PROJECT SUMMARY / ABSTRACT Binaural hearing provides substantial benefits in complex listening environments, improving the ability to understand speech and providing the ability to localize sounds. However, in order to take advantage of binaural cues, sounds from the two ears need to be integrated (binaural integration). Binaural integration does not fully occur for some populations of listeners, such as cochlear implant (CI) users. Whether, and the degree to which, binaural integration occurs depends on two aspects of the acoustic signal. One aspect is the statistical similarity between the waveforms in the left and right ear (interaural correlation). The second is the symmetry in terms of the place of stimulation in the two ears (physical interaural symmetry). Our overarching hypothesis is that interaural correlation and interaural symmetry both play a role in binaural integration, with interaural correlation also driving adaptation, altering the functional interaural asymmetry to counter the effects of the physical interaural symmetry. The proposed study will manipulate the interaural correlation and interaural symmetry of the signal as well as the cochlear region to which the signals are delivered. These experiments will provide insight into both the functioning of the auditory system and the critical factors to consider when developing device programming techniques for bilateral CI users (Specific Aim 1). While adaptation, reducing the effects of physical interaural asymmetry, has been well documented for pitch-matching tasks, we hypothesize that interaurally correlated signals drive adaptation across the entire binaural auditory system, but the magnitude and/or time-course of the effects differ across different binaural cues. These experiments will provide critical insight into the relative importance of interaurally correlated and physically interaurally symmetric signals for driving adaptation. They will also provide critical guidance as to when it is crucial to address the common issue that bilateral CI users chronically receive interaurally correlated signals at interaurally asymmetric locations (Specific Aim 2). The proposed studies will provide fundamental insight in to how the binaural auditory system combines signals from the two ears. This research will also provide insight into the factors that will influence bilateral CI users’ binaural abilities, both directly after activation, and over time. This will lay the groundwork for a paradigm shift in terms of how and when clinicians program bilateral CI users’ devices to maximize binaural benefits.