Abstract/Summary

With the aim of developing a more reliable understanding of the effects of task complexity and learner-internal factors on L2 performance, a 2 × 2 within-between participant study was designed to examine the effects intentional reasoning has on L2 performance, and whether learner language proficiency and working memory mediates these effects. Forty- eight learners of English performed two video-based narrative tasks of varying degrees of intentional reasoning, after taking Oxford Placement Test, Elicited Imitation Tasks and backward-digit span tasks. The results demonstrate that intentional reasoning had significant effects on complexity and accuracy, but no impact on fluency. Regression analyses indicated that proficiency and working memory reliably predicted accuracy across both task types. However, language proficiency and working memory contributed differentially to models predicting lexical complexity and speed fluency in the two task types, highlighting the interaction between task complexity and learner-internal factors. Keywords: second language speech performance, task complexity, intentional reasoning, language proficiency, working memory.