Students will select two peer reviewed articles One article will be in bilingualism:? Bilingualism: consequences for mind and brain

Feature Review

Bilingualism: consequences for mind and brain Ellen Bialystok1,2, Fergus I.M. Craik2 and Gigi Luk3

1 Department of Psychology, York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada

2 Rotman Research Institute of Baycrest, 3560 Bathurst Street, Toronto, ON, M6A 2E1,Canada

3 Harvard Graduate School of Education, 14 Appian Way, Cambridge, MA 02138, USA

Review

Building on earlier evidence showing a beneficial effect of bilingualism on children’s cognitive development, we review recent studies using both behavioral and neuro- imaging methods to examine the effects of bilingualism on cognition in adulthood and explore possible mecha- nisms for these effects. This research shows that bilin- gualism has a somewhat muted effect in adulthood but a larger role in older age, protecting against cognitive decline, a concept known as ‘cognitive reserve’. We discuss recent evidence that bilingualism is associated with a delay in the onset of symptoms of dementia. Cognitive reserve is a crucial research area in the context of an aging population; the possibility that bilingualism contributes to cognitive reserve is therefore of growing importance as populations become increasingly diverse.

Why bilingualism? It is generally believed that more than half of the world’s population is bilingual [1]. In each of the U.S.A.1 and Canada2, approximately 20% of the population speaks a language at home other than English. These figures are higher in urban areas, rising to about 60% in Los Angeles3

and 50% in Toronto4. In Europe, bilingualism is even more prevalent: in a recent survey, 56% of the population across all European Union countries reported being functionally bilin- gual, with some countries recording particularly high rates, such as Luxembourg at 99%5. Bilinguals, therefore, make up a significant portion of the population. Importantly, accumulating research shows that the development, efficien-

Corresponding author: Bialystok, E. ([email protected]) 1 U. S. Census Bureau (2010) The 2011 Statistical Abstract. Languages Spoken at

Home by Language: 2008, Table 53. Retrieved August 4, 2011 from http://www.census. gov/compendia/statab/cats/population/ancestry_language_spoken_at_home.html.

2 Statistics Canada (2007) 2006 Census of Canada highlight tables: Population by language spoken most often at home and age groups, 2006 counts, for Canada, provinces and territories – 20% sample data. (Catalogue number 97-555-XWE2006002). Retrieved August 4, 2011 from http://www12.statcan.ca/census-recensement/2006/dp-pd/hlt/ 97-555/T402-eng.cfm?Lang=E&T=402&GH=4&SC=1&S=99&O=A.

3 U. S. Census Bureau (2010) The 2011 Statistical Abstract. Language Spoken at Home – Cities With 100,000 Persons or More: 2008, Table 55. Retrieved August 4, 2011 from http://www.census.gov/compendia/statab/cats/population/ancestry_language_ spoken_at_home.html.

4 Statistics Canada (2007) 2006 Census of Canada highlight tables: Population by language spoken most often at home and age groups, 2006 counts, for Canada, provinces and territories – 20% sample data. (Catalogue number 97-555-XWE2006002). Retrieved August 4, 2011 from http://www12.statcan.ca/census-recensement/2006/dp-pd/hlt/ 97-555/T402-eng.cfm?Lang=E&T=402&GH=4&SC=1&S=99&O=A.

5 European Commission (2006) ‘Special Eurobarometer 243: Europeans and their Languages (Executive Summary)’ (PDF). Europa web portal. p. 3. Retrieved Novem- ber 1, 2011 from http://ec.europa.eu/public_opinion/archives/ebs/ebs_243_sum_en.pdf.

240 1364-6613/$ – see front matter � 2012 Elsevier Ltd. All rights reserv

cy, and decline of crucial cognitive abilities are different for bilinguals than for monolinguals. What are these cognitive differences and how does bilingualism lead to these changes?

