A major challenge for hearing-impaired listeners and cochlear implant users is to detect and understand speech in situations with background sound. Detecting a target sound in background noise is often easier when the background energy is non-stationary and fluctuates over time. Normal-hearing listeners can accomplish this feat by extracting target information during temporary reductions in background sound energy, a benefit known as modulation masking release (MMR). MMR is much reduced or absent in the hearing impaired. This proposal aims to identify behavioral and neuronal mechanisms for MMR, and examine how sound deprivation affects them. I believe that the results emanating from this proposal will considerably further our understanding of how hearing loss affects our capacity to combat masking, and help develop remediation strategies for hearing loss. Some of the difficulties facing hearing-impaired listeners stem not only from degraded sensory input but also from an altered central auditory system along the entire neuraxis. Because the effect of sound deprivation on MMR is poorly understood, a necessary first step is to explore how the detection of tones in noise is performed by a model organism of human auditory processing, the Mongolian gerbil (Meriones unguiculatus). We lack comprehensive knowledge that may link perception and neuronal activity associated with MMR. By combining empirical approaches in psychoacoustics and in-vivo physiology recordings from awake animals, my key goal is to improve our understanding on how the sound deprived central auditory system processes a challenging task such as MMR. First, I will train sound-deprived animals to detect a tone in noise backgrounds, and compare their performance to normal-hearing controls. Second, I will measure neuronal activity in core auditory cortex from these trained animals. The discharge patterns will reveal how controls detect a tone in fluctuating background sound and whether altered discharge patterns occur in CHL that correlate with hearing- loss related behavioral deficits. Collectively, this proposal will assess how sound deprivation affects MMR at both perceptual and cortical processing levels. The results are expected to significantly advance our understanding of the origins and scope of central processing deficits amongst the hearing impaired.
Hearing-aid and cochlear implant users often achieve the therapeutic goal of aural rehabilitation in quiet but not when there is interference from background sound. Ultimately, successful rehabilitation of auditory function in hearing-impaired individuals will depend both on delivering appropriate peripheral stimulation and on restoring the individual's ability to cognitively integrate those sensory inputs. Understanding the processes that allow normal-hearing listeners to combat interference from competing sources, and how these processes get interrupted by sound deprivation, builds an important bridge towards successful rehabilitation, and this is the goal of the proposed work.