Not All Bilinguals Are the Same: A Call for More Detailed Assessments and Descriptions of Bilingual Experiences

Brain correlates of attentional load processing reflect degree of bilingual engagement: Evidence from EEG

The present study uses electroencephalography (EEG) with an N-back task (0-, 1-, and 2-back) to investigate if and how individual bilingual experiences modulate brain activity and cognitive processes. The N-back is an especially appropriate task given recent proposals situating bilingual effects on neurocognition within the broader attentional control system (Bialystok and Craik, 2022). Beyond its working memory component, the N-Back task builds in complexity incrementally, progressively taxing the attentional system. EEG, behavioral and language/social background data were collected from 60 bilinguals. Two cognitive loads were calculated: low (1-back minus 0-back) and high (2-back minus 0-back). Behavioral performance and brain recruitment were modeled as a function of individual differences in bilingual engagement. We predicted task performance as modulated by bilingual engagement would reflect cognitive demands of increased complexity: slower reaction times and lower accuracy, and increase in theta, decrease in alpha and modulated N2/P3 amplitudes. The data show no modulation of the expected behavioral effects by degree of bilingual engagement. However, individual differences analyses reveal significant correlations between non-societal language use in Social contexts and alpha in the low cognitive load condition and age of acquisition of the L2/2L1 with theta in the high cognitive load. These findings lend some initial support to Bialystok and Craik (2022), showing how certain adaptations at the brain level take place in order to deal with the cognitive demands associated with variations in bilingual language experience and increases in attentional load. Furthermore, the present data highlight how these effects can play out differentially depending on cognitive testing/modalities - that is, effects were found at the TFR level but not behaviorally or in the ERPs, showing how the choice of analysis can be deterministic when investigating bilingual effects.

New insights into bilingual visual word recognition: State of the art on the role of orthographic markedness, its theoretical implications, and future research directions

In the past decade, research on bilingual visual word recognition has given rise to a new line of study focusing on a sublexical orthographic variable referred to as orthographic markedness, derived from the comparison of the two orthotactic distributions known by a bilingual reader. Orthographic markers have been shown to speed up language decisions but also, to some extent, to modulate language nonselectivity during lexical access (i.e., the degree of co-activation of lexical representations of the two languages). In this review, we (1) describe the results available in the literature about orthographic markedness on language membership detection and lexical access and discuss the locus of these effects, which leads us to (2) present theoretical extensions to the bilingual interactive activation models and discuss their respective adequacy to the data, finally leading us to (3) propose future research directions in the study of orthographic markedness, such as extension to different reading tasks and contexts as well as considering developmental and learning dynamics.

Foreign-language effects in cross-cultural behavioral research: Evidence from the Tanzanian Hadza

Behavioral research in traditional subsistence populations is often conducted in a non-native language. Recent studies show that non-native language-use systematically influences behavior, including in widely used methodologies. However, such studies are largely conducted in rich, industrialized societies, using at least one European language. This study expands sample diversity. We presented four standard tasks-a "dictator" game, two sacrificial dilemmas, a wager task, and five Likert-risk tolerance measures-to 129 Hadza participants. We randomly varied study languages-Hadzane and Kiswahili-between participants. We report a moderate impact of study language on wager decisions, alongside a substantial effect on dilemma decisions and responses to Likert-assessments of risk. As expected, non-native languages fostered utilitarian choices in sacrificial dilemmas. Unlike previous studies, non-native-language-use decreased risk preference in wager and Likert-tasks. We consider alternative explanatory mechanisms to account for this reversal, including linguistic relativity and cultural context. Given the strength of the effects reported here, we recommend, where possible, that future cross-cultural research should be conducted in participants' first language.

Modeling lexical abilities of heritage language and L2 speakers of Hebrew and English in Israel and the United States: a network approach

Introduction

This paper examines the productive vocabulary skills of five groups of English-Hebrew bilinguals in Israel and the United States. The juxtaposition of these five groups allows us to simultaneously compare performance across dominance profiles, acquisition contexts (L2 learned in school, HL maintained at home, immigration and immersion), and countries (Israel and the USA).

Methods

A total of 185 participants took part in study: Hebrew-dominant heritage English speakers, Hebrew-dominant L2-English speakers, English-dominant heritage Hebrew speakers, and English-dominant L2-Hebrew speakers in the US and in Israel. They were all administered the MINT assessment in both languages, as well as background questionnaires. We then employ network modeling based on a secondary data analysis of background questionnaires to consider how each group's lexical proficiency ties in to reported input factors.

Results and discussion

The MINT results indicate clear language dominance in all the groups except Hebrew-dominant heritage English speakers, who show balanced proficiency in both their languages. The network models indicate key distinctions between the groups as a function of linguistic context, and we assess our findings in the context of recent work on quantifying the bilingual experience.

LexCHI: A quick lexical test for estimating language proficiency in Chinese

A prominent methodological issue in cognitive research on bilingualism is the lack of consistency in measuring second language (L2) proficiency. To reduce the inconsistency in L2 proficiency measurements, brief and valid vocabulary tests have been developed as an objective measure of proficiency in a variety of languages (e.g., English, French, Spanish). Here, we present LexCHI, a valid lexical test to measure Chinese proficiency. This freely available short test consists of 60 two-character items presented in simplified Chinese. Although it only takes a few minutes to complete LexCHI, the LexCHI scores in two studies correlated significantly with L2 participants' performance in a translation task and a cloze test. We believe that LexCHI is a useful tool for researchers who need to objectively measure Chinese proficiency as part of their investigations.

Mapping individual aspects of bilingual experience to adaptations in brain structure

Individual differences in using multiple languages are thought to differentially affect brain structure and function. The present study assessed the neuroanatomical predictions of an emerging theory, the Unifying the Bilingual Experience Trajectories framework, which provides the most comprehensive set of predictions of how individual differences in bilingual experiences lead to specific neural and cognitive adaptations. A total of 140 young adults with variable language experiences were scanned using magnetic resonance imaging and completed demographic questionnaires. Brain structure measures implicated in predictions of the Unifying the Bilingual Experience Trajectories model were extracted and regressed against the model's experiential factors. Consistent with the model's predictions, greater intensity and diversity of bilingual language use resulted in changes in gray matter volume in cortical regions involved in executive control (including inferior frontal gyrus, middle temporal gyrus, angular gyrus, and medial frontal gyrus), indicating adaptations toward handling increased executive control demands. Conversely, duration of bilingual engagement resulted in changes within white matter microstructure (bilateral superior longitudinal fasciculus) and increases in subcortical gray matter (left caudate), indicative of adaptations toward increased efficiency of control. Overall, this research enhances our understanding of how bilingual experiences influence brain structure and provides the first direct empirical evidence for the predictions made by the Unifying the Bilingual Experience Trajectories framework.

