Bilinguals may choose to speak a language either at their own will or in response to an external demand, but the underlying neural mechanisms in the two contexts is poorly understood. In the present study, Chinese–English bilinguals named pairs of pictures in three conditions: during forced-switch, the naming language altered between pictures 1 and 2. During non-switch, the naming language used was the same. During free-naming, either the same or different languages were used at participants' own will. While behavioural switching costs were observed during free-naming and forced-switching, neuroimaging results showed that forced language selection (i.e., forced-switch and non-switch) is associated with left-lateralized frontal activations, which have been implicated in inhibitory control. Free language selection (i.e., free-naming), however, was associated with fronto-parietal activations, which have been implicated in self-initiated behaviours. These findings offer new insights into the neural differentiation of language control in forced and free language selection contexts.

Do bilinguals have similar bilingual control mechanisms in speaking and writing? The present study investigated the patterns of switch costs (reflecting reactive language control) and mixing costs (reflecting proactive language control) between Chinese (L1) and English (L2) in spoken and written productions and whether these patterns could be modulated by response-stimulus intervals (RSIs). In two experiments, unbalanced Chinese–English bilinguals completed a cued language switching task in spoken naming (Experiment 1) and written naming (Experiment 2), respectively. The results revealed asymmetrical switch costs (i.e., the larger cost in L1 than in L2) in spoken and written productions in the short RSI condition. However, there were asymmetrical mixing costs in spoken production and symmetrical mixing costs in written production both in the short and long RSIs. These findings suggest that for spoken and written productions, reactive language control operates in similar mechanisms, while proactive language control operates in specific mechanisms.

This study investigated the engagement of domain-general cognitive control during the comprehension of dense code-switching sentences. Stimulus-locked event-related potentials (ERPs) were measured while L1-dominant Chinese–English bilinguals read switch and non-switch sentences. The results of the reading task revealed language dominance effects on the N400, left anterior negativity (LAN) and late positive component (LPC). The language dominance effects at lexical level (i.e., on the N400 and LAN) were modulated by individual differences in monitoring capacity. In contrast, inhibition capacity predicted code-switching costs at the sentence level (i.e., for the LPC component). The results suggest that proactive monitoring and reactive inhibition affect different processing stages during the comprehension of dense code-switching sentences. These findings partially align with processing models of code-switching incorporating a dual control mode perspective and contribute new insight into the dynamic interplay between reactive and proactive control processes.

When bilinguals switch between their two languages, they often alternate between words whose formation rules in one language are different from the other (e.g., a noun-verb compound in one language may be a verb-noun compound in another language). In this study, we analyze behavioral performance and electrophysiological activity to examine the effects of morphological configuration on language control during production and comprehension. Chinese–English bilinguals completed a joint naming-listening task involving cued language switching. The findings showed differential effects of morphological configuration on language production and comprehension. In production, morphological configuration was processed sequentially, suggesting that bilingual production may be a combination of sequential processing and inhibition of morphological levels and language interference. In comprehension, however, bottom-up control processes appear to mask the influence of sequential processing on language switching. Together, these findings underscore differential functionalities of language control in speaking and listening.

Language control in bilinguals is often investigated with the language switching paradigm. Switch costs reflect the ease/difficulty of applying this control mechanism. The type of stimuli employed in the experiments may influence switch costs. To date, only one study has compared digit vs picture processing, reporting reduced switch costs for digits (Declerck, Koch & Philipp, 2012). This result was adjudicated to phonological overlap between the languages used. Crucially, it remains an open question whether this digit effect generalises to language combinations without phonological relation. We fill this gap by investigating language switching with two language pairs differing in relative proficiency (L1 Chinese–L2 English, L1 Chinese–L3 French), where cross-language phonological activation is not expected. Overall, a digit effect is observed in the Chinese–English pair. Contrary to Declerck et al.'s (2012) finding, digits increased switch costs. Phonological mediation cannot explain this effect; instead, we suggest its origin lies in within-language word association links.

This study investigated whether the deployment of cognitive control was modulated by the intra-sentential code-switching types during comprehension. L1-dominant Chinese–English bilinguals were administered a self-paced reading task in two reading contexts – namely, alternation context and dense code-switching context. We assessed language switch cost and reversed language dominance effect in the self-paced reading task and examined how these language control measures related to domain-general inhibition and monitoring capacities. The results showed a larger switch cost asymmetry in alternation context compared to dense CS context. In addition, bilinguals’ inhibition skills were associated with second language (L2) switch cost in alternation context, while monitoring tended to predict the language dominance effect in dense code-switching context. These findings suggest that alternation context exerts high requirement to reactive inhibition while dense code-switching context tends to induce proactive monitoring during comprehension. We conclude that intra-sentential code-switching types trigger different aspects of cognitive control during comprehension.

