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Adult Second Language Acquisition: A Cognitive Science Perspective Judith F. Kroll For cognitive scientists, the idea that speaking two languages might be the natural state of cognition has only recently come to be appreciated. Although more of the worldâs population is bilingual than monolingual, re- search on language and thought has focused almost exclusively on monolin- gual speakers. In the past decade, perhaps due in part to the recognition of the increasing cultural and linguistic diversity within the United States, this situation has changed dramatically, and there has been a virtual explosion of research on how bilingual people and second language learners negotiate their lives in two languages. The new language science of bilingualism is characterized by the convergence across the disciplines that contribute to it, including psychology, linguistics, applied linguistics and second language acquisition, and neuroscience. In the past 10 years there has been a series of new scholarly journals, books, conferences, and funding initiatives dedi- cated to aspects of second language use and the contexts in which it holds broader implications for society (for comprehensive reviews, see Bhatia and Ritchie, 2004; Doughty and Long, 2003; Kroll and de Groot, 2005). In this paper I review those aspects of the recent cognitive and cognitive â The writing of this paper was supported in part by Grant BCS-0418071 from the U.S. National Science Foundation and Grant R56-HD053146 from the National Institutes of Health to Judith F. Kroll. 1Cognitive research interprets bilingualism broadly to include anyone who actively uses two languages, not only those who are early bilinguals (i.e., bilingual since early childhood) or balanced in their language use. Typically, groups are differentiated on the basis of their proficiency, relative dominance in the two languages, and context of language acquisition and use. 106
ADULT SECOND LANGUAGE ACQUISITION 107 neuroscience research on second language acquisition and bilingualism that appear to hold promise for designing training programs for adult learners to acquire a second language. On the surface, one might approach the prob- lem of second language learning in adults with some pessimism. A theme in research on second language learning is that it is much easier for individuals to acquire a second language in early childhood than as adults. Even suc- cessful adult learners often fail to grasp subtle grammatical distinctions in the second language and speak it with a noticeable accent (e.g., Johnson and Newport, 1989; Piske, MacKay, and Flege, 2001). A full discussion of the reasons that the age of acquisition appears to constrain second language learning is beyond the scope of this paper: for two different theoretical per- spectives on the effects of the age of acquisition, see Birdsong (2005) and DeKeyser and Larson-Hall (2005). Rather than dismiss second language learning as an unattainable task for most adults, I focus on those aspects of the learner and the learning con- text that appear to enable at least some adult learners to acquire functional skills in a second language. I also examine the consequences of becoming proficient in a second language, not only for the second language, but also for processing in the first language and for cognition more generally. I sug- gest that the recent research on bilingualism and second language learn- ing provides evidence for a degree of plasticity in the organization of the language system that makes it feasible for adult learners to achieve some measure of success. LANGUAGE AND COGNITION IN ADULT BILINGUALS AND SECOND LANGUAGE LEARNERS Parallel Activity of the First and Second Languages The observation that has perhaps most critically changed understand- ing of bilingual language processing is that bilinguals do not appear to be able to switch off one of their languages when using the other language. The activity of the language not in use has been documented in even highly skilled language tasks, such as reading (Dijkstra, 2005), listening (Marian and Spivey, 2003), and speaking (Kroll, Bobb, and Wodniecka, 2006). The findings from a range of studies, including those that examine performance in the native language, suggest that a bilingual person is a mental juggler. A major goal of the research on this topic has been to determine the fac- tors that eventually control the selection of the language that the bilingual intends to use. Bilinguals do not generally use the unintended language ran- domly, but they are also able to code switch with others who are similarly bilingual (see, e.g., Muysken, 2000; Myers-Scotton, 2002), suggesting that both of the languages are highly accessible.
