With the widespread use of portable digital devices, especially smartphones, learning a new language has become a popular trend in the age of globalization. Amongst mobile-assistant language-learning applications, Duolingo is widely used and employs persuasive design techniques to inspire and encourage users to acquire new linguistic skills. Several papers have been studied based on this application by exploring pedagogical issues and discussing the misuse of gamification design. From a holistic perspective, limited research exists on how Duolingo's persuasive design motivates and engages language learners. The study utilized a walkthrough and a focus group alongside semi-structured interviews with 11 Duolingo users to investigate how persuasive design elements are employed to engage users. The findings of this study suggest that the gamification design in Duolingo is enjoyable and enhances users’ motivation; streaks make users commit to their learning plan; rewards encourage users to learn constantly; notifications play a significant role as triggers for learning behavior to occur; notifications also remind users to return to the application after a suspension. Moreover, it is important to design notifications with both the attitude and content in mind, as they have the power to affect user experience.

本論文は第二言語話者の発話を高精度で認識するための音素セットの構成方法に関する研究結果を述べている．本論文では，第二言語話者の発話をネイティブ話者の発話とは異なる音響特徴量の頻度分布を持つ情報源とみなし，これを表現する適切な音素セットを構築する手法を提案している．具体的には，対象とする第二言語と母語との調音位置や調音様式などの類似性に加え，同音異義語の発生による単語識別性能の低下を総合した基準に基づき，最適な音素セットを決定する．提案手法を日本人学生の英語発話の音声認識に適用し，種々の条件下で認識精度の向上を検証した． / This dissertation focuses on the problem caused by confused mispronunciation to improve the recognition performance of second language speech. A novel method considering integrated acoustic and linguistic features is proposed to derive a reduced phoneme set for L2 speech recognition. The customized phoneme set is created with a phonetic decision tree (PDT)-based top-down sequential splitting method that utilizes the phonological knowledge between L1 and L2. The dissertation verifies the efficacy of the proposed method for Japanese English and shows that the feasibility of building a speech recognizer with the proposed method is able to alleviate the problem caused by confused mispronunciation by second language speakers. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University