Effects of age and hearing loss on auditory temporal processing: Perceptual and electrophysiological measures - Human communication crucially depends on the ability to maintain good speech intelligibility in dynamically varying acoustic backgrounds. This ability declines with age and age-related hearing loss. Understanding the mechanisms underlying this decline is key to finding successful interventions and potential treatments for this widespread problem of high public-health relevance. Recently, magneto- and electroencephalographic (M/EEG) measures have been increasingly used to investigate changes in subcortical and cortical neural processing due to age and hearing loss. Advances in measurement and data analysis methods enable characterization of neural tracking of acoustic, and higher-level (linguistic and semantic) speech features from M/EEG recordings obtained while study participants listen to continuous speech. These techniques provide a unique window into neural tracking of the target speech and to-be-ignored competing background. However, the interpretation of these measures is hampered by poor control for differences in peripheral (cochlear) auditory function, lack of direct experimental validation for the role of specific underlying mechanisms, and often small study samples. Non-speech stimuli have been used to gain a better understanding of specific mechanisms contributing to the age- and hearing-loss-related decline in speech perception but experimental evidence that individual or group differences in neurophysiological responses to these stimuli are reflected in perception is often lacking. The goal of this proposal is to provide the missing link between measures of cortical tracking of temporal envelope fluctuations in non-speech and speech stimuli and performance in perceptual tasks, using comparable stimuli. The studies will use young normal-hearing listeners, older normal- hearing listeners, and older hearing-impaired listeners. In Aim 1, we will investigate effects of age and hearing loss on perceptual measures of modulation-rate selectivity and discrimination using non-speech well-controlled stimuli with envelope modulation rates relevant for speech perception. In Aim 2, we will measure cortical responses to the non-speech stimuli used in these perceptual tasks to establish the sensitivity of EEG-based measures to changes in perception resulting from comparable experimental manipulations. In Aim 3, we will estimate cortical responses to speech envelope for natural (continuous) speech stimuli to investigate contributions from loss of cochlear nonlinearity, changes to modulation-rate selectivity and discriminability, and changes to cognitive function to neural processing and perception of masked speech. The outcomes from this project will provide the experimental basis for interpreting noninvasive neural (cortical) measures of temporal- envelope processing, thus advancing our understanding of mechanisms contributing to deficits in speech-in- noise perception experienced by older normal-hearing and hearing-impaired adults. The results from the project will have an impact on the development of potential future interventions and treatments for communication problems that are widespread among the growing population of older individuals.
