ADVANCING CLINICAL PRACTICE AND ESTABLISHING FOUNDATIONAL THEORY FOR AUDITORY FUNCTION IN INDIVIDUALS WITH DOWN SYNDROME

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PROJECT SUMMARY/ABSTRACT Up to 80% of individuals with Down syndrome have hearing loss across the lifespan, including fluctuating conductive hearing loss and permanent sensorineural hearing loss. Early onset presbycusis is also observed for this population, consistent with precocious aging observed in other domains. However, most existing prevalence data were obtained from medical record review or assessment of individuals living in institutions complicating application to individuals with Down syndrome in the general population. Individuals with Down syndrome have structural differences in cranial anatomy compared to neurotypical individuals, including that which would predict high rates of hearing loss and otitis media with effusion (OME). However, these factors can also impact stimulus presentation level. Specifically, stenotic ear canals and OME both result in increased stimulus levels; hearing loss may be underestimated if these factors are not considered during stimulus calibration or presentation. Critically, this issue may have contributed to previous findings of shortened auditory brainstem response (ABR) waveform latency for individuals with Down syndrome relative to age-matched neurotypical peers, a metric useful for clinical diagnosis of conductive hearing loss in individuals for whom a reliable behavioral response to sound is unable to be obtained. AIM 1 defines the prevalence, type, and trajectory of hearing loss for individuals with Down syndrome in the general population. Significant innovation to clinical audiology is gained using rigorous calibration techniques, which will resolve the issue of ABR latency and provide comprehensive data on peripheral sensitivity across the lifespan. Just as for neurotypical populations, hearing loss puts individuals with Down syndrome at risk for major challenges to communication, learning, socialization, and employment opportunities. Specifically, sensorineural hearing loss results in broad auditory filter bandwidths limiting accurate identification of speech sounds. Low cerebellar and cortical volumes observed in individuals with Down syndrome are associated with temporal processing difficulties across domains and may impact the saliency of brief improvements in signal-to-noise ratio when listening in background noise. Whereas cognition and language contribute to successful masked speech recognition in neurotypical populations, high rates of language difficulties and intellectual disability are likely to undermine functional hearing abilities for individuals with Down syndrome. AIM 2 establishes foundational theory regarding the functional auditory abilities of individuals with Down syndrome guided by a model of masked speech perception that includes audibility, psychophysical measures of spectral and temporal resolution, and neuropsychological factors of selective attention, working memory, and vocabulary knowledge.