108 HUMAN BEHAVIOR IN MILITARY CONTEXTS Finding evidence for parallel activity among a bilingualâs two languages has a number of critical implications for second language learning. First, it shows that successful learning does not imply the development of an autonomous representation for the new language that is independent of the first language. Traditional accounts of late second language acquisition have characterized learners as initially dependent on transfer (e.g., Kroll and Stewart, 1994; MacWhinney, 1997), such that only with increasing proficiency does the second language develop sufficient automaticity to permit skilled performance. The new research suggests that there is no decline in the presence of first language activity once individuals become highly skilled in a second language. Although patterns of cross-language interaction change with increasing second language proficiency, particularly with respect to whether the translation equivalent of a word is available (e.g., Sunderman and Kroll, 2006; Talamas, Kroll, and Dufour, 1999), even highly proficient bilinguals continue to reveal the influence of their first lan- guage on the second language. That is, the second language never becomes entirely independent of the first language. A second implication of the evidence for parallel activity of the two lan- guages is that once individuals achieve proficiency, there are also effects of the second language on the first language. Cross-language influences on the native language have been observed for learners and proficient bilinguals at the level of lexicon (e.g., Jared and Kroll, 2001; Van Hell and Dijkstra, 2002), phonology (e.g., Sundara, Polka, and Baum, 2006), and grammar (e.g., Dussias, 2003). That the native (first) language changes in response to contact with the second language and with other second language users suggests a language system that is fundamentally permeable and open to at least some reorganization. As Grosjean (1989) once warned, a bilingual person is not two monolingual people in one. Although the degree to which each language is distinguishable from that of a monolingual person will depend on the proficiency in the second language and context of language acquisition and use, there is an interesting implication for adult learners: it is possible that only those who can tolerate the change to their native lan- guage may be able to acquire any considerable skill in a second language. Perhaps the most critical consequence of the observation that both of a bilingualâs languages are engaged in parallel is that the resulting activity appears to produce competition across the two languages that must be re- solved. Although there is some debate about whether proficient bilinguals can learn to resolve cross-language competition without the need for ac- tively inhibiting one alternative to produce the other (e.g., Costa, La Heij, and Navarrete, 2006; Finkbeiner, Gollan, and Caramazza, 2006; Green, 1998), there is agreement that proficient bilingualism requires not only linguistic knowledge, but also cognitive control. (For an illustration in the domain of bilingual word recognition for how the architecture of the lexi-
ADULT SECOND LANGUAGE ACQUISITION 109 con might reflect a distinction between an identification system and a task schema system, see Dijkstra and Van Heuven, 2002.) Crucially, the cognitive control that is developed in response to bi- lingualism appears to confer benefits in the realm of executive function. Young bilingual children are superior to their monolingual counterparts on nonlinguistic tasks that specifically reflect the ability to ignore irrel- evant information (see, e.g., Bialystok, 2001; Bialystok and Codd, 1997; Bialystok and Martin, 2004). Notably, bilingual children are not superior to monolingual children on all tasks, only those that appear to require the resolution of conflict across competing alternatives. On tasks in which no conflict is present, bilinguals are similar to monolinguals. And bilingual performance is inferior to monolingual performance in the domain of vo- cabulary acquisition (for related evidence of processing deficits for adult bilinguals, see Gollan, Montoya, Fennema-Notestine, and Morris, 2005). Thus, the bilingual advantage appears to be quite specific to the resolution of conflicting information. Bialystok and colleagues (e.g., Bialystok, Craik, Klein, and Viswana- than, 2004; Bialystok, Craik, and Ryan, 2006) have further shown that bilingualism appears to confer a benefit to bilinguals as they age. During normal aging, there are significant cognitive declines in executive control processes. While bilingualism does not prevent cognitive aging, it appears to offer some protection against the rate of cognitive decline. On atten- tional tasks that require the inhibition of irrelevant information, bilinguals appear to outperform age-matched monolinguals. The hypothesis is that a life of negotiating competition across two languages creates expertise for just those cognitive skills that are tapped by tasks that measure executive control. Bialystok et al. (2004) demonstrated the bilingualism advantage using a very simple nonlinguistic task that has been used widely in the cognitive lit- erature to examine attention and issues of stimulus-response compatibility. In the Simon task (Simon and Rudell, 1967), colored squares are presented on a screen and participants are told to press one of two keys for each color. In the congruent conditions, the position of the square and the position of the key are aligned (e.g., both on the right or both on the left). In the incongruent conditions, the position of the square and the position of the key conflict with each other. The usual result is that a person takes longer to press the key in the incongruent conditions, and people have increasingly more difficulty with the incongruent conditions as they age. Bialystok et al. replicated this finding and then showed that the performance of elderly bilinguals did not decline as precipitously as that of their age-matched monolingual counterparts. Although there is no direct evidence in this type of study to argue that the cross-language competition is causally respon- sible for the observed bilingual benefits, it is tempting to propose that such