A Preliminary Study of Executive Functioning in Preterm-Born Children: A Bilingual Advantage

BACKGROUND

Preterm-born children are at increased risk for deficits in executive function (EF). EF is a set of cognitive processes including inhibition, attention, memory, and decision-making, among others. Bilingualism, operationalized as productive capacity in 2 languages (ie, English and Spanish), may enhance EF in children born preterm and in term-born children.

PURPOSE

The purpose of this study was to examine the impact of bilingualism on executive functioning in bilingual and monolingual preterm and term-born children using a robust measure of bilingualism.

METHODS

This study examined the impact of bilingualism on EF in 17 monolingual or bilingual preterm-born children, aged 6 to 7. The preterm-born sample was also compared with a normed, term-born sample of 38 monolingual, typically developing 6- to 7-year-olds.

RESULTS

On the Creature Counting task of EF, bilingual preterm-born children performed with more accuracy and total switches than monolingual preterm-born children. There was no difference in accuracy between the term-born and entire preterm-born samples. The bilingual, preterm-born children performed more accurately than the term-born sample.

IMPLICATIONS FOR PRACTICE AND RESEARCH

This preliminarily suggests bilingualism confers an advantage to preterm-born children's EF. Further research is needed on bilingual advantage of preterm-born children.

An Evidence Accumulation Account of Masked Translation Priming in Two Bilingual Populations

This manuscript addresses the phenomenon of masked priming and the cognitive process of switching from Spanish to English while reading in sequential bilingual texts compared to heritage speakers. A lexical decision task was employed in the present study with masked translation priming, which serves as a valuable tool for elucidating the orthographic and lexical processes involved in the initial stages of reading. This study builds upon previous research conducted on monolingual masked priming, which consistently demonstrates shifts in the response time (RT) distributions when comparing related and unrelated primes. Within the framework of a diffusion model, we implemented two theoretical positions. First, we posited that translation priming operates at the orthographic level, resulting in enhanced efficiency during the encoding process. Second, we explored the possibility that translation priming operates at the semantic level, influencing the accumulation of evidence during the lexical decision task. The findings of the present study indicate that translation priming elicits outcomes similar to those observed in monolingual priming paradigms. Specifically, we observed that translation priming facilitation is manifested as shifts in the RT distributions. These findings are interpreted to suggest that the benefits derived from the encoding process are not specific to the accessed lexicon following a brief stimulus presentation.

Practice beats age: co-activation shapes heritage speakers' lexical access more than age of onset

Probabilistic associations make language processing efficient and are honed through experience. However, it is unclear what language experience factors explain the non-monolingual processing behaviors typical of L2 learners and heritage speakers (HSs). We investigated whether AoO, language proficiency, and language use affect the recognition of Spanish stress-tense suffix associations involving a stressed syllable that cues a present suffix (SALta "s/he jumps") and an unstressed syllable that cues a past suffix (SALtó "s/he jumped"). Adult Spanish-English HSs, English-Spanish L2 learners, and Spanish monolinguals saw a paroxytone verb (stressed initial syllable) and an oxytone verb (unstressed initial syllable), listened to a sentence containing one of the verbs, and chose the one they heard. Spanish proficiency measured grammatical and lexical knowledge, and Spanish use assessed percentage of current usage. Both bilingual groups were comparable in Spanish proficiency and use. Eye-tracking data showed that all groups fixated on target verbs above chance before hearing the syllable containing the suffix, except the HSs in the oxytones. Monolinguals fixated on targets more and earlier, although at a slower rate, than HSs and L2 learners; in turn, HSs fixated on targets more and earlier than L2 learners, except in oxytones. Higher proficiency increased target fixations in HSs (oxytones) and L2 learners (paroxytones), but greater use only increased target fixations in HSs (oxytones). Taken together, our data show that HSs' lexical access depends more on number of lexical competitors (co-activation of two L1 lexica) and type (phonotactic) frequency than token (lexical) frequency or AoO. We discuss the contribution of these findings to models in phonology, lexical access, language processing, language prediction, and human cognition.

Documenting heritage language experience using questionnaires

Introduction

There exists a great degree of variability in the documentation of multilingual experience across different instruments. The present paper contributes to the "methods turn" and individual differences focus in (heritage) bilingualism by proposing a comprehensive online questionnaire building on existing questionnaires and the experience of using them to document heritage bilingualism: the Heritage Language Experience (HeLEx) online questionnaire. HeLEx is validated against and contrasted to an extended version of the Language and Social Background Questionnaire designed for heritage speakers (HSs), LSBQ-H.

Methods

We compare data elicited with both questionnaires in turn from a group of Turkish HSs (n = 174, mean age=32). Our validation focuses on traditional language background variables, including language exposure and use, language proficiency, language dominance, as well as a more novel measure of language entropy. The analyses are based on a subset of key questions from each questionnaire that capture language experience for up to five languages, four modalities, and five social contexts. In a subsequent set of analyses, we explore the impact of different types of response scales, response mechanisms, and manners of variable derivation on the informativity of the data they can provide, in terms of the scope, granularity and distributional properties of the derived measures.

Results and Discussion

Our results show that both HeLEx and LSBQ-H are successful at detecting the important distributional patterns in the data and reveal a number of advantages of HeLEx. In the discussion, we consider the impact of methodological choices regarding question phrasing, visual format, response options, and response mechanisms. We emphasize that these choices are not trivial and can affect the derived measures and subsequent analyses on the impact of individual differences on language acquisition and processing.

No bilingual advantage in children's attentional disengagement: Congruency and sequential congruency effects in a large sample of monolingual and bilingual children

According to recent accounts, bilingualism in childhood confers an advantage in a specific domain of executive functioning termed attentional disengagement. The current study tested this hypothesis in 492 children (245 boys; M_age = 10.98 years) from Canada, China, and Lebanon by testing for an association between language status and measures of attentional disengagement. Across the entire sample, monolinguals responded more quickly and accurately than bilinguals on a measure of attentional disengagement but differed in age, socioeconomic status, and general cognitive ability. Differences between monolinguals and bilinguals disappeared when the influence of these confounding variables was controlled using a matched samples analysis (ns = 105). Bayesian analyses further confirmed that the evidence was more likely under the null hypothesis than under the alternative hypothesis. In sum, there was little evidence of an association between language status and attentional disengagement in children.

