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L2 proficiency, age of L2 acquisition, and working memory: Evidence from Mandarin–English bilingual students

Xiaoxuan Li, Early career researcher at University of Oxford - Department of Education

Working memory (WM) is a limited-capacity mechanism that temporarily stores information in the mind and manipulates it when it is no longer perceptually present (Cowan, 2008). WM abilities have been associated with many significant facets of daily living, ranging from academic success to language learning. In the area of bilingualism, bilingual speakers have been observed to be cognitively superior to monolinguals in terms of cognitive flexibility, inhibition and WM (see for example Bialystok et al., 2006). To control both languages effectively, bilinguals constantly process the language they are focusing on while disregarding the non-target language that is also active in their minds. This intentional and controlled cognitive effort required for language management finally results in bilingual advantages in working memory.

The linguistic automatisation hypothesis (Vejnovic et al., 2010) proposes that individuals who master a second language have better working memory. Higher second language (L2) proficiency allows for more processing automatisation in that language, which lowers the costs associated with cognitive processing. Ullman (2015) suggested that due to bilinguals’ increased L2 automatisation, L2 experts employ procedural memory (that is, unconscious memory to automatically execute cognitive and motor skills), which is also used by native speakers; while L2 beginners depend on declarative memory (that is, conscious memory to intentionally collect concepts and factual information). As a consequence of this processing efficiency, fewer cognitive resources are employed while a larger proportion of the cognitive resources become accessible, which might lead adept L2 speakers to exhibit superior WM performance. Moreover, WM performance is related to the length of bilingual experience measured by the age of L2 acquisition. Early bilinguals experience a longer and more rigorous quantity of practice managing the two languages compared with late bilinguals (Kovelman et al., 2008). As a result, this longer-lasting experience with dual language management leads to better WM skills.

My study investigated the correlation between L2 proficiency, age of L2 acquisition, and working memory performance. Sixty-one Mandarin–English bilinguals studying at UK and Chinese universities were recruited. Linguistic questionnaires were used to collect participants’ demographics and prior language experience. Meanwhile, digit span and reading span tasks were conducted to measure participants’ WM skills. The digit span was a non-verbal task in which participants were required to recall the sequence of digits in both forward (such as 1, 2, 3, 4) and backward (such as 4, 3, 2, 1) orders. On the other hand, the reading span was a more complex task, where participants were instructed to recall letters while simultaneously evaluating sentence accuracy. Results revealed that participants’ performance in forward digit span and backward digit span were positively correlated with each other. In addition, increased L2 proficiency correlated with increased accuracy in reading span performance, while earlier age of L2 acquisition was associated with better performance in both backward digit and reading span tasks.

‘Increased second-language (L2) proficiency correlated with increased accuracy in reading span performance, while earlier age of L2 acquisition was associated with better performance in both backward digit and reading span tasks.’

As language learners with higher L2 proficiency are associated with better working memory capacities, the finding facilitates students’ learning processes across all subjects to achieve a better learning outcome. For instance, a language teacher can employ various teaching methods to enhance students’ WM capacities, including repetition, chunking and visualisation. Consequently, vocabulary and grammatical rules may be better retained and remembered, which ultimately improves language proficiency. Moreover, providing opportunities for students to use their L2 skills in real-life settings might further help them become more proficient in L2 and develop their WM abilities. Parents can encourage their children to learn a second language at an early age, as it may have positive effects on working memory and cognitive abilities. It is also useful for educators and policymakers to design language programmes that prioritise early language learning.


Bialystok, E., Craik, F. I., & Ruocco, A. C. (2006). Dual-modality monitoring in a classification task: The effects of bilingualism and ageing. Quarterly Journal of Experimental Psychology, 59(11), 1968–1983.

Cowan, N. (2008). What are the differences between long-term, short-term, and working memory?. Progress in Brain Research, 169, 323–338. 

Kovelman, I., Baker, S. A., & Petitto, L. A. (2008). Age of first bilingual language exposure as a new window into bilingual reading development. Bilingualism: Language and Cognition, 11(2), 203–223.

Ullman, M. T. (2015). The declarative/procedural model: A neurobiologically motivated theory of first and second language. In B. VanPatten & J. Williams (Eds), Theories in second language acquisition (pp. 147–172). Routledge.

Vejnović, D., Milin, P., & Zdravković, S. (2010). Effects of proficiency and age of language acquisition on working memory performance in bilinguals. Psihologija, 43(3), 219–232.