Publications

2016
Dunn EC, Busso DS, Raffeld MR, Smoller JW, Nelson CA, Doyle AE, & Luk G. Does developmental timing of exposure to child maltreatment predict memory performance in adulthood? Results from a large, population-based sample. Child Abuse & Neglect [Internet]. 2016. Publisher's Version
Pliatsikas, C., & Luk G. Executive control in bilinguals: A concise review on fMRI studies. Bilingualism: Language and Cognition. 2016;19 (4) :699-705.
Guerrero SL, Smith S, & Luk G. Home language usage and executive function in bilingual preschoolers. Cognitive Control and Consequences of Multilingualism [Internet]. 2016. Publisher's Version
Luk G, Christodoulou JA. Assessing and understanding the needs of dual-language learners. In: N. Lesaux & S. Jones. The Leading Edge of Early Childhood Education: Linking Science To Policy for A New Generation of Pre-K. Cambridge, MA: Harvard Education Press ; 2016. pp. 67-90.
Luk G, Pliatsikas C. Converging diversity to unity: Commentary on the neuroanatomy of bilingualism. Language, Cognition, & Neuroscience. 2016.
2015
Grady CL, Luk G, Craik FIM, Bialystok E. Brain network activity in monolingual and bilingual older adults. Neuropsychologia [Internet]. 2015;66 :170-181. Publisher's VersionAbstract

Bilingual older adults typically have better performance on tasks of executive control (EC) than do their monolingual peers, but differences in brain activity due to language experience are not well understood. Based on studies showing a relation between the dynamic range of brain network activity and performance on EC tasks, we hypothesized that life-long bilingual older adults would show increased functional connectivity relative to monolinguals in networks related to EC. We assessed intrinsic functional connectivity and modulation of activity in task vs. fixation periods in two brain networks that are active when EC is engaged, the frontoparietal control network (FPC) and the salience network (SLN). We also examined the default mode network (DMN), which influences behavior through reduced activity during tasks. We found stronger intrinsic functional connectivity in the FPC and DMN in bilinguals than in monolinguals. Although there were no group differences in the modulation of activity across tasks and fixation, bilinguals showed stronger correlations than monolinguals between intrinsic connectivity in the FPC and task-related increases of activity in prefrontal and parietal regions. This bilingual difference in network connectivity suggests that language experience begun in childhood and continued throughout adulthood influences brain networks in ways that may provide benefits in later life.

Dunn EC, Busso DS, Raffeld MR, Smoller JW, Nelson CA, Doyle AE, Luk G. Does developmental timing of exposure to child maltreatment predict memory performance in adulthood? Results from a large, population-based sample. Child Abuse & Neglect. 2015.Abstract

Although maltreatment is a known risk factor for multiple adverse outcomes across the lifespan, its effects on cognitive development, especially memory, are poorly understood. Using data from a large, nationally representative sample of young adults (Add Health), we examined the effects of physical and sexual abuse on working and short-term memory in adulthood. We examined the association between exposure to maltreatment as well as its timing of first onset after adjusting for covariates. Of our sample, 16.50% of respondents were exposed to physical abuse and 4.36% to sexual abuse by age 17. An analysis comparing unexposed respondents to those exposed to physical or sexual abuse did not yield any significant differences in adult memory performance. However, two developmental time periods emerged as important for shaping memory following exposure to sexual abuse, but in opposite ways. Relative to non-exposed respondents, those exposed to sexual abuse during early childhood (ages 3-5), had better number recall and those first exposed during adolescence (ages 14-17) had worse number recall. However, other variables, including socioeconomic status, played a larger role (than maltreatment) on working and short-term memory. We conclude that a simple examination of "exposed" versus "unexposed" respondents may obscure potentially important within-group differences that are revealed by examining the effects of age at onset to maltreatment.

