The advent of psycholinguistic and neurolinguistic methodologies has provided new insights into theories of language acquisition. Sequential multilingualism is no exception, and some of the most recent work on the subject has incorporated a particular focus on language processing. This chapter surveys some of the work on the processing of lexical and morphosyntactic aspects of third or further languages, with different offline and online methodologies. We also discuss how, while increasingly sophisticated techniques and experimental designs have improved our understanding of third language acquisition and processing, simpler but clever designs can answer pressing questions in our theoretical debate. We provide examples of both sophistication and clever simplicity in experimental design, and argue that the field would benefit from incorporating a combination of both concepts into future work.

We review studies that investigated pragmatic acquisition and processing in multilingual children and adults, and third language (L3) learners. Studies on pragmatic differentiation in simultaneous multilingual children show that they can differentially and appropriately use their languages in a context-sensitive manner from the age of two. The evidence on implicature reveals that multilinguals exhibit interpretation skills comparable to monolinguals; and that degree of multilingualism, measured continuously, has a positive effect. Research that examined speech acts from the perspective of crosslinguistic influence has provided some evidence (though mixed and unclear) that the L1 can affect L2 and L3 speech act performance. This influence can also occur from the L3 to the L1 and L2 in young children. Moreover, work on speech acts has shown that bilinguals, and especially balanced bilinguals, enjoy an advantage in learning the pragmatics of an additional language. We close the chapter by suggesting directions for future work.

In this chapter, we review studies of multilingual people with language impairments, specifically autism, dyslexia, and developmental language disorder in children, and aphasia and traumatic brain injury in adults. We address three topics that have emerged: disadvantages and advantages of being multilingual, the manifestation of impairments across different languages, and cross-language effects following intervention. Whereas the field of language impairment and bilingualism has seen a growth in the number of publications, only a few studies have focused specifically on multilingual people, and even fewer have compared multilingual to bilingual individuals. Methodological differences among the studies and the limited amount of data for each communication disorder impede our ability to draw consistent conclusions. Despite these limitations, we discuss common themes and point to future directions. Furthermore, we propose that the study of more than two languages can add to our understanding of key aspects of language impairment, representation, and processing.

This chapter presents and discusses the methodological approach of case study in connection with research on third language acquisition and other areas of multilingualism and gives an overview of occurring case studies in these fields. After a brief introduction, the first section deals with the purpose of case study and characteristic features such as the real-life orientation and the holistic perspective, as well as the issue of generalizability. The second section discusses the nature and development of multilingual linguistic repertoires. Case studies here often cover large and complex repertoires. The overview of studies in the next section has a main focus on the third language acquisition area, but also deals with related thematic areas such as intercomprehension processes, polyglotism, linguistic autobiographies, and studies visualizing the multilingual subject.

Teaching in multilingual classrooms requires careful consideration of the type of learners, their background languages, acquisitional paths and current usage patterns in those languages. Morphosyntactic features causing errors for some learners can be assets for others at the same time.

We begin by illustrating several different scenarios present with heterogeneous learners, as well as influential factors associated with the acquisition and teaching of multiple languages. Next, we focus on the existing models of morphosyntactic transfer in third language acquisition to be able to discuss how these can be applied to actual teaching in the third language classroom. Then, we discuss the role of contrastive analysis and review classroom-based and classroom-relevant implications for instructed third language acquisition. In conclusion, we outline corresponding teaching- and research-related calls for action and implications for language teaching in multilingual classrooms with the main goal of bridging the gap between these current fields.

Multilingualism in education consists in the teaching and learning of local majority languages, together with languages with an international status and new minority languages. Its long-standing history worldwide is rooted in colonialism, as well as the revitalization of indigenous languages. More recently, multilingual education worldwide has had to encompass English as ‘capital’ for the young generations, resulting in the use of English as a Lingua Franca (ELF) and English-Medium Instruction (EMI) for internationalization, in the era of computer-mediated communication. The changing nature of multingual education is the result of three driving forces: language per se, languages in society, and educational policies, as respectively reflected in the L3/Ln acquisition model encompassing transfer, the translanguaging model advocating heteroglossic practices against monoglossic, and the Continua of Language Education model. Research on primary, secondary, and tertiary education–level showcases the efficacy of well-planned multilingual education and the challenges of technology and informal multimodal learning.

Multilinguals are impressive masters of flexibility. They can speak in only one language at a time without any apparent trouble, but also switch their languages easily if necessary. This apparent paradox has led researchers to ask whether multilinguals’ knowledge of their languages – such as the knowledge of words – is stored and accessed separately or together. This chapter summarizes what we currently know about the structure and workings of the tri- and multilingual lexicon, reviewing findings for word recognition, word production, and translation, as well as evidence from neurocognitive studies. It shows that the answer to the question how the trilingual mental lexicon is organized is not a simple, black-or-white one (i.e., ‘integrated’ or ‘separate’). Rather, the available evidence supports a nuanced view of trilingual word processing that is co-determined by characteristics of the individual and their acquisition history, the properties of the involved languages, and the nature of the task.