The context for examining how bilingualism affects cog- nitive ability is functional neuroplasticity, that is, the study of how experience modifies brain structure and brain func- tion. Such modifications have been found following experi- ences as diverse as juggling [2], video-game playing [3], careers in architecture [4], taxi-driving [5], and musical training [6,7]. Bilingualism is different from all of these: like juggling and playing video games, it is intense, and, like architecture and driving taxis in London, it is sustained, but, unlike these experiences, bilinguals are not typically pre- selected for talent or interest. Although bilinguals undoubt- edly differ from monolinguals in certain ways, they gener- ally did not choose bilingualism. Rather, the circumstances of their family, place of birth, or immigration history simply required that they learn more than one language.

What is different about bilingual minds? It has long been assumed that childhood bilingualism affected developing minds, but the belief was that the consequences for children were negative: learning two languages would be confusing [8]. A study by Peal and Lambert [9] cast doubt on this belief by reporting that children in Montreal who were either French-speaking monolinguals or English–French bilinguals performed dif- ferently on a battery of tests. The authors had expected to find lower scores in the bilingual group on language tasks but equivalent scores in non-verbal spatial tasks, but instead found that the bilingual children were superior on most tests, especially those requiring symbol manipu- lation and reorganization. This unexpected difference be- tween monolingual and bilingual children was later explored in studies showing a significant advantage for bilingual children in their ability to solve linguistic prob- lems based on understanding such concepts as the differ- ence between form and meaning, that is, metalinguistic awareness [10–16] and non-verbal problems that required participants to ignore misleading information [17,18].

Research with adult bilinguals built on these studies with children and reported two major trends. First, a large body of evidence now demonstrates that the verbal skills of bilinguals in each language are generally weaker than are those for monolingual speakers of each language.

ed. doi:10.1016/j.tics.2012.03.001 Trends in Cognitive Sciences, April 2012, Vol. 16, No. 4

Review Trends in Cognitive Sciences April 2012, Vol. 16, No. 4

Considering simply receptive vocabulary size, bilingual children [19] and adults [20] control a smaller vocabulary in the language of the community than do their monolingual counterparts. On picture-naming tasks, bilingual partici- pants are slower [21–24] and less accurate [25,26] than monolinguals. Slower responses for bilinguals are also found for both comprehending [27] and producing words [28], even when bilinguals respond in their first and dominant lan- guage. Finally, verbal fluency tasks are a common neuro- psychological measure of brain functioning in which participants are asked to generate as many words as they can in 60 s that conform to a phonological or semantic cue. Performance on these tasks reveals systematic deficits for bilingual participants, particularly in semantic fluency con- ditions [29–33], even if responses can be provided in either language [34]. Thus, the simple act of retrieving a common word is more effortful for bilinguals.

In contrast to this pattern, bilinguals at all ages demon- strate better executive control than monolinguals matched in age and other background factors. Executive control is the set of cognitive skills based on limited cognitive resources for such functions as inhibition, switching attention, and work- ing memory [35]. Executive control emerges late in develop- ment and declines early in aging, and supports such activities as high-level thought, multi-tasking, and sustained atten- tion. The neuronal networks responsible for executive control are centered in the frontal lobes, with connections to other brain regions as necessary for specific tasks. In children, executive control is central to academic achievement [36], and, in turn, academic success is a significantpredictor of long term health and well being [37]. In a recent meta-analysis, Adesope et al. [38] calculated medium to large effect sizes for the executive control advantages in bilingual children, and Hilchey and Klein [39] summarized the bilingual advantage over a large number of studies with adults. This advantage has been shown to extend into older age and protect against cognitive decline [21,40,41], a point to which we turn below.

In this review, we examine the evidence for bilingual advantages in executive control and explore the possible mechanisms and neural correlates that may help to ex- plain them. Our conclusion is that lifelong experience in managing attention to two languages reorganizes specific brain networks, creating a more effective basis for execu- tive control and sustaining better cognitive performance throughout the lifespan.