Olsen RK, Pangelinan MM, Bogulski C, Chakravarty MM, Luk G, Grady CL, Bialystock E. The effect of lifelong bilingualism on regional grey and white matter volume. Brain Research. 2015;1612 :128-139.Abstract

Lifelong bilingualism is associated with the delayed diagnosis of dementia, suggesting bilingual experience is relevant to brain health in aging. While the effects of bilingualism on cognitive functions across the lifespan are well documented, less is known about the neural substrates underlying differential behaviour. It is clear that bilingualism affects brain regions that mediate language abilities and that these regions are at least partially overlapping with those that exhibit age-related decline. Moreover, the behavioural advantages observed in bilingualism are generally found in executive function performance, suggesting that the frontal lobes may also be sensitive to bilingualism, which exhibit volume reductions with age. The current study investigated structural differences in the brain of lifelong bilingual older adults (n=14, mean age=70.4) compared with older monolinguals (n=14, mean age=70.6). We employed two analytic approaches: 1) we examined global differences in grey and white matter volumes; and, 2) we examined local differences in volume and cortical thickness of specific regions of interest previously implicated in bilingual/monolingual comparisons (temporal pole) or in aging (entorhinal cortex and hippocampus). We expected bilinguals would exhibit greater volume of the frontal lobe and temporal lobe (grey and white matter), given the importance of these regions in executive and language functions, respectively. We further hypothesized that regions in the medial temporal lobe, which demonstrate early changes in aging and exhibit neural pathology in dementia, would be more preserved in the bilingual group. As predicted, bilinguals exhibit greater frontal lobe white matter compared with monolinguals. Moreover, increasing age was related to decreasing temporal pole cortical thickness in the monolingual group, but no such relationship was observed for bilinguals. Finally, Stroop task performance was positively correlated with frontal lobe white matter, emphasizing the importance of preserved white matter in maintaining executive function in aging. These results underscore previous findings implicating an association between bilingualism and preserved frontal and temporal lobe function in aging.

Pollack C, Luk G, Christodoulou JA. A meta-analysis of functional reading systems in typically developing and struggling readers across different alphabetic languages. Frontiers in psychology [Internet]. 2015;6. Publisher's VersionAbstract

Functional neuroimaging research has identified multiple brain regions supporting reading-related activity in typical and atypical readers across different alphabetic languages. Previous meta-analyses performed on these functional magnetic resonance imaging findings typically report significant between-group contrasts comparing typical readers and readers with reading difficulty or a clinical diagnosis of developmental dyslexia. In order to advance our understanding of cross-linguistic convergence of reading-related brain activations for these reader groups, analyses using activation likelihood estimation were carried out separately for typical and atypical readers who ranged from children to adults. Contrasts were analyzed for tasks involving rhyming or reading of letter or word stimuli presented visually in English, Dutch, Italian, German, French, or Norwegian. Typical readers showed reliable activation in only left lateralized regions, including the inferior frontal area, precentral area and middle temporal gyrus. Atypical readers also showed activation in the left inferior frontal area and precentral region, in addition to significant activations in the right hemisphere, including the superior, medial and inferior frontal regions, lingual gyrus and the inferior occipital area. These results distinguish between typical and atypical reader group activations, showing common and distinct regions of activation when engaged in reading-related activities, extending previous meta-analyses on identifying brain regions relevant to reading to include cross-linguistic analyses for alphabetic scripts. Results support the universality of a signature pattern of brain activation in developmental dyslexia across alphabetic languages.

Friesen DC, Luo L, Luk G, Bialystok E. Proficiency and control in verbal fluency performance across the lifespan for monolinguals and bilinguals. Language, cognition and neuroscience. 2015;30 (3) :238-250.Abstract

The verbal fluency task is a widely used neuropsychological test of word retrieval efficiency. Both category fluency (e.g., list animals) and letter fluency (e.g., list words that begin with F) place demands on semantic memory and executive control functions. However, letter fluency places greater demands on executive control than on category fluency, making this task well suited to investigating potential bilingual advantages in word retrieval. Here we report analyses on the category and letter fluency for bilinguals and monolinguals at four ages, namely, 7-year-olds, 10-year-olds, young adults and older adults. Three main findings emerged: (1) verbal fluency performance improved from childhood to young adulthood and remained relatively stable in late adulthood; (2) beginning at 10-year-olds, the executive control requirements for letter fluency were less effortful for bilinguals than monolinguals, with a robust bilingual advantage on this task emerging in adulthood and (3) an interaction among factors showed that category fluency performance was influenced by both age and vocabulary knowledge, but letter fluency performance was influenced by bilingual status.

