Despite abundant evidence of malleability in speech production, previous studies of the effects of late second-language learning on first-language production have been limited to advanced learners. This dissertation examines these effects in novice learners, finding that experience in a second language rapidly, and possibly inexorably, affects production of the native language. In a longitudinal study of Korean acquisition, native English-speaking adult learners (n = 19) produced the same English words at weekly intervals over the course of intensive elementary Korean classes. Results of two acoustic case studies indicate that experience with Korean rapidly influences the production of English, and that the effect is one of assimilation to phonetic properties of Korean. In case study 1, experience with Korean stop types is found to influence the production of English stop types in terms of voice onset time (VOT) and/or fundamental frequency (f [subscript 0) onset as early as the second week of Korean classes, resulting in the lengthening of VOT in English voiceless stops (in approximation to the longer VOT of the perceptually similar Korean aspirated stops) and the raising of f[subscript 0] onset following English voiced and voiceless stops (in approximation to the higher f[subscript 0] levels of Korean). Similarly, in case study 2, experience with the Korean vowel space is found to have a significant effect on production of the English vowel space, resulting in a general raising of females' English vowels in approximation to the overall higher Korean vowel space. These rapid effects of second-language experience on first-language production suggest that cross-language linkages are established from the onset of second-language learning, that they occur at multiple levels, and that they are based not on orthographic equivalence, but on phonetic and/or phonological proximity between languages. The findings are discussed with respect to current notions of cross-linguistic similarity, exemplar models of phonology, and language teaching and research practices. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]