110 HUMAN BEHAVIOR IN MILITARY CONTEXTS a relationship might exist from a life spent sharpening cognitive skills that function to reduce interference from one language to the other. This summary suggests that bilinguals are experts in resolving compe- tition across competing cognitive systems. What are the implications for adult learning of a second language? One possibility is that individuals who come to the task of language learning with strong cognitive skills on those dimensions that are most affected by bilingualism will be most likely to succeed. I next consider the empirical evidence that is available to evaluate this hypothesis. Individual Differences in Adult Second Language Learning Although folk wisdom suggests that some people are more talented language learners than others, there is a relatively limited research litera- ture on individual differences that have been documented to affect second language learning (Michael and Gollan, 2005; Miyake and Friedman, 1998; Segalowitz, 1997). One of the problems facing research on this topic is that not all aspects of language processing may be sensitive to the same cogni- tive factors. For example, it seems clear from studies of age of acquisition that the development of the lexicon, grammar, and phonology in a second language may follow a different course. Studies of childhood overhearers who are exposed to a second language during early childhood but never become proficient speakers suggest that there are savings to the phonology but not to the grammar (e.g., Au, Knightly, Jun, and Oh, 2002; but see Pallier et al., 2003). Likewise, a recent study (Slevc and Miyake, 2006) reports a relationship between musical ability and the acquisition of a second language phonology but little relationship between musical ability and lexical or grammatical acquisition. Thus, the factors that make people sensitive to the sound structure of a new language may be distinct from those that enable them to comprehend or speak words and sentences in that language. A number of studies investigating the neurocognitive basis of second language learning have also shown that age of acquisition appears to affect sensitivity to syntax but not to semantics (see, e.g., Hahne and Friederici, 2001; Weber-Fox and Neville, 1996). Again, the implication is that the same individual differences will not affect all aspects of language processing similarly. The brief review of research on the parallel activity of the two lan- guages in proficient bilinguals suggests that those individuals who are able to effectively negotiate competition may be better able to tolerate the de- mands induced by the presence of a second language. Because the second language may also make greater demands on working memory resources (e.g., Hasegawa, Carpenter, and Just, 2002), individuals with greater mem- ory capacity may also have an advantage in learning a second language.
ADULT SECOND LANGUAGE ACQUISITION 111 The evidence on the role of working memory resources in second language learning is mixed. Some older studies have shown that working memory span is correlated with aspects of the acquisition of grammar (e.g., Harrington and Sawyer, 1992; Miyake and Friedman, 1998), but more recent studies claim that the relation between working memory and second language performance is weak (e.g., Juffs, 2004). At the level of the lexicon, there is evidence that the time to translate from one language to the other is affected by working memory resources (e.g., Kroll, Michael, Tokowicz, and Dufour, 2002) and that memory resources affect the strategies that learners adopt. Kroll et al. (2002) found that learners with low working memory span were faster to translate words that had cognate translations (i.e., transla- tions that are lexically identical or similar across languages) than learners with high working memory span. The results suggest that low-span learners may be more likely to exploit surface cues that are potentially unreliable and do not generalize across the full vocabulary when translations are not similar or when the surface similar is deceptive, as in the case of interlingual homographs or âfalse friendsâ (e.g., the word âroomâ in Dutch means cream in English). In contrast, high-span learners appear better able to de- rive the meaning of new words in the second language (see further below). An interesting observation in the Kroll et al. study was that all learners, regardless of their memory resources, revealed a cost to the first language in a simple word naming task relative to a group of highly proficient bilin- guals. The learners were slower and more error prone to name words in the second language than the proficient speakers, but they were also slower to name words in the first language, the native language of both groups. This result obtained even when word naming was blocked by language. The observed cost suggests that second language learning may impose process- ing costs even on native language tasks that have been taken to be highly automatic for adults, such as naming words aloud. In addition to research on the relation between working memory and second language processing, a number of studies suggest that measures of phonological working memory specifically correlate significantly with second language vocabulary acquisition in both laboratory (Papagno, Valentine, and Baddeley, 1991; Papagno and Vallar, 1995) and classroom settings (Cheung, 1996; Service, 1992; Service and Kohonen, 1995), with high-span learners acquiring new words in the second language more easily than learners with more limited capacity. Whether these different measures are tapping into distinct or common processes is unclear. Few studies have investigated how the components of inhibitory con- trol might differentially affect second language acquisition. The findings of Bialystok et al. (2004) showing that elderly bilinguals are better than age-matched monolinguals on measures of inhibitory control (such as the
