Investigation of factors behind foreign accent in the L2 acquisition of Japanese lexical pitch accent by adult English speakers
The productions of adult second language (L2) learners are often detected as having a foreign accent by native speakers of the target language. However, there is no clear answer for what kind of problems contribute to L2 learners’ foreign accent. This thesis aims to investigate potential factors behind foreign accent. We intend to achieve this goal by examining cross-linguistic empirical evidence of the L2 acquisition of Japanese lexical pitch accent by English learners. L2 prosody has been found to significantly influence native speakers’ auditory impression of foreign accent. L2 prosody also allows us to test crosslinguistic differences in the function of the key acoustic correlates of L2 contrasts. In this thesis we examine F0, which signals both lexical pitch accent and phrasal distinctions in Japanese, but which signals only phrasal distinctions, not lexical distinctions, in English. For adult L2 learners to achieve target-like productions, the literature suggests that three abilities are the key factors: 1) learners’ ability to differentiate the acoustic correlate of the target L2 contrasts, 2) ability to articulate the acoustic correlate of the target L2 contrasts and 3) ability to categorize the target L2 contrasts. This thesis evaluates all three of these potential factors. The main contribution of this thesis is to provide a comprehensive view of foreign accent, by investigating possible interactions between the factors and by examining the different abilities of the same learners. Another contribution is to provide empirical evidence for the nature of learners’ problems with foreign accent during L2 acquisition, by testing two groups of English learners of Japanese (experienced and inexperienced) in comparison with Japanese native speakers. The first experiment used intelligibility scores and overall F0 patterns to quantify the degree of foreign accent in the learners’ productions of Japanese lexical pitch accent. The second experiment showed that the learners’ ability to differentiate F0 contours in a nonspeech context was equal to that of the native speakers. The third experiment showed that the learners’ ability to articulate the F0 contours in a non-speech context differed from that of the native speakers. The fourth experiment showed that although learners were able to hear the phonetic differences between the target L2 contrasts, due to poor formation of the target L2 categories and poor lexical assignment ability, the inexperienced learners seem to have greater difficulty than experienced learners both in categorizing boundary items into the target L2 categories and in assigning the L2 categories to lexical items. Overall, the foreign accent of adult L2 learners’ productions is explained through a combination of articulation and categorization factors. Importantly, this cross-sectional study has indicated how learners’ problems with foreign accent change as they gain L2 experience. Whereas experienced learners seem to have problems mainly in the articulation and phonetic realization of the L2 contrasts, the inexperienced learners seem to have mainly problems in phonetic and lexical-phonological representations of the target L2 categories in addition to articulation and phonetic realization. This study offers both theoretical insights for the field of L2 speech acquisition research and also practical insights for the L2 classroom.