Socio-cognitive research on bilinguals points to a moral foreign-language effect (MFLE), with more utilitarian choices (e.g., sacrificing someone to save more people) for moral dilemmas presented in the second language (L2) relative to the first language. Yet, inconsistent results highlight the influence of subject-level variables, including a critical underexplored factor: L2 proficiency (L2p). Here we provide a systematic review of 57 bilingualism studies on moral dilemmas, showing that L2p rarely modulates responses to impersonal dilemmas, but it does impact personal dilemmas (with MFLEs proving consistent at intermediate L2p levels but unsystematic at high L2p levels). We propose an empirico-theoretical framework to conceptualize such patterns, highlighting the impact of L2p on four affective mediating factors: mental imagery, inhibitory control, prosocial behavior and numerical processing. Finally, we outline core challenges for the field. These insights open new avenues at the crossing of bilingualism and social cognition research.

From the beginning of this century fascinating work has been carried out on the simultaneous acquisition of two languages from birth in the form of diary studies for example, that by Ronjat (1913). Many aspects of monolingual language acquisition have been studied in the same way, whereby researchers generally observed their own children, for example, Stern and Stern (1928). The modern research strategy is to audiotape or videotape the speech of young children at fixed intervals. Of course, a quantitative analysis can be carried out for both diary studies and more recent types of longitudinal study. However, researchers such as Ronjat (1913) do not provide us with exact quantitative results. Notwithstanding, these studies deserve to be taken seriously and I think it is possible to interpret some of the observations they contain as good and “reliable” evidence and compare these with results from modern longitudinal studies, where exact quantification is an important issue. I therefore think that the quantitative results of my review of existing studies on the acquisition of German subordinate clauses in bilingual children can be taken seriously, although I agree with François Grosjean and Elizabeth Lanza, who object that the quantitative differences between monolingual and bilingual children's errors are perhaps artefacts of the setting in which the children have been recorded. That I considered diary studies as well disappointed one commentator, Annick De Houwer, who would have preferred a comparison of modern studies only.

The present study aimed to explore the lexical processing abilities of bilingual school-aged children compared to their monolingual peers. Therefore, word form processing tasks (auditory lexical decision, rapid naming, rhyming), as well as traditional vocabulary tasks (word-picture matching and picture naming), were conducted in a cross-sectional design in a sample of 163 German monolingual and 39 bilingual primary school children (6-9 years), speaking German and another language. Regression analyses revealed that age, gender, and vocabulary size, but not bilingualism have an impact on performance in word form processing tasks. Group comparisons after propensity matching on age, gender, and vocabulary size revealed no significant group differences between monolingual and bilingual children in word form processing tasks. After the sample was divided into two age groups, bilingual children showed an initial weakness at ages 6 to 7 that seems to be overcome during primary school age.

The five papers in this issue cover a range of perspectives on the acquisition and use of the Spanish copulas ser and estar in a variety of contexts, including language contact, bilingual language acquisition, and classroom second language learning. The fact that these papers cite work in this area as far back as the early part of the 20th century with each subsequent decade being represented suggests the continual importance and complexity of the distinction between the two copular forms and shows how this complexity is played out in acquisition and bilingual use. Over the past century different perspectives have been taken on this multifaceted issue with linguistic explanations and the role of the native language being primary. In this epilogue, we focus on some of these same issues, but expand our commentary to include the new dimensions represented in this collection of papers: (i) context of learning (input), (ii) prior knowledge as represented by other language(s) known, (iii) item-learning and lexical development, and (iv) innovations in methodology.

Semantic feature-based treatments (SFTs) are effective rehabilitation strategies for word retrieval deficits in bilinguals with aphasia (BWA). However, few studies have prospectively evaluated the effects of key parameters of these interventions on treatment outcomes. This study examined the influence of intervention-level (i.e., treatment language and treatment sessions), individual-level (baseline naming severity and age), and stimulus-level (i.e., lexical frequency, phonological length, and phonological neighborhood density) factors on naming improvement in a treated and untreated language for 34 Spanish–English BWA who completed 40 hours of SFT. Results revealed significant improvement over time in both languages. In the treated language, individuals who received therapy in their L1 improved more. Additionally, higher pre-treatment naming scores predicted greater response to treatment. Finally, a frequency effect on baseline naming accuracy and phonological effects on accuracy over time were associated with differential treatment gains. These findings indicate that multilevel factors are influential predictors of bilingual treatment outcomes.

Several multilingual language production models assume that language control is instigated by conflict monitoring. In turn, conflict adaptation, a control process which makes it easier to resolve interference if previously a high-interference context was detected, should also occur during multilingual production, as it is triggered by conflict monitoring. Because no evidence has been provided for conflict adaptation in the multilingual production literature, we set out to investigate this process using the n-3 effect. Our study showed that the n-3 effect can be observed during multilingual production, and thus provides evidence for conflict adaptation during multilingual production.