Luk G. Who are the bilinguals (and monolinguals)?. Bilingualism: Language and Cognition. 2015;18 :35-36.Abstract

In the keynote article, “Bilingualism and Cognition”, Valian (2014) has reviewed current research on comparing executive function (EF) in monolingual and bilingual individuals across the lifespan. The conclusion is that there are inconsistent EF advantages from bilingualism and all other cognitive challenging activities primarily because individual differences in these cognitive challenging experiences may collectively attribute to superior EF resulting in inconsistent EF benefit attributable to a single experience. In essence, variability in study participants’ experience and tasks contributes to the inconsistency in the behavioral outcomes observed in monolinguals and bilinguals. Notably, Valian suggests that monolinguals may also engage in other cognitively challenging activities, which have not been accounted for in individual studies, thereby resulting in improved EF similar in magnitude to that related to bilingual experience. Although it was not specified which cognitively challenging activity is more likely to be engaged by monolinguals more than by bilinguals, the question at heart is: is there an EF advantage that can be specifically attributed to bilingual experience? The review addressed in the keynote demonstrates seemingly inconsistent patterns of results. In this commentary, I would like to suggest that, in addition to task measurements, individual bilingual experience is dynamic and multifaceted. Moreover, bilingual experience varies in different communities. Consequently, one potential source of explanation for the inconsistent results in between-group EF performances is the characteristics of the bilinguals (and monolinguals) and their social environments included in these studies.

2013
Luk G, Bialystock E. Bilingualism is not a categorical variable: Interaction between language proficiency and usage. Journal of Cognitive Psychology. 2013;25 (5) :605-621.Abstract

Bilingual experience is dynamic and poses a challenge for researchers to develop instruments that capture its relevant dimensions. The present study examined responses from a questionnaire administered to 110 heterogeneous bilingual young adults. These questions concern participants' language use, acquisition history, and self-reported proficiency. The questionnaire responses and performances on standardised English proficiency measures were analysed using factor analysis. In order to retain a realistic representation of bilingual experience, the factors were allowed to correlate with each other in the analysis. Two correlating factors were extracted, representing daily bilingual usage and English proficiency. These two factors were also related to self-rated proficiency in English and non-English language. Results were interpreted as supporting the notion that bilingual experience is composed of multiple related dimensions that will need to be considered in assessments of the consequences of bilingualism.

Pollack C, Christodoulou JA, Luk G. Meta-analysis of functional reading systems in readers with and without dyslexia in different languages. Journal of Cognitive Neuroscience. 2013 :231.
2012
Luk G. Bialystock, Ellen. In: The Encyclopedia of Applied Linguistics. Wiley Online Library ; 2012.Abstract

Ellen Bialystok (1948– ) is a Distinguished Research Professor in the Department of Psychology at York University, Toronto, Canada. She has bridged studies of language and cognition through her investigation of bilingualism. Her pioneering interdisciplinary research examines the cognitive consequences of bilingualism both in linguistic and nonlinguistic domains across the lifespan. Most notably, Professor Bialystok has reported a bilingual advantage in tasks assessing executive function, which is a set of skills that are necessary for planning, cognitive flexibility, suppressing distracting information, and selectively attending to relevant information. These research findings have significant implications for education, linguistics, cognitive science, psychology, and neurology.

Bialystok E, Craik FIM, Luk G. Bilingualism: Consequences for mind and brain. Trends in Cognitive Sciences. 2012;16 :240-250.Abstract

Building on earlier evidence showing a beneficial effect of bilingualism on children's cognitive development, we review recent studies using both behavioral and neuroimaging methods to examine the effects of bilingualism on cognition in adulthood and explore possible mechanisms for these effects. This research shows that bilingualism 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.

