in more recent studies, Clahsen and colleagues suggested that L2 learners may be less affected by internal morphological structure than native speakers (for a discussion, see Clahsen, Felser, Neubauer, Sato, & Silva, 2010). Clahsen and Felser (2006b) also suggest that L2 learners may have difficulty computing agreement dependencies, with nativelike processing being restricted to local domains such as “morphosyntactic agreement between closely adjacent constituents” (p. 111). This then makes the prediction that although L2 learners may be able to decompose morphologically complex words, they should have difficulty computing agreement when it is not local. Keating (2009) tested this prediction in an eye-tracking study on gender agreement with beginner, intermediate, and advanced English L2 learners of Spanish. He found that advanced L2 learners, but not beginner or intermediate L2 learners, were sensitive to gender agreement violations, and, unlike native speakers, they showed this sensitivity only when the agreement dependency was between two adjacent words (e.g., *una fiesta pequeño “a small-masc party-fem”). Keating concluded that his results support SSH, but he admitted that linear and structural distances were confounded in his study. Using self-paced reading experiments, Sagarra (2007) and Sagarra and Herschensohn (2010) similarly found that intermediate English L2 learners of Spanish, but not beginner L2 learners, were sensitive to gender and number violations that occurred between two adjacent words (e.g., *el prototipo famosa “the prototype-masc famous-fem”), whereas Jiang (2004, 2007) reported that, unlike native speakers, intermediate to advanced Chinese L2 learners of English were not sensitive to number agreement violations in sentences where the two words in the agreement dependency were not adjacent (e.g., *The bridge to the island were about ten miles away). The distance between two words in an agreement dependency may thus contribute to L2 learners’ lack of sensitivity to number agreement violations. In contrast, Foote (2011) found that both advanced English L2 learners of Spanish and native Spanish speakers slowed down when parsing gender and number agreement violations, even when the two words in the agreement dependency were not adjacent (e.g., *El pollo del taco está rica pero picante “The chicken-masc of the taco is tasty-fem but spicy”). Her findings perhaps revealed proficiency differences between her group of L2 learners and those in Keating (2009), suggesting that nativelike attainment is not impossible, even in longer agreement dependencies. Other behavioral studies have indeed shown that high-proficiency L2 learners Applied Psycholinguistics 34:3 619 Coughlin & Tremblay: Nonnative speakers’ sensitivity to agreement can perform similarly to native speakers in experiments that require them to use agreement morphology in sentence processing (e.g., Havik, Roberts, Van Hout, Schreuder, & Haverkort, 2009; Hopp, 2006, 2010), and recent ERP studies have even reported that very advanced L2 learners can detect agreement violations in a qualitatively similar way (i.e., eliciting a LAN effect and a P600 effect) as native speakers (Ojima, Nakata, & Kakigi, 2005; Rossi, Gugler, Friederici, & Hahne, 2006); the ease with which L2 learners detect such violations, however, is at least partially dependent on whether the native language has a similar agreement rule (e.g., Foucart & Frenck-Mestre, 2011; Tokowicz & MacWhinney, 2005). The results of Jiang (2004) and Keating (2009) suggest that linear distance between two elements in an agreement dependency can potentially increase the difficulty with which L2 learners process such dependencies. Such a difficulty should arise if long-distance agreement dependencies impose a higher WM load on L2 learners than short-distance ones. We might thus expect a relationship between L2 learners’ ability to process such dependencies and their WM capacity. A third type of account that predicts such a relationship is McDonald’s (2006) cognitive processing account. McDonald (2006) proposed that L2 learners’ variable use of and sensitivity to grammatical structures is due to difficulties in basic cognitive processes that depend in part on grammatical knowledge (i.e., these processes should improve with increasing proficiency) but that are not grammar specific: “(1) low L2 [working-]memory capacity, (2) poor L2 decoding ability, and (3) slow L2 processing speed” (p. 382). Previous research has indeed shown that learners tend to have a lower WM capacity in the L2 than in the native language (e.g., Harrington & Sawyer, 1992; Osaka & Osaka, 1992; Service, Simola, Mesanheimo, & Maury, 2002; Van den Noort, Bosch, & Hugdahl, 2006), suggesting that potential limitations in proficiency may have a negative outcome on L2 learners’ performance in WM tasks. Furthermore, L2 learners have been found to have more difficulty identifying words in noise (e.g., Mayo, Florentine, & Buus, 1997; Meador, Flege, & MacKay, 2000; Van Wijngaarden, Steeneken, & Houtgast, 2002) and to have slower processing times than native speakers (for discussion, see Frenck-Mestre, 2002). McDonald (2006) proposed that these cognitive processes interact with grammatical processing such that L2 learners’ performance on corresponding cognitive tasks should correlate with their