Preprint manuscript, data files, and complete analytic code for: Li, J. J., Ayala, S., Harel, D., Shiller, D., & McAllister, T. (In press). Individual predictors of response to biofeedback training for second-language production. Published in *Journal of the Acoustical Society of America*. doi: https://doi.org/10.1121/1.5139423 **Abstract**: While recent research suggests that visual biofeedback can facilitate speech production training in clinical populations and L2 learners, individual learners’ responsiveness to biofeedback is highly variable. This study investigated the hypothesis that the type of biofeedback provided, visual-acoustic versus ultrasound, could interact with individuals’ acuity in auditory and somatosensory domains. Specifically, it was hypothesized that learners with lower acuity in a sensory domain would show greater learning in response to biofeedback targeting that domain. Production variability and phonological awareness were also investigated as predictors. 60 female native speakers of English received 30 minutes of training, randomly assigned to feature visual-acoustic or ultrasound biofeedback, for each of two Mandarin vowels. On average, participants showed a moderate magnitude of improvement (decrease in Euclidean Distance from a native-speaker target) across both vowels and biofeedback conditions. The hypothesis of an interaction between sensory acuity and biofeedback type was not supported, but phonological awareness and production variability were predictive of learning gains, consistent with previous research. Specifically, high phonological awareness and low production variability post-training were associated with better outcomes, although these effects were mediated by vowel target. This line of research could have implications for personalized learning in both L2 pedagogy and clinical practice.