Language processing in bilinguals Joint activation of languages

A logical possibility for the organization of a bilingual mind is that it consists of two independently-represented lan- guage systems that are uniquely accessed in response to the context: a fluent French–English bilingual ordering coffee in a Parisian café has no reason to consider how to form the request in English, and a Cantonese–English bilingual studying psychology in Boston does not need to recast the material through Chinese. Yet, substantial evi- dence shows that this is not how the bilingual mind is organized. Instead, fluent bilinguals show some measure of activation of both languages and some interaction between them at all times, even in contexts that are entirely driven by only one of the languages.

The evidence for this conclusion comes from psycholin- guistic studies using such tasks as cross-language priming (in which a word in one language facilitates retrieval of a semantically related word in the other language) and lexical decision (in which participants decide whether a string of letters is an actual word in one of the languages) that show the influence of the currently unused language for both comprehension and production of speech [42–48]. Further evidence comes from patient studies showing intrusions from the irrelevant language or inappropriate language switches [49], and imaging studies indicating involvement of the non-target language while performing a linguistic task in the selected language [50–52]. Using eye-tracking technology, for example, Marian, Spivey, and Hirsch [53] reported that English–Russian bilinguals per- forming a task in English in which they had to look at the named picture from four alternatives were distracted by a picture the name of which shared phonology with Russian, even though there was no connection to the meaning of the target picture and no contextual cues indicating that Rus- sian was relevant. Similarly, Thierry and Wu [54] pre- sented English monolinguals, Chinese–English bilinguals, and Chinese monolinguals with pairs of words in English (translated to Chinese for Chinese monolinguals) and asked participants to decide if the words were semantically related or not. The manipulation was that half of the pairs contained a repeated character in the written Chinese forms, even though that orthographic feature was unrelat- ed to the English meaning. Waveforms derived from anal- yses of electroencephalography (EEG) are used to indicate the neuronal response to language on a millisecond by millisecond scale. An event-related potential (ERP) called the N400 (i.e. a negative-going waveform peaking approxi- mately 400 msec after the onset of a target stimulus) signals the effort associated with integrating the meaning of words. The more similar the words are to each other, the smaller is the amplitude of the N400. In the study by Thierry and Wu, semantic relatedness was associated with significantly smaller N400 amplitude in all groups as expected, but the repeated character also led to smaller N400 for the two Chinese groups. Thus, although irrele- vant to the task, participants were accessing the Chinese forms when making judgments about the semantic relation between English words. Subsequent research has refined these results by showing their basis in the phonology rather than the orthography of spoken language [55] and extended the phenomenon to the phonological hand forms of American Sign Language [56].

This joint activation is the most likely mechanism for understanding the consequences of bilingualism for both linguistic and non-linguistic processing. For linguistic pro- cessing, joint activation creates an attention problem that does not exist for monolinguals: in addition to selection constraints on such dimensions as register, collocation, and synonymy, the bilingual speaker also has to select the correct language from competing options. Although joint activation creates a risk for language interference and language errors, these rarely occur, indicating that the selection of the target language occurs with great accuracy. However, this need to select at the level of language system makes ordinary linguistic processing more effortful for

241

Review Trends in Cognitive Sciences April 2012, Vol. 16, No. 4

bilinguals than monolinguals and explains some of the costs in psycholinguistic studies described above. For non-linguistic processing, the need to resolve competition and direct attention is primarily the responsibility of gen- eral cognitive systems, in particular executive functions. The possible influence of linguistic processes on non-lin- guistic executive control has significant consequences for lifespan cognition and is discussed in the next section.

Consequences of joint activation

An appealing suggestion for how the executive control system achieves linguistic selection in the context of joint activation is through inhibition of the non-target language. At least two influential models have been proposed that place inhibition at the center of this selection. The first, the Inhibitory Control model [57] is based on the Supervisory Attentional System [58] and extends a domain-general and resource-limited attention system to the management of competing languages. The second, the Bilingual Interac- tive Activation Model (BIA+) [59], uses computer simula- tion to model lexical selection from both intralingual and extralingual competitors. Although both models assign a primary role to inhibition, they are very different from each other and address a different aspect of the selection prob- lem. It is useful, therefore, to consider the distinction between global inhibition and local inhibition proposed by De Groot and Christoffels [60]. Global inhibition refers to suppression of an entire language system, as in inhibit- ing French when speaking English, and local inhibition refers to inhibition of a specific competing distractor, such as the translation equivalent of the required concept. Both processes are required for fluent language selection but the two are carried out differently. Guo, Liu, Misra, and Kroll [61] used functional magnetic resonance imaging (fMRI) to demonstrate the recruitment of different systems for each of global inhibition (dorsal left frontal gyrus and parietal cortex) and local inhibition (dorsal anterior cingulate cor- tex, supplementary motor area) in a sample of Chinese– English bilinguals, and validated their distinct roles in bilingual language control. Although Green’s inhibitory control model is consistent with both types of inhibition, Dijkstra’s BIA+ model is limited to modeling item selection in local inhibition.

