根據自我決定理論，本研究調查自主性對於台灣大學生在英文單字學習活動的動機及參與度之影響。從問卷和教室觀察發現，可自由選擇目標單字的學生比不能自由選擇目標單字的學生表現出較高的動機和參與度，但學生對英文的整體學習態度並未受到自主性提供與否而改變。另外，本研究也描述了學生在進行為期十四週的單字學習活動時學習動機和活動參與度的波動變化。研究結果顯示提供自主性的單字學習活動可提高學習動機。

The current study investigates EFL college learners’ motivation and engagement during English vocabulary learning tasks. By adopting self-determination theory (SDT; Deci & Ryan, 1985, 2000), the study looked into the impact of autonomy on college students’ task motivation and engagement with vocabulary learning tasks and their general English learning motivation (i.e. trait motivation). Changes in task motivation over 14 weeks of research were also investigated. The results of quantitative analyses obtained from questionnaires and observations over 14 weeks uncovered that the participants who were given the freedom to choose their own target words showed higher task motivation and task engagement than those who were required to learn pre-selected target words. Learners’ general attitude toward English learning, however, was not influenced by the provision of choice in the vocabulary learning tasks. The 14-week experimental research also depicts the changes of task motivation and engagement over time. Even with the same settings and task procedures, learners’ task motivation fluctuated. In accordance with SDT, the findings in the present study support the importance of creating autonomy-supportive vocabulary learning tasks.