The proposed supplement is relevant to the INCLUDE project, by enhancing our understanding of hearing loss, a co-occurring condition in Down Syndrome (DS), specifically in children. We focus on an aspect of INCLUDE Component 1: Targeted, high risk-high reward, basic science studies in areas highly relevant to DS. The parent grant has shown success to date in recruitment and testing of young adults with DS, however, there is also a paucity of auditory studies in children with DS. The incidence of hearing loss in infants and children with DS is higher than in the general population. While the Center for Disease Control reports that up to 75% of children with DS are affected by hearing loss (Data statistics on Down Syndrome, 2019), screening is not standard. Many children with DS who pass universal newborn hearing screenings are identified with significant hearing loss at older ages, thus, hearing loss can go undetected during development. If detected, the type/degree of hearing loss and thus treatment, need to be incorporated into clinical practices that serve children with DS. The compounded impact of hearing loss on developmental delays that occur in children with DS remains unknown. The goal of the supplement is to collet pilot data in children with DS, establishing feasibility for a new parent R01 on auditory function and its association with cognition, language and brain structure and function in children with DS. The research will be conducted at the Waisman Center, a premier research institute at the University of Wisconsin Madison, where the PI’s lab is situated. Waisman is one of the named Intellectual & Developmental Disabilities (IDD) Research Centers in the US, where scientific discovery is aimed at advancing knowledge and developing treatment in developmental disabilities. This project will leverage important, unique resources at the Waisman Center: (1) Auditory perceptual measures of hearing speech in noise, spatial hearing and brain function using EEG were developed for young listeners in the Litovsky lab, recently implemented in the parent R01 for young adults with DS, will be piloted and revised as needed for a younger population of children with DS. (2) Cognitive measures and MRI neuroimaging to evaluate brain structure are well established in the Hartley’s lab, and in the Alexander lab, respectively. (3) The Waisman Center will be launching a new research cohort development project, under Hartley’s leadership, that will bring dozens of children with DS to the Waisman Center, providing a robust participant pool for this supplement.