This proposal seeks to understand mechanisms of auditory training (AT) and potential of AT to mitigate hearing issues that promote risk of development of Alzheimer’s disease and related dementias (ADRD). Reports from the Lancet Commission (Livingstone and colleagues, 2020), and others, show midlife hearing loss is one of the greatest predictors of late-life dementia, and hearing aids protect against development of ADRD. While this has promoted a push for greater distribution of hearing aids, research from Gates and colleagues (2011) suggests that central hearing processes may be greater predictors of onset of ADRD than peripheral hearing (as addressed through hearing aids). Central auditory processing abilities are fundamental to understand speech, appreciate music, and separate competing environmental sound sources. Hearing challenges experienced with increasing age, especially understanding speech in noisy ambient environments, cause frustration with interpersonal verbal communication and detrimental long-term effects on functional independence, cognitive abilities, and overall quality of life, including increased risk for ADRD. Nevertheless, despite extensive research conducted across multiple fields, clinicians and researchers still disagree about the best ways to address the diversity of hearing difficulties individuals face throughout their lives. The guiding premise of the current proposal is the need for robust and reliable data sets to clarify the underlying mechanisms of AT and to identify the mediators and moderators that impact training outcomes. The overarching goal of this proposal is that better understanding of mechanisms of AT, with focus on speech in competition, can address the most prevalent hearing complaints reported by people as they age, and in turn mitigate transition to ADRD. To address this, we will recruit a large and diverse sample of older adults, including those with prodromal ADRD, and a comparison group of younger adults (1260 participants across training conditions, including separate samples of young and older adults). We will research how baseline cognitive and hearing measures predict training outcomes (moderators) and how these interact with training methods (mediators). To enhance rigor and reproducibility, we will release data sets and training/assessment tools to enable other researchers to conduct analyses, replicate our studies, and test their own training methods using common outcome measures. The proposed research will address four Specific Aims. Aim 1 – Determine the relationship of stimulus complexity and AT outcomes. Aim 2 – Determine the relationship of AT training structures and AT outcomes. Aim 3 – Determine relationships between participant characteristics (moderators) and AT approaches (mediators) on training outcomes. Aim 4 – Create an AT platform that facilitates faithful replication and modelling. Through the collection and dissemination of a large, unique, and comprehensive dataset, this proposal has potential for transformative impact by clarifying moderators and mediators of AT, and will afford translational opportunities to contribute to the mitigation of hearing and cognitive decline in individuals who may be at risk for the development of ADRD.