DESCRIPTION (provided by applicant): Sound localization is a fundamental auditory ability that is important for safety and for connecting a person to his/her environment. Further, the separate localization of target and interfering sources of sound facilitates better attention to, detection of, and recognition of the source of interest. Due to a phenomenon known as the precedence effect, good sound localization abilities are preserved even when typical room reflections are present that would otherwise be expected to severely disrupt localization. The first of two specific aims of this research is to advance the scientific knowledge of the precedence effect in order to uncover the multiple and currently mysterious mechanisms that underlie it. The project will employ newly developed stimulus conditions as well as physiological experiments in animal models to better understand how spatial hearing is maintained in the face of acoustic reflections. The second aim is to apply this new knowledge to a large but understudied population of listeners with unequal hearing loss in the two ears. The asymmetric inputs these listeners receive present challenges for sound localization. Studies of both objective performance and listener self- report show that these individuals have difficulty in situations where integration across the two ears would normally be of benefit. However, the choices available for people with unbalanced hearing vary widely and the ability to help them through evidence-based clinical decision-making is not nearly sufficient. This project will be the first to investigate the multiple aspects of the precedence effect in listeners with hearing threshold asymmetries, and will not only document the major issues they face, but also discover the bases of these problems through detailed evaluation of the processing of individual localization cues. The results will lead to a better scientific understanding of the extent to whic listeners with asymmetric hearing thresholds cope with their unbalanced hearing, ultimately leading to better-informed professional management of asymmetric hearing loss.