Working memory and second language comprehension and production: a meta-analysis.

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.