論 文 審 査 の 要 旨

博士の専攻分野の名称

博 士 （ 学 術 ）学位授与の要件

学位規則第４条第①・２項該当

氏名

Yajie Li論 文 題 目
Exploring the Role of Vocabulary in Writing: Predicting Lexical Diversity Scores, Differentiating
Writing Proficiency, and Investigating Vocabulary Knowledge Development Over Time
論文審査担当者
論文審査担当者
准教授

Jon Clenton

印

審査委員

教授

Carolin Funck

印

審査委員

教授

Itaru Nagasaka

印

審査委員

教授

Katsumi Iwasaki

印

審査委員

教授

Simon Fraser

印

審査委員

准教授

Noriko Yamane

印

審査委員

准教授

Masahiro Shinya

印

主査〔論文審査の要旨〕
This dissertation investigates the role of vocabulary knowledge in L2 writing: the extent to which
vocabulary knowledge scores can predict vocabulary use in writing activities for participants withdifferent proficiency levels; how vocabulary knowledge scores can distinguish participant writingscores; and to what extent vocabulary knowledge scores and written production can track acquired
vocabulary knowledge. To explore these questions, four experiments (three cross-sectional and one
longitudinal) and a range of vocabulary tasks were conducted.
The dissertation begins by distinguishing between receptive and productive vocabulary knowledge.
Receptive vocabulary knowledge requires participants to understand the form and meaning of words,
and productive vocabulary knowledge demands participants to produce words. Vocabulary tasks areused as effective tools to test participants’ vocabulary knowledge. Lexical diversity measures offer analternative tool for exploring the variety of different words used in written texts or spoken production.
By using lexical diversity measurements, it is possible to estimate vocabulary knowledge in writing use,writing competence, and overall language proficiency levels.
The first experimental chapter partially replicates Treffers-Daller et al. (2018) and explores potential
relationships between vocabulary tasks and L2 written production for participants at the Common
European Framework of Reference (CEFR) A2 level (Council of Europe, 2001). It examines whether
vocabulary scores can predict participants’ vocabulary in writing use with 29 L1 Chinese participants.
Participants responded to four vocabulary knowledge tasks and one IELTS writing topic. The tasks usedwere Lex30, a task based on word association; G_Lex, a single-word gap-fill task; the ProductiveVocabulary Levels Test (the PVLT), a sentence completion task; and the Vocabulary Levels Test (theVLT), a form-meaning matching task assessing receptive vocabulary knowledge.
The second experimental chapter focuses on productive vocabulary knowledge tasks and investigates
potential relationships between productive vocabulary tasks and L2 written production for participants at
CEFR levels B1 to C1. This experiment examines 91 L1 Japanese participants with higher proficiency
levels than in the first study chapter.
The third experimental chapter examines how productive vocabulary tasks can differentiate between
IELTS writing scores. 63 L1 Japanese speakers and 35 L1 French speakers took part in this experiment.
Qualified IELTS raters marked all the writing samples based on the IELTS writing rubric.
The fourth experimental chapter explores how productive vocabulary knowledge task scores and lexical
diversity measure scores relate over a short study period. It investigates whether participants’ vocabularyknowledge and lexical diversity scores improve through a pre- and post-test design over a short-term
intervention (approximately 12 weeks). Participants from a single language background (L1 Japaneseparticipants, N=51) with similar proficiency levels took part in the experiment.
The findings from the four experimental chapters raise several key issues to discuss and explore further:i) disparities in accessing vocabulary knowledge used in written production, as evidenced by vocabularyknowledge measures (vocabulary knowledge measures differ in task features and task embeddedness);(ii) measuring vocabulary knowledge can differentiate levels of proficiency in IELTS writing; (iii)selecting appropriate measures of lexical diversity depends on the specific research question or goal, asdifferent measures may have different strengths and limitations. Earlier (simple) lexical diversity
measure scores show stronger significant correlations with vocabulary knowledge scores in writing use,
whereas more recently devised (sophisticated) lexical diversity measures show better performance intracking vocabulary knowledge development in written production; (iv) G_Lex shows greater power intracking vocabulary knowledge improvement than the PVLT and Lex30; and, (v) using online flashcards
learning with 2K NGSL lemma-based word lists offers an effective means to improve vocabularyknowledge and vocabulary in writing use.
The dissertation concludes by highlighting issues regarding the dynamic relationship between
vocabulary knowledge and written production to support future research. The findings’ implications are
significant for L2 writing class and vocabulary knowledge assessment.
Published papers connected to the thesis include two peer-reviewed journal articles. The experimental
findings reported in the thesis have received significant praise from lead researchers in the vocabulary
field.
As a result of the above examination, the author of this thesis is found to be fully qualified to be awarded
the degree of "Doctor of Philosophy”.