Research on the effects of bi- and multi-lingualism on brain structure has so far yielded variable patterns. Although it cannot be disputed that learning and using additional languages restructures grey (cortical, subcortical and cerebellar) and white matter in the brain, both increases and reductions in regional volume and diffusivity have been reported. This paper revisits the available evidence from simultaneous and sequential bilinguals, multilinguals, interpreters, bimodal bilinguals, children, patients and healthy older adults from the perspective of experience-based neuroplasticity. The Dynamic Restructuring Model (DRM) is then presented: a three-stage model accounting for, and reinterpreting, all the available evidence by proposing a time-course for the reported structural adaptations, and by suggesting that these adaptations are dynamic and depend on the quantity and quality of the language learning and switching experience. This is followed by suggestions for future directions for the emerging field of bilingualism-induced neuroplasticity.

We examine first language (L1) attrition among 30 L1 Spanish – L2 English speakers living in the United Kingdom. We also tested 30 recently-arrived Spaniards to the UK as a baseline. We present several key findings: 1) attrition fluctuates over time and does not affect all individuals equally; 2) entropy can explain said fluctuation of attritional affects over time such that while length of residence and age of arrival may affect the depth of attrition, how often one is exposed to her native language, how often she uses it and for how long each day, who her friends are, and to which types of input she is regularly exposed, seemingly aid in the maintenance or loss of linguistic knowledge; 3) though offline scalar interpretations among bilinguals were predicted by canonical sociolinguistic variables, the online data revealed an overall insensitivity to pragmatic violations. Thus, offline and online methods combine to be more explanatory regarding the comprehension and processing of implicature generating quantifiers.

The psycholinguistic literature suggests that the length of a to-be-spoken phrase impacts the scope of speech planning, as reflected by different patterns of speech onset latencies. However, it is unclear whether such findings extend to first and second language (L1, L2) speech planning. Here, the same bilingual adults produced multi-phrase numerical equations (i.e., with natural break points) and single-phrase numbers (without natural break points) in their L1 and L2. For single-phrase utterances, both L1 and L2 were affected by L2 exposure. For multi-phrase utterances, L1 scope of planning was similar to what has been previously reported for monolinguals; however, L2 scope of planning exhibited variable patterns as a function of individual differences in L2 exposure. Thus, the scope of planning among bilinguals varies as a function of the complexity of their utterances: specifically, by whether people are speaking in their L1 or L2, and bilingual language experience.

As a rule, listening is easier in first (L1) than second languages (L2); difficult L2 listening can challenge even highly proficient users. We here examine one particular listening function, adaptation to novel talkers, in such a high-proficiency population: Dutch emigrants to Australia, predominantly using English outside the family, but all also retaining L1 proficiency. Using lexically-guided perceptual learning (Norris, McQueen & Cutler, 2003), we investigated these listeners’ adaptation to an ambiguous speech sound, in parallel experiments in both their L1 and their L2. A control study established that perceptual learning outcomes were unaffected by the procedural measures required for this double comparison. The emigrants showed equivalent proficiency in tests in both languages, robust perceptual adaptation in their L2, English, but no adaptation in L1. We propose that adaptation to novel talkers is a language-specific skill requiring regular novel practice; a limited set of known (family) interlocutors cannot meet this requirement.

Our keynote, “Understanding heritage languages” (Polinsky & Scontras, 2019), and the commentaries to it make the following main points.

Nonword repetition is typically impaired in dyslexia. Conversely, native-like performance is early achieved by bilingual children whose second language has a simple phonotactic system, like Italian. Our study aimed at comparing the performance of monolingual and bilingual children with and without dyslexia in a nonword repetition task modeled after Italian. We assessed nonword repetition in 111 school-aged children: 24 Italian L2 bilingual dyslexics, 24 Italian monolingual dyslexics, 30 Italian L2 bilingual controls and 33 Italian monolingual controls. We administered an original task composed of 40 nonwords ranging from two to five syllables; the complexity of the syllables was also manipulated. Results showed that both groups of dyslexics underperformed controls at each syllable length. No differences were found between monolingual and bilingual controls. Conversely, bilingual dyslexics underperformed monolingual dyslexics only with four-syllable nonwords. The possible use of nonword repetition tasks to assist in the identification of dyslexia in bilingual children is also discussed.

To investigate whether similar control processes are used during single and dual language production, we compared register switching (formal and informal speech in the same language) vs. language switching (French and English). The results across two experiments showed a positive correlation of overall register- and language-switch costs and similar formal French switch costs across the two switching tasks. However, whereas increasing the cue-to-stimulus interval resulted in a reduction of language-switch costs, register-switch costs were unaffected by the interval manipulation. This difference in switch-cost pattern indicates that control processes are not entirely identical during single and dual language production.

