Project Summary/Abstract The proportion of bilingual speakers in the United States is increasing and the majority of the world's population is bilingual or multilingual, yet most accounts of human cognition are based on monolingualism. The proposed research uses bilingualism as a means to study general principles underlying human language, cognition, and the brain, as well as an end in itself to understand how the rapidly growing bilingual segment of the population processes language and performs on cognitive tasks. The objective of the proposed research is to examine the relationship between language interaction and higher order cognition in bilinguals and to study the consequences of language co-activation for memory (Aim 1), decision making (Aim 2), and semantic organization (Aim 3). The approach relies on interdisciplinary methods that include eye-tracking, EEG, advanced multilevel statistical modeling, and cognitive and linguistic testing of Spanish-English bilinguals (the largest bilingual population in the U.S.) and Korean-English bilinguals (to dissociate effects of phonology and orthography). Our previous research has shown that bilinguals co-activate both languages in parallel during language comprehension. Studies 1-3 aim to uncover how co-activation of the two languages during visual search influences later memory for previously-seen target and competitor items. Studies 4-6 focus on the influence of bilingualism and language co-activation on decision making. Studies 7-9 examine how experience with two interacting languages changes the organization of the semantic network. Within each Aim, the first experiment establishes the key phenomenon, the second takes a fine-grained look at the underlying mechanisms, and the third tests the generalizability of the main effect under more stringent conditions. The proposed research is innovative in linking language co-activation and higher order cognition in bilinguals and in looking at how online sensory and linguistic processing of auditory and visual input impacts what bilinguals subsequently remember, how they make decisions, and how they represent knowledge. The proposed studies are theoretically significant by providing insight into the relationship between language and higher order cognition from the unique vantage point of bilingualism and by contributing to understanding how experience with multiple languages reconfigures cognitive architecture. Addressing broader societal needs, this work has applied significance for the large segment of the population speaking more than one language, for whom clinical, educational, and social outcomes can be improved by developing interventions that capitalize on the interaction between the two languages -- for example, to improve memory in individuals who experience memory decline (including older adults), to optimize decision making (including in healthcare settings), and to promote learning and semantic development across the lifespan. Public health ...