The ability to localize and segregate sound sources in space is important for communication and environmental awareness. Normal-hearing (NH) human listeners effectively localize and segregate sound sources on the basis of interaural time and level differences (ITD and ILD) - binaural acoustic cues to sound source azimuth. Hearing-impaired individuals who use hearing aids (HAs) and cochlear implants (CIs) are often significantly or profoundly impaired in their abilities to detect these cues, leading to significan communication difficulties in everyday listening environments. Such deficits are believed to arise from a combination of patient factors, such as prolonged auditory deprivation leading to altered central function, and clinical device limitations, such as inadequate temporal precision in signal processing or bilateral asymmetry in automatic gain control algorithms. An improved understanding of signal-related limitations on binaural hearing performance will lead to an enhanced basic understanding of the binaural system and may lead to consequent improvements in clinical device technology and patient outcomes. Therefore, the broad long-term goal of the proposed research is to elucidate the effects of binaural cue degradations on sound localization and segregation, toward improved understanding of normal and impaired binaural hearing.
The specific aims of the proposed research are: (1) To characterize the effects of interaural decorrelation and time-varying ILD compression on normal-hearing psychophysical sensitivity to ILD, ITD and virtual sound source location and (2) to characterize the effects of such distortions on the encoding of ILD, ITD and virtual sound source azimuth by neurons of the inferior colliculus. Experiments will integrate (1) behavioral tasks including discrimination, intracranial lateralization, and virtual space localization for characterization of psychophysical sensitivity to control and binaurally degraded stimuli, including simulated "device-processed" stimuli generated from our recent measurements of actual bilateral HA outputs and (2) in vivo extracellular recording techniques for characterization of physiological (neural) sensitivity to control and degraded stimuli. Behavioral and neural data will be related using Fisher information to compare behavioral and neural binaural discrimination performance. Simultaneous with these experiments, the Applicant will regularly meet with clinicians (including the Co- Sponsor) and observe clinical sessions to gain additional perspective on communicative and other listening difficulties faced by people with hearing loss. Such meetings will enrich the Applicant's training and may provide insights for the design of follow-up of future experiments. The proposed work will support the mission of NIDCD by advancing basic understanding of the binaural auditory system and exogenous (signal-related) limitations on binaural benefit from bilateral clinical devices (especially HAs).
The ability to determine where sounds are coming from is an important part of hearing. Individuals with normal, healthy hearing are very good at locating sound sources, even in noisy settings like classrooms and work environments where multiple sound sources and their echoes can degrade signals of interest. This task is much more difficult and sometimes impossible for hearing-impaired individuals, even with the use of hearing aids or cochlear implants. The proposed research aims to clarify how degradations of spatial-acoustic cues, including those occurring as a result of clinical device processing, might contribute to degraded sound location perception, offering to elucidate needed improvements in device technology.