Luk G, Green DW, Abutalebi J, Grady CL. Cognitive control for language switching in bilinguals: A quantitative meta-analysis of functional neuroimaging studies. Language and Cognitive Processes. 2012;27 (10) :1479-1488.Abstract

In a quantitative meta-analysis, using the activation likelihood estimation method, we examined the neural regions involved in bilingual cognitive control, particularly when engaging in switching between languages. The purpose of this study was to evaluate the bilingual cognitive control model originally proposed as a qualitative analysis of functional neuroimaging studies. After reviewing 128 peer-reviewed articles, 10 neuroimaging studies met our inclusion criteria and in each study, bilinguals switched between languages in response to cues. We isolated regions involved in voluntary language switching, by including reported contrasts between the switching conditions and high-level baseline conditions involving similar tasks but requiring the use of only one language. Eight brain regions showed significant and reliable activation: left inferior frontal gyrus, left middle temporal gyrus, left middle frontal gyrus, right precentral gyrus, right superior temporal gyrus, midline pre-supplementary motor area, and bilateral caudate nuclei. This quantitative result is consistent with bilingual aphasia studies that report switching deficits associated with lesions to the caudate nuclei or prefrontal cortex. It also extends the previously reported qualitative model. We discuss the implications of the findings for accounts of bilingual cognitive control.

Bialystok E, Luk G. Receptive vocabulary differences in monolingual and bilingual adults. Bilingualism: Language and Cognition. 2012;15 :397-401.Abstract

English receptive vocabulary scores from 797 monolingual and 808 bilingual participants between the ages of 17 and 89 years old were aggregated from 20 studies to compare standard scores across language groups. The distribution of scores was unimodal for both groups but the mean score was significantly different, with monolinguals obtaining higher standard scores than bilinguals. Consistent with previous research, older adults had higher vocabulary scores than younger adults. The results are discussed in terms of the implications for theoretical conceptions of linguistic processing and clinical diagnosis in bilingual populations.

2011
Luk G, Anderson JAE, Craik FIM, Grady CL, Bialystok E. Distinct neural correlates for two types of inhibition in bilinguals: Response inhibition versus interference suppression. Brain and Cognition. 2011;74 :347-357.Abstract

To examine the effects of bilingualism on cognitive control, we studied monolingual and bilingual young adults performing a flanker task with functional MRI. The trial types of primary interest for this report were incongruent and no-go trials, representing interference suppression and response inhibition, respectively. Response times were similar between groups. Brain data were analyzed using partial least squares (PLS) to identify brain regions where activity covaried across conditions. Monolinguals and bilinguals activated different sets of brain regions for congruent and incongruent trials, but showed activation in the same regions for no-go trials. During the incongruent trials, monolinguals activated the left temporal pole and left superior parietal regions. In contrast, an extensive network including bilateral frontal, temporal and subcortical regions was active in bilinguals during the incongruent trials and in both groups for the no-go trials. Correlations between brain activity and reaction time difference relative to neutral trials revealed that monolinguals and bilinguals showed increased activation in different brain regions to achieve less interference from incongruent flankers. Results indicate that bilingualism selectively affects neural correlates for suppressing interference, but not response inhibition. Moreover, the neural correlates associated with more efficient suppression of interference were different in bilinguals than in monolinguals, suggesting a bilingual-specific network for cognitive control.

Luk G, Bialystok E. Language representation and cognitive control in bilinguals: An insight for cross-linguistic dyslexic research, in Dyslexia across languages: Orthography and the brain-gene-behavior link. Baltimore, MD: Brookes Publishing ; 2011.
Luk G, Bialystok E, Craik FIM, Grady CL. Lifelong bilingualism maintains white matter integrity in older adults. Journal of Neuroscience. 2011;31 :16808-16813.Abstract

Previous research has shown that bilingual speakers have higher levels of cognitive control than comparable monolinguals, especially at older ages. The present study investigates a possible neural correlate of this behavioral effect. Given that white matter (WM) integrity decreases with age in adulthood, we tested the hypothesis that bilingualism is associated with maintenance of WM in older people. Using diffusion tensor imaging, we found higher WM integrity in older people who were lifelong bilinguals than in monolinguals. This maintained integrity was measured by fractional anisotropy (FA) and was found in the corpus callosum extending to the superior and inferior longitudinal fasciculi. We also hypothesized that stronger WM connections would be associated with more widely distributed patterns of functional connectivity in bilinguals. We tested this by assessing the resting-state functional connectivity of frontal lobe regions adjacent to WM areas with group differences in FA. Bilinguals showed stronger anterior to posterior functional connectivity compared to monolinguals. These results are the first evidence that maintained WM integrity is related to lifelong naturally occurring experience; the resulting enhanced structural and functional connectivity may provide a neural basis for “brain reserve.”

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