Language distance modulates cognitive control in bilinguals

Language Distance Moderates the Effect of a Mixed-Language Environment on New-Word Learning for 4-Year-Old Children

As bilingual families increase, the phenomenon of language mixing among children in mixed-language environments has gradually attracted academic attention. This study aims to explore the impact of language mixing on vocabulary acquisition in bilingual children and whether language distance moderates this impact. We recruited two groups of bilingual children, Chinese-English bilinguals and Chinese-Japanese bilinguals, to learn two first-language new words in a monolingual environment and a mixed-language environment, respectively. The results showed that the participants could successfully recognize the novel words in the code-switching sentences. However, when we compared the performance of the two groups of bilingual children, we found that the gaze time proportion of the Chinese-English bilingual children under the code-switching condition was significantly higher than that of the Chinese-Japanese bilingual children, while there was no significant difference under the monolingual condition. This suggests that language mixing has an inhibitory effect on vocabulary acquisition in bilingual children and that this inhibitory effect is influenced by language distance, that is, the greater the language distance, the stronger the inhibitory effect. This study reveals the negative impact of language mixing on vocabulary acquisition in bilingual children and also implies that there may be some other influencing factors, so more research is needed on different types of bilingual children.

Does Diglossia Impact Brain Structure? Data from Swiss German Early Diglossic Speakers

(1) Background: Bilingualism has been reported to shape the brain by inducing cortical changes in cortical and subcortical language and executive networks. Similar yet different to bilingualism, diglossia is common in Switzerland, where the German-speaking population switches between an everyday spoken Swiss German (CH-GER) dialect and the standard German (stGER) used for reading and writing. However, no data are available for diglossia, defined as the use of different varieties or dialects of the same language, regarding brain structure. The aim of our study is to investigate if the presence of this type of diglossia has an impact on the brain structure, similar to the effects seen in bilingualism. (2) Methods: T1-weighted anatomical MRI scans of participants were used to compare the grey matter density and grey matter volume of 22 early diglossic CH-GER-speaking and 20 non-diglossic French-speaking right-handed university students, matched for age, linguistics and academic background. The images were processed with Statistical Parametric Mapping SPM12 and analyzed via voxel- and surface-based morphometry. (3) Results: A Bayesian ANCOVA on the whole brain revealed no differences between the groups. Also, for the five regions of interest (i.e., planum temporale, caudate nucleus, ACC, DLPFC and left interior parietal lobule), no differences in the cortical volume or thickness were found using the same statistical approach. (4) Conclusion: The results of this study may suggest that early diglossia does not shape the brain structure in the same manner as bilingualism.

A neural mechanism of cognitive reserve: The case of bilingualism

Cognitive Reserve (CR) refers to the preservation of cognitive function in the face of age- or disease-related neuroanatomical decline. While bilingualism has been shown to contribute to CR, the extent to which, and what particular aspect of, second language experience contributes to CR are debated, and the underlying neural mechanism(s) unknown. Intrinsic functional connectivity reflects experience-dependent neuroplasticity that occurs across timescales ranging from minutes to decades, and may be a neural mechanism underlying CR. To test this hypothesis, we used voxel-based morphometry and resting-state functional connectivity analyses of MRI data to compare structural and functional brain integrity between monolingual and bilingual older adults, matched on cognitive performance, and across levels of second language proficiency measured as a continuous variable. Bilingualism, and degree of second language proficiency specifically, were associated with lower gray matter integrity in a hub of the default mode network - a region that is particularly vulnerable to decline in aging and dementia - but preserved intrinsic functional network organization. Bilingualism moderated the association between neuroanatomical differences and cognitive decline, such that lower gray matter integrity was associated with lower executive function in monolinguals, but not bilinguals. Intrinsic functional network integrity predicted executive function when controlling for group differences in gray matter integrity and language status. Our findings confirm that lifelong bilingualism is a CR factor, as bilingual older adults performed just as well as their monolingual peers on tasks of executive function, despite showing signs of more advanced neuroanatomical aging, and that this is a consequence of preserved intrinsic functional network organization.

Dynamic effects of bilingualism on brain structure map onto general principles of experience-based neuroplasticity

Bilingualism has been linked to structural adaptations of subcortical brain regions that are important for controlling multiple languages. However, research on the location and extent of these adaptations has yielded variable patterns, especially as far as the subcortical regions are concerned. Existing literature on bilingualism-induced brain restructuring has so far largely overseen evidence from other domains showing that experience-based structural neuroplasticity often triggers non-linear adaptations which follow expansion-renormalisation trajectories. Here we use generalised additive mixed models to investigate the non-linear effects of quantified bilingual experiences on the basal ganglia and the thalamus in a sample of bilinguals with a wide range of bilingual experiences. Our results revealed that volumes of the bilateral caudate nucleus and nucleus accumbens were significantly related to bilingual experiences. Importantly, these followed a non-linear pattern, with increases followed by plateauing in the most experienced bilinguals, suggesting that experience-based volumetric increases are only necessary up to a certain level of bilingual experience. Moreover, the volumes of putamen and thalamus were positively predicted by bilingual experiences. The results offer the first direct evidence that bilingualism, similarly to other cognitively demanding skills, leads to dynamic subcortical structural adaptations which can be nonlinear, in line with expansion-renormalisation models of experience-dependent neuroplasticity.

Does Language Distance Modulate the Contribution of Bilingualism to Cognitive Reserve in Seniors? A Systematic Review

We report a systematic review and exploratory meta-regression investigating the hypothesis that the effects of bilingualism on cognitive reserve are modulated by the distance between the pair of languages a bilingual uses. An inclusive multiple database search was performed in order to identify all relevant published research conducted in bilingual seniors. A combination of qualitative and quantitative synthesis methods were used in order to investigate our research questions. Results suggest that healthy bilingual seniors speaking more distant language pairs show improved monitoring performance on cognitive tasks. Evidence regarding a modulatory influence of language distance (LD) on the age of dementia diagnosis was inconclusive due to the small number of published studies meeting our inclusion criteria. We recommend more detailed reporting of individual differences in bilingual experience to assess the impact of LD and other variables on typical cognitive aging and the development of dementia. Linguistic differences in samples should also be considered as a constraint on bilingual advantages in future studies. Preregistration: PROSPERO CRD42021238705; OSF DOI 10.17605/OSF.IO/VPRBU.

What Is a Language? Who Is Bilingual? Perceptions Underlying Self-Assessment in Studies of Bilingualism

Research on the cognitive consequences of bilingualism typically proceeds by labeling participants as "monolingual" or "bilingual" and comparing performance on some measures across these groups. It is well-known that this approach has led to inconsistent results. However, the approach assumes that there are clear criteria to designate individuals as monolingual or bilingual, and more fundamentally, to determine whether a communication system counts as a unique language. Both of these assumptions may not be correct. The problem is particularly acute when participants are asked to classify themselves or simply report how many languages they speak. Participants' responses to these questions are shaped by their personal perceptions of the criteria for making these judgments. This study investigated the perceptions underlying judgments of bilingualism by asking 528 participants to judge the extent to which a description of a fictional linguistic system constitutes a unique language and the extent to which a description of a fictional individual's linguistic competence qualifies that person as bilingual. The results show a range of responses for both concepts, indicating substantial ambiguity for these terms. Moreover, participants were asked to self-classify as monolingual or bilingual, and these decisions were not related to more objective information regarding the degree of bilingual experience obtained from a detailed questionnaire. These results are consistent with the notion that bilingualism is not categorical and that specific language experiences are important in determining the criteria for being bilingual. The results impact interpretations of research investigating group differences on the cognitive effects of bilingualism.