The effect of bilingualism on executive functions when languages are similar: a comparison between Hungarian-Serbian and Slovak-Serbian young adult bilinguals

Among the factors argued to contribute to a bilingual advantage in executive function (EF), the combination of languages spoken by the bilingual is often overlooked. In this study, we explored the role of language similarity on memory and EF task by comparing performance of three groups of young adults-Hungarian-Serbian and Slovak-Serbian early balanced bilinguals, and Serbian-speaking monolinguals. Slovak is typologically related to Serbian, which are both Slavic, in contrast to Hungarian, which is Finno-Ugric. On the computerized tasks from the CANTAB battery (CANTAB Cognition, 2016, www.cantab.com), differences between monolinguals and bilinguals emerged on the EF tasks: Stockings of Cambridge (SOC) and Attentional Set Shifting (AST), but not the memory tasks: Delayed Matching to Sample (DMS), Paired Associate Learning (PAL), Spatial Working Memory (SWM). Both Hungarian-Serbian and Slovak-Serbian bilinguals outperformed the monolinguals on the more difficult SOC tasks, solved using more than a minimally required number of moves. This is in line with reports that bilinguals perform better under more complex conditions that require more monitoring and switching. However, bilinguals speaking Hungarian and Serbian spent less time preparing to execute the simpler SOC tasks, which can be solved in a minimum of two or three moves; they also exhibited reduced local switching cost and were faster overall on AST than both the Slovak-Serbian bilinguals and Serbian monolinguals. The advantageous performance of speakers of the typologically unrelated languages in our study suggests that these bilinguals may have more efficient attention switching and inhibition systems than bilinguals who speak typologically similar languages.

Language athletes: Dual-language code-switchers exhibit inhibitory control advantages

Recent studies have begun to examine bilingual cognition from more nuanced, experienced-based perspectives. The present study adds to this body of work by investigating the potential impact of code-switching on bilinguals’ inhibitory control abilities. Crucially, our bilingual participants originated from a predominantly dual-language environment, the interactional context which is believed to require (and therefore, potentially train) cognitive control processes related to goal-monitoring and inhibition. As such, 266 French Canadian bilinguals completed an online experiment wherein they were asked to complete a domain-general (Flanker) and a language-specific (bilingual Stroop) inhibitory control task, as well as extensive demographic and language background questionnaires. Stepwise multiple regressions (including various potential demographic and linguistic predictors) were conducted on the participants’ Flanker and Stroop effects. The results indicated that the bilinguals’ propensity to code-switch consistently yielded significant positive (but unidirectional) inhibitory control effects: dual-language bilinguals who reported more habitual French-to-English switching exhibited better goal-monitoring and inhibition abilities. For the language-specific task, the analysis also revealed that frequent unintentional code-switching may mitigate these inhibition skills. As such, the findings demonstrate that dual-language code-switchers may experience inhibitory control benefits, but only when their switching is self-reportedly deliberate. We conclude that the bilinguals’ interactional context is thus of primary importance, as the dual-language context is more conducive to intentional code-switching. Overall, the current study highlights the importance of considering individualistic language experience when it comes to examining potential bilingual executive functioning advantages.

Color naming in Tsimane'-Spanish bilinguals indicates that differential experience with content domains affects lexical access

A standard assumption in the bilingual language processing literature is that the ease of access of a word in a language is determined by the speaker's overall proficiency in the language. Alternatively, it could be that proficiency varies across semantic categories of the bilingual's two languages. Here, we investigated lexical access in color terms in Tsimane'-Spanish bilinguals. Given that color terms are generally more frequent in Spanish than Tsimane', participants may have better lexical access for color words in Spanish despite being overall more proficient in Tsimane'. Twenty-two Tsimane'-Spanish bilinguals took part in a picture naming task where participants labeled colors and animals. Participants were equally fast and accurate at naming animals in Tsimane' and Spanish. However, participants were faster and more accurate at naming colors in Spanish than Tsimane' except for the three color words that are most frequent (jaibes ~ white, tsincus ~ black, jaines ~ red) in Tsimane', for which they were equally fast in both Tsimane' and Spanish. These results suggest that category-specific proficiency is a better predictor for lexical access than overall proficiency.

Assessing language background and experiences among heritage bilinguals

The language backgrounds and experiences of bilinguals have been primarily characterized using self-report questionnaires and laboratory tasks, although each of these assessments have their strengths and weaknesses. The Electronically Activated Recorder (EAR), an audio recording device, has recently become more prominent as a method of assessing real-world language use. We investigated the relationships among these three assessment tools, to understand the shared variance in how these measures evaluated various aspects of the bilingual experience. Participants were 60 Southern California heritage bilingual college students who spoke a variety of heritage languages and began to learn English between the ages of 0-to 12-years. Participants completed both self-report and laboratory-based measures of language proficiency and use, and they wore the EAR for 4  days to capture representative samples of their day-to-day heritage language (HL) use. The results indicated that self-reported HL use and English age of acquisition were significant predictors of real-world language use as measured by the EAR. In addition, self-reported HL proficiency and laboratory-based HL proficiency, as measured by verbal fluency, were mutually predictive. While some variability was shared across different assessments, ultimately, none of the measures correlated strongly and each measure captured unique information about the heritage bilingual language experience, highlighting the dissociation between language experience measured at a single point in time and an accumulated life history with a heritage language. These findings may provide guidance for bilingualism researchers about which assessment tool, or combination of tools, may be best for their specific research questions.

Re-Examining Labels in Neurocognitive Research: Evidence from Bilingualism and Autism as Spectrum-Trait Cases

Despite the fact that the urge to investigate bilingualism and neurodevelopmental disorders as continuous indices rather than categorical ones has been well-voiced among researchers with respect to research methodological approaches, in the recent literature, when it comes to examining language, cognitive skills and neurodivergent characteristics, it is still the case that the most prevalent view is the categorisation of adults or children into groups. In other words, there is a categorisation of individuals, e.g., monolingual vs. bilingual children or children with typical and atypical/non-typical/non-neurotypical development. We believe that this labelling is responsible for the conflicting results that we often come across in studies. The aim of this review is to bring to the surface the importance of individual differences through the study of relevant articles conducted in bilingual children and children with autism, who are ideal for this study. We concur with researchers who already do so, and we further suggest moving away from labels and instead shift towards the view that not everything is either white or black. We provide suggestions as to how this shift could be implemented in research, while mostly aiming at starting a discourse rather than offering a definite path.