performance on grammatical tasks, and the impact of these cognitive processes should increase as the complexity of grammatical structure increases. Given the research that shows strong ties between L2 WM capacity and L2 comprehension (e.g., Altekin & Erçetin, 2010; Harrington & Sawyer, 1992; Miyake & Friedman, 1998; Service et al., 2002; Walter, 2004), she predicted L2 grammatical performance to be more strongly dependent on WM capacity in the L2 than on WM capacity in the native language. To test these predictions, McDonald (2006) conducted a first set of experiments with L2 learners of English from various language backgrounds and native English speakers. The participants’ grammatical performance was assessed using an auditory grammaticality judgment task that included agreement violations (regular past tense, third person singular, regular plural, present progressive, irregular past tense, irregular plural). WM capacity was assessed by asking the participants to report a list of English words they had heard in order of sizes (i.e., from smallest to largest; for details, see Montgomery, 2000). Decoding ability was assessed with Applied Psycholinguistics 34:3 620 Coughlin & Tremblay: Nonnative speakers’ sensitivity to agreement a gating task in which the participants identified words after hearing segments of the words. Processing speed was assessed by asking the participants to detect words in sentences. Note that L2 learners’ performance on all the cognitive tasks depended in part on their proficiency in English, at least their knowledge of words and phonological processes. The L2 learners’ results on each of the tasks were significantly different from those of the native speakers: L2 learners evidenced poorer grammaticality judgments, smaller WM capacity, poorer decoding abilities (i.e., more gates necessary), and slower word detection times than native speakers. Significant correlations (in the predicted directions) were found between L2 learners’ judgments (accuracy and/or response times) and their WM capacity and decoding ability. Because the word detection task involved the recognition of words in complete sentences, McDonald (2006) suggested that it may have involved too much syntactic knowledge to be a good measure of processing speed alone. In a second set of experiments, McDonald (2006) asked groups of native English speakers to complete the same grammaticality judgment task under processing loads related to either WM capacity (low or high digit loads), decoding ability (listening through white noise), or processing speed (eliciting responses under time pressure or presenting compressed speech). The participants also completed the same WM and decoding (i.e., gating) tasks as in the first set of experiments. The results showed poorer performance under a load (in the second set of experiments) than under no load (in the first set of experiments) for all the groups except for the group under a low memory load. For the grammaticality judgment task, significant correlations were found between the performances of (a) the participants under a memory load and their WM capacity, (b) the participants under a decoding load and their decoding ability (as measured by the gating task), and (c) the participants under time pressure and their response times in the grammaticality judgment task. The performances of the native speakers who had a high memory load or who listened to speech through white noise correlated most with L2 learners’ performance. The findings of this study, specifically those for native speakers, suggest relationships between the above cognitive processes (i.e., WM capacity, decoding ability, and processing speed) and grammatical accuracy. For L2 learners, because their performance on the cognitive tasks (at least those testing for decoding ability and processing speed) should have been correlated with their general proficiency in English (including lexical and phonological knowledge), it is unclear whether it was these cognitive abilities rather than their general proficiency that were significant predictors of grammatical accuracy. Decoding ability and processing speed, in particular, may be strongly tied to L2 learners’ automaticity in the target language, which increases with proficiency (for discussion, see Segalowitz & Hulstijn, 2005). Although WM capacity should improve with increasing proficiency (e.g., Service et al., 2002; Van den Noort et al., 2006), it is likely to be less dependent on proficiency than decoding ability and processing speed, as native speakers show a great deal of variability in their WM capacity (e.g., Baddeley & Wilson, 1985; Daneman & Carpenter, 1980; Roberts & Gibson, 2002; Salthouse, 1990; Turner & Engle, 1989; Waters & Caplan, 1996a, 1996b). Hence, by testing for both general proficiency and WM capacity and by disentangling them, researchers may capture a great deal of variation among L2 learners in their Applied Psycholinguistics 34:3 621 Coughlin & Tremblay: Nonnative speakers’ sensitivity to agreement sensitivity to agreement morphology. Different models of WM capacity make different predictions for L2 learners’ processing of agreement morphology, however. Let us consider some of these models before we discuss the role of WM capacity in L2 morphosyntactic processing. WM CAPACITY AND ITS ROLE IN L2 MORPHOSYNTACTIC