112 HUMAN BEHAVIOR IN MILITARY CONTEXTS Simon task) might be taken to suggest that individuals who are able to ef- fect control on similar tasks might also be advantaged language learners. A recent study by Weiss, Gerfen, Mitchel, and Rizzo (2007) examined differ- ences in the ability of adults to segment conflicting speech streams in artifi- cial languages as a function of the salience of available cues and individual differences in performance on the Simon task. When the available linguistic cues were in conflict, segmentation performance was highly correlated with Simon performance, again suggesting that the ability to negotiate conflict across competing conditions is modulated by an individualâs cognitive re- sources. Few other studies have investigated the specific effects of inhibitory control on the success of second language learning. A theme in the recent cognitive work on inhibitory control (e.g., Friedman and Miyake, 2004) is to begin to identify the specific components associated with different inhibitory functions (e.g., suppressing prepotent responses, switching between tasks, and selective attention). This is clearly a promising direction for research on second learning: also see Abutalebi and Green (2007) for a related discussion of the neural mechanisms that might support inhibitory control in bilingual production. CONTEXTS OF SECOND LANGUAGE LEARNING For adults exposed only to classroom instruction, second language ac- quisition is typically slow and only partly successful. In contrast, learners in immersion contexts are often more successful, particularly in acquiring oral proficiency in the second language (e.g., Segalowitz and Freed, 2004; see also the introduction to a special issue of Studies in Second Language Ac- quisition on learning contexts by Collentine and Freed, 2004). An obvious feature of the immersion environment is the frequency of second language input. However, from a cognitive perspective, immersion learning may also enable learners to more effectively inhibit their first language, both because there are potentially fewer opportunities to use it and because the cues to it in the larger environment are reduced. Kroll, Michael, and Sankaranarayanan (1998) attempted to simulate this aspect of second language learning in the lab by teaching new second language vocabulary paired with English translation equivalents or with pictures of the objects to which the concepts referred. The pictures were sometimes presented in their canonical (or usual) orientation; other times they were presented in an odd, noncanonical orientation (e.g., upside down or sideways). The idea was to provide a unique cue to the second language and simultaneously slow down access to the first language name of the ob- ject. The results showed that learners were later faster to translate second language words that were associated with noncanonical representations of objects even in the absence of the object itself, suggesting that the locus of
ADULT SECOND LANGUAGE ACQUISITION 113 the effect was abstract and conceptual. If this sort of learning can take place in the laboratory in a few brief sessions, then it certainly should be possible to see these benefits in the presence of the richer context available during immersion in the language and culture of another country. Two recent studies in my laboratory explored the interaction between an immersion learning context and individual learner characteristics. In these studies, English was the native (first) language, and Spanish was the second language. In one experiment, Tokowicz, Michael, and Kroll (2004) examined the errors made by learners on a word translation task as a func- tion of whether or not they had studied abroad and how they scored on an operation span task (Turner and Engle, 1989). Learners often make errors of omission in translation when they simply donât know the word, particu- larly when translating from their first to their second language. However, they occasionally make other sorts of errors as well. In this study, learners who had both high working memory span as well as immersion experience were more likely to make meaning errors than high-span learners with with- out immersion experience or low-span learners. The result suggests that the combination of high span and immersion may encourage the development of oral proficiency. Although these high-span learners still made errors by producing translations that were only approximate, it may very well be a critical step towards increased second language skill. In a second study (Linck, Kroll, and Sunderman, 2007), we investigated language processing performance by learners of Spanish while they were immersed in a study abroad program in Spain. Their performance was compared with a group of classroom learners matched on second language experience (if anything, the classroom participants had more second lan- guage experience than the participants abroad) and on their scores on a reading span task. Each group performed two tasks: a translation recogni- tion task in which they had to decide whether the second of two words was the correct translation of the first and a verbal fluency task in which they were asked to generate as many exemplars of a given semantic category they could think of in 30 seconds. In the translation task, the first word always appeared in Spanish and the second word in English. On half of the trials, the second words were indeed the correct translation of the first. However, among the incorrect translation trials, there were three types of critical foils: (1) the Spanish word resembled the lexical form of the English word (e.g., mano-man, when mano means hand in Spanish); (2) the Spanish word resembled the lexical form of the translation of the English word (e.g., hambre-man, when hambre means hunger in Spanish and the correct translation of man is hom- bre); and (3) the Spanish word was semantically related to the English word (e.g., mujer-man, when mujer means woman in Spanish). The classroom learners were sensitive to each of these conditions in that they were slower
