ABSTRACT OF FUNDED PARENT AWARD (1R01DC020229) (NO CHANGE) The goal of this project is to characterize the speech perception and auditory abilities of infants, children, and adults with Down syndrome. Prior research involving individuals who are neurotypical has highlighted the importance of early perceptual development on long-term speech and language outcomes, but little is currently known about the factors that support communication outcomes for individuals with Down syndrome. We do know that the development of functional hearing skills in children who are neurotypical (such as understanding speech when several people are talking at the same time) requires years of experience with sound, extensive language knowledge, and maturation of executive function. These observations suggest that attainment of speech perception and hearing milestones is likely to be delayed or disrupted for children with Down syndrome, due to limitations in intellectual functioning, language knowledge, and cognitive processing. The first aim of this project evaluates phoneme perception in infants, children, and adults with Down syndrome, with a focus on characterizing infants’ discrimination of native and non-native speech contrasts and examining effects of hearing loss on the consonant identification in children and adults. The second aim tests the hypothesis that maturation of selective listening strategies follows a delayed time course of development for individuals with Down syndrome, resulting in greater susceptibility to interference from competing background sounds. The third aim characterizes the ability to recognize speech in the presence of competing background sounds in children and adults with Down syndrome, accounting for individual differences in factors such as linguistic knowledge and working memory. The results generated by this project are expected to inform theoretical models regarding the development of speech perception and hearing abilities in individuals with Down syndrome, and have the potential to provide preliminary guidance for strategies to maximize speech communication outcomes in noisy environments such as classrooms.