Date of Award

Spring 2015

Document Type

Dissertation

Degree Name

Doctor of Audiology (AuD)

Department

Department of Communication Sciences and Disorders

Advisor(s)

Christopher G. Clinard

Abstract

Difficulty understanding speech in the presence of noise is a common complaint of middle-aged and older adults with and without hearing loss. There is an incomplete picture of what contributes to difficulties understanding speech-in-noise in adults who have normal audiograms. As humans we listen binaurally, so declines in binaural processing may contribute to speech-in-noise difficulties. We examined the effects of age on the upper frequency limit of interaural phase difference (IPD) detection and IPD detection at fixed frequencies. We also examined a speech-in-noise measure of spatial separation across young and middle-aged, normal-hearing individuals.

Participants were young (n=12) and middle-aged (n=8) adults with normal and symmetrical hearing from 250-8000 Hz. Two interaural phase difference tasks were undertaken. The first assessed interaural phase difference discrimination across frequencies and the second assessed interaural phase difference discrimination at fixed frequencies (500, 750, 1000, 1125 Hz). In addition, the speech-in-noise measure of benefit from spatial separation was assessed by having subjects complete the words-in-noise test with speech and noise at 0° and again with speech at 0° and noise at 90°.

The young group had significantly higher (better) upper frequency limits for interaural phase difference discrimination. There was no statistically significant difference between the IPD discrimination at fixed frequencies for the young and middle-aged group, contrary to what was hypothesized. The young group also did not have a greater benefit from spatial separation compared to the middle-aged group.

The outcomes from this study add to a growing body of literature suggesting a decline in the upper frequency limit of IPD discrimination with advancing age. This negative effect of aging begins in middle-aged, normal-hearing listeners. The results from this study also suggest that factors other than age and IPD discrimination affect spatial processing in middle-aged adults with clinically normal audiograms. Knowing what contributes to difficulty understanding speech-in-noise will aid in counseling patients and will improve approaches to aural rehabilitation.

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