Minimally traumatic surgical techniques and atraumatic electrodes have led to an increasing number of individuals with preserved acoustic hearing in the implanted ear allowing for combined electric and acoustic stimulation (EAS). Although we have learned a great deal about cochlear implantation with hearing preservation over the past decade and the associated benefit for speech understanding and spatial hearing, there is much to be learned about the integration of combined EAS. In fact, despite the increasing incidence of hearing preservation, we have little empirical understanding about factors driving this benefit and the clinical management of cochlear implant (CI) recipients with binaural acoustic hearing. The latter point is one of critical importance given that all three FDA approved CI systems promote atraumatic electrodes for hearing preservation and each has integrated hearing aid (HA) circuitry within the implant sound processor. This proposal aims to provide the first dataset explaining the basic underlying mechanisms responsible for EAS benefit. This is important for us to understand the way in which the auditory system is able to integrate information from two very distinctive modalities. Further the outcomes of this proposal will provide data-driven guidance for the clinical management of EAS patients. We aim to provide the data necessary to approach audiologic and otologic management of the EAS patient within the framework of personalized medicine - taking into account individual characteristics and potentially predictive EAS variables beyond that offered by the EAS variables beyond that offered by the current one size fits all approach.