Emotional experiences are often dulled in one's second language. We tested whether emotion concepts are more strongly associated with first language (L1) than second language (L2) emotion words. Participants (140 L1-Swedish–L2-English bilinguals) saw a facial expression of an emotion (cue) followed by a target, which could either be another facial expression, an L1 emotion word, or an L2 emotion word. Participants indicated whether the cue and target represented the same or different emotions as fast as possible. Participants were faster and more accurate in both the L1 and L2 word conditions compared to the face condition. However, no significant differences emerged between the L1 and L2 word conditions, suggesting that emotion concepts are not more strongly associated with L1 than L2 emotion words. These results replicate prior research showing that L1 emotion words speed facial emotion perception and provide initial evidence that words (not only first language words) shape emotion perception.

This study investigates bilingualism-induced neuroplastic and cognitive-reserve effects in the Caudate Nucleus (CN), a structure believed to support both bilingual language control and domain-general executive functioning. We computed a generalized bilingualism index incorporating several dimensions of bilingual experience in a sample of bilingual young adults and tested whether this index would predict behavioral executive performance (measured using a Flanker task) and volumetric differences in the CN. Moreover, we investigated whether bilingualism mitigates the relationship between CN volume and executive performance, a sign of cognitive reserve. Our results indicate that bilingualism facilitates executive performance and induces an inverted U-shaped neuroplastic trajectory in bilateral CN, consistently with the view that structural increases are replaced by functional improvements as bilingual experience progresses. The emergence of bilingualism-induced cognitive reserve effects in CN further supports the view that bilinguals rely progressively less on the availability of structural resources in the face of increased functional efficiency.

Bilingualism is an experience that varies across a continuum and can change across the lifespan. Psychometric research is an underexplored avenue with the potential to further our understanding of the mechanisms and traits underlying bilingual experiences. Here, we developed and validated a social network questionnaire to measure sociolinguistic features in 212 individuals via personal social network. Confirmatory factor analysis examined the measurement structure of the variables. Compared to a one-factor model, the best fitting model was a two-factor model in which the language experience of the individual (i.e., ego) and the language experience of the individual's network (i.e., alters) were correlated latent factors under which aspects of the bilingual experience loaded. Additional analyses revealed other potential ways to examine the data in future analyses. These results provide the first measurement model of bilingual experiences, and provide support for theoretical accounts suggesting differential neuropsychological outcomes based on individual bilingual variability. The results also support the use of social network tools to capture differences in bilingualism.

Both ageing and bilingualism can have positive as well as adverse cognitive effects. We investigated their combined impact on subcomponents of attention. We used the Attention Network Task to examine alerting, orienting, executive control and task-switching costs. Group comparisons revealed age-related declines for alerting alongside benefits for executive control, for mono- and bilinguals alike. For orienting, age-related decline was more pronounced for bilinguals than monolinguals. Task-switching was unaffected by age or language group. Within bilinguals, we found limited impact of individual differences in L2 proficiency, language switching or mixing: proficiency improves orienting and decreases switch costs, for young and older bilinguals alike; but no other individual differences effects were found. Thus, attention is a multi-faceted network, with clear adverse (alerting) and protective (executive control) ageing effects. We found these to be largely similar for mono- and bilinguals, with variability within bilinguals having only limited impact.

Previous research suggests that bilingual language control requires domain-general cognitive control. Recent research suggests that exploration of individual differences is key for understanding the relationship between bilingual language control and cognitive control. The current study used multi-voxel pattern analysis (MVPA) to examine within-subject patterns of fMRI activity in the dorsolateral prefrontal cortex (DLPFC) during bilingual language switching and non-linguistic task-switching. We hypothesized that bilinguals would have identifiable, within-subject patterns of DLPFC activity for both types of switching and that bilinguals and monolinguals would differ in patterns of DLPFC activity for task-switching. We were unable to identify patterns of DLPFC activity associated with bilingual language switching. Task-switching was related to patterns of left DLPFC activity for both bilinguals and monolinguals, and there were identifiable patterns of right DLPFC activity for the bilinguals only. These findings suggest that the DLPFC is not the key brain structure connecting bilingual language and task-switching.