114 HUMAN BEHAVIOR IN MILITARY CONTEXTS to reject the foils than unrelated controls. In contrast, the immersed learners produced no interference for lexical foils but a large effect of interference for the semantic foils. The absence of lexical interference for words resembling the transla- tion equivalent has been taken in past studies as an index of increased second language proficiency (e.g., Sunderman and Kroll, 2006; Talamas, Kroll, and Dufour, 1999). However, the absence of a lexical interference for direct lexical neighbors stands in direct contrast to the findings for highly proficient bilinguals in word recognition tasks (for a recent review, see Dijkstra, 2005). The result suggests that in the immersion context there may be active suppression of the first language. Performance on the verbal fluency measure further supports the hypothesis that the first language is more effectively inhibited when learners are immersed in a second language. Although all learners, regardless of context, produced a larger number of exemplars in English than in Spanish, the immersed learners produced significantly fewer exemplars in English than their counterparts in the classroom, again suggesting that the first language was less accessible for immersed learners. In the Linck et al. (2007) study, the classroom and immersed groups were matched on reading span scores and it was also possible to ask how span affected performance for each group. For the classroom learners, there was more lexical than semantic interference for the low-span learn- ers. However, the pattern reversed for the high-span learners, suggesting that memory resources alone were sufficient to enable high-span learners to process the second language conceptually. For the immersed learners, there was greater semantic than lexical interference for both low- and high-span participants; the effect of span was simply to enhance the semantic effect for the high span learners. A striking result was that the performance of the low-span learners who were immersed resembled the high-span learners in the classroom, suggesting that the immersion context was able to provide information that low-span learners could not otherwise derive themselves. There are a number of critical questions about language immersion that remain to be investigated, including the respective contributions of language and cultural influences. One approach to evaluating the consequences of language immersion on its own is to examine performance in domestic im- mersion programs (such as the summer programs at Middlebury College). Unlike immersion in a foreign country, U.S. domestic programs typically require students to agree not to speak English. In a sense, this requirement can be viewed as an effective means to enforce suppression of the first lan- guage. Again, there has been little research on language processing that has exploited the unique properties of this environment. In one study in our lab (Jacobs, Gerfen, and Kroll, 2007), we tested students immersed in a domes- tic summer program in Spanish. The fact that learners in domestic programs
ADULT SECOND LANGUAGE ACQUISITION 115 are typically not allowed to use their first language imposed restrictions on our experimental design because only processing in the second language could be evaluated without direct comparisons to the first language. We asked how simple word production in Spanish, at the level of pro- cessing and also in the form of realizing the produced speech, would be affected by the immersion context relative to a group of control learners matched on overall second language proficiency. The critical materials in this study were Spanish cognates that were orthographically similar to their English translations. Because the phonology of cognates is never identical across two languages, it was possible to examine the voice onset times (VOTs) and articulatory duration for cognates and phonetically matched controls to determine whether cognates are less likely to reveal the influ- ence of English in the immersion environment than in the classroom. The results showed that this was indeed the case. The learners in the immersion program, although no more proficient than their classroom counterparts in other respects, were more likely to produce the phonology of Spanish without the influence of the first language. Their VOTs were more similar to a group of advanced Spanish learners than to the proficient-matched con- trols, suggesting that reducing the activity of the first language may enhance the acquisition of the second language phonology. Note that if the learn- ersâ performance were simply a matter of completely acquiring particular aspects of the second language phonology, then cognates and noncognates with similar phonology should have been produced similarly. Although cognitive and psycholinguistic research on contexts of lan- guage learning is at an early stage of development, there are reasons to think that a better understanding of language immersion and its correlated features are likely to provide useful directions for enhancing adult learner outcomes. For individuals identified as having high levels of cognitive resources, either with respect to memory capacity, attentional skills, or sensitivity to phonology, it may be possible to exploit the immersion envi- ronment as a means to jump-start rapid second language learning. STRUCTURAL PROPERTIES OF THE SECOND LANGUAGE In addition to the cognitive characteristics of learners and the learning context, there is also a question about how the structural relation between a native language and a new second language affects the trajectory of second language learning. Some models of learning assume that learners transfer all possible aspects of the first language to the second language. For example, the competition model (e.g., Bates and MacWhinney, 1982; MacWhinney, 1997) proposes that learners begin with a set of biases that are associated with the preferences of their native language. Thus, in English, word order is a salient syntactic cue; in other languages animacy may be more critical.
