CAREER: The role of the cortico-striatal system in implicit sound category learning

Language learning starts with learning the sounds of that language (e.g., telling the difference between the sounds of /bear/ and /pear/ in English). Within the first year of life, infants readily pick up the speech sounds of their native language. However, learning new speech sounds is much more difficult in adulthood even after long-term training with explicit instruction and performance feedback. Recent studies have shown that adults can learn new sound categories implicitly—without consciously trying or realizing it—by relying on the brain’s reward system. This project focuses on how to better leverage this implicit learning system to enhance adults’ ability to learn new sounds and how this process is implemented in the brain. This work may inform classroom-based language instruction and improve language learning methods for adults, while also providing broader insights into understanding brain plasticity in adulthood. In addition to the scientific work, the project also includes student training and outreach in local schools, language classes, and science centers. These efforts give students hands-on experience in communicating science to the community. In detail, this project tests the hypothesis that the rhythmic presentation of new sound categories enhances learning by engaging the implicit, reward-based cortico-striatal learning system. Specifically, this project tests whether rhythmic presentations generate temporal predictions and trigger reward signals, which play a key role in inducing brain plasticity for learning across the brain regions connected within the implicit learning circuit. The project uses a combination of well-controlled behavioral tasks, electroencephalography (EEG), magnetic resonance imaging (MRI), and noninvasive brain stimulation to obtain converging evidence across several experiments that test the role of rhythmic presentation in enhancing sound category learning. By investigating learning of both speech and non-speech sounds, the overall goal is to develop a neurobiological model of implicit learning for sound categories and better understand how to promote neuroplasticity in the mature brain. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.