Adults with hearing loss have a higher risk for Alzheimer’s and other cognitive disorders. Individuals with moderate to severe hearing loss are up to five times more likely to develop Alzheimer's disease and dementia, compared to those with normal hearing. Nonhuman primates (NHP) are crucial animal models for research on Alzheimer's disease and its related dementias because of their close evolutionary relationship to humans, with whom they share similar anatomy, physiology, and genetic interactions. The common marmoset (Callithrix jacchus) is a NHP model of increasing importance for aging research. This new world primate provides some unique advantages for the study of aging and aging-related disorders, including its relatively short lifespan among all the NHP used in biomedical research. Marmosets also show patterns of age-related hearing loss similar to humans and are known to develop amyloidosis, a major biological marker for Alzheimer’s disease, naturally at old age. Amyloidosis is also transmissible to this species, making it an extremely promising NHP model for Alzheimer’s disease. The goal of this administrative supplement application is to fill in gaps in our knowledge of auditory processing by aging marmosets. Such knowledge will be extremely valuable to the scientific community studying Alzheimer's disease and its related dementias. Our laboratory is a leader in marmoset neuroscience research and has pioneered many behavioral and physiological techniques for marmoset studies. We plan to take the advantage of this unique model system in response to NIH RFA NOT-AG-20-034. The proposed aims are within the scope of the parent R01 award (DC003180) and this RFA.