Barbara Shinn-Cunningham, PhD / Sharon G. Kujawa, MD
Recent basic research in animals as well as in human listeners suggests that noise exposure and associated accelerated auditory aging leads to cochlear neuropathy, which can produce suprathreshold hearing deficits without any elevation of hearing thresholds. This supra-threshold hearing loss (STHL), currently undiagnosed with standard audiometric tests, causes degraded encoding of amplitude modulation and leads to poor speech understanding, especially in noisy environments. As many as 5-15% of patients seeking audiological care are found to have normal hearing thresholds (i.e., can detect the presence of quiet sounds as easily as healthy young adults). Such listeners typically seek help specifically because they have trouble understanding speech in social settings (e.g., group conversations in cocktail parties). These communication difficulties, caused by the “hidden” supra-threshold hearing loss, can lead to social isolation, withdrawal, and depression. Current approaches to aid such listeners are unsatisfactory and do not take into account the form of the underlying perceptual deficits, in part because their root cause is only now coming to light. In addition, a common complaint of hearing aid users is that their hearing aids do not allow them to converse in restaurants or other noisy settings.
Many of these listeners may suffer from a mixture of traditional hearing loss and STHL, but current hearing aid processing schemes focus only on amplifying sound to overcome elevated thresholds. For a listener with STHL, such amplification can decrease the perceptual salience of information-conveying amplitude modulation; thus current amplification strategies are likely to interfere with rather than enhance speech understanding in listeners with STHL. This may explain why some listeners do not benefit from hearing aids in social settings. This project seeks to develop novel, individualized hearing-aid signal processing strategies to overcome “hidden” hearing deficits. The research community is beginning to recognize the prevalence and importance of such “hidden hearing loss,” which arises from a loss of ascending auditory nerve fibers (cochlear neuropathy) and results in degraded speech understanding in noisy settings. Yet, this knowledge has not yet reached the broad clinical community, and there are no effective clinical interventions or treatments to ameliorate the effects of neuropathy. Our team has developed diagnostic approaches to quantify the extent of cochlear neuropathy in individual listeners as well as computational models to predict the perceptual consequences of different patterns of nerve-fiber loss. From these quantitative predictions, we seek to devise an algorithm that will optimize, for each individual listener, perception of speech in noisy settings. In addition, behavioral and electrophysiological measures will be developed to identify listeners with STHL, to characterize their loss, and to demonstrate the efficacy of individualized hearing-aid processing on their ability to understand speech in noise. The diagnostic measures and individualized processing strategy developed and validated in this project will not only benefit listeners with STHL and mixtures of traditional hearing loss and STHL, but also hearing aid companies, audiologists, and hearing aid dispensers.