GSE Scholarly Articles

Recent years have seen a surge in research comparing bilinguals to monolinguals, yet synthesizing this literature is complicated by the diversity of language and social backgrounds behind these dichotomous labels. The current study examines the labels and descriptions reported in 186 studies comparing bilinguals and monolinguals published between 2005-2015 in order to understand how bilingualism has been operationalized and describe the degree to which different facets of bilingual experience are reported. Proficiency and usage were the most frequently reported features (77% and 79%), followed by language history (67%) and the language of schooling (60%). However, less than half of the studies measured proficiency objectively or reported proportional usage, and even less - 30% - described the sociolinguistic context from which the sample was drawn. Given the increase in language contact due to globalization, more transparent and comprehensive reporting of participant characteristics is critical to building our understanding of how bilingualism affects experience.

The investigation of bilingualism and cognition has been enriched by recent developments in functional magnetic resonance imaging (fMRI). Extending how bilingual experience shapes cognition, this review examines recent fMRI studies adopting executive control tasks with minimal or no linguistic demands. Across a range of studies with divergent ages and language pairs spoken by bilinguals, brain regions supporting executive control significantly overlap with brain regions recruited for language control (Abutalebi & Green, this issue). Furthermore, limited but emerging studies on resting-state networks are addressed, which suggest more coherent spatially distributed functional connectivity in bilinguals. Given the dynamic nature of bilingual experience, it is essential to consider both task-related functional networks (externally-driven engagement), and resting-state networks, such as default mode network (internal control). Both types of networks are important elements of bilingual language control, which relies on domain-general executive control.

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.

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 category fluency, making this task well-suited to investigating potential bilingual advantages in word retrieval. Here we report analyses on 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-years-old, 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; 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.

Ninety-six participants, who were younger (20 years) or older (68 years) adults and either monolingual or bilingual, completed tasks assessing working memory, lexical retrieval, and executive control. Younger participants performed most of the tasks better than older participants, confirming the effect of aging on these processes. The effect of language group was different for each type of task: Monolinguals and bilinguals performed similarly on working memory tasks, monolinguals performed better on lexical retrieval tasks, and bilinguals performed better on executive control tasks, with some evidence for larger language group differences in older participants on the executive control tasks. These results replicate findings from individual studies obtained using only 1 type of task and different participants. The confirmation of this pattern in the same participants is discussed in terms of a suggested explanation of how the need to manage 2 language systems leads to these different outcomes for cognitive and linguistic functions.

We report the results of two studies investigating lexical access in bilinguals. In Study 1,monolinguals performed better than bilinguals on tests of naming and letter fluency, but not on category fluency. When vocabulary size was considered, most of the effects disappeared or were reduced. In Study 2, a larger group of bilinguals was studied to compare the effect of vocabulary size,and a more restrictive version of the letter fluency task was used to increase executive processing involvement. In this case, bilinguals with matched vocabulary scores outperformed monolinguals on letter fluency, and bilinguals with lower vocabulary scores performed at the same level as monolinguals. The results are discussed in terms of the contributions of vocabulary size and executive control to performance on lexical retrieval tasks.

We use a time-course analysis to examine the roles of vocabulary size and executive control in bilinguals’ verbal fluency performance. Two groups of bilinguals and a group of monolingual adults were tested in English with verbal fluency subtests from the Delis– Kaplan Executive Function System. The two bilingual groups were equivalent in their self-rated English proficiency but differed in levels of receptive and expressive vocabulary. We hypothesized that the difference between the two bilingual groups in vocabulary and between the monolingual and bilingual groups in executive control would lead to differences in performance on the category and letter fluency tests and dissociate the roles of vocabulary knowledge and executive control in verbal production. Bilinguals and monolinguals performed equivalently in category fluency, but the high-vocabulary bilingual group outperformed both monolinguals and low-vocabulary bilinguals in letter fluency. An analysis of the retrieval time-course functions in letter fluency showed dissociable effects of resources available at the initiation of the trial, considered to reflect vocabulary size, and ability to monitor and retrieve new items using a novel phonemic-based word searching strategy, considered to reflect executive control. The difference in slope of the best-fitting curves reflected enhanced executive control for both bilingual groups compared to monolinguals, whereas the difference in the starting point of the logarithmic functions reflected higher levels of vocabulary for high-vocabulary bilinguals and monolinguals compared to low-vocabulary bilinguals. The results are discussed in terms of the contributions of linguistic resources and executive control to verbal performance.

Four groups of children in first grade were compared on early literacy tasks. Children in three of the groups were bilingual, each group representing a different combination of language and writing system, and children in the fourth group were monolingual speakers of English. All the bilingual children used both languages daily and were learning to read in both languages. The children solved decoding and phonological awareness tasks, and the bilinguals completed all tasks in both languages. Initial differences between the groups in factors that contribute to early literacy were controlled in an analysis of covariance, and the results showed a general increment in reading ability for all the bilingual children but a larger advantage for children learning two alphabetic systems. Similarly, bilinguals transferred literacy skills across languages only when both languages were written in the same system. Therefore, the extent of the bilingual facilitation for early reading depends on the relation between the two languages and writing systems.

Two hundred and four 5- and 6-year-olds who were monolingual English-, bilingual English–Chinese-, or Chinese-speaking children beginning to learn English (2nd-language learners) were compared on phonological awareness and word decoding tasks in English and Chinese. Phonological awareness developed in response to language exposure and instruction but, once established, transferred across languages for both bilinguals and 2nd-language learners. In contrast, decoding ability developed separately for each language as a function of proficiency and instruction in that language and did not transfer to the other language. Therefore, there was no overall effect of bilingualism on learning to read: Performance depended on the structure of the language, proficiency in that language, and instructional experiences with that writing system. These results point to the importance of evaluating the features of the languages and instructional context in which children become biliterate.