These types of inhibition also differ in their primary domain of influence, with local inhibition largely affecting linguistic performance and global inhibition affecting both linguistic and cognitive performance. The linguistic out- comes of inhibition are reduced speed and fluency of lexical access for bilinguals as described above. However, perfor- mance also requires a selection bias towards the target language, showing a role for activation [62,63] as well as inhibition. These alternatives are not mutually exclusive but indicate the need for a more complete description of how attention is managed in bilingual language proces- sing. Ultimately the degree of both inhibition and activa- tion are relative rather than absolute and will be modulated by contextual, linguistic, and cognitive factors. The cognitive outcomes of linguistic inhibition are en- hanced attentional control and will be described more fully in the next section. Importantly, the cognitive and linguis- tic outcomes are related. Three studies have reported a

242

relationship between inhibition and ability in verbal and non-verbal tasks by showing a correlation between Stroop task performance and competing word selection [64], Si- mon task performance and language switching in picture naming [65], and cross-language interference and a variety of executive control measures [66]. Such results point to an extensive reorganization of cognitive and linguistic pro- cesses in bilinguals.

Cognitive networks in bilinguals Bilingual performance on conflict tasks

Early evidence that bilingual children solved non-verbal conflict tasks differently from monolingual children was reported in a study by Bialystok and Majumder [17]. Eight- year-old children were given a variety of non-verbal problems to solve, some of which contained perceptual distraction (block design from the Wechsler Intelligence Scale for Children, WISC [67]) and some which did not (Noelting’s Juice Task [68,69]). Bilingual children outper- formed monolinguals on the conflict tasks, but children in the two groups were comparable on tasks that did not include distracting perceptual information. This pattern has been confirmed in studies of both children and adults using a flanker task (children: [70,71]), theory of mind task (children: [72,73]; adults: [74]), Simon task (children: [75]; adults: [40]). Other studies with adults have shown better performance by bilinguals in naming the font color in a Stroop task [21], smaller costs in task switching [76], better ability to maintain task set in an attention task [77], and more susceptibility to negative priming, presumably be- cause of greater inhibition [78].

Some studies have extended these bilingual advantages into older age. Bialystok, Craik, Klein and Viswanathan [40] reported an experiment in which middle-aged and older adults who were either monolingual or bilingual were given a version of the Simon task. Participants were shown either a green or a red square on each trial, and the task was to press an associated response key as rapidly as possible. The keys were located at each side of the presen- tation screen. In one condition, the squares appeared centrally on the screen, so there was no spatial conflict between the location of stimuli and responses; in this condition there were no reaction-time (RT) differences between language groups. In a second condition, the col- ored squares appeared laterally on the screen, either di- rectly above the appropriate response key (congruent condition) or on the other side of the screen, above the incorrect response key (incongruent condition). The RT difference between congruent and incongruent response trials (the Simon effect) is a measure of attentional control. Bilinguals produced smaller Simon effects than monolin- guals at all ages.

