BME PhD Dissertation Defense - Lengshi Dai

  • Starts: 1:00 pm on Thursday, December 7, 2017
Title: "Perceptual and Physiological Measures of Auditory Selective Attention in Normal-Hearing and Hearing-Impaired Listeners" Committee: Prof. Barb Shinn-Cunningham, BME (Advisor) Prof. Kamal Sen, BME (Chair) Prof. Steve Colburn, BME Prof. Gerald Kidd, SAR Department of Speech, Language and Hearing Sciences Prof. Virginia Best, SAR Department of Speech, Language and Hearing Sciences Abstract: Human listeners can direct top-down spatial auditory attention to listen selectively to one sound source amidst competing sounds. However, many listeners with hearing loss (HL) seem to have trouble on tasks requiring selective auditory attention; even listeners with normal hearing thresholds (NHTs) differ in this ability. The ability depends on top-down executive control and coding fidelity of the peripheral auditory system. Here we explore the low-level sensory perception and high-level attentional modulation for auditory selective attention for both NHT and HL listeners. Firstly, we designed a paradigm to allow simultaneous measurement of envelope following responses (EFRs), onset event-related potentials (ERPs), and behavioral scores. We varied the conditions to alter the degree to which the bottleneck on behavior was due to fine stimulus details vs. to attentional focus. We find attention modulates ERPs but not EFRs. Importantly, when coding fidelity limits the task, EFRs but not ERPs correlate with behavior. In contrast, when sensory cues for segregation are robust, individual differences correlate with both EFR strength and the strength of attentional modulation of ERPs. Secondly, we use behavioral experiments and ERPs to explore how HL affects control of auditory selective attention. Listeners with either NHTs or with HL identified a simple melody that was presented simultaneously with two competing melodies at different spatial locations. Compared to NHT listeners, HL listeners both performed more poorly and showed less robust attentional modulation of cortical ERPs. While both groups showed some cortical suppression of distracting streams, this modulation was weaker in HL listeners, especially when the spatial separation between the attended and distracting streams was small. Finally, we focus on the difference from low-level sensory perception. We measure the behavioral performances and EFRs to explore the coding fidelity of envelope cues. For NHT listeners, strong correlations between behavioral and electrophysiological measurements were observed in high sensation level but not in low sensation level. We hypothesized that hearing deficits may co-occur with normal hearing despite upshifted thresholds, while potential loss of low spontaneous firing rate fibers in cochlea is possibly cause of the individual differences. Besides, we confirmed enhanced amplitude modulation sensitivity from HL listeners.
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