abstract: Much evidence has shown that first language (L1) plays an important role in the formation of L2 phonological system during second language (L2) learning process. This combines with the fact that different L1s have distinct phonological patterns to indicate the diverse L2 speech learning outcomes for speakers from different L1 backgrounds. This dissertation hypothesizes that phonological distances between accented speech and speakers' L1 speech are also correlated with perceived accentedness, and the correlations are negative for some phonological properties. Moreover, contrastive phonological distinctions between L1s and L2 will manifest themselves in the accented speech produced by speaker from these L1s. To test the hypotheses, this study comes up with a computational model to analyze the accented speech properties in both segmental (short-term speech measurements on short-segment or phoneme level) and suprasegmental (long-term speech measurements on word, long-segment, or sentence level) feature space. The benefit of using a computational model is that it enables quantitative analysis of L1's effect on accent in terms of different phonological properties. The core parts of this computational model are feature extraction schemes to extract pronunciation and prosody representation of accented speech based on existing techniques in speech processing field. Correlation analysis on both segmental and suprasegmental feature space is conducted to look into the relationship between acoustic measurements related to L1s and perceived accentedness across several L1s. Multiple regression analysis is employed to investigate how the L1's effect impacts the perception of foreign accent, and how accented speech produced by speakers from different L1s behaves distinctly on segmental and suprasegmental feature spaces. Results unveil the potential application of the methodology in this study to provide quantitative analysis of accented speech, and extend current studies in L2 speech learning theory to large scale. Practically, this study further shows that the computational model proposed in this study can benefit automatic accentedness evaluation system by adding features related to speakers' L1s. / Dissertation/Thesis / Doctoral Dissertation Speech and Hearing Science 2018

Second language learners of English often experience difficulties in English lexical stress perception. This has traditionally been attributed to transfer of prosodic unit or settings from their first language (L1). Similarly, the problem of Chinese learners with English stress perception was assumed to arise from tonal transfer. However, little research has been devoted to the investigation of the phonetic details of second language (L2) stress perception. The present research focuses on the perception of English lexical stress by Chinese learners of English. The purpose of this study is to reveal the use of acoustic cues in stress perception by Chinese learners of English. In the experiment, F0, duration and intensity were manipulated, each with five steps, on three disyllabic nonsense words to result in a total of 375 nonsense tokens. A group of native speakers of English (NE) and a group of Chinese learners of English (CE) participated in the study and judged whether the stress was on the first or second syllable in the test stimuli. The responses of Chinese learners of English in stress judgment were compared against the baseline of native English speakers. The statistical tests of reliance measures and logistic regression models were used in data analysis. Results indicated that, similar to NE participants, performance by CE participants showed systematic variation as a result of the manipulation of the three acoustic cues. However, CEs were different from NEs in their reliance on the three cues. CE had significantly lower duration and intensity reliance scores but significantly higher F0 than NE. In logistic regression analysis, compared to the NE group, F0 contributed most to the CE models, while the contribution of duration and intensity was minimal. It is concluded from this study that while all three cues have significant effects on stress perception for native English speakers, only F0 has a decisive effect on stress judgments by Chinese learners of English. This study reveals that, rather than transfer of tone at the phonological level, there is transfer of reliance on F0 in the acquisition of L2 English stress. It is suggested that the investigation of phonetic details of learners’ problems with L2 stress acquisition is necessary for L2 speech learning theories and also for L2 stress teaching.