116 HUMAN BEHAVIOR IN MILITARY CONTEXTS For example, in a sentence such as âThe dog chased the car,â only the dog is an animate noun that can be doing the chasing, and in some languages, that may be a syntactic cue. The development of second language skill is then proposed to be a competitive process in which different syntactic cues compete until the cues associated with the new language are sufficiently strong. In this model, the more structurally similar two languages are, the more easily a learner can effectively utilize existing second language knowledge. At the level of the phonology (e.g., the perceptual assimilation model [Best, 1995] and the speech learning model [Flege, 1988]) and at the level of the lexicon (e.g., Kroll and Stewart, 1994), there is also evidence that acquisition of the second language is initially processed with respect to the first language. Although there is other empirical evidence for the pres- ence of constraints in this process, the system is impressively pliable, with changes that appear to reflect the nature of the second language exposure (e.g., Escudero and Boersma, 2004). What is not apparent from the existing research is how the relative contribution of similarity or distinctiveness at each level of language rep- resentation and processing shapes the overall skills of the second language learners. For example, when two languages share the same alphabet, there is an opportunity for ambiguity in reading, with similar words that may or may not share the same meaning in both languages. In a language with a distinctive script, there is no opportunity for ambiguity at this level. Thus, facilitation in acquiring rudimentary literacy skills may be offset to some degree by the presence of cross-language ambiguity and resulting competition. At each level of language processing, there may be analogous tradeoffs, with similarity imposing both costs and benefits depending on the goals of a particular task. The available studies that have examined structurally distinct languages in second language speakers provide some support for the claim that differences in the surface form of a language do not appear to eliminate the types of cross-language interactions described above (e.g., Gollan, Forster, and Frost, 1997; Jiang, 1999). To the extent that skill in a second language is based on the acquisi- tion of an abstract level of representation, the results of these studies sug- gest that both the lexicon and the grammar share properties that prevent bilinguals from functionally separating the two languages even when the languages are quite distinct. Some recent studies of bimodal bilinguals who use spoken English and American Sign Language (Emmorey, Borinstein, and Thompson, 2005) suggest that even in the extreme case of two lan- guages that use different modalities, there is evidence for cross-language interactions, demonstrating that the structural differences associated with the languages do not prevent access to lexical and grammatical representa- tions that are fundamentally open to the influence of the other language. An interesting hypothesisâwhich to my knowledge has not been explored
ADULT SECOND LANGUAGE ACQUISITION 117 systematicallyâis whether structurally distinct languages impose a greater processing load than similar languages and therefore require enhanced cognitive resources to achieve levels of second language proficiency that are comparable to structurally similar languages. OTHER PROMISING DIRECTIONS The Declarative/Procedural Model Ullman (2001, 2004) has made a provocative claim about why second language learning is typically more difficult for adults than for young chil- dren. According to the declarative/procedural model, different memory sys- tems support access to the lexicon and to grammar. Grammatical, rule-based processing is hypothesized to be computed on-line (that is, processed in real time, as it actually occurs) and to be controlled by the neural mechanisms common to other tasks that also require procedural memory and skill learn- ing. In contrast, lexical knowledge is hypothesized to be stored in declara- tive memory, drawing on neural resources that are common to the storage of facts and explicit meanings. The claim is that second language learning is typically difficult for adults because they no longer have access to the same procedural system that underlies the acquisition and use of rule-based grammar in their first language. Because procedural memory systems are hypothesized to be relatively unavailable to late second language learners, all forms must initially be stored and retrieved from declarative memory. To the extent that distinct brain structures support procedural and declarative systems, a different profile of neural functioning is predicted for learning a second language than for learning a first. In addition, learners who have superior declarative memory (e.g., women relative to men, see Ullman et al., 2002) are predicted to be more successful language learners. Technology for Language Learning Contemporary classroom instruction has changed radically with the introduction of computer-assisted technology for language delivery. How- ever, very little research has been conducted from a cognitive perspective to determine how the method of delivery and context of learning affect the acquisition of second language skills. A study by Payne and Whitney (2002) explored the interesting hypothesis that the use of computer chat rooms might enable second language learners to acquire oral proficiency skills. The theoretical logic was that speech planning engages a series of components up to the point at which the speaker can articulate the intended utterance (e.g., Levelt, 1989). These components, from the conceptualization of the utterance to lexical retrieval and phonological encoding, are hypothesized
