Graduation Year

2022

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Communication Sciences and Disorders

Major Professor

Ann C. Eddins, Ph.D., M.B.A., CCC-A

Committee Member

David A. Eddins, Ph.D., CCC-A

Committee Member

Timothy L. Boaz, Ph.D.

Committee Member

Erol J. Ozmeral, Ph.D.

Keywords

Cortical tracking, Hemispheric asymmetry, Spectral enhancement, Temporal enhancement

Abstract

Perception of spectral and temporal acoustic cues is fundamental to most auditory tasks including speech discrimination, sound localization, and segregation of speech in background competition. Although neuroimaging studies have shown hemispheric asymmetry in processing spectral and temporal features, where right hemisphere is dominant for spectral processing while left hemisphere is dominant for temporal processing, the effects of aging on hemispheric asymmetry and associated auditory perceptual consequences have not been well studied. Neurocognitive aging studies support that due to limited neural resources, older adults may use different neural circuits than younger adults to maintain perceptual and cognitive performance during the same perceptual and cognitive tasks. Discovering whether cortical activity during spectral and temporal encoding in older adults follows the hemispheric asymmetry model or shows alteration due to age-related neural reorganization or attention would help guide and advance potential therapeutic approaches for improving perception in older adults. Using multi-channel electroencephalography (EEG), this project will investigate age-related differences in neural encoding and cortical allocation during spectral and temporal envelope perception. The impact of stimulus type (nonspeech, speech), cognitive influence (passive, attention), and perceptual cue strength (reduced, neutral, enhanced) will be used to evaluate the hypotheses that, due to poorer encoding and processing of the acoustic stimulus: 1) younger listeners demonstrate explicit hemispheric asymmetry in the processing of spectral and temporal envelope cues, while older listeners show reduced hemispheric asymmetry for both cues, and 2) top-down cognitive influence further modulates cortical allocation for processing these cues, but the degree of hemispheric asymmetry differs based on age and individual cue preference. To test these hypotheses, the project uses a novel stimulus set and analytic approach with the following studies. Study 1 will discover the impact of age on behavioral and cortical measures of spectral and temporal envelope processing with non-speech signals. Spectral and temporal envelope detection tasks and an EEG acoustic change complex paradigm will be used to determine perceptual and neural sensitivity to both envelope cues. Study 2 will discover the impact of age on behavioral and cortical measures of spectral and temporal envelope processing with speech signals. The Coordinate Response Measure (CRM) corpus will be modified to reduce or enhance spectral and temporal envelope cues as a means of modulating cue strength in the stimuli. Simultaneous behavioral and EEG responses will be analyzed with the multivariate Temporal Response Function (mTRF) analysis tool to assess the effects of age, cognitive influence, and cue dependence on perception and neural tracking of ongoing speech. The outcomes of the study will provide a better understanding of neural organization during spectral and temporal processing in younger and older adults and critical information about individual cue preference in perception and encoding of spectral and temporal envelopes. The long-term goal is to determine if age-related declines in processing may be improved with targeted acoustic feature enhancement in hearing devices, assistive technologies, and rehabilitative strategies to improve auditory perception and daily communication abilities in older populations.

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