Mixed languages like Media Lengua incorporate grammar from one source language (here, Quichua) but lexicon from another (here, Spanish). Due to their linguistic profile, they provide a unique window into bilingual language usage and language representation. Drawing on sociolinguistic, structural and psycholinguistic perspectives, the current dissertation examines syntactic processes in Media Lengua on the basis of word order variation in order to gain a deeper understanding of the representations of grammar and lexicon in the bilingual mind. In particular, I investigate whether Media Lengua's syntactic processes have been impacted by Spanish, the language that supplies Media Lengua's lexical items. Data from a corpus, from within and between-language structural priming and from a language switching task suggest that Media Lengua is robustly framed by Quichua morphosyntax. The corpus analysis revealed that different word order patterns correspond to discourse-related factors such as persistence of the object referent and its animacy rather than factors directly related to language contact with Spanish. The structural priming analysis showed that, even when participants have the chance to repeat a prime practically verbatim, it was only the inclusion of the primed Spanish verb in responses that significantly led to the incorporation of primed Spanish word order; in all other cases, participants default to the Quichua patrimonial word order. Lastly, data from a language switching task provided evidence that Media Lengua and Quichua employ identical morphosyntactic frames while the co-activation of (head-final) Media Lengua and (head-initial) Spanish morphosyntactic frames led to competition and increased language switching costs. In sum, the results establish Media Lengua as a separate language with clearly defined and robust structural and lexical characteristics and suggest that Media Lengua's lexical items are not identical to their Spanish cognate counterparts -- a finding that challenges the widely held view that contact-induced languages are likely to show effects of convergence with the European language that provided their lexical material. These considerations refine our theories of how languages interact and are represented in the minds of bilinguals, particularly in the presence of large numbers of form-similar lexical items. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]