Finding the tipping point

Abstract Research suggests that the role of language aptitude and working memory in L2 learning is dependent on learners’ overall level of L2 proficiency—a construct typically operationalized in terms of categories. In the present study, we investigated the moderating role of proficiency operationalized as a continuous variable, with a view to identifying the precise tipping point at which the role of specific cognitive abilities changes from facilitative to neutral, or vice versa. L1 Croatian participants ( N = 83) completed the LLAMA aptitude test suite, a serial reaction time task, and measures of phonological and executive working memory, as well as outcome measures focusing on selected L2 English morphosyntactic structures: a self-paced reading task, oral elicited imitation, and gap-fill tests. L2 proficiency was operationalized as speaking skill in terms of complexity, accuracy, and fluency. Multilevel modeling confirmed the predictive power of explicit and implicit aptitude and working memory for L2 knowledge of the target structures. Proficiency was identified as a moderator: beneficial effects of explicit aptitude decreased significantly as proficiency increased, while the facilitative effects of implicit aptitude came to the fore, though nonsignificantly. Crucially, we identified the exact point on the proficiency continuum at which explicit aptitude loses its significant positive impact.