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Title Masking and the phase response of the auditory system
URL
Publication Date
Degree PhD
Discipline/Department Speech and Hearing Science
Degree Level doctoral
University/Publisher The Ohio State University
Abstract When a complex sound consisting of harmonic components is used as a masker for simple signals, the ability to simply detect a sound in that complex depends in part on power spectra of the sound, or signal, and that of the complex, or masker. This idea can be simply expressed in the ratio of power from the signal and that of the masker within a certain frequency range. If the phases of the harmonic complex are manipulated to create different waveforms, the amount of masking produced by the complexes can differ by a large amount. This difference in masking based on the phase relationships of the components is called the masker phase effect, or MPE.The most prevalent explanation for this effect draws on models and simulations, and describes the MPE as the product of differentially modulated output waveforms from the basilar membrane. This research has commonly used so-called Schroeder maskers, which have similarly flat acoustic envelopes but are thought to produce different basilar membrane activation based on the rate of the instantaneous frequency sweep. This dissertation expands our understanding of the MPE over the course of three manuscripts. The first tests the role of the rate of the instantaneous frequency sweep in producing MPE with Schroeder maskers and maskers that share superficial features with Schroeder maskers. It also tests detection of spectrotemporally complex signals in order to provide an intermediate step between pure tone signal detection and speech recognition MPEs. The results from this study support the hypothesis that the MPE is dependent on the rate of the instantaneous frequency sweep of the masker. It also shows MPEs of greater magnitude for a 1 kHz signal and using harmonic complex maskers with phases set according to estimates of traveling wave delay. The MPE for spectrotemporally complex signals is shown to be similar to that for pure tones, and larger than what is reported for spectrotemporally complex speech. The second manuscript tests whether the MPE can be observed in an objective threshold estimate, the wave V of the ABR. As the proposed location of the primary physiological mechanism driving the MPE is the cochlea, the differences in masking produced by the Schroeder maskers should be observable at all subsequent stages of processing. Previous reports of the MPE in humans, however, have been limited to behavioral data and one cortical MEG experiment. Thresholds for a 4 kHz tone burst were estimated using wave V for twenty subjects in Schroeder maskers, and a significant MPE (9.5 dB) was found. This is consistent with the anatomical locii of the MPE being peripheral to the inferior colliculi. The smaller MPE than has been reported in behavioral experiments may be a result of the short duration of the signal or overshoot.The final manuscript details a new adaptive procedure for psychophysically estimating the phase curvature of the basilar membrane. This procedure uses a small number of trials at multiple phase curvature maskers and adapts the signal level until only some maskers are…
Subjects/Keywords Audiology; Psychology
Contributors Feth, Lawrence (Advisor)
Language en
Rights unrestricted ; This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.
Country of Publication us
Format application/pdf
Record ID oai:etd.ohiolink.edu:osu1449152348
Repository ohiolink
Date Indexed 2016-12-22
Grantor The Ohio State University

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