Multifactorial approaches to study bilingualism in the aging population: Past, present, future

A better understanding and more reliable classification of bilinguals has been progressively achieved through the fine-tuning methodology and simultaneously optimizing the measurement tools. However, the current understanding is far from generalization to a larger population varying in different measures of bilingualism-L2 Age of acquisition (L2 AOA), L2 usage and exposure, and L2 proficiency. More recent studies have highlighted the importance of modeling bilingualism as a continuous variable. An in-depth look at the role of bilingualism, comparing groups, may be considered a reductionist approach, i.e., grouping based on one measure of bilingualism (e.g., L2 AOA) may not account for variability in other measures of bilingualism (L2 exposure, L2 use or L2 proficiency, amongst others) within and between groups. Similarly, a multifactorial dimension is associated with cognitive performance, where not all domains of cognition and subcomponents are equally influenced by bilingualism. In addition, socio-cultural and demographical factors may add another dimension to the impact of bilingualism on cognitive performance, especially in older adults. Nevertheless, not many studies have controlled or used the multiple socio-cultural and demographical factors as a covariate to understand the role of different aspects of bilingualism that may influence cognitive performance differently. Such an approach would fail to generalize the research findings to a larger group of bilinguals. In the present review paper, we illustrate that considering a multifactorial approach to different dimensions of bilingual study may lead to a better understanding of the role of bilingualism on cognitive performance. With the evolution of various fine-tuned methodological approaches, there is a greater need to study variability in bilingual profiles that can help generalize the result universally.

The Multifaceted Nature of Bilingualism and Attention

Attention has recently been proposed as the mechanism underlying the cognitive effects associated with bilingualism. However, similar to bilingualism, the term attention is complex, dynamic, and can vary from one activity to another. Throughout our daily lives, we use different types of attention that differ in complexity: sustained attention, selective attention, alternating attention, divided attention, and disengagement of attention. The present paper is a focused review summarizing the results from studies that explore the link between bilingualism and attention. For each level of attention, a brief overview of relevant theoretical models will be discussed along with a spotlight on paradigms and tasks used to measure these forms of attention. The findings illustrate that different types and levels of attention are modified by the variety of bilingual experiences. Future studies wishing to examine the effects of bilingualism on attention are encouraged to embrace the complexity and diversity of both constructs rather than making global claims about bilingualism and attention.

Am I truly monolingual? Exploring foreign language experiences in monolinguals

Monolingualism has typically been understood as a homogeneous phenomenon. The linguistic experiences of monolinguals are usually overlooked when analysing the impact of foreign language experiences on language processing and cognitive functioning. In this study, we analyse the linguistic experiences of 962 English-speaking individuals from the United Kingdom (UK) who identified as monolinguals. Through an online survey, we found that more than 80% of these monolinguals had learned at least one foreign language, dialect, or type of jargon. More than half of this 80% of monolinguals also used languages they had learned at some point in their lives. Moreover, nearly 40% of all the studied monolinguals confirmed that they had been passively exposed to foreign languages or dialects in their environment; approximately a fourth of these monolinguals who declared exposure to at least one foreign language (or dialect) confirmed that they also used these languages. Furthermore, activities that involved passive use of languages (i.e., activities that require reading or listening but do not require speaking or writing; e.g., watching TV) were occasionally carried out in foreign languages: around 26% of these monolinguals confirmed the passive use of more than one language. Lastly, around 58% of monolinguals who had visited one or more non-English-speaking countries declared the active use of foreign languages during their stay(s). These results suggest that the linguistic experiences of monolinguals from the UK often include exposure to and use of foreign languages. Moreover, these results show the need to consider the specificity of the monolingual language experience when analysing the impact of foreign languages on cognitive functioning, as differences in the language experiences of bilinguals also have divergent impacts on cognition. Lastly, monolingual experiences are different from bilingual experiences; therefore, existing questionnaires that evaluate language experiences should be adapted to capture the particular linguistic experiences of monolinguals.

Not all bilinguals are the same: A meta-analysis of the moral foreign language effect

Emerging evidence shows bilinguals employ different decision-making strategies in their foreign language compared to their native language (known as the Foreign Language Effect). When completing moral dilemmas, accumulating research findings indicate that bilinguals are more likely to endorse the utilitarian option. We conducted a meta-analysis to investigate whether linguistic variables (proficiency, immersion, and language similarity) moderate utilitarian responding to moral dilemmas in a foreign language. A systematic literature search extracted experiments comparing binary responses to moral dilemmas among bilingual participants. Analyses confirmed a moral Foreign Language Effect within personal dilemmas, though this effect was moderated by self-reported reading proficiency, whereby bilinguals with higher self-reported reading proficiency were less likely to make a utilitarian choice. Our findings suggest that not all bilinguals may experience a Foreign Language Effect, with low self-reported reading proficiency being the most likely indicator of whether their response tendencies to a moral dilemma change in the foreign language.

Bilingual Language Development in Infancy: What Can We Do to Support Bilingual Families?

Many infants and children around the world grow up exposed to two or more languages. Their success in learning each of their languages is a direct consequence of the quantity and quality of their everyday language experience, including at home, in daycare and preschools, and in the broader community context. Here, we discuss how research on early language learning can inform policies that promote successful bilingual development across the varied contexts in which infants and children live and learn. Throughout our discussions, we highlight that each individual child's experience is unique. In fact, it seems that there are as many ways to grow up bilingual as there are bilingual children. To promote successful bilingual development, we need policies that acknowledge this variability and support frequent exposure to high-quality experience in each of a child's languages.