While research on bilingual language processing is sensitive to different usage contexts, monolinguals are still often treated as a homogeneous control group, despite frequently using multiple varieties that may require engagement of control mechanisms during lexical access. Adapting a language-switching task for speakers of (Scottish) Standard English and Orcadian Scots, we demonstrate switch cost asymmetries with longer naming latencies when switching back into Orcadian. This pattern, which is reminiscent of unbalanced bilinguals, suggests that Orcadian is the dominant variety of these participants – despite the fact they might be regarded as English monolinguals because of sociolinguistic factors. In conjunction with the observed mixing cost and cognate facilitation effect (indicative of proactive language control and parallel language activation, respectively), these findings show that ‘monolinguals’ need to be scrutinised for routine use of different varieties to gain a better understanding of whether and how mechanisms underlying their lexical access resemble those of bilinguals.

Language control is important for bilinguals to produce words in the right language. While most previous studies investigated language control using visual stimuli with vocal responses, language control regarding auditory stimuli and manual responses was rarely examined. In the present study, an alternating language switching paradigm was used to investigate language control mechanism under two input modalities (visual and auditory) and two output modalities (manual and vocal) by measuring switch costs in both error percentage and reaction time (RT) in forty-eight Cantonese–English early bilinguals. Results showed that higher switch costs in RT were found with auditory stimuli than visual stimuli, possibly due to shorter preparation time with auditory stimuli. In addition, switch costs in RT and error percentage could be obtained not only in speaking, but also in handwriting. Therefore, language control mechanisms, such as inhibition of the non-target language, may be shared between speaking and handwriting.

This study investigated the predictive effects of executive functions on bilingual language control processes. We used a flanker task, a switching task and an n-back task to investigate inhibition, shifting, and updating, respectively. We adopted a cued language switching task to investigate the language control processes during bilingual word production. Results of linear mixed effects models showed that picture naming in switch trials was significantly slower and elicited larger stimulus-locked N2 and N400-like components. The results further showed that the flanker effect alone robustly predicted the variability of the N2 but not N400-like switch effects. These findings suggest that domain-general inhibition appears to predict the intensity of inhibition exerted on the lexical items in the non-target language during bilingual word production, but bilingual language control only partially overlaps with executive functions.

This study aimed at identifying linguistic factors that could contribute to understanding individual differences in executive control among bilinguals. Directionality and type of natural language switching, age of second language acquisition, and language proficiency were evaluated in a sample of 112 early bilingual adults. Participants performed several computerized tasks tapping into three dimensions of executive control: inhibition of interference, working memory updating, and shifting. Regression analyses showed that frequent switching to the second language was associated with more efficient executive processing, enhanced working memory updating processes, and better shifting ability. Moreover, higher frequency of unintended language switches was associated with lower interference control abilities. Frequency of language switching behavior was the principal predictor of executive control, beyond age of second language acquisition and language proficiency. Results suggest that frequent language switching is related to enhanced executive control, while the unintended switching of languages could be associated with low interference control.

Interpreting is a complex bilingual task, placing high demands on both language control (i.e., source language not interfering in target language production) and processing control (i.e., multi-tasking carried out in concert under time pressure). On the basis of empirical evidence in the literature, we propose an attentional control model to account for both language control and processing control. Specifically, language control in interpreting is achieved by a structural framework of language-modality connections (established in interpreting training and stored as task schema), and by focused attention that helps build, strengthen and adapt the framework through monitoring, target enhancement, task disengagement, shifting, and working memory. In contrast, processing control in interpreting is achieved by divided attention via coordination and working memory, and by language processing efficiency that includes mastery of both languages and the appropriate use of interpreting strategies. Implications of this model for general bilingual language control are discussed.

Simultaneous interpreting is a complex cognitive task that requires the concurrent execution of multiple processes: listening, comprehension, conversion of a message from one language to another, speech production, and self-monitoring. This requires the deployment of an array of linguistic and cognitive control mechanisms that must coordinate the various brain systems implicated in handling these tasks. How the brain handles this challenge remains an open question, and recent brain imaging investigations have begun to complement the theories based on behavioural data. fMRI studies have shown that simultaneous interpreting engages a network of brain regions encompassing those implicated in speech perception and production, language switching, self-monitoring, and selection. Structural imaging studies have been carried out that also indicate modifications to a similar set of structures. In the present paper, we review the extant data and propose an integrative model of simultaneous interpreting that piggybacks on existing theories of multilingual language control.