Three other results from this study are noteworthy. First, the decrease in attentional control in older adults was reduced in the bilingual groups, suggesting that bilin- gualism may be protective against the effects of cognitive aging. Second, whereas a bilingual advantage was expected for incongruent stimuli, it was also found for congruent stimuli. This result has been replicated in sub- sequent studies [39] and is difficult to account for in terms of response conflict or inhibition. Third, prolonged practice

Review Trends in Cognitive Sciences April 2012, Vol. 16, No. 4

reduced both the Simon effect and the size of the bilingual advantage. Apparently all participants can learn to disre- gard the distracting effects of interfering stimuli given sufficient practice on a task, but it seems that bilinguals can learn this type of inhibition more rapidly. One inter- esting question in this regard is the extent to which this attenuation of attentional control is specific to the prac- ticed situation, or whether it generalizes to tasks tapping attentional control in a different manner. Our conjecture is that the attenuation effect is context specific.

A complication that has emerged as more results are reported is that the bilingual advantage is not always found in samples of young adults. For example, a study examining performance on the Simon task in 5-year-olds, young, middle-aged and older adults found a bilingual advantage in RT in the 5-year-olds and in the older adults, but not in the young adult group [79]. Similarly, a study of the Stroop effect in younger and older adults found a bilingual advantage in both age groups but when the same participants performed the Simon arrow task the bilingual advantage was found only in the older adults [21]. Simi- larly, Salvatierra and Rosselli [41] used a simple version of the Simon task and reported a bilingual advantage for older but not younger adults. There is thus some evidence that the bilingual advantage is greatest in children and in older adults, but less constantly present in young adults – perhaps because the young adult group is at the develop- mentally peak age for cognitive control.

It appears that bilingual advantages for young adults tend to emerge on tasks or conditions that are difficult. For example, Bialystok [80] found that bilingual young adults outperformed their monolingual counterparts on the direc- tional arrow Simon task, but only on the condition that included more monitoring and switching than a simpler condition. Similarly, several studies by Costa and collea- gues have reported a bilingual advantage in young adults [71,81,82] but only under some conditions. For example, Costa et al. [81] demonstrated that the bilingual advantage on a flanker task held only under high monitoring condi- tions. In versions where most of the trials were of one type (congruent or incongruent), no bilingual advantage was observed; the advantage was found, however, in a condition involving 25% incongruent and 75% congruent trials, al- though even there the advantage decreased over blocks of the experiment (cf. [44]). Costa et al. [81] concluded that the bilingual advantage reflects a more efficient monitoring system for conflict resolution, in that bilinguals may be better at determining when the misleading information can be safely ignored. Finally, Hernández et al. [82] used a non-linguistic version of the Stroop effect and found a trend towards both reduced interference and enhanced facilita- tion in young adult bilinguals compared with monolinguals (cf. older participants in [21]). One interesting aspect of the studies by Costa, Hernández and colleagues is that the monolinguals were Spanish speakers and the bilinguals’ two languages were Catalan and Spanish. Most of the participants were undergraduate students and were not immigrants, so the two groups were well equated apart from the language difference. In summary, the evidence for a bilingual advantage in younger adults is more sporadic than in other age groups, although at all ages there are

some reports of studies showing no difference between monolinguals and bilinguals performing a conflict task.

Neural correlates of cognitive reorganization

Recently, studies have begun to investigate the neural correlates of bilingual processing examined in the behav- ioral research. The majority of this research has used fMRI to study bilinguals performing a linguistic task in their two languages. Typically, participants name pictures or gener- ate words in response to a cue signaling the required language, and performance is compared for single lan- guage and mixed language conditions. Two early studies revealed promising results. The first led to the surprising finding that language switching was accompanied by acti- vation in the dorsolateral prefrontal cortex (DLPFC), an area known to be part of the general executive control system [24]. Less surprising was a study showing the involvement of Broca’s area as well as a left frontal area in a language switching task [83]. Subsequent re- search has corroborated the involvement of these systems and has shown that language switching elicits a spatially- distributed activation pattern involving bilateral frontal and precentral areas, bilateral caudate, bilateral (or mid- line) pre-supplementary areas (pre-SMA), and bilateral temporal regions. This pattern has been found for Ger- man-French bilinguals [84], Spanish-Catalan bilinguals [85], Chinese–English bilinguals [61,86,87] and Span- ish–English bilinguals [88]. A few studies [61,84] have also reported activation in anterior cingulate cortex (ACC), but activation in this area is not consistently observed. Abu- talebi and colleagues [89] extended this finding to show activation of ACC for both language switching and non- verbal switching. Importantly, these studies confirm that frontal systems involved in executive control are recruited by bilinguals to manage attention to language.

