An Introduction to the Cognitive Neuroscience of Second and Artificial Language Learning
2020-06-01

Besides acquiring one's first language(s) in infancy, learning an additional language at a later point in life is one of the most fascinating accomplishments of the human mind. It is so fascinating that it verges on the miraculous. Scientists are not usually fond of the term, however, and many a scholar has striven to identify, characterize, and quantify, if not resolve, the cognitive and neural mechanisms underlying this uniquely human ability. The study of language learning is rendered particularly challenging by the fact that the process is driven by the complex interplay of essential learner-intrinsic and learner-extrinsic variables. Moreover, a great deal of language learning happens outside conscious awareness, that is, without the learner relying on explicit processes involving declarative memory or metacognitive awareness. It follows that subjective and questionnaire-based assessments provide limited insights into the cognitive adventure that represents the learning of a language. In order to gain theoretical insights, we must thus turn to methods that go beyond the description of overt manifestations of language knowledge and “surface” indicators of performance (i.e., external manifestations of comprehension and production). This explains the spectacular expansion of the cognitive neuroscience of language over the past three decades, involving increasingly sophisticated and diversified methods, such as neuropsychological testing, reaction time experiments, computational modeling, eye-tracking, electrodermal conductivity, electrophysiology, magnetoencephalography, positron emission tomography, functional magnetic resonance imaging, near-infrared spectroscopy, transcranial magnetic stimulation, and transcranial direct current stimulation. The risks attached to using such sophisticated methods should not be underestimated, however, because the more sophisticated the method, the more abstract the data obtained, and the less intuitive the interpretation. This special issue on the cognitive neuroscience of second and artificial language learning (CoNSALL) covers a range of key topics in the study of how we learn and use novel languages. Far from being monolithic, the collection of contributions covers a spectrum of questions, approaches, methods, and considerations. The seven empirical studies and three conceptual reviews deal with a variety of target populations, including child and adult learners; monolinguals, bilinguals, and multilinguals. They cover a wide range of languages, from natural ones such as Basque, Dutch, English, German, Italian, and Spanish to artificial miniature systems, and they focus on different language areas, from vocabulary to morphology and syntax. The studies employ pictures, speech, words, sentences, animations, and videos to study lexical development, the learning of syntactic features such as grammatical gender or word order, and conceptual mapping, from the early stage of learning a second or an artificial language, to full proficiency, and even attrition of the native language. The data are based on a wide range of methodologies, from questionnaires and behavioral (psycholinguistic) measures to event-related potentials, brain stimulation, as well as structural and functional neuroimaging. In order to help readers choose a path through the CoNSALL special issue, or perhaps identify those contributions that they will find particularly relevant, we have compiled Table 1, which conveys the diversity of approaches and methods whilst highlighting overlaps among the papers. Accuracy RTs Learning of L2 word meanings, plasticity, L1 Attrition Liu and van Hell Behavioral ERPs Definition learning Semantic priming Reading and button press Accuracy LPC, N400 Bultena et al. Bilingual and multilingual learners Dutch- German Behavioral ERPs Pictures Written words Exposure + feedback 2AFC decision Confidence rating Reading and button press Accuracy RTs, Ratings ERN, CRN L1 interference during L2 grammatical gender learning Recall 4AFC MCQ Translation Listening or reading and writing Word error rate Accuracy Semantic similarity Pliatsikas et al. Children Adults Gray matter volume Brain metabolism Behavioral ERPs Pictures Definitions Accuracy RTs P300 German-English Italian- English Behavioral ERPs Accuracy RTs LAN, P600 Vocabulary learning exposure, matching, and production Syntactic priming Viewing, speaking, matching, and reading Accuracy Scores Priming effect English- Varied Artificial Animations Spoken sentences 2AFC task Vocabulary test Grammatical judgement Viewing, listening and button press Accuracy Procedural memory Declarative memory Neuroimaging Neurostimulation Patient studies Activation levels Accuracy, RTs The diversity that characterizes this special issue is representative of research in second language acquisition and artificial language learning. It should not be seen as a weakness; on the contrary, we believe that the wide range of dimensions covered offer excellent opportunities for transfer of knowledge across research domains and cross-disciplinary applications of methods. And this is not just a fuzzy-warm, well-intended, diplomatic statement. Truly interdisciplinary science does not suddenly happen just because a group of open-minded academics have been invited to exchange ideas and interact in a given venue for a day or two. A process of discovery and gradual adaptation is required, which entails not only the consideration of questions slightly different from our own, but also what the issues are that critically matter to researchers in neighboring fields, as well as an understanding of how other methods can shed light on the questions we have. Toward the end of this introduction we propose ways in which the different studies, reviews, and opinions presented in the special issue can be related to one another to further our understanding of language learning and use in the future, and how we see them offering interesting opportunities for novel research endeavors and cross-fertilization. This special issue of the Cognitive