Electronic Theses and Dissertations

Identifier

3737

Date

2016

Date of Award

7-21-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Audiology

Concentration

Audiology

Committee Chair

Lisa Lucks Mendel

Committee Member

Eugene H Buder

Committee Member

Gavin Bidelman

Committee Member

Stephanie Marie Huette

Abstract

In suboptimal listening environments when noise hinders the continuity of the speech, the normal auditory-cognitive system perceptually integrates available speech information and “fills in” missing information with help from higher level feedback mechanisms. However, individuals with cochlear implants (CIs) find it difficult and effortful to understand interrupted speech compared to their normal hearing (NH) counterparts. Little is known about CI listeners’ ability to restore missing speech when they are exposed to challenging listening environments. In this dissertation, three experimental paradigms were used to evaluate listeners’ ability to utilize their acquired linguistic skills in normal hearing individuals using simulated cochlear implant processing and in individuals with cochlear implants. In the first experiment, listeners’ abilities to use semantic context when speech was intact or interrupted was evaluated under various spectral resolution conditions. The results suggested that higher level processing facilitates speech perception up to a point but it fails to facilitate speech understanding when speech signals are significantly degraded. In the second experiment, high level processing was investigated using the phonemic restoration effect where sentences were interrupted with and without filler noise at different interruption rates. Both groups failed to show top-down restoration, except the CI users showed some amount of higher level processing at the lowest interruption rate. In the third experiment, a gated word recognition task was used and listeners with CIs required comparatively more acoustic-phonetic information to recognize a word than the NH listeners. In the final experiment, when speech was presented in noise, both groups relied significantly on contextual cues to perceive the speech. Overall, the results from successive experiments indicated CI users rely heavily on contextual cues when they are available. However, when they listen to speech with severe degradations, they may not benefit from semantic context as the incoming speech does not provide enough information to trigger top-down processes. If the signal fidelity (spectral resolution) is improved, their benefit from higher level linguistic feedback processes can be maximized.

Comments

Data is provided by the student.

Library Comment

dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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