Abutalebi and Green [90] conducted a qualitative review of these studies and proposed that the ACC, left prefrontal cortex, left caudate and bilateral supramarginal gyri (SMG) constitute the neural correlates of the control mechanism for bilingual language production. This model was confirmed in a quantitative meta-analysis examining bilingual language switching [91] (Figure 1). Both the qualitative and quanti- tative analyses point to multiple cortical regions in which functional activity is altered by bilingualism, but an out- standing question is whether activity in these regions is synchronous, forming a neural network that is responsive to bilinguals’ experience of managing two languages. To this end, a study by Nakamura and colleagues [92] showed strong connectivity between left inferior frontal gyrus (IFG) and left middle temporal gyrus (MTG) in a group of Japanese–English bilinguals performing a cross-language priming task. The connectivity was stronger in the frontal- temporal coupling than in the reverse direction. This pat- tern was replicated using transcranial magnetic stimulation (TMS) with Japanese–English bilingual participants per- forming the same cross-language priming task. Nakamura and colleagues [92] interpreted the results as indicating top- down control from left IFG to left MTG in a bilingual context.

Taken together, fMRI research on bilingual language switching has implicated distributed cortical activation that converges in the frontal regions. Intriguingly, the

243

Left Right

TRENDS in Cognitive Sciences

Figure 1. Bilingual influence on brain function and structure. Transparent brains showing the left and right hemispheres. Green voxels depict grey matter regions showing

high activation during bilingual language switching in a meta-analysis [90]. Red–yellow voxels indicate regions of higher white matter integrity in bilingual older adults

relative to monolinguals [107]. Together, the functional and structural data indicate that neural correlates of bilingualism are observed in the frontal lobes, generally

responsible for higher cognition such as executive functions.

Review Trends in Cognitive Sciences April 2012, Vol. 16, No. 4

brain regions related to bilingual switching are also critical for general attention and cognitive control [93,94]. This overlap in brain regions activated for bilingual switching and cognitive control implies that the same mechanisms may be involved in both activities, and that these shared processes might help to explain the superior performance of bilinguals on non-verbal conflict tasks. In other words, using these cognitive control networks for bilingual lan- guage processing may reconfigure them for other purposes, providing part of the explanation for the behavioral differ- ences between monolinguals and bilinguals found in non- verbal conflict tasks. Specifically, the evidence suggests that cognitive control networks may be more broadly based in bilinguals as a result of their dual function. However, fMRI studies on language switching in bilinguals can only show that these networks are included in bilingual lan- guage selection. Determining whether or not such recon- figuration occurs can only be evaluated …

Creative Commons Attribution-Non Commercial 4.0 August 2019 • NEUROLOGY 101

Acquired Language Disorders in Bilinguals

Authors: *Elisa Cargnelutti,1 Barbara Tomasino,1 Franco Fabbro2,3

1. Scientific Institute, IRCCS E. Medea, Dipartimento/Unità Operativa Pasian di Prato, Udine, Italy

2. Cognitive Neuroscience Laboratory, DILL, University of Udine, Italy 3. PERCRO Perceptual Robotics Laboratory, Scuola Superiore Sant’Anna, Pis

Collepals.com Plagiarism Free Papers

Are you looking for custom essay writing service or even dissertation writing services? Just request for our write my paper service, and we'll match you with the best essay writer in your subject! With an exceptional team of professional academic experts in a wide range of subjects, we can guarantee you an unrivaled quality of custom-written papers.

Get ZERO PLAGIARISM, HUMAN WRITTEN ESSAYS

Why Hire Collepals.com writers to do your paper?

Quality- We are experienced and have access to ample research materials.

We write plagiarism Free Content

Confidential- We never share or sell your personal information to third parties.

Support-Chat with us today! We are always waiting to answer all your questions.