Neuroscience Series of Language Learning is based on an international conference held at Bangor University, Wales, in September 2018, with the same title as this special issue (conference URL: http://consall.bangor.ac.uk). The conference brought together over 60 scholars from 17 countries and from a wide range of disciplines with a strong interest in how languages are learned, from linguistics and computer science to psychology and neuroscience. Papers and communications were invited that deal with the cognitive and neural bases of the acquisition and use of a second language or of an artificial language. In the call for papers, the following questions were particularly emphasized: How are the novel representations of a second language neuroanatomically organized or neurophysiologically implemented in relation to representations of the first? How do they dynamically interact? How do the characteristics of the first language influence second and artificial language processing, and, in turn, how do the characteristics of a second or artificial language influence first language processing? How much functional autonomy do language representations enjoy from generic cognitive control systems during and after learning? Having attended the conference ourselves, and having perused the feedback received from delegates, CoNSALL certainly appears to have delivered passionate moments of communication and interactions between scholars with highly different perspectives on language learning. Keynotes were given by Janet van Hell, Gary Oppenheim, and Patrick Rebuschat, and invited presentations were delivered by Laura Batterink, Jon Andoni Duñabeitia, Rob Hartsuiker, Kara Morgan-Short, Karsten Steinhauer, and John Williams, all of whom were invited to contribute a paper to this special issue. In addition, two papers were invited on the basis of ratings and comments received in the process of abstract evaluation for the selection of oral presentations. Two authors were selected to make a contribution at this stage: Sybrine Bultena and Christos Pliatsikas. Thus, at least one author of each of the articles presented in this special issue participated in the conference, whether by invitation or through the selection process. The only exception was Morten Christiansen who, despite having a keen interest in participating in the conference, was unable to do so as he was delivering the University of Alberta's 41st Annual Distinguished Scholar lecture series in the same week as CoNSALL was held. Morten thus received an independent invitation to join in the special issue venture at a later time. The first three articles of the special issue deal with the early learning of specific language features: novel (made-up) words, second language words, and grammatical gender in individuals who have little or no knowledge of gender in their native language. Oppenheim, Griffin, Peña, and Bedore (2020) adopt a skill-based view of language, according to which we learn language (and other skills) incrementally, through extensive practice, and possibly also lose language as competing linguistic systems are developed. This view has clear implications for the study of bilingual language acquisition and use. It assumes that, in bilingual populations, the ability to speak two languages should depend on how much each language is practiced and not just on the order of acquisition. It also raises the possibility that extensive use of a second language could cause gradual “unlearning” of the first language, a matter of concern for learners, parents, and educators, as well as communities and society as a whole. To explore these issues, Oppenheim and colleagues observed the lexical development of 139 Spanish-English bilingual children for several years as they transitioned from mostly-Spanish homes to mostly-English schools. During this period, the children's English proficiency predictably overtook that of their Spanish. However, the children's Spanish skills continued to improve, thus demonstrating that losing one's first language (here, Spanish) is not an inevitable consequence of becoming dominant in one's second language (English). On the contrary, continued practice of both languages permits the consistent improvement of both languages. Liu and van Hell (2020) investigated how monolingual adults learn novel words from definitions when they have had no significant experience of new word learning as adults. The authors used well established indices of word learning, the late positive component (LPC, indexing lexicalization) and the N400 (indexing consolidation) to show that, although inexperienced learners manifested signs of having lexicalized novel words after 24 hours of offline consolidation, the meaning of learned words had not become consolidated enough to modulate the amplitude of the N400 component. This pattern of results resembles that seen in experienced learners (bilingual individuals), who also did not show N400 modulations after 24 hours of offline consolidation, but who, in contrast to inexperienced learners, appeared to have lexicalized novel words immediately after exposure to definitions (Bakker et al., 2015). Bultena, Danielmeier, Bekkering, and Lemhöfer (2020) relied on an electrophysiological index of error monitoring, namely the error-related negativity (ERN), to study the early stages of learning Dutch grammatical gender in native speakers of German. While participants initially made errors based on intuitions deriving from misguided generalizations of their native German grammar, they improved considerably over three learning sessions with corrective feedback. Interestingly, in the case of cognates with mismatching gender across the two languages, a stronger ERN effect was elicited by answers that were correct in the new language and a weaker ERN was elicited by errors (which aligned with the correct gender in the native language). The author interpreted these findings as a sign of overreliance on intuitions derived from native language knowledge. But, as participants became more accurate and knowledgeable regarding grammatical gender in Dutch, the ERN pattern gradually inverted to match