Prospective memory in bilinguals and monolinguals: ERP and behavioural correlates of prospective processing in bilinguals

Prospective memory (PM) allows us to form intentions and execute them in the future. Successful retrieval of prospective intentions depends on adequate context monitoring and disengagement from the ongoing task. These processes are also central in predicting incoming language information and guiding language production in bilinguals. We investigated if different bilingual experiences (early/late bilinguals, monolinguals) modulate performance in PM tasks that varied in attentional requirements (focal vs. non-focal). Behavioural and event-related potential (ERP) results indicated that early bilinguals differed from late bilinguals and monolinguals in how they performed the prospective task. Specifically, they showed larger differences between the ongoing activity and the prospective task in the N300 and P3b components when performing the more difficult non-focal PM task, indicating that they engaged in monitoring/updating to adapt to the task's demands. These differences were not observed in late bilinguals and monolinguals, suggesting that prospective processing is dependent on the bilingual experience.

The effects of bilingualism on hippocampal volume in ageing bilinguals

Long-term management of more than one language has been argued to contribute to changes in brain and cognition. This has been particularly well documented in older age, where bilingualism has been linked to protective effects against neurocognitive decline. Since memory difficulties are key aspects of this decline, herein we examine potential effects of bilingualism on the hippocampus, a brain structure related to memory that is particularly vulnerable to cognitive ageing. Hippocampal volume has been shown to increase as a result of second language learning and use in younger adults. However, it is unknown if this is maintained throughout the lifespan. We examine hippocampal volume and episodic memory performance in a participant sample consisting of healthy older individuals with a wide range of experiences in exposure and using a second language. Results reveal greater hippocampal volume calibrated to degree of quantified dual language use. Our results mirror those of immersive active bilingualism in younger populations, suggesting that long-term active bilingualism leads to neuroprotective effects in the hippocampus. We discuss this in the context of literature proposing bilingualism-induced brain reserve in the older age.

Bilingualism, Executive Function, and the Brain: Implications for Autism

Autism spectrum disorder (ASD) is associated with marked heterogeneity with respect to the development of executive function abilities. The bilingual advantage refers to the observation that individuals who speak two languages perform better on executive function tasks than monolinguals under some circumstances. There is not yet consensus, however, as to whether this advantage can be reliably demonstrated, nor is there consensus regarding under which conditions it emerges. Bilingual and monolingual children with ASD have comparable developmental outcomes, particularly in the areas of core ASD symptoms, cognitive function, and language. Still, despite the potential advantages that bilingualism may confer, clinicians commonly advise against providing a bilingual environment for children with ASD. The purpose of the present review is to provide an up-to-date assessment of the limited literature on bilingualism in children with ASD in order to inform evidence-based practice. Studies suggest a potential bilingual advantage in ASD in the areas of nonverbal intelligence quotient, adaptive functioning, and expressive vocabulary. A limited yet growing literature provides preliminary evidence for enhanced executive function ability in some children with ASD. Taken together, current evidence suggests that although a bilingual advantage may not be universally present in typical development, it may manifest under specific circumstances, conferring advantage for populations in which executive function is compromised. Further work is needed to develop consistent, evidence-based guidelines around language recommendations for families of children with ASD and to better understand the cognitive and brain mechanisms giving rise to the bilingual advantage in clinical developmental populations.

The Domain-General Multiple Demand Network Is More Active in Early Balanced Bilinguals Than Monolinguals During Executive Processing

The bilingual experience may place special cognitive demands on speakers and has been argued to lead to improvements in domain-general executive abilities, like cognitive control and working memory. Such improvements have been argued for based on both behavioral and brain imaging evidence. However, the empirical landscape is complex and ridden with controversy. Here we attempt to shed light on this question through an fMRI investigation of relatively large, relatively homogeneous, and carefully matched samples of early balanced bilinguals (n = 55) and monolinguals (n = 54), using robust, previously validated individual-level markers of neural activity in the domain-general multiple demand (MD) network, which supports executive functions. We find that the bilinguals, compared to the monolinguals, show significantly stronger neural responses to an executive (spatial working memory) task, and a larger difference between a harder and an easier condition of the task, across the MD network. These stronger neural responses are accompanied by better behavioral performance on the working memory task. We further show that the bilingual-vs.-monolingual difference in neural responses is not ubiquitous across the brain as no group difference in magnitude is observed in primary visual areas, which also respond to the task. Although the neural group difference in the MD network appears robust, it remains difficult to causally link it to bilingual experience specifically.

Why not both? Rethinking categorical and continuous approaches to bilingualism

AIMS AND OBJECTIVES

Bilingualism is a complex construct, and it can be difficult to define and model. This paper proposes that the field of bilingualism can draw from other fields of psychology, by integrating advanced psychometric models that incorporate both categorical and continuous properties. These models can unify the widespread use of bilingual and monolingual groups that exist in the literature with recent proposals that bilingualism should be viewed as a continuous variable.

APPROACH

In the paper, we highlight two models of potential interest: the factor mixture model and the grade-of-membership model. These models simultaneously allow for the formation of different categories of speakers and for continuous variation to exist within these categories. We discuss how these models could be implemented in bilingualism research, including how to develop these models. When using either of the two models, researchers can conduct their analyses on either the categorical or continuous information, or a combination of the two, depending on which is most appropriate to address their research question.

CONCLUSIONS

The field of bilingualism research could benefit from incorporating more complex models into definitions of bilingualism. To help various subfields of bilingualism research converge on appropriate models, we encourage researchers to pre-register their model selection and planned analyses, as well as to share their data and analysis scripts.

ORIGINALITY

The paper uniquely proposes the incorporation of advanced statistical psychometric methods for defining and modeling bilingualism.

SIGNIFICANCE

Conceptualizing bilingualism within the context of these more flexible models will allow a wide variety of research questions to be addressed. Ultimately, this will help to advance theory and lead to a fuller and deeper understanding of bilingualism.

Clear Theories Are Needed to Interpret Differences: Perspectives on the Bilingual Advantage Debate

The heated debate regarding bilingual cognitive advantages remains ongoing. While there are many studies supporting positive cognitive effects of bilingualism, recent meta-analyses have concluded that there is no consistent evidence for a bilingual advantage. In this article we focus on several theoretical concerns. First, we discuss changes in theoretical frameworks, which have led to the development of insufficiently clear theories and hypotheses that are difficult to falsify. Next, we discuss the development of looking at bilingual experiences and the need to better understand language control. Last, we argue that the move from behavioural studies to a focus on brain plasticity is not going to solve the debate on cognitive effects, especially not when brain changes are interpreted in the absence of behavioural differences. Clearer theories on both behavioural and neural effects of bilingualism are needed. However, to achieve this, a solid understanding of both bilingualism and executive functions is needed first.

