<p>The question of whether second languages (L2s) are best learned implicitly or explicitly has been a topic of much empirical discourse, with the majority of studies pointing to the benefits of explicit instruction when learning L2 grammar rules. However, given the focus on grammar, it is unclear how generalizable these findings are to other linguistic domains, such as L2 speech and L2 vocabulary. The previous focus on laboratory-based settings, and the language bias in the literature, also make it unclear how ecologically valid and applicable these findings are to the real world. To address these macro research questions, two experiments were carried out on English-speaking L2 learners of German.</p> <p>Experiment I (ExI) investigated the effects of implicit and explicit learning on the acquisition of Final Obstruent Devoicing and Dorsal Fricative Assimilation. The effect of the two learning conditions on L2 perception was also measured using a perceptual discrimination task and a perceptual identification task. Experiment II (ExII) investigated the effects of explicit historical instruction on the learning of English-German cognates, which were compared to the effects of a non-explicit learning condition. To examine whether declarative knowledge of relevant historical changes can aid in vocabulary learning, an explicit condition received instruction on the Second Germanic Sound Shift, Ingvæonic Palatalization, and relevant historical semantic changes. Both experiments followed a pre-/post-/delayed-post-test design.</p> <p>Results indicate that the two explicit conditions significantly outperformed the non-explicit conditions, suggesting that explicit learning and explicit instruction can be beneficial when learning L2 speech and L2 vocabulary. In ExI, acoustic analyses of learner speech samples indicate that the explicit condition was more successful in the learning of the two phonological rules. In ExII, the explicit condition was more successful in the identification and learning of cognates, suggesting that knowledge of language history, and instruction on applied historical linguistics, can be beneficial when learning a language that is historically related to a language that learners already speak. The results from this dissertation are discussed in the context of implicit and explicit learning and instruction, the role of attention, and the role of declarative knowledge, with concluding remarks pointing to the importance of metacognitive and metalinguistic awareness in adult or university-level language courses.</p>

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

(in English): The work in this diploma contains an analysis of speech accuracy and fluency of Russian speaking and English speaking students of Czech language, based on case studies. For these case studies two Russian speaking students and two English speaking students were chosen to take part. The results were compared to the results of one native Czech speaker. The accuracy and fluency analysis was carried out based on the language principles of Rod Ellis. Within the accuracy analysis, the number of error free clauses and the average number of mistakes per one hundred words were measured. Accuracy of speech is examined through concrete grammatical phenomena like the usage of reflexive particle se/si and the usage of the verb to be in the past tense. The work in this diploma also considers the ability of analysed speakers to switch between language codes and to distinguish features of formal and spoken Czech language (spoken language in informal situations). The fluency of speech is studied based on the speech rate of all analysed speakers by counting the number of syllables per one hundred words. Subsequently, the number of false starts, repetition of words or phrases, the frequency of usage of parasite words and hesitation sounds were also examined. One of the diploma hypothesis is the statement...