The growth in globalization across traditional language boundaries suggests a need for efficient second language (L2) acquisition training regimens. One of the most significant challenges for adult language learners is learning to hear fine distinctions among non-native sounds not used in the native language; such learning may require decades of experience with the second language. A classic example is the difficulty native Japanese have learning English /r/ and /l/, a sound contrast not present in Japanese. With prior NSF support, Drs. Holt and Lotto have uncovered principles of auditory learning using controlled experiments with non-speech sounds and have used these principles to design optimal training regimens. This project uncovered how characteristics of training, feedback and presentation mode affected auditory learning. The present project will apply these findings to adult learning of non-native speech sounds, with the aim of producing more efficient L2 learning. One series of studies will investigate the benefits of video-game-based training (found to foster non-speech category learning) in learning non-native speech sounds. Another series of experiments will test whether manipulation of the variability of sound cues, found to be important in non-speech auditory learning in prior research, is effective in shifting the attention listeners give to these cues in second-language learning. Such shifts appear to be important for many cases of L2 learning, such as native Japanese speakers learning English /r/ and /l/. Beyond practical application in adult second language learning, the project has important theoretical implications for understanding human auditory perception and language processing. Such understanding is a prerequisite to developing rehabilitative techniques for disorders such as autism, dyslexia, central auditory processing disorder and specific language impairment.