How bilinguals switch between languages depends on the context. In a voluntary context, bilinguals are free to decide when to switch, whereas in a cued context they are instructed when to switch. While using two languages may be more costly than using one in cued switching ('mixing cost'), recent evidence suggests that voluntarily using two languages may be less effortful than using one ('mixing benefit'). Direct comparisons between mandatory and voluntary switching, however, are needed to better understand the effects of the interactional context on bilingual language control. The current study compared mandatory and voluntary switching within the same task, thus keeping the overall task characteristics the same. We observed overall slower mandatory responses and larger mandatory than voluntary mixing and switching effects. Thus, using two languages is more costly in a mandatory than voluntary context, showing that the interactional context can affect the effort needed to control two languages.

In bilinguals, language proficiency has been advanced to influence the involvement of domain-general control networks in language selection. We assessed, in university student translators with moderate- to high-second language (L2) proficiency depending on their translation educational level, the functional activity in the key language and control areas (the caudate nucleus, anterior cingulate, and prefrontal cortex), during task- and language-selection in an oral production context. We found that L2 proficiency influenced the relative involvement of our regions of interest during language selection vs domain-general cognitive control processes. While the left middle frontal and left caudate areas were more involved during linguistic than alphanumeric task selection in the low L2 proficiency group, these regions were similarly involved in both tasks in the high-L2 proficiency group. These findings suggest that language selection relies primarily on a network within domain-general cognitive control system with an increase in resource needs when L2 proficiency is low.

DTI is an established method to study cerebral white-matter microstructure. Two established measures of DTI are fractional anisotropy (FA) and mean diffusivity (MD) and both differ for bilingual and monolingual speakers. Less is known about differences in two other measures called radial (RD) and axial diffusivity (AD). We report differences in mean RD and AD-values in the right superior longitudinal fasciculus (SLF) and forceps minor between bilingual (Hindi–English) and monolingual (English) speakers as well as differences in mean FA-values in the anterior thalamic radiation, right inferior fronto-occipital and inferior longitudinal fasciculus (ILF) and mean MD-values in forceps minor and bilateral SLF. Noteworthy, a positive correlation between L2 proficiency and mean RD-values in the right SLF was observed. We suggest that changes in the geometry of white matter tracts reflect regular bilingual language experience and contend that neuroplasticity in right SLF results from demands on cognitive control for bilingual speakers.

The present study examined the plasticity of the lexical selection mechanism in bilingual word production by training a group of unbalanced Chinese–English bilinguals with a language switching task. The experimental group received an 8-day language switching training, while the control group received no training. Before and after training, the behavioral and event-related potential (ERP) data of both groups in a cued picture naming task were collected. ERP results revealed a training effect such that after training, the N2 peak latency in cue-locked ERPs was shortened only in the experimental group. These results suggest that short-term language switching experience could improve the efficiency to establish the target language task schema, and that the language control mechanism of word production in unbalanced bilinguals could be modulated by language switching experience.

Language control, bilinguals’ ability to regulate which language is used, has been posited to recruit domain-general cognitive control. However, studies relating language control and cognitive control have yielded mixed results in adults and have not been undertaken in children. The current study examined the contributions of nonlinguistic task-shifting to language control in Spanish–English bilingual children (ages 5–7) during a cued-switch picture-naming task. Language control was assessed at two levels: (1) cross-language errors, which indexed the success of language selection, and (2) naming speed, which indexed the efficiency of lexical selection. Nonlinguistic task-shifting was a robust predictor of children's cross-language errors, reflecting a role for domain-general cognitive control during language selection. However, task-shifting predicted naming speed only in children's non-dominant language, suggesting a more nuanced role for cognitive control in the efficiency of selecting a particular lexical target.

Cued language switching is used to examine language-control processes by comparing performance in language-switch trials with performance in repetition trials. In 1:1 cue-to-language mappings, language repetitions involve cue repetitions and language switches involve cue switches. Hence, the observed switch costs might reflect cue-switch costs rather than language-related control processes. By introducing a 2:1 cue-to-language mapping, we dissociated language switches (cue and language switched vs. cue switched, but language repeated) and cue switches (repeated language, with vs. without switched cue). We found cue-switch costs, but language-related switch costs were substantial, too, presumably reflecting language-control processes in cued language switching.