With the rise of bilinguals globally, extensive research has been conducted to understand how bilingualism affects cognitive functions differently from monolingualism, with significant implications for bilingual education, healthcare, and other fields. Specific to language processing, differences have been identified between second language (L2) speakers and monolinguals, particularly in contexts such as speech perception in noise and executive control. Despite the advances in this field of language processing, there remains a critical gap in understanding how bilinguals' phonological awareness of their first language (L1) and L2 influences their phonetic encoding and categorization. In this dissertation, I examine how various top-down and bottom-up factors modulate phonemic encoding in bilinguals, both behaviorally and neurophysiologically. The first chapter investigates how ambiguous audiovisual situations result in a default phonetic perception, providing a foundation for the second chapter. The second chapter explores how visual information influences the phonetic encoding of specific phonemes by Spanish-English bilinguals. Lastly, the third chapter addresses the influence of selective attention, lexicosemantic encoding, and low-level sound encoding on bilingual phonetic encoding, focusing on how bilinguals respond to phonemic restoration. This experiment is conducted using electroencephalography (EEG) to provide insights into the neurophysiological mechanisms underlying these processes. By integrating behavioral and neurophysiological approaches, this dissertation aims to uncover the complex mechanisms underlying phonetic encoding in bilinguals, contributing to a comprehensive understanding of bilingual cognitive processing and its broader implications. [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.]