Moving From Bilingual Traits to States: Understanding Cognition and Language Processing Through Moment-to-Moment Variation

The study of how bilingualism is linked to cognitive processing, including executive functioning, has historically focused on comparing bilinguals to monolinguals across a range of tasks. These group comparisons presume to capture relatively stable cognitive traits and have revealed important insights about the architecture of the language processing system that could not have been gleaned from studying monolinguals alone. However, there are drawbacks to using a group-comparison, or Traits, approach. In this theoretical review, we outline some limitations of treating executive functions as stable traits and of treating bilinguals as a uniform group when compared to monolinguals. To build on what we have learned from group comparisons, we advocate for an emerging complementary approach to the question of cognition and bilingualism. Using an approach that compares bilinguals to themselves under different linguistic or cognitive contexts allows researchers to ask questions about how language and cognitive processes interact based on dynamically fluctuating cognitive and neural states. A States approach, which has already been used by bilingualism researchers, allows for cause-and-effect hypotheses and shifts our focus from questions of group differences to questions of how varied linguistic environments influence cognitive operations in the moment and how fluctuations in cognitive engagement impact language processing.

Structural brain changes with second language learning: A longitudinal voxel-based morphometry study

The underlying mechanisms that adapt with L2 learning are still poorly understood. The present longitudinal study examined the effects of L2 learning on grey matter structure of Chinese college freshmen majoring in English. Participants were scanned twice, one year apart. Our voxel-based morphometry analyses revealed that gray matter volume (GMV) decreased in the left anterior cingulate cortex (ACC) and right inferior frontal gyrus (IFG) after L2 learning for one year. Critically, these structural adaptations correlated with changes in participants' language control ability across L2 learning. Moreover, age of acquisition of L2 was a significant predictor of volumetric change in the left ACC and L2 proficiency was a significant predictor of volumetric change in the right IFG. Overall, these findings enrich our understanding of the dynamic nature of structural brain adaptations, and the mechanisms these adaptations index, as a function of classroom L2 learning.

The Quest for Signals in Noise: Leveraging Experiential Variation to Identify Bilingual Phenotypes

Increasing evidence suggests that bilingualism does not, in itself, result in a particular pattern of response, revealing instead a complex and multidimensional construct that is shaped by evolutionary and ecological sources of variability. Despite growing recognition of the need for a richer characterization of bilingual speakers and of the different contexts of language use, we understand relatively little about the boundary conditions of putative “bilingualism” effects. Here, we review recent findings that demonstrate how variability in the language experiences of bilingual speakers, and also in the ability of bilingual speakers to adapt to the distinct demands of different interactional contexts, impact interactions between language use, language processing, and cognitive control processes generally. Given these findings, our position is that systematic variation in bilingual language experience gives rise to a variety of phenotypes that have different patterns of associations across language processing and cognitive outcomes. The goal of this paper is thus to illustrate how focusing on systematic variation through the identification of bilingual phenotypes can provide crucial insights into a variety of performance patterns, in a manner that has implications for previous and future research.

Assessing the Evidence for Asymmetrical Switch Costs and Reversed Language Dominance Effects - A Meta-Analysis

Two seemingly counterintuitive phenomena - asymmetrical language switch costs and the reversed language dominance effect - prove to be particularly controversial in the literature on language control. Asymmetrical language switch costs refer to the larger costs for switching into the dominant language compared to switching into the less dominant language, both relative to staying in either one language. The reversed language dominance effect refers to longer reaction times when in the more dominant of the two languages in situations that require frequent language switching (i.e., mixed-language blocks). The asymmetrical language switch costs are commonly taken as an index for processes of transient, reactive inhibitory language control, whereas the reversed language dominance effect is taken as an index for sustained, proactive inhibitory language control. In the present meta-analysis, we set out to establish the empirical evidence for these two phenomena using a Bayesian linear mixed effects modelling approach. Despite the observation of both phenomena in some studies, our results suggest that overall, there is little evidence for the generality and robustness of these two effects, and this holds true even when conditions - such as language proficiency and preparation time manipulations - were included as moderators of these phenomena. We conclude that asymmetrical switch costs and the reversed language dominance effect are important for theory development, but their utility for theory testing is limited due to their lack of robustness and the absence of confirmed moderatory variables.

Differential impacts of natural L2 immersion and intensive classroom L2 training on cognitive control

The relationship between bilingualism and cognitive control has been controversial. We believe that the discrepant findings are likely driven by the complexities of the bilingual experience, which is consistent with the Adaptive Control Hypothesis. The current study investigates whether the natural language immersion experience and the classroom intensive language training experience have differential impacts on cognitive control. Among unbalanced Chinese-English bilingual students, a natural L2 (second language) immersion group, an L2 public speaking training group, and a control bilingual group without immersion or training experience were compared on their cognitive control abilities, with the participants' demographic factors strictly controlled. The results showed that the L2 immersion group and the L2 speaking group had faster speed than the control group in the Flanker task, whereas the L2 immersion group had fewer errors than the other two groups in the Wisconsin Card Sorting Test (WCST). These results generally provide evidence in favour of the Adaptive Control Hypothesis, specifying that natural L2 immersion and L2 public speaking training experiences are distinctively related to cognitive control. The current study is the first of its kind to link specific bilingual experiences (natural L2 immersion vs. intensive L2 public speaking) with different components of cognitive control.

General principles governing the amount of neuroanatomical overlap between languages in bilinguals

The literature has identified many important factors affecting the extent to which languages in bilinguals rely on the same neural populations in the specific brain region. The factors include the age of acquisition of the second language (L2), proficiency level of the first language (L1) and L2, and the amount of language exposure, among others. What is lacking is a set of global principles that explain how the many factors relate to the degree to which languages overlap neuroanatomically in bilinguals. We are offering a set of such principles that together account for the numerous sources of data that have been examined individually but not collectively: (1) the principle of acquisition similarity between L1 and L2, (2) the principle of linguistic similarity between L1 and L2, and (3) the principle of cognitive control and effort. Referencing the broad characteristics of language organization in bilinguals, as presented by the principles, can provide a roadmap for future clinical and basic science research.

