The prevalence of clinically-significant hearing loss is ~63% in adults over 70 years of age (Lin et al., 2011). Moreover, untreated hearing loss in older adults has been linked to more rapid cognitive declines and greater risk of dementia (Lin et al., 2013). Difficulty following conversations in noisy settings is the most common hearing-related complaint, regardless of whether audibility is compensated by amplification. The remarkable ability humans have to focus on a desired sound source (e.g., speech, music, environmental sounds) in the presence of competing sounds depends to a large extent on spatial hearing. It is known that many aspects of spatial hearing decline with normal aging but the mechanisms responsible for that decline are not known. Likewise, it is known that top-down control of sensory processing, including focused attention, declines with age but age-related changes in selective auditory spatial attention have not been well documented and are poorly understood. The goal of this project is to investigate the processes involved in auditory spatial tuning in oldr listeners, leveraging simultaneous electroencephalography and behavioral measurements. Experiments have been designed to evaluate specific hypotheses associated with potential changes in the opponent- channel (OC) mechanisms underlying spatial processing. The experiments focus on low-frequency stimuli, since spatial cues below ~1500 Hz are dominated by interaural time differences, and timing deficits are a hallmark of presbycusis. A goal of Aim 1 is to determine whether or not older listeners (with normal hearing sensitivity) exhibit altered spatial tuning relative to younger listeners. A second goal is to use measures of spatial tuning to evaluate the potential mechanisms underlying the OC model and the potential influence of either age-related down-regulation of inhibition and/or temporal precision on spatial processing deficits.
In Aim 2, parallel experiments are used to probe the possibility that, with advancing age, broadened spatial attention further limits spatial advantages available to older listeners. In addition, long-term goals of this work are to identify appropriate diagnostic methods and remediation targets, to evaluate and possibly alter the way hearing enhancement devices and auditory training methods may be used to ameliorate existing deficits, and to develop outcome metrics useful should treatments that slow or reverse age-related hearing loss be discovered. The training program outlined provides a strong mentoring environment both from an immediate laboratory setting as well as the institutional setting. The fellowship applicant is determined to work towards establishing the tools and experience necessary to transition in the future to an independent academic research career.
A hallmark of age-related hearing loss (presbycusis) is difficulty following conversations when competing sounds are present - a product of poor coding of auditory features over time and across space. This project will advance our understanding of age-related changes in sensory and cognitive contributions to binaural processing. Using a combination of behavioral and electrophysiological techniques, results will provide the empirical and theoretical bases to guide appropriate remediation methods.