Date of Award

8-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Speech and Hearing Science

Major Professor

Ashley W. Harkrider

Committee Members

James W. Thelin, Mark S. Hedrick, Patrick N. Plyler, Jim Hall

Abstract

Acceptable noise level (ANL) is a measure of a listener’s acceptance of background noise when listening to speech. A consistent finding in research on ANL is large intersubject variability in the acceptance of background noise. This variability is not related to age, gender, hearing sensitivity, type of background noise, speech perception in noise performance, cochlear responses, or efferent activity of the medial olivocochlear bundle pathways. Moreover, across ANL studies, young and elderly individuals with both hearing impairment and normal-hearing sensitivity display equivalent means and ranges for ANLs, indicating that acceptance of background noise may be an inherent characteristic of the individual that does not change with age, or the development of hearing loss. In the present study, auditory evoked potentials and encephalography (EEG) were examined in 40 adults with mild-to-moderately-severe sensorineural hearing impairment with low, mid-range, and high ANLs to determine whether or not differences in judgments of background noise are related to differences measured in aggregate physiological responses from the auditory nervous system. Group differences in the auditory brainstem response, auditory middle latency, cortical, auditory late latency, and EEG responses indicate that differences in more central regions of the nervous system contribute to the variability in the willingness of a listener with hearing impairment to accept background noise when listening to speech.

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