This study explores the conceptual system of adult Korean learners of English with three different levels of exposure to a second language (L2) cultural background. Assuming that different exposure to an L2 socio-cultural backgrounds plays a significant role in modifying a learner's conceptual system that operates both an L1 as well as an L2 channel, this study examines the influence of L2 cultural background knowledge on (previously developed) L1-based conceptual knowledge of lexical items in production. The cross-cultural difference of lexical-conceptual knowledge is characterized by the lexical items (pairs of L1-L2 lexical items) existing in both in their first language (L1) and in L2 language but that differing at the conceptual and the socio-cultural load. Participants consisted of two baseline groups of subjects monolingual in Korean (N=29) and United States English (N=30), and three experimental (i.e. comparison) groups of Korean-English bilingual subjects (N=85). The latter were organized as follows depending on their level of L2 exposure: Korean learners of English living in the U.S. for at least two years (KESL), Korean learners of English living in Korea (KEFL), and Korean heritage speakers in the U.S. (H). In the concept-elicitation task, learners' spontaneous production of conceptual knowledge such as thoughts, images, contexts, and feelings were compared with those of monolingual speakers in order to track their conceptual development, assumed to move along the L1-L2 continuum. As an additional task, they were asked to rewrite an L2 story in L1 to see whether and how L2 learners' modified conceptual system affect the use of L1 lexical items when switching from L2 to L1. This task reflects the extent to which conceptual knowledge is modified according to the level of L2 cultural exposure such that L2 learners either make a conceptual switch or lexical switch when they have to move from L2 to L1. The findings of the study showed that L2 learners with long-term exposure to an L2 sociocultural background differed from learners with less or no exposure quantitatively and qualitatively. For example, KESL learners not only produced more L2-based conceptual knowledge than KEFL learners, but they also shared more L2-based qualitative features. In the L1-L2 conceptual knowledge comparison, both learner groups produced more L1-based than L2-based contexts. Specifically, KESL learners were further than KEFL learners from L1-based qualitative features. Although the heritage group produced mixed results, they showed more proximity to L2-based conceptual knowledge, which distinguished them from learner groups. The statistical results also showed that the heritage group was significantly different from the learner groups in terms of the conceptual knowledge underlying their lexical items. In the task of rewriting an L2 story in the L1, similar results were also observed, indicating the different effects of levels of cultural exposure on the conceptual system, which was reflected in the learners' conceptual production and L1 lexical use. Despite long exposure to L2 socio-cultural exposure, certain L1-based concepts were maintained, which means that learners were reluctant to develop L2 conceptual knowledge. In contrast, there were certain L2 concepts that were easily subject to change. [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.]