Disentangling language status and country-of-origin explanations of the bilingual advantage in preschoolers

Bilingual preschoolers from East Asia outperform monolingual preschoolers from North America or Europe in executive functioning tasks, which has been interpreted as evidence of a bilingual advantage in executive functioning. This study tested whether these differences actually reflect country-of-origin effects given that East Asian preschoolers frequently outperform North American or European children in executive functioning tasks. Consistent with previous findings, Korean-English bilingual preschoolers made fewer errors in an age-appropriate executive functioning task than did English monolingual children in Canada. However, Korean-English bilingual preschoolers performed comparably to Korean monolingual preschoolers in Korea. Differences between Korean and Canadian children's executive functioning were not attributable to differences in parental cultural values or attitudes. The current findings suggest that differences between East Asian bilingual and North American monolingual preschoolers' executive functioning is related to differences in country of origin rather than language status.

Bilingual experience and intrinsic functional connectivity in adults, aging, and Alzheimer's disease

The past decade marked the beginning of the use of resting-state functional connectivity (RSFC) imaging in bilingualism studies. This paper intends to review the latest evidence of changes in RSFC in language and cognitive control networks in bilinguals during adulthood, aging, and early Alzheimer's disease, which can add to our understanding of brain functional reshaping in the context of second language (L2) acquisition. Because of high variability in bilingual experience, recent studies mostly focus on the role of the main aspects of bilingual experience (age of acquisition (AoA), language proficiency, and language usage) on intrinsic functional connectivity (FC). Existing evidence accounts for stronger FC in simultaneous rather than sequential bilinguals in language and control networks, and the modulation of the AoA impact by language proficiency and usage. Studies on older bilingual adults show stronger FC in language and frontoparietal networks and preserved FC in posterior brain regions, which can protect the brain against cognitive decline and neurodegenerative processes. Altered RSFC in language and control networks subsequent to L2 training programs also is associated with improved global cognition in older adults. This review ends with a brief discussion of potential confounding factors in bilingualism research and conclusions and suggestions for future research.

Bilingualism: Pathway to Cognitive Reserve

Cognitive reserve is characterized by a dissociation between cognitive level and brain structure, thereby reducing the impact of deteriorating brain structure on cognitive function. Cognitive reserve is therefore a promising approach to maintaining cognitive function and protecting against symptoms of dementia. The present paper evaluates evidence supporting the claim that bilingualism contributes to cognitive reserve. Four types of evidence are presented: (i) brain and cognitive function in healthy aging, (ii) age of onset of symptoms of dementia, (iii) relation between clinical level and neuropathology for patients, and (iv) rate of cognitive decline in later stages of dementia. In all cases, bilinguals revealed patterns that were consistent with the interpretation of protection from cognitive reserve when compared with monolinguals.

Can Machines Find the Bilingual Advantage? Machine Learning Algorithms Find No Evidence to Differentiate Between Lifelong Bilingual and Monolingual Cognitive Profiles

Bilingualism has been identified as a potential cognitive factor linked to delayed onset of dementia as well as boosting executive functions in healthy individuals. However, more recently, this claim has been called into question following several failed replications. It remains unclear whether these contradictory findings reflect how bilingualism is defined between studies, or methodological limitations when measuring the bilingual effect. One key issue is that despite the claims that bilingualism yields general protection to cognitive processes (i.e., the cognitive reserve hypothesis), studies reporting putative bilingual differences are often focused on domain specific experimental paradigms. This study chose a broader approach, by considering the consequences of bilingualism on a wide range of cognitive functions within individuals. We utilised 19 measures of different cognitive functions commonly associated with bilingual effects, to form a "cognitive profile" for 215 non-clinical participants. We recruited Welsh speakers, who as a group of bilinguals were highly homogeneous, as means of isolating the bilingualism criterion. We sought to determine if such analyses would independently classify bilingual/monolingual participant groups based on emergent patterns driven by collected cognitive profiles, such that population differences would emerge. Multiple predictive models were trained to independently recognise the cognitive profiles of bilinguals, older adults (60-90 years of age) and higher education attainment. Despite managing to successfully classify cognitive profiles based on age and education, the model failed to differentiate between bilingual and monolingual cognitive ability at a rate greater than that of chance. Repeated modelling using alternative definitions of bilingualism, and just the older adults, yielded similar results. In all cases then, using our "bottom-up" analytical approach, there was no evidence that bilingualism as a variable indicated differential cognitive performance - as a consequence, we conclude that bilinguals are not cognitively different from their monolingual counterparts, even in older demographics. We suggest that studies that have reported a bilingual advantage (typically recruiting immigrant populations) could well have confounded other key variables that may be driving reported advantages. We recommend that future research refine the machine learning methods used in this study to further investigate the complex relationship between bilingualism and cognition.

Measuring Bilingualism: The Quest for a "Bilingualism Quotient"

The study of bilingualism has a history that extends from deciphering ancient multilingual texts to mapping the structure of the multilingual brain. The language experiences of individual bilinguals are equally diverse and characterized by unique contexts of acquisition and use that can shape not only sociocultural identity, but also cognitive and neural function. Perhaps unsurprisingly, this variability in scholarly perspectives and language experiences has given rise to a range of methods for defining bilingualism. The goal of this paper is to initiate a conversation about the utility of a more unified approach to how we think about, study, and measure bilingualism. Using concrete case studies, we illustrate the value of enhancing communication and streamlining terminology across researchers with different methodologies within questions, different questions within domains, and different domains within scientific inquiry. We specifically consider the utility and feasibility of a Bilingualism Quotient (BQ) construct, discuss the idea of a BQ relative to the well-established Intelligence Quotient (IQ), and include recommendations for next steps. We conclude that though the variability in language backgrounds and approaches to defining bilingualism presents significant challenges, concerted efforts to systematize and synthesize research across the field may enable the construction of a valid and generalizable index of multilingual experience.

