Although working memory (WM) figures centrally in many theories of second language (L2) proficiency development and processing, some have argued that the importance of WM is overstated (e.g., Juffs, Transactions of the Philological Society, 102, 199-225, 2004). Despite many studies over the past two decades, the literature lacks a quantitative synthesis of the extant results. In this article, we report a meta-analysis of data from 79 samples involving 3,707 participants providing 748 effect sizes. The results indicate that WM is positively associated with both L2 processing and proficiency outcomes, with an estimated population effect size (ρ) of .255. In additional analyses, we assessed whether the WM-criterion relationship was modulated by potential covariates identified in the literature search (i.e., participant characteristics, WM measure features, criterion measure factors, and publication status). The results of the covariate analyses indicated larger effect sizes for the executive control (vs. storage) component of WM, and for verbal (vs. nonverbal) measures of WM. Minimal publication bias was detected, suggesting that WM has a robust, positive relationship with L2 outcomes. We discuss the implications of these results for models of WM and theories of L2 processing and L2 proficiency development.

Adults are notoriously poor second-language (L2) learners. A context that enables successful L2 acquisition is language immersion. In this study, we investigated the effects of immersion learning for a group of university students studying abroad in Spain. Our interest was in the effect of immersion on the native language (L1), English. We tested the hypothesis that immersion benefits L2 learning as a result of attenuated influence of the L1. Participants were English-speaking learners of Spanish who were either immersed in Spanish while living in Spain or exposed to Spanish in the classroom only. Performance on both comprehension and production tasks showed that immersed learners outperformed their classroom counterparts with respect to L2 proficiency. However, the results also revealed that immersed learners had reduced L1 access. The pattern of data is most consistent with the interpretation that the L1 was inhibited while the learners were immersed.

Few adult second language (L2) learners successfully attain high‐level proficiency. Although decades of research on beginning to intermediate stages of L2 learning have identified a number of predictors of the rate of acquisition, little research has examined factors relevant to predicting very high levels of L2 proficiency. The current study, conducted in the United States, was designed to examine potential cognitive predictors of successful learning to advanced proficiency levels. Participants were adults with varying degrees of success in L2 learning, including a critical group with high proficiency as indicated by standardized language proficiency tests and on‐the‐job language use. Results from a series of group discrimination analyses indicate that high‐level attainment was related to working memory (including phonological short‐term memory and task set switching), associative learning, and implicit learning. We consider the implications for the construct of high‐level language aptitude and identify future directions for aptitude research.

This study investigated the role of domain-general inhibitory control in trilingual speech production. Taking an individual differences approach, we examined the relationship between performance on a non-linguistic measure of inhibitory control (the Simon task) and a multilingual language switching task for a group of fifty-six native English (L1) speakers learning French (L2) and Spanish (L3). Better inhibitory control was related to reduced switch costs, but only when switching into or out of the more dominant L1, where inhibitory control has been theorized to be most important (Green, 1998). The results provide evidence of a direct link between inhibitory control abilities and language switching capabilities, and suggest constraints on the conditions under which a domain-general inhibitory control mechanism supports language switching.