Date of Award
Doctor of Philosophy
Communication Sciences & Disorders
One of the most commonly reported complaints related to hearing is difficulty understanding speech-in-noise (SIN). Numerous individuals struggle to effectively communicate in adverse listening conditions, even those with normal hearing. These difficulties are exacerbated due to age and hearing-related deficits such as hearing loss and auditory processing disorders. Despite the high prevalence of SIN deficits in individuals across the lifespan, the neural mechanisms underlying successful speech comprehension in noise are not well understood. Communication in noise is an incredibly complex process that requires efficient processing throughout the entire auditory pathway as well as contributions from higher-order cognitive processes including working memory, inhibition, and attention. In a series of studies using electrophysiologic (EEG) and behavioral measures, this dissertation evaluated the neural correlates of SIN perception across subcortical and cortical levels of the auditory system to identify how top-down and bottom-up influences aid SIN understanding. The first study examined the effects of hearing loss on SIN processing in older adults at the cortical level using frequency-specific neural oscillations (i.e., brain rhythms) and functional connectivity (i.e., directed neural transmission). We found that low-frequency alpha and beta oscillations within and between prefrontal and auditory cortices reflect the ability to flexibly allocate neural resources and recruit top-down predictions to compensate for hearing-related declines and facilitate efficient SIN perception. The second study, in younger adults, investigated the role of attention in SIN processing and how it interacts with early sensory encoding. Hierarchical processing in brainstem and cortex was assessed by simultaneously recording frequency-following responses (FFRs) and event-related potentials (ERPs) at the source level. We found that attention modulates SIN processing at both subcortical and cortical levels and strengthens bidirectional neural signaling within the central auditory pathway. A relative disengagement of corticofugal transmission was observed in noise but only for passive listening suggesting attention aids SIN perception by maintaining top-down reinforcement of acoustic feature encoding within the primary auditory pathways. Taken together, these results indicate that the neural networks engaged during SIN perception depend on a complex interplay between bottom-up and top-down factors including signal clarity, listeners hearing status, and attentional deployment.
Dissertation or thesis originally submitted to ProQuest
Price, Caitlin Elise Nelms, "Neural Mechanisms Underlying Hierarchical Speech-in-Noise Processing" (2020). Electronic Theses and Dissertations. 2946.