The Lexical Development In L2 Writing In A Theme-Based Course:A Case Study

Theme-Based Instruction(TBI)is a type of Content-Based Instruction(CBI),a continuum ranging from total immersion to language classes with frequent use of content for language practice(Met,1999).This dissertation reports an attempt to investigate the lexical development in L2 writing in a Theme-Based(TB)course by identifying the mechanisms of lexical retrieval in the writing process and depicting the effectiveness of TB activities on lexical developmental process.Data were collected from the written products,interviews and learning diaries obtained from four tertiary-level English learners who participated in a four-month TB course.Many studies have proved the influence of TBI on language learning and content understanding,but most existing literature on TBI is result-oriented.The question how specific learning activities in TB courses have afifected language learning and use remains largely unanswered.Therefore,the purpose of this dissertation is to reveal the proeess of lexical learning and development in TB courses.It addresses two issues:mechanisms of lexical retrieval in L2 writing and the influence of the TB activities on lexical noticing,processing,retrieval and application.Mechanisms of retrieving lexical units during the writing process were investigated.The mechanisis,being categorized according to whether the lexical unit was completely or partially retrieved,were divided into:(1)complete retrieval of lexical units encountered during the TB course and(2)partial retrieval of lexical units encountered during the TB course.The effectiveness of the TB activities on lexical development in L2 writing was discussed based on the dynamic cycle of language learning and use proposed by Ellis(2008)and the mechanisms of lexical problem solving proposed by Xu(2011).The study yielded the following findings:The learners applied different mechanisms of lexical retrieval during the writing process based on the lexical knowledge they had obtained through the activities in the TB course including reading,presentation,discussion and writing.The mechanisms of lexical retrieval were categorized into "complete retrieval of lexical units encountered during the TB course" and "partial retrieval of lexical units encountered during the TB course." The learners employed the mechanisms of "direct use of memorized units,""upgrading-repair" and "repetition-avoidance" when they fully processed and learned the target units in TB activities.Different mechanisms such as“borrowing,""dictionary-reference" and "reduction" were applied when the learners obtained partial knowledge of the target units in the TB course and had to make further efforts before the units were used in their L2 writings.The four participants showed differences in individual preferences when applying the mechanisms of lexical retrieval during the writing process.Two participants were more dependent on the lexical units that had been memorized.Memorization helped them in gaining confidence in lexical retrieval and use.The third participant favored the strategies of "upgrading-repair" and"repetition-avoidance" compared with the other three participants.In order to express her intention accurately,she made efforts to search for more appropriate lexical units after the appearance of the first candidate.The application of these two mechanisms contributed to her consistent ascending of TB lexical variation in the ten writing tasks.The fourth participant was more dictionary-dependent in contrast to his peers in this study.The development of lexical units was found to be related to the TB activities in the course.To adapt to the developmental paths of lexical units in L2 writing,the dynamic cycle of Ellis(2008)was modified in this study to yield the following path of lexical learning:(1)noticing leading to lexical processing;(2)lexical processing leading to retrieval;and(3)retrieval leading to application.A hypothesized model was proposed to display the developmental paths of lexical units and to illustrate the effectiveness of TB activities.Four major paths were revealed in the model.(1)Noticing?Processing?complete retrieval?application,(2)Noticing?processing?partial retrieval?application,(3)Noticing?processing?partial retrieval?processing?application and(4)Noticing?processing?partial retrieval?reduction?application.The study has some theoretical and pedagogical implications.First,it proposes a hypothesized model of lexical development thus enriching the understanding of the process of lexical development in L2 writing and specifying the paths of lexical development.Second,it investigates the effectiveness of TB activities on language development so as to reveal the counterbalance between the learning of "themes" and the development of "language." Pedagogically,it helped L2 teachers guide their students to learn vocabulary through activities and helped students produce lexical units effectively in the writing process.