Abstract
Frequency effects have been proposed by language researchers recently. This study aims to investigate the effects of task frequency on lexical richness of L2 writing. 20 subjects involved in the study were randomly assigned into two equal-size groups (an experimental group and a control group), to conduct a five-week study. Each group was required to write an argumentative essay at the beginning and the end of the study respectively (pretest and posttest). Between these two tests, the experimental group took three additional writing practice tasks. Analysis of data collected shows that both groups were at the same level in lexical richness on the pretest. On the posttest, however, statistically significant differences were found between the two groups in both lexical sophistication measured by academic word ratio and lexical variation measured by standardized type-token ratio. The results of this study confirmed that task frequency in writing could improve the lexical richness of students’ L2 writing.
Keywords   task frequency   lexical sophistication   lexical variation  L2 writing

近年来，频次作用（Frequency Effects）对语言学习的影响开始重新受到学者们的重视。本研究旨在讨论练习频率对二语写作中词汇丰富性（词汇复杂性和词汇多样性）的影响。本研究中的20名受试者被随机分为实验组和控制组，每组10人，在为期5周的时间内分别在实验初期进行前测，实验末期进行后测。其中，实验组在前后测之间还进行三次写作任务。研究结果显示，两组在前测时处于同一水平；而在后测时，两组在词汇复杂性和词汇多样性上均具有显著性差异。本研究的结果说明了写作练习频率对二语写作中词汇丰富性有着积极影响。
关键词  练习频率   词汇复杂度   词汇多样性   二语写作

Since the 21st century, some tremendous changes have been taken place in the field of second language acquisition. The theory that man’s knowledge of language is innate has gradually faded out-of-sight. Instead, some usage-based theories, such as frequency effects and connectionism, have been proposed by researchers.