Research on language learners' attention suggests that manipulating attention is beneficial in the language learning process as it facilitates the "noticing" of specific linguistic aspects. The current study investigated the effects of directing learners' attention to segments and prosody in English phonetic training. Korean learners of English as a Foreign Language (EFL) were divided into two groups: one received segment-oriented training focusing on coda voicing contrasts, and the other received prosody-oriented training focusing on low vs. high attachments in relative clauses. The results showed that both groups successfully acquired segmental contrasts, with no significant difference between the two groups, suggesting that segmental learning can occur through automatic processes without explicit attentional focus. However, the prosody-oriented group demonstrated significant improvement in prosodic contrasts, including pause duration, mean pitch, and mean intensity, which were maintained in retention tests. In contrast, the segment-oriented group did not show significant improvement in prosodic contrasts. The study also highlighted the critical role of cognitive factors, particularly attention and executive function, in prosodic perception. While cognitive characteristics did not significantly affect segmental perception, the Flanker test results positively influenced prosodic perception accuracy, emphasizing the importance of selective attention and inhibitory control in processing prosodic features. These findings underscore the necessity of explicit attentional focus and targeted training for acquiring prosodic contrasts in production. Prosodic contrasts require higher-level attentional processes and explicit focus to be effectively learned, whereas segmental contrasts rely more on automatic detection and less on such attentional processes. This research contributes to a deeper understanding of the mechanisms underlying L2 learning and informs more effective pedagogical strategies for language educators. [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.]