Second Language Effects on Ambiguity Resolution in the First Language

The processing of homonyms is complex considering homonyms have many lexical properties. For instance, train contains semantic (a locomotive/to instruct) and syntactic (noun/verb) properties, each affecting interpretation. Previous studies find homonym processing influenced by lexical frequency (Duffy et al., 1988) as well as syntactic and semantic context (Folk & Morris, 2003; Swinney, 1979; Tanenhaus et al., 1979). This cross-modal lexical-decision study investigates second language (L2) effects on homonym processing in the first language (L1). Participants were monolingual English speakers and Canadian English/French bilinguals who acquired L2 French at distinct periods. The early bilinguals revealed no significant differences compared to monolinguals (p=.219) supporting the Reordered Access Model (Duffy et al., 1988). However, the late bilinguals revealed longer reaction times, syntactic priming effects (p<.001), and lexical frequency effects (p<.001), suggesting a heightened sensitivity to surface cues influencing homonym processing in the L1 due to a newly-acquired L2 (Cook, 2003). Introduction The age at which a speaker acquires a second language (L2) may be one of the most influential factors affecting many speakers. Indeed, age of L2 acquisition may not only affect the extent to which a speaker can master his/her L2, but it may also affect the speaker’s first language (L1) (Cook, 2003). This is not to say that acquiring a L2 will cause a speaker to be unable to achieve a native-like acquisition in either language. Rather, acquiring a L2 at varying periods of development has been found to correspondingly affect both languages to varying degrees in terms of proficiency, reaction times (RTs), and neurological organisation as shown in lexical retrieval and processing (e.g., Cook, 2003). The current behavioural study discusses the possible effects acquiring a L2 might have on the mental lexicon. We employed a cross-modal lexical decision task involving lexical ambiguities to investigate on-line processing differences, as evidenced by RT and accuracy. The study was conducted in English – the L1 of all participants. Canadian French was the only L2 and no participants were functionally proficient in any other language. Unfortunately, no proficiency score tasks were available at the time of testing, and therefore we are unable to report the possible effects that proficiency might have in this particular study. Bilingual participants were grouped according to the age at which they acquired French, enabling a comparison investigating the effects of acquiring an L2 at varying stages of development. More specifically, the study examined the effect of priming on syntacticallydisambiguated homonyms versus ambiguous homonyms. The aim was to investigate how learning an L2 later in life might affect one’s ability or strategy to process homonyms in the L1 which are either a) constrained to only one appropriate meaning due to the priming sentential frame, or b) presented in unconstrained sentential frames and thus remain ambiguous as to the intended meaning. As varying ages of L2 acquisition has been found to result in differences in language processing in the L2 (see Meisel, 2009, among others), as well as the L1 (Cook, 2003; van Hell & Dijkstra, 2002), any differences found between groups in processing the homonyms of this study were to be considered evidence of the speaker’s mental lexicon having been affected by acquiring the second language at certain periods of language development. The mental lexicon The acquisition of an L2 adds a dimension of complexity to considerations regarding the mental lexicon, since any theory of language processing needs to account for the storage and retrieval of lexical items from more than one language. A number of studies have attempted to resolve the issue of whether speakers with two languages maintain a single lexicon or recruit separate ones for their two languages (e.g. Fabbro, 2000; Hernandez et al., 2005; Klein et al., 1999; Klein et al., 2006; Perani et al., 1996). These studies have dealt with factors such as proficiency and age of acquisition, since acquiring a L2 can be achieved at any age, albeit with varying degrees of success. It is these differing degrees of success that have led a number of studies to suggest that the age of acquisition of a L2 may be one of the most important determinants of the structure of a mental lexicon involving more than one language (i.e. Hernandez, 2000). It appears that the physiology of a L2 learners’ mental lexicon varies depending on the age at which the L2 was acquired. Speakers who acquired both languages early in childhood – before the age of seven (Fabbro, 2001) – have been found to recruit the same language areas in the brain for language processing as monolingual speakers (Fabbro, 1997; Fabbro, 2000; Hernandez, et al., 2005; Paradis, 1998, 2001; Ullman, 2001a; 2001b). In contrast, speakers who acquired their L2 after puberty (late L2 learners) appear to recruit other areas (Paradis, 1998; Hernandez, et al., 2005; Osterhout, et al., 2008; Ullman, 2001b). As such, the mental lexicon of early bilinguals appears to resemble the monolingual mental lexicon more closely than the mental lexicon of late bilinguals. These findings suggest two things: 1) the existing models of the mental lexicon (Bock & Levelt, 1994; Gaskell & Marslen-Wilson, 1997; Jackendoff, 2003; Marslen-Wilson, 1984; Ullman, 2001a) need to account for the apparent similarities between early bilinguals and monolinguals compared to