本研究通过对比应用语言学和计量语言学词汇指标，基于大规模学习者语料库考察口语表现的任务复杂度效应。结果表明，前者只在词汇密度和词汇复杂度上体现显著影响，而后者在词汇变化性、词汇密度、词汇复杂度方面都能测量任务复杂度效应且能捕捉语言产出的细微变化；相较于应用语言学指标，计量指标呈现非线性变化趋势，更贴合人类语言的复杂动态变化特征。本研究表明数据驱动的计量语言学方法可拓展二语习得领域核心问题的研究。

Based on a large learner corpus, this study aims to make a comparison between lexical measures in applied linguistics and those in quantitative linguistics to investigate the effects of task complexity on linguistic complexity in Chinese English-as-a-foreign-language learners’ oral texts. The results show that measures in applied linguistics reflect task complexity effects on learners’ oral performance only in the dimensions of lexical density and lexical sophistication, while quantitative metrics can measure task complexity effects in all three dimensions of lexical variation, lexical density and lexical sophistication, and capture the nuanced changes in tasks with varying degrees of complexity. Compared with measures in applied linguistics, the changes of quantitative measures display non-linear tendencies, which embodies the complex and dynamic changes of human language. The study demonstrates that the data-driven quantitative linguistic method can extend the research on core issues in second language acquisition.