Linguistic Approaches to Bilingualism - Volume 6, Issue 5, 2016

Studies on the effect of bilingualism on executive functioning have sometimes failed to find significant differences between performance of monolingual and bilingual young adults. This paper examines the interpretation of these null findings and considers the role of three factors: definition of bilingualism, appropriateness of statistical procedures and interpretations, and the range of data considered. The conclusion is that a correct interpretation of this important issue will require careful consideration of all the data and scrupulous attention to design details.

Executive functions (EFs), such as response inhibition, interference control, and set shifting, are general-purpose control mechanisms that enable individuals to regulate their thoughts and behaviors. Because bilingual individuals use EF-like processes during language control, researchers have become interested in the hypothesis that this use might train EFs, resulting in better performance on non-linguistic EF tasks. Although this bilingual advantage hypothesis seems straightforward to test, it involves a number of important decisions in terms of how to assess bilingualism and EFs. In this article, I focus on the complexity of measuring EFs, drawing on individual differences research (conducted with participants not selected for bilingualism). Specifically, I discuss issues related to (1) the measurement of EFs (particularly the effects of task impurity and unreliability) and (2) the multicomponent nature of EFs. Within each of these topics, I elaborate on consequences for research on bilingual advantages and provide some recommendations.

I begin with some personal history that illuminates my background and my interest in the questions posed in this article’s title (What cognitive processes are likely to be exercised by bilingualism and does this exercise lead to extra-linguistic cognitive benefits?). A brief overview of historical interest in these questions follows, with emphasis on the landmark study by Peel and Lambert (1962) and the seminal ideas in Bialystok’s (2001) book: Bilingualism in Development: Language, Literacy and Cognition. Three cognitive processes (monitoring, selection mediated by inhibition, and switching) are likely to be “exercised” in the bilingual mind and, especially, in the bilingual context. Yet, despite a few early studies that reported evidence for bilingual advantages in these cognitive processes, the thorough empirical reviews presented here and in previous papers by Hilchey ( Hilchey & Klein, 2011 ; Hilchey, Saint-Aubin & Klein, 2015 ) and others, suggest that there are no extra-linguistic cognitive benefits of multi-lingual mastery.

Three important issues bear on understanding the connection between bilingualism and executive function. The first is the absence of a fine-grained task analysis for executive functions and other cognitive processes. The second is the absence of a theory of the cognitive mechanisms underlying the deployment of two or more languages and thus the absence of a solid basis on which to make predictions about what domain-general performances, if any, bilinguals should excel in. The third is the relation between neural and behavioral consequences of bilingualism. These three issues must be taken in account in trying to understand the variability among findings showing benefits of bilingualism for executive function.

While findings on the bilingual advantage in adults are mixed, the data from children are more consistent but still show variations. A number of factors influence the outcomes, such as individual bilingual characteristics, variations in target functions, and differences in task type. Our goal is to demonstrate that there is a complex relationship among these variables and that the outcomes of executive function (EF) studies depend on the interactions among these factors. Performance on EF is influenced by children's language proficiency, language use, age, socioeconomic status, and culture. These individual features show different interactions with different executive components. Bilingual and monolingual children differ in some EFs but not in others. Variations in tasks and other measurement issues further increase the differences in the results. We may better understand the nature of the bilingual advantage in children if we combine aspects of developmental science and language processing with hypotheses about bilingualism.

Recent studies of bilingualism as a protective factor in cognitive aging have reported conflicting findings, and researchers have begun to explore the methodological complications that may explain differences across studies. This article details the current research landscape and addresses several issues relevant to the study of bilingualism and late-life cognitive function: study design, establishing causal relationships, confounding factors, operationalizing bilingualism, predicting cognitive level versus cognitive change, and incorporating brain structural variables to interrogate cognitive reserve.

This study attempts to tease apart a variety of factors that may contribute to performance on executive function tasks. Data from the Simon task is re-examined to determine the contributions of age, SES, language proficiency/vocabulary, general cognitive performance, and bilingualism on performance. The results suggest influence from a variety of factors, with a major contribution from relative age and from language proficiency, as measured by vocabulary. Bilingualism showed some effect in relation to older adults’ accuracy of performance, in both congruent and incongruent conditions, but not to reaction time.

Bilingualism is reported to re-structure executive control networks, but it remains unknown which aspects of the bilingual experience cause this modulation. This study explores the impact of three code-switching types on executive functions: (1) alternation, (2) insertion, and (3) dense code-switching or congruent lexicalisation. Current models hypothesise that different code-switching types challenge different aspects of the executive system because they vary in the extent and scope of language separation. Two groups of German-English bilinguals differing in dense code-switching frequency participated in a flanker task under conditions varying in degree of trial-mixing and resulting demands to conflict-monitoring. Bilinguals engaging in more dense code-switching showed inhibitory advantages in the condition requiring most conflict-monitoring. Moreover, dense code-switching frequency correlated positively with monitoring skills. This suggests that dense code-switching is a key experience shaping bilinguals’ executive functioning and highlights the importance of controlling for participants’ code-switching habits in bilingualism research.

Recent research has shown that the bilingual experience has positive effects on non-linguistic cognition ( Bialystok 2009 ; Costa and Sebastian-Gallés 2014 ) but also negative effects on language, for example on vocabulary size and lexical fluency ( Pearson et al. 1993 ). While most of the linguistic ‘disadvantages’ of bilingualism have been discussed in the lexical domain, this question is scaled up here to the sentence level and a novel theoretical framework is proposed which explicitly connects psychological and linguistic research. It is suggested that the bilingual experience may (a) affect the reciprocal interactions between language and general cognition, and (b) modulate the relation between components of executive functions. These effects may in turn influence the processing of particular linguistic structures, such as anaphoric expressions, and lead to bilingual-monolingual differences that could be regarded as ‘disadvantages’ but are in fact the result of normal adaptive changes due to the bilingual experience. Future experimental research validating this proposal may benefit both linguistic models of anaphora resolution and psychological models of cognitive control in monolinguals and bilinguals.

In this article we discuss methods for investigating grammatical processing in bilinguals. We will present a methodological approach that relies on: (i) linguistic theory (in our case, morphology) for the construction of experimental materials; (ii) a design that allows for direct (within-experiment, within-participant, and within-item) comparisons of the critical conditions; and (iii) data analysis techniques that make both linear and non-linear gradient effects visible. We review recent studies of masked morphological priming in bilinguals in which the application of these methodological principles revealed highly selective interactions of age of acquisition (and the native/non-native contrast) with the linguistic distinction between inflection and derivation. We believe that such considerations are not only relevant for grammatical processing experiments, but also for studying bilingualism, and its potential cognitive advantages, more generally.

Literature on bilingualism and cognition is characterised by a large amount of conflicting evidence. In some studies, bilinguals perform better then monolinguals on executive tasks involving inhibition, monitoring and switching but are slower on tasks of lexical processing. Other studies don’t find any significant effects and challenge the very existence of cognitive differences between monolinguals and bilinguals. In this paper I question the assumption that different studies performed in different parts of the world should yield the same results. I argue that the environment (in the widest sense of the word) in which an experiment is conducted can exert profound influence on its outcome. Against the background of the current debate about the replication crisis in science, I propose that conflicting evidence is not a threat to the trustworthiness of scientific research but a sign of the health of a discipline and a welcome opportunity to identify new relevant variables.