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CENTRAL VERSUS MONOTIC MASKING IN NON-SIMULTANEOUS MASKING CONDITIONS

Ahmadi, Seyedeh Mahnaz
http://rave.ohiolink.edu/etdc/view?acc_num=osu1268166584

Abstract Details

2010, Doctor of Philosophy, Ohio State University, Speech and Hearing Science.
Evidence based on physiological and psychophysical data suggests that the efferent system, especially the medial olivocochlear bundle (MOCB), has a role in protecting the auditory system from damaging sounds. It is also assumed that this system may improve the detection of sound in noise, which in turn improves speech intelligibility in noisy environments. Some have hypothesized that central masking is mediated via the MOCB. Indeed, this notion is supported by the central masking effect measured in psychoacoustic studies on animals. It has been demonstrated that central masking was reduced, or eliminated when the MOCB was sectioned at the floor of the fourth ventricle in macaque monkeys (Smith et al., 2000). In a normal conversational environment, a listener is exposed to various acoustic stimuli which are fluctuating in the time domain. These fluctuations do not occur simultaneously. The time disparity between the signal and the noise will affect a listener’s ability to detect a signal in a noisy environment. This effect can be studied in a non-simultaneous masking paradigm. Comparing non-simultaneous central masking to monotic masking may show the MOCB influence on our ability to detect a signal in noise. The purpose of the present study was to compare the amount of masking as a function of signal-to-noise time delay in dichotic versus monotic masking conditions. Another aim was to compare on-frequency versus off-frequency masking, for forward monotic and dichotic listening in time intervals of 0, 5, and 20 ms. Detection thresholds of four normal adult listeners were measured utilizing a 2AFC up-down adaptive-tracking procedure. Signal-to-masker time intervals were 0, 2, 5, 10, 20, and 50 ms. Brief sinusoidal signals at 0.5, 1, 2, and 4 kHz were masked by a two-octave band of noise of 200 ms duration. The psychoacoustic study was conducted running a computer based program coded in MATLAB, utilizing the psychoacoustic software PsyLab 2.1. The masker was centered on and off the frequency of the signal. The hearing thresholds were obtained in quiet and with ipsilateral and contralateral maskers separately. Then, the hearing thresholds with noise were subtracted from the threshold in quiet. This value represented the threshold shift and was used for further statistical analysis. The amount of masking decreased as a function of time interval in both monotic and dichotic conditions. A non-simultaneous masking effect existed in shorter time intervals. Backward central masking did not occur, even in the shortest intervals. High frequency signals produced more central masking than low frequencies. However, signals with lower frequencies were more effective in monotic masking. Central masking did not clearly occur with an off-frequency masker in both simultaneous and non-simultaneous masking conditions. The rate of growth of central masking was noticeably slower than monotic masking for on-frequency maskers. Results of this study were consistent with neurophysiologic findings on MOCB response characteristics, and also with psychophysical findings in central masking. The present findings supported the idea that central masking, either in simultaneous or non-simultaneous masking conditions, is mediated by efferent fibers in humans.
Lawrence L. Feth (Advisor)
Robert A. Fox (Committee Member)
Kamran Barin (Committee Member)
125 p.
Audiology
Masking; efferent system

Recommended Citations

Citations

  • Ahmadi, S. M. (2010). CENTRAL VERSUS MONOTIC MASKING IN NON-SIMULTANEOUS MASKING CONDITIONS [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1268166584

    APA Style (7th edition)

  • Ahmadi, Seyedeh Mahnaz. CENTRAL VERSUS MONOTIC MASKING IN NON-SIMULTANEOUS MASKING CONDITIONS. 2010. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1268166584.

    MLA Style (8th edition)

  • Ahmadi, Seyedeh Mahnaz. "CENTRAL VERSUS MONOTIC MASKING IN NON-SIMULTANEOUS MASKING CONDITIONS." Doctoral dissertation, Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1268166584

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.