Date of Award

Spring 1-1-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Speech, Language & Hearing Sciences

First Advisor

Anu Sharma

Second Advisor

Kathryn Arehart

Third Advisor

Phillip Gilley

Fourth Advisor

Christine Yoshinaga-Itano

Fifth Advisor

Kristin Uhler

Abstract

Background: Auditory Neuropathy Spectrum Disorder (ANSD) is a recently discovered form of hearing loss, which is characterized by a lack of neural synchrony at the brainstem. However, there is very little information on the impact of sub-cortical dys-synchrony on cortical development, functioning and behavioral outcomes in ANSD. Purpose: Two experiments are presented. The first experiment examines auditory cortical development and phase synchrony in cortical responses in a pediatric patient with unilateral ANSD. The second experiment utilizes time-frequency analysis of single trial EEG data to examine differences in cortical phase synchrony between 91 children with auditory neuropathy spectrum disorder (ANSD), 50 children with sensorineural hearing loss, and 41 children with normal hearing. Methods: In Experiment 1, cortical auditory evoked potentials (CAEPs), dipole and current-density analyses, independent component analyses (ICA), inter-trial coherence, and the patient's performance on measures of speech perception were compared for the ear with normal hearing (NH) and the ear with ANSD. In Experiment 2, inter-trial coherence (ITC) analyses were performed on CAEPs from each group. The peak strength of ITC and the time and frequency ranges of significant ITC were compared between groups and subgroups categorized by hearing loss, technology intervention types and cortical maturation. Results: In Experiment 1, differences were observed between the NH ear and the ear with ANSD for all test measures. In Experiment 2, no correlation was found between test age and the ITC measures examined for the normal hearing group. Clinical diagnosis, degree of hearing loss, intervention type and cortical maturation showed significant relationships with ITC measures. Conclusions: Children with ANSD show significant cortical deficits, which include abnormal cortical organization, high degrees of inherent cortical variability, and deficits in cortical phase synchronization to speech. Given the importance of normal cortical maturation and functioning for speech and language acquisition in children, the results suggest new evidence for behavioral outcomes associated with children with ANSD.

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