Discriminability of Interaural Time Disparities by Normal Listeners and Listeners With High-Frequency Sensorineural Hearing Loss
Smoski, Walter John
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https://hdl.handle.net/2142/70672
Description
Title
Discriminability of Interaural Time Disparities by Normal Listeners and Listeners With High-Frequency Sensorineural Hearing Loss
Author(s)
Smoski, Walter John
Issue Date
1981
Department of Study
Speech and Hearing Science
Discipline
Speech and Hearing Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Health Sciences, Audiology
Abstract
Four listeners with high-frequency, sensorineural hearing loss and two normal listeners served as subjects in experiments concerning the detection of interaural time-delays using a 500 Hz pure tone, a sinusoidally-amplitude-modulated 4 kHz tone and narrow band noises centered on either 500 Hz or 4 kHz.
The stimuli were presented binaurally (1) with equal sound pressure level; (2) at an equal number of dB above detection threshold (sensation level); (3) so that the stimuli in each ear were equally loud; (4) at levels that produced a midline or "centered" intracranial image.
When the sounds were presented binaurally at equal sound pressure level and the stimuli were either the 500 Hz tone or narrow-band noise centered on 500 Hz, the hearing-impaired listeners could detect small values of interaural time-delay almost as well as could normal listeners. When the stimuli were centered on 4 kHz, however, the hearing-impaired subjects required four to eight times more time delayed to perform as well as the normal listeners. This severe insensitivity to time-delay was accompanied by extremely steeply-sloped psychometric functions.
When the stimuli were presented at 25 dB sensation level, the most dramatic effects were observed in the data provided by the normal listeners at high signal frequencies. They now required extremely large time-delays; not unlike those required by the hearing-impaired listeners. Interestingly, the slopes of the psychometric functions for the normal subjects increased dramatically.
The results of the study clearly establish that very steep psychometric functions and relative insensitivity to interaural time-delay occur when stimuli are presented only 25 dB or so above a subject's threshold of detection. For normal subjects, one may simply increase the levels of the stimuli and note improvements in the ability to detect interaural time-delay. For hearing-impaired subjects, however, the physical levels of the stimuli are very high even when the stimuli are only about 25 dB above threshold. It remains to be seen whether amplification would result in greater sensitivity to interaural time-delay for the hearing-impaired subjects. Such efforts will have to take into account the effects of aural distortion and any acoustic trauma that may ensue.
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