Bidialectalism and Bilingualism: Exploring the Role of Language Similarity as a Link Between Linguistic Ability and Executive Control

Abstract

The notion of bilingual advantages in executive functions (EF) is based on the assumption that the demands posed by cross-language interference serve as EF training. These training effects should be more pronounced the more cross-language interference bilinguals have to overcome when managing their two languages. In the present study, we investigated the proposed link between linguistic and EF performance using the similarity between the two languages spoken since childhood as a proxy for different levels of cross-language interference. We assessed the effect of linearly increasing language dissimilarity on linguistic and EF performance in multiple tasks in four groups of young adults (aged 18-33): German monolinguals (n = 24), bidialectals (n = 25; German and Swiss German dialect), bilinguals speaking two languages of the same Indo-European ancestry (n = 24; e.g., German-English), or bilinguals speaking two languages of different ancestry (n = 24; e.g., German-Turkish). Bayesian linear-mixed effects modeling revealed substantial evidence for a linear effect of language similarity on linguistic accuracy, with better performance for participants with more similar languages and monolinguals. However, we did not obtain evidence for the presence of a similarity effect on EF performance. Furthermore, language experience did not modulate EF performance, even when testing the effect of continuous indicators of bilingualism (e.g., age of acquisition, proficiency, daily foreign language usage). These findings question the theoretical assumption that life-long experience in managing cross-language interference serves as EF training.

Keywords: bidialectalism; bilingualism; executive functions; language similarity; linguistic processing.

FIGURE 1

Distribution of the self-reported language variables in each group. (A,B) show age of acquisition and proficiency, respectively, in German, Swiss German, and the L2. (C) shows the total number of languages learned, whereas (D) shows the number of languages learned before the age of seven. Finally, (E) presents the daily percentage usage of languages other than German/Swiss German.

FIGURE 2

Graphical representation of the tasks administered. See text for details. CSI, cue-stimulus interval. (A,B) Linguistic tasks. (C,D) Inhibition tasks. (E) The figural and numerical versions of the shifting tasks. (F) The figural and numerical versions of the monitoring tasks. (G) The figural and numerical versions of the working memory (WM) tasks.

FIGURE 3

Task scores (z-transformed; solid dots) and model predictions (transparent dots and error bars) as a function of language group. Predictions are means (dot) and 95% HDI (error bars) of the posterior of the linear contrast over language similarity. Each panel (A–G) shows a different ability. Mono, monolinguals; Bidial, bidialectals; Biling, bilinguals; Sim, similar; Dissim, dissimilar; Lexic, lexical decision; Rec, recognition; Fluency, verbal fluency.

FIGURE 4

Posterior distribution of the slope of the language similarity effect for each cognitive ability. Each panel (A–G) shows the mean (dot) and the 95% HDI (bar underneath the curve) of the slope, and the proportion of the HDI that is below or above 0 (which represents the null).

FIGURE 5

Posterior distribution of the effect of the continuous bilingual predictors that yielded substantial evidence for the alternative hypothesis over the null. Each panel (A–E) shows the mean (dot) and the 95% HDI (bar underneath the curve) of the effect, and the proportion of the HDI that is below or above 0 (which represents the null). Note that the x-axis varies between panels. Figures of the posteriors of the effects of all continuous predictors on all assessed abilities can be found on the OSF.