This chapter on a critical sociolinguistics offers a revealing angle on the acquisition of a third language by providing qualitative information about the context in which acquisition takes place. It is an approach that places at the center of inquiry, concerns of power, inequality, and social inclusion. The goal is to promote reflection on certain assumptions and methodologies associated with mainstream L3 acquisition research and, also, to present data and cases from qualitative ethnographic studies that seek to challenge current thinking. Despite ontological differences regarding the sorts of questions and frameworks to account for knowledge in the field of third language acquisition, many researchers recognize the need to go beyond the boundaries of processing and cognitive predictions and their related methodologies to provide a more holistic, dynamic, and comprehensive understanding. This recognition of the social – even if it is defined as a limited to a set of variables (i.e., age, gender, class) or assigned to a cognitive subsystem – allows L3 researchers to account for the wide variation in individual developmental differences in the process of acquiring a third or additional language.

Code-switching is the fluid alternation between languages in text or during speech. Despite its ubiquity within multilingual communities, the processing of code-switches is associated with processing costs. Recent research attempts to reconcile this apparent contradiction by investigating how linguistic, cognitive, social, and experiential factors attenuate or modify potential switch costs in comprehension. This complex interaction of factors is incorporated into recent experience-based models of bilingualism such as the Adaptive Control hypothesis (Green & Abutalebi, 2013). In this chapter we review this literature, which is based primarily on bilingual speakers, and highlight instances where lab-based studies on multilingual code-switching can provide significant theoretical contributions. We summarize three recent studies on Algerian multilinguals that illustrate how these factors extend to multilingual scenarios and conclude with a special emphasis on the social context of multilingual communities as a critical foundation for future experimental studies on multilingual code-switching.

Multilingualism affects cognitive, behavioral, and neural function across the lifespan. Here, we review the neuroimaging literature on bilingualism, multilingualism, and executive functions, focusing on three multilingual groups who rely on language control to varying degrees to overcome competition from other languages: third-language learners, multilingual adults, and simultaneous interpreters. In third-language learners, changes in brain regions underlying executive functions occur during the early stages of acquiring another language. In multilingual adults, effects of language experience reflect a qualitative difference between monolingual and multilingual processing rather than cumulative effects of increased linguistic knowledge. In simultaneous interpreters, changes in gray matter volume and white matter integrity are found in areas underlying language selection and executive functions, reflecting neural efficiency due to experience with rapid translation. The implications of these findings for our understanding of multilingualism and the value of moving beyond the monolingual–bilingual dichotomy are discussed.

Over the last years it has become clear that the investigation of the complexity and the dynamics of multilingual development and use needs to be approached from a new research perspective. This challenging scientific undertaking is not considered an additional approach but a replacement for the common traditional monolingual framework still applied in studying language development.By drawing on recent international research in the field of applied linguistics, this chapter provides an update of the Dynamic Model of Multilingualism (DMM) authored by Herdina and Jessner (2002) which presents the first monograph applying a CDST (complexity and dynamic systems theoretical) approach to multilingual development and use. The holistic perspective of multilingual development and use as a necessary prerequisite of the approach presented in the DMM will be unfolded by increasing the complexity in interaction of levels of inquiry in the study of third language acquisition and multilingualism.

This chapter introduces Bayesian data analysis and shows how such an approach can better deal with the intricacies of Ln acquisition data. The data analyzed is simulated based on Rothman’s (2010) study to demonstrate how we can use Bayesian models to estimate variables of interest in R. The chapter discusses (1) how to tackle smaller sample sizes and (2) how to incorporate theoretical principles and assumptions into our statistical analysis. As will be shown, in addition to its general advantages, Bayesian data analysis provides an effective toolset to address both (1) and (2). It also offers a much more nuanced and comprehensive approach to meet the methodological needs in the field.

This chapter provides an introduction to the handbook. It succintly overviews the key questions in the field of L3/Ln acquisition and summarizes the scope of all the chapters included. The chapter ends by raising some outstanding questions that the field needs to address.

In this chapter we discuss how existing theoretical approaches stemming from different linguistic traditions may account for multilingual code-switched speech (i.e. the use of more than two languages in the same conversation). To date, most code-switching research has focused on bilingual populations, with little attention being paid to communities where three or more languages are used. Previous research on multilingual code-switching is largely grounded in sociolinguistic, educational, and acquisition approaches, with little attention paid to the grammatical outcomes. Irrespective of the various traditions, which account (or not) for multilingual data in the same way as bilingual data, this chapter illustrates how we are still collectively searching for the most effective way to explain the complex phenomenon that is code-switching.