the traditional response to errors. The article opens an interesting new avenue for monitoring learning progress at the interface between implicit indices (electrophysiological) and explicit measures (performance). The next four articles move on from the case of learners of completely new words or properties of a second language to the case of individuals who already have achieved a certain level of proficiency in their second languages: bilinguals. In their contribution, Culbertson, Andersen, and Christiansen (2020) validate a faster and simpler method to assess second language proficiency. Determining a speaker's language proficiency is important for a variety of well-known reasons, from employment, university admissions, and placement in language courses to experimentation and research. However, proficiency testing is often time-consuming, and many tests may not provide reliable indications of how the learner would fare in real-world conversations. Culbertson and colleagues explored whether our ability to listen to and recall an utterance in the second language (here, Spanish) could function as a reliable test of second language proficiency. Recall taps into our ability to process language input in real-time, as needed, for example, in a conversation in the real world. The authors found that their recall measure was a better predictor of a learner's ability to translate heard sentences than a shortened version of a standardized listening multiple-choice comprehension test. These findings suggest that recall of naturalistic utterances may provide an accurate and efficient alternative to traditional tests for predicting foreign language proficiency. Pliatsikas, DeLuca, and Voits (2020) take a neuroimaging approach to present a timely reminder that bilingualism is, in fact, a highly abstract construct and that bilingual individuals’ behavior and performance are first and foremost determined by exposure and by many (often neglected) factors beyond those of age of acquisition and modes of learning. The dynamic restructuring model proposed by the authors makes an interesting distinction between long-term, experienced bilinguals, who show adaptations in brain regions mainly related to language control and bilinguals who are still in the process of acquiring, or have limited experience of using, their second language, and who tend to show neurostructural changes in regions related to vocabulary acquisition. Pliatsikas and colleagues make a compelling case for more consideration to be given to individual differences in research on bilingualism. They also invite us to harness the power of longitudinal approaches and they highlight the importance of the apparent link between long-term bilingualism and cognitive resilience in aging (see also, Zhang, Wu, & Thierry, 2020). Antón, Thierry, Dimitropoulou, and Duñabeitia (2020) provide new evidence, neurophysiological this time, that storage of new conceptual information is unaffected by the language context (single or mixed) in which definitions are learned. Their participants were shown unfamiliar artificial objects and quickly learned to associate these with two definitions that likened the novel object to existing familiar objects. But, critically, it did not appear to matter whether the two definitions learned were presented in the native language (in this case, Basque), or if one definition was presented in the native and the other in the second language (Spanish). This null result is interesting because it stands at odds with the intuition that mixing language during tuition should be avoided, which is sometimes reflected in policies implemented in bilingual educational contexts. The study is particularly convincing because of its reliance on implicit measures of object recognition directly derived from brain activity using a wave of event-related potentials well known to index detection of a target (P300). Steinhauer and Kasparian (2020) open Pandora's box of language attrition: They review and discuss the first unambiguous evidence from electrophysiology that the native language can suffer some form of decay in individuals who have become heavily or even exclusively reliant on a later acquired, second language. Native speakers of Italian who have ceased using their native language for a long period of time can perceive perfectly grammatical sentences in their native language as ungrammatical. But such effect is only seen in individuals who have become dominant in their second language and have almost ceased using their native language entirely. Consistent with the views developed in the article by Pliatsikas and colleagues (2020), the level of plasticity revealed in long-term bilinguals is astounding, shattering old beliefs that a native language is one's native language for life. The evidence presented in this review article is particularly compelling because it relies upon well-established indices of semantic and syntactic violation detection by the brain, namely, the N400 and the P600. The last three articles echo the first three of the special issue by addressing questions of learning new words and grammatical constructs, but this time in relation to an artificial rather than a second language. Muylle, Bernolet, and Hartsuiker (2020) investigated the representation of syntax in bilingual speakers. It is often assumed that syntactic representations of two (or more) languages are shared in cases where sentence structures are similar across the two languages (e.g., the passive structure in Dutch and English) but it is not clear how similar syntactic representations need to be for sharing to take place. Muylle and colleagues addressed 2020 by comparing syntactic priming effects between Dutch and three artificial languages varying in terms of word order and case marking. They found evidence for syntactic sharing between Dutch and the artificial languages, though this was limited to transitive sentences. They also observed similar patterns across the three versions of the artificial language, suggesting that neither case-marking nor word order differences adversely affected the sharing of syntax. Walker, Monaghan, Schoetensack, and