Both bilingualism and attention contribute to the development of executive functioning (EF), with higher levels of both leading to better outcomes. The present study treats bilingualism and attention as continuous variables to investigate their impact on EF. Eighty-two 9-year-olds who were attending a French school in an anglophone community completed a flanker task. Children's progress in French represented their level of bilingualism, and attention was assessed through a standard standardized instrument. Degree of bilingualism and degree of attention were both positively related to performance, but exposure to a third language in the home did not further affect outcomes.

Many human infants grow up learning more than one language simultaneously but only recently has research started to study early language acquisition in this population more systematically. The paper gives an overview on findings on early language acquisition in bilingual infants during the first two years of life and compares these findings to current knowledge on early language acquisition in monolingual infants. Given the state of the research, the overview focuses on research on phonological and early lexical development in the first two years of life. We will show that the developmental trajectory of early language acquisition in these areas is very similar in mono- and bilingual infants suggesting that these early steps into language are guided by mechanisms that are rather robust against the differences in the conditions of language exposure that mono- and bilingual infants typically experience.

Early regular experience with dual-language management is thought to shape executive function (EF) circuitry during development. However, previous investigations of bilingual children's EF have largely focused on behavioral measures, or on cognitive aspects of EF. The first part of this study compared monolingual and bilingual preschoolers’ performance on more purely cognitive and more affective versions of a card-sort task, and the second part investigated Error-related negativity (ERN) event-related potential (ERP) waveforms to understand error-awareness mechanisms underlying task performance. Behavioral results showed bilingual advantages in reaction times but not accuracy, and interaction effects of language background, level of challenge, and affective/motivational salience on reaction times. Electrophysiological results revealed smaller ERN peak amplitudes in bilinguals compared to monolinguals in frontal and frontocentral midline regions. Results highlight that bilingualism may shape motivational mechanisms and neural learning mechanisms such as error-detection, such that bilinguals may be less focused on their errors.

Most existing studies on the relationship between code-switching and executive functions have focused on experimentally induced language-switching, which differs fundamentally from naturalistic code-switching. This study investigated whether and how bilinguals’ code-switching practices modulate different aspects of executive functioning. Our findings suggest that existing processing models of code-switching should be extended by a dual control mode perspective, differentiating between reactive and proactive monitoring. Bilinguals engaging in code-switching types that keep languages more separate (Alternation) displayed inhibitory advantages in a flanker task inducing reactive control. Dense code-switching, which requires bilinguals to constantly monitor cross-linguistic competition, explained performance in proactive monitoring conditions. Furthermore, a correlation between Dense code-switching and response inhibition suggests that linguistic co-activation may persist during articulatory stages of language processing. Crucially, bilinguals outperformed monolinguals at those aspects of the executive system that were trained by their most frequent code-switching habits. This underlines the importance of sociolinguistic variables in bilingualism research.

For close to a century, experiments using artificial languages (hereafter ALs) have been a staple of psycholinguistic research (Esper, 1925). Contemporary AL research has spanned numerous levels of linguistic inquiry, from phonetic learning through syntax (see Culbertson & Schuler, 2019). This approach has also been successfully applied across development, from infants and children (see Saffran & Kirkham, 2018) through older adults (e.g., Schwab, Schuler, Stillman, Newport, Howard & Howard, 2016), even spanning cross-species comparisons (e.g., Wilson, Slater, Kikuchi, Milne, Marslen-Wilson, Smith & Petkov, 2013). Given the proliferation of AL methods for investigating issues related to first language acquisition, it is not surprising that research on bilingualism has also embraced this approach. This special themed section comprises four concise review articles describing how AL research has informed questions related to bilingualism and second language learning. The articles also discuss the strengths and limitations of this approach, as well as pointing to future directions for the field.

Vocabulary acquisition is a critical part of learning a new language. Yet, due to structural, historical, and individual variability associated with natural languages, isolating the impact of specific factors on word learning can be challenging. Artificial languages are versatile tools for addressing this problem, allowing researchers to systematically manipulate properties of the language and control for learners’ past experiences. Here, we review how artificial languages have been used to study bilingual word learning, with a particular focus on the influences of language input (e.g., word properties) and language experience (e.g., bilingualism). We additionally discuss the advantages and limitations of artificial languages for bilingual research and suggest resources for researchers considering the use of artificial languages. Used and interpreted properly, artificial language studies can inform our understanding of a wide range of factors relevant to word learning.