late L2 learners, and 2) further research needs to investigate possible differences between early bilinguals and monolinguals, such as varying processing strategies for issues such as lexical ambiguity resolution. Since simultaneous bilinguals acquire two native languages concurrently from birth, current theories of language processing have been concerned with how simultaneous bilinguals might be different from monolinguals neurologically. Compared to adults, young children’s brains have been found to be more plastic (Klein et al., 2006), enabling them to organise themselves much more easily than older brains (Paradis, 1998, 2001). This early flexible period of acquisition raises much speculation as to the effect of L2 learning on the organization of the younger mental lexicon. Do the mental lexicons of simultaneous bilinguals resemble those of monolinguals, since they are acquiring two L1s in the same developmental stage as monolingual acquirers? Or do the mental lexicons of simultaneous bilinguals more closely resemble those of other L2 learners, either early or late? Although the current study presents behavioural evidence to attempt to answer these questions, we draw on recent neurophysiological studies which suggest the younger the brain, the more plastic it is. Linguistically speaking, this suggests that a prepubescent brain is flexible enough to acquire and store lexical items of two languages within the same memory system, supported by fMRI studies which have shown earlier L2 learners recruiting two overlapping locations of neural substrates (Hernandez, et al., 2000; Hernandez, Li, & MacWhinney, 2005; Kim et al., 1997; Klein et al., 1999; Klein et al., 2006; Proverbio, Čok & Zani, 2002), whereas later L2 learners recruit two non-overlapping locations (Hernandez, 2005). This may reflect early bilinguals organising their two languages as two native languages or 2L1s, with a shared storage for object representations (Costa & Caramazza, 1999; Green, 1998; La Heij, 2005). If we consider simultaneous bilinguals to have two locations of overlapping neural substrates for each language, one semantic representation may be stored with networks to words in each language. Thus, as the representation is accessed and processed based on phonological information, both words, one in each language, are activated for processing. This is commonly referred to as competition (Costa & Caramazza, 1999; Dijkstra, Van Heuven, & Grainger, 1998; Green, 1998; La Heij, 2005; Marian & Spivey, 2003; Spivey & Marian, 1999). It has further been suggested that there are no factors strong enough for most proficient bilinguals to inhibit or “switch off” the other language (Van Assche et al., 2009). This calls into question studies which have recruited native speakers to carry out a task in the L1 and have reported these participants as monolinguals speakers even though they may have been exposed to a second or even third language. By screening our participants carefully according to a set of strict criteria (see Methods), we hope to understand the varying effects that the L2 has on the L1 as well as the relationship between these variations and the age at which the learner acquired the L2. Such evidence that 2L1 speakers have the same overall locus of processing within the brain (Hernandez et al., 2000, among others) also supports the notion that 2L1 speakers must access and process language in the same manner as monolinguals. However, simultaneous bilinguals have displayed delays in behavioural and on-line tasks compared to those of monolinguals (Fabbro, 2001; Paradis, 1998, 2001). Yet, the question of whether grammatical processing differs between simultaneous bilinguals and monolinguals remains to be investigated. It is this question which the present study addresses by attempting to investigate the effects that acquiring an L2 has on ambiguity resolution in a speaker’s L1. Grammatical processing evidence suggests simultaneous and early bilinguals have a similar system to monolinguals, where the lexicon and grammar are two systems with distinct computational, psychological, and neural bases which play parallel roles in the access and processing of lexical items (Ullman, 2001b). Thus, save for a timing delay, the effects of constraining syntactic context and neutral semantic context on lexical processing are not likely to differentially affect these groups. However, it is not known whether these contexts will affect later L2 learners differently even when processing in their L1. Contextual influences on lexical decisions Modular theories of language processing suggest that syntactic and semantic modules may be recruited independently for lexical processing (Fodor, 1983), and the order in which these may occur varies according to differing research. While some studies have found semantic and syntactic effects to occur independently and in a parallel manner (Van den Brink & Hagoort, 2004), others have found semantic context dominating lexical processing (Swinney, 1979), or syntactic context preceding semantic context and influencing lexical processing (Folk & Morris, 2003). Still others have found that listeners access multiple readings of ambiguous words even when syntactic context constrains against one of those meanings (Tanenhaus et al., 1979; Tanenhaus & Donnenwerth-Nolan, 1984). There is evidence that syntactic context affects lexical decisions without aid or influence of semantic context effects, supporting the possibility of syntactic processing dominating semantic processing. Goodman, McClelland & Gibbs (1981) found that lexical decisions were faster to target