This dissertation investigated how a bilingual's experiences can affect how their first language pronunciation can differ from monolingual speakers of their two languages. We used a methodology incorporating quantitative phonetic measurements of voice onset time and vowel formants, grammar and vocabulary tests, and qualitative measures of language attitudes and background of a single subject. This protocol of inquiry is also an attempt to develop new research designs/methodologies as recommended by Flege to provide sufficient single-speaker data, and novel ways to interpret data to investigate the SLM-r. In this case, our subject moved from Peru to the United States at the age of 10. She abruptly switched from using Spanish at school and with friends to using English, and slowly started using more English at home. Some of her Spanish consonants remain strongly Spanish-like, even shifting quality as though to keep her English and Spanish distinct. Her English consonants were between Spanish and English monolinguals. Her vowels each behaved differently. The study also examines how her attitudes about language use and the language use choice manifestations of her language identity correlate with her production data. [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.]