118 HUMAN BEHAVIOR IN MILITARY CONTEXTS to engage abstract representations that are then specified for articulation. The medium of articulation can take any number of different forms, from speaking to typing or writing, or signing for a person who uses sign lan- guage, but the abstract stages of planning speech prior to articulation are shared. Payne and Whitney (2002) argued that what was critical for second language learners was gaining skill in the cognitive components of speech planning. They hypothesized that the computer chat environment would enhance that process because learners would be able to read the text that had been generated and therefore benefit from a reduction in the load on working memory that would normally be required in ordinary spoken discourse. This was indeed what they found, with the added result that the chat context appeared to be particularly beneficial for learners who had been identified as being relatively lower in their phonological memory capacity. Assessing Learner Outcomes A contribution of cognitive psychology and cognitive neuroscience to the field of second language acquisition is an emphasis on tasks that mea- sure processes as they happen and thus more sensitively than metalinguistic judgments or after the fact assessments. A key issue for designing training programs for adult learners will be to determine whether the goals of a particular learning situation require that the second language be fully ac- cessible for immediate performance (that is, on-line), or whether accuracy when there is no time pressure (an off-line task) will be sufficient for spe- cific purposes. For example, it is notoriously difficult for adult learners to use subject-verb agreement correctly in a second language. However, Jiang (2004) demonstrated that the same Chinese-English learners who were ap- parently unable to process subject-verb agreement correctly in English in an on-line comprehension task were in fact capable of performing the same constructions accurately in an off-line measure. More generally, the point is that second language learners may possess knowledge of a structure but be unable to use that knowledge under the time pressures associated with speeded comprehension and production tasks. A recent study by McLaughlin, Osterhout, and Kim (2004) provided evidence for a surprising dissociation between behavioral performance and brain activity in second language learners. The researchers examined lexical decision performance in a group of learners who had literally just begun to study French in an introductory university-level course. Lexical decision is difficult for learners because they have to discriminate letter strings that form real words from those that are nonwords in the new language. Indeed, lexical decision is often used in the literature as a measure of language pro-
ADULT SECOND LANGUAGE ACQUISITION 119 ficiency to differentiate the relative skill level of learners who have many years of second language study (e.g., Huibregtse, Admiraal, and Meara, 2002). What McLaughlin et al. found was that learners in a first course in French predictably had chance probability in performing lexical decision. However, when they measured event-related potentials (ERPs) for the same conditions, they found evidence that suggested that after only 14 hours of second language study, learners were beginning to differentiate words and nonwords in French despite the fact that there were unable to do so consciously. A related set of findings was reported by Tokowicz and MacWhinney (2005), who examined sensitivity to syntactic violations in a grammaticality judgment task. They found that second language learners were at chance in making explicit judgments of grammaticality but revealed sensitivity to violations of the second language grammar in the ERP measure. Tokow- icz and MacWhinney argued that this method of identifying sensitivity to second language structures that learners are not able to process explicitly might provide an important method for identifying milestones in language development that could then be exploited by explicit instruction. Third Language Learning by Bilinguals Are individuals who are already proficient bilinguals better able to acquire a third language than monolinguals acquiring a second language? There are only a few studies that have explicitly addressed this issue: the available evidence suggests a positive answer to the question. For example, in the realm of vocabulary acquisition, Van Hell and Candia Mahn (1997) compared the performance of two groups learning new vocabulary. One group consisted of highly proficient Dutch-English bilinguals learning new words in Spanish and the other groups consisted of native English speakers who were functionally monolingual learning new words in Dutch. The bi- lingual group outperformed the monolingual group. An interesting feature of this particular bilingual group is that they were highly proficient but late second language learners, as Dutch children first learn English in school at ages 10-12. The result thus suggests that a bilingual advantage in third language acquisition may not depend on early bilingualism. A recent set of studies on language-switching performance also sug- gests that there may be some advantage for proficient bilinguals when confronted with a third language. When bilinguals are required to switch from one language to the other, there are costs to the processing speed that are thought to reflect the requirement for inhibition of the unintended language. Ironically, it is often more difficult for bilinguals to switch into the more dominant (first) language than into the weaker (second) language (see, e.g., Meuter and Allport, 1999). The interpretation of an asymmetry