words when they were syntactically-appropriate continuations of a phrase following a prime word, such as he agreed, compared to syntactically-inappropriate continuations, such as no agreed. These findings suggest that the processing of lexemes may involve a bottom-up manner of processing as the recruitment of the syntactic module precedes semantic module recruitment. However, levels of processing other than the syntactic level have been found during early stages of processing. In reading sentences, lexical and syntactic factors have been found to interact (Keller, Carpenter & Just, 2001), while in lexical decisions, lexico-semantic information has been found to be processed separately from syntactic information (Green, 1998). In an auditorily-presented lexical decision task, Bilenko et al. (2008) found that lexical information such as the frequency of a word affects the access routes and speed of lexical processing within the brain. In the case of ambiguity, the two meanings are rarely balanced in frequency, resulting in one meaning being dominant over the other (Duffy et al., 1988, among others). Contextual influences on lexical ambiguity To test semantic context effects on lexical access of ambiguous words, Swinney (1979) carried out a cross-modal lexical decision task involving homonyms. The results revealed that semantic context does not direct lexical access, since immediately following the appearance of an ambiguous word, such as bug, all meanings for that word were momentarily accessed during sentence comprehension. Thus, without semantic context to facilitate one meaning over the other, bug could equally mean insect or spy device as both possible readings were accessed initially, as evidenced by equivalent RTs to targets related to both (Swinney, 1979). The only evidence of semantic context effects was found when appropriately-related target words were presented four syllables after presentation of the ambiguity. This delay suggests that semantic context effects appear to be the result of some process which follows lexical access and are not a reflection of the access process itself (Cairns & Hus, 1979; Swinney, 1979), suggesting that the influence dominating lexical decisions may be syntactic. The role of syntactic context in the resolution of lexical ambiguity has been addressed in such studies by Folk & Morris (2003) and Tanenhaus et al. (1979), among others. Investigating homonyms of differing syntactic categories, Folk & Morris found that listeners used preceding syntactic context to decipher appropriate meanings without distinguishing semantic context. For example, in “Construction workers often duck on site”, as duck is preceded by the adverb often, the only meaning appropriate is duck the verb. However, in “Construction workers will often see a duck on site”, duck is preceded by the article a, and so the appropriate meaning is duck the noun. These examples illustrate the possible influence of syntactic context (Gorrell, 1989) in interpreting ambiguous lexical items with differing syntactic categories without the influence of semantic context (Folk & Morris, 2003). Models of lexical ambiguity resolution Without prior disambiguating context, models of lexical processing suggest that all possible meanings of an ambiguous word are accessed initially, and it is only in the subsequent selection stage that one meaning is preferred. The timing of this appears to be influenced by the relative frequency of the various meanings. That is, for ambiguous words with two equally likely and frequently-used meanings, the two meanings are accessed simultaneously (Seidenberg et al., 1982; Swinney, 1979; Tanenhaus & Donnenwerth-Nolan, 1984). However, for ambiguous words with one dominant meaning, that is more likely and more frequently-used than the other subordinate meaning, the dominant meaning becomes available earlier than the subordinate meaning (Duffy et al., 1988; Simpson & Burgess, 1985). However, according to the Reordered Access Model (Duffy et al., 1988), prior disambiguating context affects the access process by increasing the availability of the appropriate meaning without influencing the alternative meaning. This causes competition when the appropriate meaning is the subordinate meaning as the model predicts that the subordinate meaning would become available earlier than usual and consequently simultaneously with the dominant meaning. Eye-tracking studies investigating the roles of preceding sentential context and meaning dominance in lexical ambiguity resolution in monolinguals (Duffy et al., 1988; Sheridan et al., 2009) have shown that preceding context and meaning dominance tend to interact and influence the timing of the availability of meanings. Duffy et al. (1988) found that fixation times were longer on homonymous nouns when the preceding sentential context biased them towards only the subordinate meaning compared to control words, an effect now known as the Subordinate Bias Effect (Kambe et al., 2001; Pacht & Rayner, 1993; Rayner et al., 1994). However, fixation times on homonyms and control words did not differ when presented with a preceding neutral context or a context that supported the dominant meaning only (Duffy et al., 1988). Conversely, in a previous study, balanced homonymous nouns presented in a neutral context resulted in longer fixation times compared to control words (Rayner & Duffy, 1986). Unlike the Reordered Access Model, Duffy, Morris, and Rayner (1988) claimed that neither modular nor interactive theories of language processing could account for these findings. They argued that modular theories could