The present study explores the influence of individual differences in experience, perceptual acuity, and working memory on the development of both declarative and automatized aspects of L2 phonological vocabulary knowledge. A total of 486 Japanese English-as-a-foreign-language (EFL) students took part in two vocabulary tests designed to measure declarative (meaning recognition) and automatized knowledge (lexicosemantic judgement task). Their performance was tied to the quantity and quality of their EFL experience, as well as their scores in auditory processing and working memory. While several significant, modest correlations between experience, aptitude, and vocabulary outcomes were observed, certain predictor variables were uniquely associated with either declarative or automatized vocabulary performance. Specifically, individuals with more extensive, typically language-focused EFL training and greater working memory demonstrated higher levels of declarative knowledge. Conversely, those who pursued extracurricular practice outside the classroom – exposing themselves to auditory materials and/or participating in study-abroad experiences – showed a more automatic execution of vocabulary knowledge.

Bilingual infants rely differently than monolinguals on facial information, such as lip patterns, to differentiate their native languages. This may explain, at least in part, why young monolinguals and bilinguals show differences in social attention. For example, in the first year, bilinguals attend faster and more often to static faces over non-faces than do monolinguals (Mercure et al., 2018). However, the developmental trajectories of these differences are unknown. In this pre-registered study, data were collected from 15- to 18-month-old monolinguals (English) and bilinguals (English and another language) to test whether group differences in face-looking behaviour persist into the second year. We predicted that bilinguals would orient more rapidly and more often to static faces than monolinguals. Results supported the first but not the second hypothesis. This suggests that, even into the second year of life, toddlers’ rapid visual orientation to static social stimuli is sensitive to early language experience.

Pieter Muysken's keynote paper, “Language contact outcomes as a result of bilingual optimization strategies”, undertakes an ambitious project to theoretically unify different empirical outcomes of language contact, for instance, SLA, pidgins and Creoles, and code-switching. Muysken has dedicated a life-time to researching, rather successfully, various sub-fields of language contact, so I am very pleased to see him develop a synergistic model that reduces the complexities of different bilingual contact phenomena to four optimization strategies, the specific permutations of which yield the different, linguistically significant, generalizations. Such attempts are necessary, certainly, if the field of language contact has to make progress, theoretically. The success of such a theoretical unification, however, depends to a large extent on (i) the empirical mileage such unification receives; (ii) how well the assumptions underlying the logic of unification are theoretically motivated, to yield precise predictions about the orderliness of bilingual behavior; and (iii) the conceptual clarity required to understand the various links among the outcomes of language contact. On all these counts, Muysken's paper comes close to achieving success, though one notices several areas of fuzziness that need to be addressed for a competent model to fully emerge. In this short essay, I will point out two areas that need theoretical attention so that subsequent revisions of the present version of the model can address them. I will restrict my comments to code-switching, an extremely productive area of language contact, with which I am most familiar.

Pieter Muysken's article on modeling and interpreting language contact phenomena constitutes an important contribution.The approach chosen is a top–down one, building on the author's extensive knowledge of all matters relating to language contact. The paper aims at integrating a wide range of factors and levels of social, cognitive, and linguistic accounts, incorporating findings on bilingual individuals in the same way as on language systems in contact and bilingual speech communities. It enables the reader to place seemingly disparate phenomena in a wider perspective and to relate quite divergent manifestations of language contact to one another in a principled way. In accordance with its ambitious goal, the paper proposes a high level of generalization, or abstraction.

We investigated cross-modal influences between speech and sign in hearing bimodal bilinguals, proficient in a spoken and a sign language, and its consequences on visual attention during message preparation using eye-tracking. We focused on spatial expressions in which sign languages, unlike spoken languages, have a modality-driven preference to mention grounds (big objects) prior to figures (smaller objects). We compared hearing bimodal bilinguals’ spatial expressions and visual attention in Dutch and Dutch Sign Language (N = 18) to those of their hearing non-signing (N = 20) and deaf signing peers (N = 18). In speech, hearing bimodal bilinguals expressed more ground-first descriptions and fixated grounds more than hearing non-signers, showing influence from sign. In sign, they used as many ground-first descriptions as deaf signers and fixated grounds equally often, demonstrating no influence from speech. Cross-linguistic influence of word order preference and visual attention in hearing bimodal bilinguals appears to be one-directional modulated by modality-driven differences.

Does a concurrent verbal working memory (WM) load constrain cross-linguistic activation? In a visual world study, participants listened to Hindi (L1) or English (L2) spoken words and viewed a display containing the phonological cohort of the translation equivalent (TE cohort) of the spoken word and 3 distractors. Experiment 1 was administered without a load. Participants then maintained two or four letters (Experiment 2) or two, six or eight letters (Experiment 3) in WM and were tested on backward sequence recognition after the visual world display. Greater looks towards TE cohorts were observed in both the language directions in Experiment 1. With a load, TE cohort activation was inhibited in the L2 – L1 direction and observed only in the early stages after word onset in the L1 – L2 direction suggesting a critical role of language direction. These results indicate that cross-linguistic activation as seen through eye movements depends on cognitive resources such as WM.