Engaging proactive control: Influences of diverse language experiences using insights from machine learning

We used insights from machine learning to address an important but contentious question: Is bilingual language experience associated with executive control abilities? Specifically, we assess proactive executive control for over 400 young adult bilinguals via reaction time (RT) on an AX continuous performance task (AX-CPT). We measured bilingual experience as a continuous, multidimensional spectrum (i.e., age of acquisition, language entropy, and sheer second language exposure). Linear mixed effects regression analyses indicated significant associations between bilingual language experience and proactive control, consistent with previous work. Information criteria (e.g., AIC) and cross-validation further suggested that these models are robust in predicting data from novel, unmodeled participants. These results were bolstered by cross-validated LASSO regression, a form of penalized regression. However, the results of both cross-validation procedures also indicated that similar predictive performance could be achieved through simpler models that only included information about the AX-CPT (i.e., trial type). Collectively, these results suggest that the effects of bilingual experience on proactive control, to the extent that they exist in younger adults, are likely small. Thus, future studies will require even larger or qualitatively different samples (e.g., older adults or children) in combination with valid, granular quantifications of language experience to reveal predictive effects on novel participants. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Factors Modifying the Amount of Neuroanatomical Overlap between Languages in Bilinguals-A Systematic Review of Neurosurgical Language Mapping Studies

Neurosurgery on individuals with lesions around language areas becomes even more complicated when the patient is bilingual. It is thus important to understand the principles that predict the likelihood of convergent versus separate neuroanatomical organization of the first (L1) and the second language (L2) in these individuals. We reviewed all English-language publications on neurosurgical language mapping in bilinguals before January 2020 in three databases (e.g., PubMed). Our search yielded 28 studies with 207 participants. The reviewed data suggest several principles of language organization in bilingual neurosurgical patients: (1) separate cortical areas uniquely dedicated to each language in both anterior and posterior language sites are the rule rather than occasional findings, (2) In cases where there was a convergent neuroanatomical representation for L1 and L2, two factors explained the overlap: an early age of L2 acquisition and a small linguistic distance between L1 and L2 and (3) When L1 and L2 diverged neuroanatomically, more L1-specific sites were identified for early age of L2 acquisition, high L2 proficiency and a larger linguistic distance. This work provides initial evidence-based principles predicting the likelihood of converging versus separate neural representations of L1 and L2 in neurosurgical patients.

Investigating the Effects of Language-Switching Frequency on Attentional and Executive Functioning in Proficient Bilinguals

Recent studies have proposed that the executive advantages associated with bilingualism may stem from language-switching frequency rather than from bilingualism per se (see, for example, Prior and Gollan, 2011). Barbu et al. (2018) showed that high-frequency switchers (HFLSs) outperformed low-frequency switchers (LFLSs) on a mental flexibility task but not on alertness or response inhibition tasks. The aim of the present study was to replicate these results as well as to compare proficient (HFLSs and LFLSs) to a control group of monolingual participants. Two groups of proficient bilingual adults (30 HFLSs and 21 LFLSs) and a group of 28 monolinguals participated in the study. The results showed superior mental flexibility skills in HFLSs compared to (LFLSs) and monolinguals; furthermore, the two latter groups showed no difference in mental flexibility skills. These results provide novel support for the hypothesis that the so-called bilingual advantage is, in fact, a result of language-switching habits.

Dynamic Language Network in Early and Late Cantonese-Mandarin Bilinguals

The brain representation of language in bilinguals is sculptured by several factors, such as age of acquisition (AoA) and proficiency level (PL) in second language. Although the effect of AoA-L2 on brain function and structure has been studied, little attention is devoted to dynamic properties of the language network and their differences between early and late bilinguals. In this study, we acquired resting-state fMRI data from early and late Cantonese (L1)–Mandarin (L2) bilinguals with high PLs of verbal fluency in both languages. We then analyzed dynamic functional connectivity (dFC) by using the sliding-windows approach, estimated the dFC states by using the k-means clustering algorithm, and calculated the dynamic topological properties of the language network for the early and late bilinguals. We detected four dFC states, State 1, State 2, State 3, and State 4, which may be related to phonetic processing, semantic processing, language control, and syntactic processing, respectively. Compared to the late bilinguals, the early bilinguals showed higher dFC between the inferior frontal area and the temporal area in State 1 and State 2, while higher dFC between the cerebellum and other regions in State 3. The early bilinguals showed a higher clustering coefficient and local and global efficiency in State 1 and State 3, but lower characteristic path length in State 1, than the late bilinguals. Together, these results suggested that AoA-L2 affects temporal neural activation and dynamic topological properties of the language network. These findings provide new information to understand the effect of experience of L2 acquisition on language network in bilinguals.

Are the Effects of Variation in Quantity of Daily Bilingual Exposure and Socioeconomic Status on Language and Cognitive Abilities Independent in Preschool Children?

Bilingual exposure (BE) and socioeconomic status (SES) are associated with children's development, but their specific and unique effects are still unclear. This study analyzed the influence of these environmental factors on a set of cognitive and linguistic abilities in preschoolers to disentangle their effects. One hundred-eleven Italian-speaking preschool children (mean age = 61 months; SD = 6.8) growing in a monolingual or multilingual context completed an assessment of cognitive (theory of mind, inhibition, attention shifting and working memory) and linguistic abilities (vocabulary, grammar, narrative comprehension, lexical access). The results of hierarchical regressions with predictors variation in BE (both Length and Daily exposure) and SES on each ability, shown a specific contribution of variation in SES, after controlling for BE, in vocabulary, grammar, and working memory (WM), and a specific contribution of variation in BE, over and above effect of SES, in vocabulary, narrative comprehension and WM. In addition, we found an interaction between these factors in predicting the performance of the theory of mind task (ToM). To conclude, variations in BE and SES are related independently to individual differences in linguistic and cognitive skills of children in preschool.

Active bilingualism delays the onset of mild cognitive impairment

Lifelong bilingualism may contribute to cognitive reserve (CR) in neurodegenerative diseases as shown by a delay of the age at symptom onset in bilinguals with Alzheimer's disease (AD) and Mild Cognitive Impairment (MCI). However, some studies have failed to show this bilingual advantage, suggesting that it might depend on the type and degree of bilingualism. In the present study, we tested the hypothesis that active bilingualism, defined as the continuous use of the two languages as opposed to second language exposition only, may protect against cognitive decline. Moreover, we investigated whether bilingualism as a CR factor may be explained by an advantage within the executive control (EC) system. To do so, we collected clinical measures (age at onset of cognitive symptoms, age at the first medical visit for cognitive impairments, and age at diagnosis) in patients with MCI and patients with AD with different degrees of language experience and usage of Catalan and Spanish. Additionally, all participants were tested on four EC tasks and one long-term memory recognition task. First, results from multiple regression analyses showed that active bilingualism was a significant predictor of delay in the age at onset for all the clinical measures in MCI, but not AD patients. Second, the effect of active bilingualism was independent of occupation, educational level and job attainment across the individuals' lifespan. Finally, although we did not find an effect of active bilingualism across all EC tasks, we did find an effect for conflict resolution. These results are discussed in the context of CR hypotheses, suggesting that compensatory mechanisms may play a role in protecting against cognitive decline.