Since the lifting of martial law in 1987, the rapid liberalization and democratization of Taiwan has led to the transformation of its political structure from a single-party system to a full-fledged two-party system. Along with this political opposition are the two contrastive concepts, the North and the South. Located in this background, this dissertation focuses on two groups of Taichung people ("Taizhong" "central Taiwan") in two different sociopolitical contexts. One group resides in Taichung, their home region, and the other group migrates to Taipei, the capital located in northern Taiwan. Taichung is chosen because it serves as the main city on the north-to-south corridor and its speakers are known for their distinctive variety of Mandarin. This dissertation examines linguistic behavior and ideologies of speakers who stay in their home region versus speakers who migrate from one dialect area to another. Employing the methodology of sociolinguistic variation studies, coupled with qualitative analyses, this study specifically examines two salient dialectal features of Taichung Mandarin: (1) the realization of T4, the high-falling tone, as T1, the level tone, and (2) the substitution of lateral [l] for retroflex approximant [r\']. Qualitative analyses of speakers' social identities, attitudes, ideologies and language practices complement quantitative analyses of patterns of phonological variation. The study finds that the migrant group does make changes in their linguistic production upon constant exposure to a new dialect. Furthermore, the result suggests that speakers' linguistic behavior is significantly linked with their social networks, identities, language attitudes and ideologies, and the broader sociopolitical context of contemporary Taiwan. An interesting finding emerges after the examination of how linguistic behavior is conditioned by internal linguistic constraints and external factors such as gender, age, political affiliation, and occupation. The analysis of the data suggests that external factors play a more important role in the substitution of [l] for [r], whereas internal constraints precede external factors in the realization of T4 as T1. I argue that different status and social meanings of the two linguistic variables explain how they pattern in each residence group and how they trigger or fail to trigger accommodation by speakers migrating to Taipei. Issues examined in this dissertation add to our understanding of voice (identities, attitudes and ideologies) in the border that is generally unheard and unresearched when the contesting ideologies between the north and the south are so dramatic. Additionally, this dissertation provides a detailed understanding of how different linguistic resources (varieties of Mandarin, Taiwanese, and codeswitching to Taiwanese or English from Mandarin) are associated with different social meanings and how speakers use the resources to construct their identities. Finally, combining quantitative rigor and qualitative methods, this dissertation contributes to a broader understanding of identity and language use since the complexity of language use cannot be understood within one single analysis. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]