Rebuschat (2020) present data from an artificial language learning paradigm involving rather delightful alien characters pushing and jumping over each other, as participants come to grips with sentences made of completely new words arranged in an unfamiliar syntax. The study features an insightful analysis relating individual differences in working memory, implicit and explicit learning skills, and on the one with judgement regarding word order, and word on the and colleagues were to show that adult learners could novel words and syntactic structures as a result of exposure and without feedback. They observed that and syntax were by and that the effects after 24 the authors found that declarative memory initially learn and memory initially with and after 24 memory became more The special issue with a by (2020), which a highly and review of selected and studies in an to between implicit learning and language The is if the processes in implicit learning of an artificial those in language processing, it should that brain regions by and neuropsychological research into implicit artificial learning at least in observed in research into language The is complex and not without The for Morgan-Short, & and the diversity of make it particularly to direct between the two a by a of key structures and brain in language that also appear to a in implicit artificial learning, namely, and the same time, the contrast existing between domains and some The author by highlighting questions that we must be to if we to better the neural of both language acquisition and that of implicit learning in The contributions in this special issue provide an at the of second and artificial language learning and they us to how the in the the one the articles an from the CoNSALL conference on which the special issue was progress in the study of language learning us to our individual and with scholars and of other It is to take for but it is often perhaps even to see how little across research with scholars in and neuroscience often the (see also Rebuschat & Monaghan, the conference, the special issue together from all of whom have an interest in how we learn language(s) and who are to in with those colleagues with a different in articles that deal with similar questions, such as vocabulary and learning, but that use different such as performance or electrophysiological index and sometimes we the special issue to the of this essential cross-disciplinary this not just the reading of from fields, more understanding how a method different from our can shed light on the same we are to one's into the is the first into and the special issue one to do this when reading related articles that use In this special issue, the of Liu and van Hell with that of Oppenheim and contrast Steinhauer and approaches with those of Pliatsikas and findings from Muylle and colleagues with made by But beyond the for interdisciplinary discovery by this special issue, the approaches by invite between studies and open for research. studies of artificial learning (e.g., Muylle et al., et al., would from using the electrophysiological indices that to a detection of performance errors or grammatical in natural language (e.g., Bultena et al., Steinhauer & 2020). In the study by and if a or is learned through exposure to an artificial language, of such words when they the conceptual of a or should influence the component known to to such violation in natural language (e.g., LAN, or see & the of using the measure of language proposed by Culbertson et al. (2020) in experiments, which have little time to to the of language proficiency, such an and measure could highly when used as a in or as a in index of error detection such as the ERN (e.g., Bultena et al., explicit measures of performance in Culbertson et al., Liu & van Hell, Oppenheim et al., would an index of of their errors. In other words, this additional data would shed light on ability to not only errors but errors as such that they to have learned words or grammatical an on our objects of The research in this special issue on how we learn and use language(s) a first linguistic is least in that is, second language and To the the studies employ natural languages artificial languages (see Table Artificial languages have been used for to a years as miniature of how language is learned outside the these systems has many example, they excellent control of the input in the that the can control what the participants are being to (e.g., the same time, are several which need to be example, many artificial systems are of a semantic that is, learners are to with that are or their are highly This is if artificial languages are used to us on how languages are learned in the a process that relies on learning to and utterances with a syntactic structure that can be more complex than that used in most artificial language this it would be important for studies to the development of artificial systems that natural languages more thus the of artificial language research to the study of natural language acquisition. In addition, it would be important for research to directly the link between artificial and natural language learning. have been made (e.g., Morgan-Short, & and is evidence that the of artificial systems as to study language learning (see Williams, but a and is still This special issue, and the which would not have been without the and contributions of many are to for all over and the and for their with abstract and conference go to and with and to for and in not only the and but most for the that some to be the point of the The was and by in of and and It was made by from the for Wales, and we are to for it we would to our and all the for participating in CoNSALL and the conference so and would to particularly all the authors of this special issue for their as well as our who each and feedback. our and Liu for sharing with us the task of the special issue, and with our for error that may and that should be our are also to our and and the and passionate of Language our for invitation to on this adventure in the first and we for the CoNSALL conference and its of and in relation to