Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Communication Sciences and Disorders

First Advisor

Janet D. Koehnke

Second Advisor

Joan M. Besing

Abstract

The ability to discriminate interaural differences in complex signal and to localize those signals was examined in listeners with normal hearing (NH) and with bilateral high frequency sensorineural hearing impairment (IH). Just noticeable differences for interaural time and intensity were obtained using 1/3-octave narrow band noise (NBN) stimuli centered at 500 and 4000 Hz in three conditions: (1) the NBNs played in isolation; (2) the NBNs played simultaneously with congruent interaural information across frequency; and (3) the NBNs played simultaneously with either the 500 Hz band dichotic and the 4000 Hz band diotic (a) or the 500 Hz band diotic and the 4000 Hz band dichotic (b). The best interaural time discrimination was seen for the IH listeners when the 500 Hz NBN contained the relevant information and the best intensity discrimination in the IH listeners was seen when both bands contain congruent interaural information (2). Results indicate reduced sensitivity to interaural time differences for all subjects when the 500 Hz band is diotic and discrimination is based on the 4000 Hz band (3b). The IH listeners also demonstrate poorest interaural intensity discrimination for this condition (3b). Results suggest that IH subjects may benefit from congruent interaural information in more than one frequency region. In Experiment II a measure of localization accuracy was obtained in three conditions: (1) the NBNs played in isolation; (2) the NBNs played simultaneously with one as the target and the 2nd (interferer) at a fixed location; and (3) the NBNs played simultaneously with the interferer at a random location. The NH subjects performed similarly on all tasks with the same target band, though accuracy was reduced with a 4000 Hz NBN target. Best performance by the IH subjects was seen with a 500 Hz NBN target, whether or not the interferer was present. The IH subjects performed most poorly with a 4000 Hz NBN target and a random interferer. Results suggest that in IH subjects, localization is more difficult when forced to rely on interaural information in the higher frequency region with competing interaural information at low frequencies.

Pages

191

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