not account for the different types of preceding context resulting in differing fixation times and that interactive theories were inconsistent with the Subordinate Bias Effect due to the expectation of preceding disambiguating context selectively accessing the subordinate meaning without any processing delays. According to the Reordered Access Model, lexical access is exhaustive, and the order by which meanings are accessed is determined by both preceding contextual information and meaning dominance, with contextually-biased meanings and higher frequency meanings being accessed faster than unbiased and lower frequency meanings. Possible interactions of these factors can result in two or more meanings simultaneously becoming available and competing for processing, which lead to processing delays. For instance, if the subordinate (less frequent) meaning of a homonym is supported by preceding sentential context, the access to that meaning speeds up, causing the subordinate meaning to become available at the same time as the usually more available dominant (more frequent) meaning, resulting in the Subordinate Bias Effect. The current study employs a cross-modal lexical decision task to investigate whether both meanings of ambiguous noun/noun and noun/verb homonyms are accessed when presented with neutral or preceding syntactically-constraining context. Based on the studies discussed above, we anticipate, at least at the initial stages of lexical processing, a facilitation of lexical access for the slightly more subordinate meaning in the syntactically-constrained context condition. In consequence, both the dominant and subordinate meanings of the homonym might be retrieved at about the same time for this condition, resulting in lexical competition and observed longer reaction times. Specifically, according to the Reordered Access Model, biasing of the subordinate meaning in the syntactically-constrained condition should facilitate lexical access of this subordinate meaning such that it is more likely to compete with the dominant meaning, resulting in longer reaction times in the lexical decision task. In contrast, the neutral context condition is anticipated to support both the dominant and subordinate meanings, thereby reducing the likelihood of lexical competition and resulting in a slightly shorter reaction time for the slightly more dominant meaning. As the task is carried out in English, we anticipate the monolingual English speakers to reveal lexical frequency effects when presented with unconstrained homonyms: those called the semantic condition. A shorter RT after presentation of a dominant lexical item will be considered evidence of such a frequency effect. In the case of syntactically-constrained homonyms, it is unclear whether this population will reveal evidence of syntactic priming or whether the syntactically-biasing context and meaning dominance will occur simultaneously. That is, to process the syntactically-biasing context while inhibiting the dominant meaning in order to facilitate and process the primed and appropriate, yet subordinate, meaning. A shorter RT upon presentation of appropriately-related target words, such as wrist, primed by syntactically-constrained homonyms, such as “...a fine new watch...” will be considered evidence of syntactic priming. On the other hand, if syntactic and semantic modules are recruited in a parallel manner, with priming and frequency effects competing, inappropriately-related target words, such as view primed by “...a fine new watch...”, are expected to have reaction times equal to or shorter than appropriately-related target words. As simultaneous bilinguals acquired both languages as two L1s, we expect this population to resemble monolinguals in accuracy scores and manner of processing. However, we hypothesise that the existence of a greater lexical store could have an effect on L1 lexical ambiguity resolution in the case of later bilinguals. That is, the early acquisition of a L2 could affect lexical ambiguity resolution even though the task is being carried out in the L1. Given postulations of the activation of multiple lexemes within the mental lexicons of earlier bilinguals (Fabbro, 2001; Paradis, 1998, 2001; Van Assche et al., 2009), evidence of longer RTs is expected as additional resources are recruited for these two populations to not only resolve competition between lexical frequencies, but also to inhibit the inappropriate translation equivalents of each. Even though the task is being carried out in the L1 with non-cognate stimuli (phonologically and orthographically controlled to be dissimilar from French words), we anticipate that the later L2 bilingual group will reveal L2 effects due to the more recent acquisition of the L2 compared to the simultaneous and early bilingual groups. Differences in processing are expected to illustrate the theory that the earlier a bilingual acquires the L2; the more closely he or she resembles a monolingual speaker. This suggests that later L2 learners can no longer be considered monolingual native speakers of English. Indeed, according to Clahsen & Felser (2006) later L2 learners rely more on lexico-semantic information and other surface cues for interpretation during online sentence processing in their L2 (Neubauer & Clahsen, 2009). However, it is unclear to what extent such a strategy for processing in the L2 will affect processing in the L1. In cases where homonyms lack biasing syntactic context, we expect this group to reveal frequency effects, as evidenced in a shorter RT with presentation of a dominant meaning compared to subordinate.