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Title: Dead regions in the cochlea : diagnosis and perceptual consequences
Author: Huss, M.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2004
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“Threshold equalising noise” (TEN) was designed to produce approximately equal masked thresholds for all signal frequencies for people without DRs. When the signal falls inside a DR and is therefore detected via neurones with characteristic frequencies different from the signal frequency, the masked threshold is unusually high. the TEN test was validated by comparison with psychophysical tuning curves and was found to be an appropriate clinical tool for the identification of DR. Hearing-impaired subjects who do not perceive pure tones with a clear pitch were often assumed to have DRs. A systematic study based on subjective ratings of tone clarity showed that tones falling more than ~ 1.5 octaves inside a DR were indeed always rated as somewhat unclear, but a noise-like percept was not necessarily associated with a DR. No correlation was found between noisiness ratings and absolute thresholds across frequencies within ears, but average ratings increased with the severity of the hearing loss. An extensive study of perceived pitch was conducted by obtaining pitch matches across ears of unilaterally hearing-impaired subjects, or within ears using octave matches. The results indicate that tones falling within a DR are perceived with an unclear pitch that is different from “normal”, particularly for tones falling well inside low- or high-frequency DRs. The results indicate that the pitch of low-frequency tones is not conveyed solely by a temporal code, although some temporal information is still available. Possibly, a correspondence between place and temporal information is necessary for a “normal” pitch to be perceived. The pitch of high-frequency tones falling in a DR is probably solely determined by place information. Normally, a sustained tone remains audible when presented at a level well above threshold, except at the upper frequency limit of hearing. In an extensive study using subjects with and without DRs, no consistent association was found between the degree of tone decay and the presence of a DR.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available