120 HUMAN BEHAVIOR IN MILITARY CONTEXTS in language switch costs is that unbalanced bilinguals will have to inhibit their first language more strongly to speak the second language than the reverse (Green, 1998). Costa and Santesteban (2004) demonstrated that highly proficient and relatively balanced bilinguals did not reveal this asym- metry; they showed switch costs that were similar for their two languages. Most critically, when these bilinguals were asked to switch between their first language and a third language in which they were less proficient, they continued to produce a pattern of switch costs that was symmetric, in con- trast to learners and less proficient bilinguals who show the typical switch cost asymmetry. Costa and Santesteban (2004) argued that the absence of a switch cost asymmetry suggested that skill as a bilingual provides a means to control the two languages without active inhibition. Although the specific interpre- tation of these results may be debated, what is clear is that the way in which an equally weak new language is processed differs for those for whom it is a third language and for those for whom it is a second language. The more general implication is that the cognitive consequences of bilingualism, particularly those that affect attentional control, may have equal or pos- sibly greater significance for acquiring a third language than such factors as the structural similarity of the new language to the old languages (e.g., MacWhinney, 1997). UNRESOLVED ISSUES AND OBSTACLES: CROSS-DISCIPLINARY CONNECTIONS A clear priority for research is to better exploit appropriate connections between cognitive and cognitive neuroscience approaches to second lan- guage acquisition and the research on this topic from more traditional edu- cational and sociolinguistic perspectives (e.g., Watson-Gegeo and Nielsen, 2003; DÃ¶rnyei and Skehan, 2003). A problem in bridging these approaches is that the historical tradition of research in each of the disciplines has been shaped by differences in the questions that bring researchers to the problem of second language learning. The cognitive approach is relatively more theoretical, with a focus on how learning itself takes place and how second language learning is a model for that process. The âgrain sizeâ of the research tends to be narrow and concerned with outcomes that can be studied in the laboratory. Few cognitive scientists have direct experience in instructing second language learners. For educators, and particularly for those who come to research from foreign-language classroom experience, there is a more immediate concern for pedagogical implications. There is also reliance on research methods that are as likely to be qualitative as quantitative, and when they are quantitative, to be large-scale and correlational rather than fine-grained
ADULT SECOND LANGUAGE ACQUISITION 121 experimental analyses of individual behavior. As in other areas of research that have a rich cross-disciplinary mix, there are probably some aspects of second learning that could benefit from closer collaboration across the disciplines and other aspects that are better suited to specific disciplinary approaches. A quick glance at any of the recent edited handbooks on bilingualism, second language acquisition, or applied linguistics reveals a move towards greater inclusiveness across the disciplines. However, inclusiveness itself is only a sign of recognition that different approaches make legitimate contributions to the field, not an indication of research that is genuinely interdisciplinary. But it is first step. A number of obvious barriers make the next stages of research difficult. The academic cultures and resource associated with the disciplines that comprise second language acquisition are distinct. Language departments are typically located in colleges of humanities; cognitive science and neuro- science are located in colleges of science and social science. Until recently, it was unheard of for a faculty member in a language department to have access to a laboratory, although that situation is changing as programs in the language sciences begin to emerge. A second focus of cross-disciplinary work is related to translational research that bridges clinical and cognitive approaches to language devel- opment. An emerging body of research, performed primarily in the context of programs in communication disorders and speech and hearing sciences, addresses the problems that young children face when they enter U.S. schools without English language skills (e.g., Bedore, PeÃ±a, GarcÃa, and Cortez, 2005). These children are at risk for academic failure and also for the misdiagnosis of language disorders because the traditional methods of assessing language are almost entirely in English. As they acquire English, their performance may differ from monolingual native speaker norms be- cause they genuinely have a language disorder or because their bilingualism affects their performance in both their first and second languages. Although some of this research may appear to have an agenda that is quite distinct from the goals for adult learners, there is a shared concern with develop- ing methods that might facilitate the rapid acquisition of literacy and oral proficiency in a second language. Finally, recent developments in social neuroscience will certainly benefit studies of second language learning. The affective side of second language learning has only recently begun to receive attention from both sociocul- tural and experimental perspectives (e.g., Harris, AyÃ§iÃ§egi, and Gleason, 2003; Pavlenko, 2005). Few studies have addressed the issue of how ac- culturation might be assessed rigorously and how it might affect second language learning (e.g., Stephenson, 2000) and how personality, emotional, and affective states might modulate the experience of immersion in a new
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