Binaural Masking Release in Children With Down Syndrome

Objectives: Binaural hearing results in a number of listening advantages relative to monaural hearing, including enhanced hearing sensitivity and better speech understanding in adverse listening conditions. These advantages are facilitated in part by the ability to detect and use interaural cues within the central auditory system. Binaural hearing for children with Down syndrome could be impacted by multiple factors including, structural anomalies within the peripheral and central auditory system, alterations in synaptic communication, and chronic otitis media with effusion. However, binaural hearing capabilities have not been investigated in these children. This study tested the hypothesis that children with Down syndrome experience less binaural benefit than typically developing peers. Design: Participants included children with Down syndrome aged 6 to 16 years (n = 11), typically developing children aged 3 to 12 years (n = 46), adults with Down syndrome (n = 3), and adults with no known neurological delays (n = 6). Inclusionary criteria included normal to near-normal hearing sensitivity. Two tasks were used to assess binaural ability. Masking level difference (MLD) was calculated by comparing threshold for a 500-Hz pure-tone signal in 300-Hz wide Gaussian noise for N0S0 and N0S&pgr; signal configurations. Binaural intelligibility level difference was calculated using simulated free-field conditions. Speech recognition threshold was measured for closed-set spondees presented from 0-degree azimuth in speech-shaped noise presented from 0-, 45- and 90-degree azimuth, respectively. The developmental ability of children with Down syndrome was estimated and information regarding history of otitis media was obtained for all child participants via parent survey. Results: Individuals with Down syndrome had higher masked thresholds for pure-tone and speech stimuli than typically developing individuals. Children with Down syndrome had significantly smaller MLDs than typically developing children. Adults with Down syndrome and control adults had similar MLDs. Similarities in simulated spatial release from masking were observed for all groups for the experimental parameters used in this study. No association was observed for any measure of binaural ability and developmental age for children with Down syndrome. Similar group psychometric functions were observed for children with Down syndrome and typically developing children in most instances, suggesting that attentiveness and motivation contributed equally to performance for both groups on most tasks. Conclusions: The binaural advantages afforded to typically developing children, such as enhanced hearing sensitivity in noise, were not as robust for children with Down syndrome in this study. Children with Down syndrome experienced less binaural benefit than typically developing peers for some stimuli, suggesting that they could require more favorable signal-to-noise ratios to achieve optimal performance in some adverse listening conditions. The reduced release from masking observed for children with Down syndrome could represent a delay in ability rather than a deficit that persists into adulthood. This could have implications for the planning of interventions for individuals with Down syndrome.