Brain plasticity and phonetic training for English-as-a-second-language learners

English as a second language (ESL) education has gained an increasingly important role in career development in science, business, and industry on the global stage. One great challenge for adult ESL learners is to reduce or eliminate "foreign accent" in their English pronunciation. Decades of behavioral and brain research have shown that language experience early in life leaves an indelible mark on speech perception and production. There is converging evidence for a selfreinforcing bonding process in the brain in the course of largely implicit learning, leading to a system that is neurally committed to the articulatory, acoustic, and perceptual properties of sounds and sound patterns in the first language. As a consequence, it is often difficult for adults to learn the speech sounds in a second language that do not conform to the phonology of the first language. This chapter examines the underlying causes for the foreign accent problem in second language learning and discusses the approaches to promote brain plasticity through phonetic training. The first section provides a summary of the main research findings to illustrate the role of phonetic knowledge in language learning, the neural mechanisms of speech perception, and the relationship between perception and production. The second section outlines a theoretical framework of brain plasticity for phonetic learning, featuring quantifiable measures to test relevant hypotheses about second language acquisition in terms of neural sensitivity, neural efficiency, neural specificity, and neural connectivity and their behavioral correlates.The third section introduces a synergistic Speech Assessment and Training (SAT) software program, to overcome first-language interference. The chapter concludes with a discussion of the implications for second-language education and future research.