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Is overshoot caused by an efferent reduction in cochlear gain?

Is overshoot caused by an efferent reduction in cochlear gain?
Is overshoot caused by an efferent reduction in cochlear gain?
Under certain conditions, detection of a masked tone is improved by a preceding sound (“precursor”). This phenomenon is referred to as the “temporal effect” or “overshoot”. A prevalent model of overshoot, referred to as the “gain reduction model”, posits that overshoot is caused by efferent reduction in cochlear gain mediated by the medial olivocochlear (MOC) bundle. The model predicts that reduction in cochlear gain will reduce masking when masking is suppressive or when masking is excitatory and the signal-to-masker ratio is high. This study was aimed at testing the validity of these predictions. It consisted of two experiments. The first experiment investigated the relative contributions of suppressive versus excitatory masking to overshoot. The signal was a short 4-kHz tone pip, and the masker and precursor were limited to contain energy either only within (­on-frequency) or only outside (off-frequency) the cochlear filter around the signal frequency. The on-frequency masker would be expected to cause mainly excitatory masking, whereas masking by the off-frequency masker would be expected to be mainly suppressive. Only the off-frequency masker and precursor yielded ­significant overshoot. This suggests that measurable overshoot requires suppressive masking. The second experiment sought to quantify the effect of a precursor on cochlear ­suppression more directly by measuring the amount of suppression caused by a 4.75-kHz suppressor on a lower-frequency (4-kHz) suppressee with and without a precursor present. Suppression was measured using a forward-masking paradigm. While we found large suppression and large overshoot, we found no reduction in suppression by the precursor. This is contrary to the gain reduction model. Taken together, our results indicate that measurable overshoot requires off-frequency masking and that off-frequency overshoot must be caused by a mechanism other than MOC-mediated reduction in cochlear suppression.
65-82
Springer
Fletcher, Mark
ac11588a-fafe-4dbb-8b3c-80a6ff030546
de Boer, Jessica
6d0d618a-e1ed-4642-95b3-2c88bfeb6746
Krumbholz, Katrin
7ede3a74-0680-4d57-8673-5e7a240ba277
Fletcher, Mark
ac11588a-fafe-4dbb-8b3c-80a6ff030546
de Boer, Jessica
6d0d618a-e1ed-4642-95b3-2c88bfeb6746
Krumbholz, Katrin
7ede3a74-0680-4d57-8673-5e7a240ba277

Fletcher, Mark, de Boer, Jessica and Krumbholz, Katrin (2013) Is overshoot caused by an efferent reduction in cochlear gain? In, Basic Aspects of Hearing: Physiology and Perception. (Advances in Experimental Medicine and Biology, 787) 16th International Symposium on Hearing (22/07/12 - 26/07/12) New York. Springer, pp. 65-82. (doi:10.1007/978-1-4614-1590-9_8).

Record type: Book Section

Abstract

Under certain conditions, detection of a masked tone is improved by a preceding sound (“precursor”). This phenomenon is referred to as the “temporal effect” or “overshoot”. A prevalent model of overshoot, referred to as the “gain reduction model”, posits that overshoot is caused by efferent reduction in cochlear gain mediated by the medial olivocochlear (MOC) bundle. The model predicts that reduction in cochlear gain will reduce masking when masking is suppressive or when masking is excitatory and the signal-to-masker ratio is high. This study was aimed at testing the validity of these predictions. It consisted of two experiments. The first experiment investigated the relative contributions of suppressive versus excitatory masking to overshoot. The signal was a short 4-kHz tone pip, and the masker and precursor were limited to contain energy either only within (­on-frequency) or only outside (off-frequency) the cochlear filter around the signal frequency. The on-frequency masker would be expected to cause mainly excitatory masking, whereas masking by the off-frequency masker would be expected to be mainly suppressive. Only the off-frequency masker and precursor yielded ­significant overshoot. This suggests that measurable overshoot requires suppressive masking. The second experiment sought to quantify the effect of a precursor on cochlear ­suppression more directly by measuring the amount of suppression caused by a 4.75-kHz suppressor on a lower-frequency (4-kHz) suppressee with and without a precursor present. Suppression was measured using a forward-masking paradigm. While we found large suppression and large overshoot, we found no reduction in suppression by the precursor. This is contrary to the gain reduction model. Taken together, our results indicate that measurable overshoot requires off-frequency masking and that off-frequency overshoot must be caused by a mechanism other than MOC-mediated reduction in cochlear suppression.

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More information

e-pub ahead of print date: 16 April 2013
Published date: 1 August 2013
Venue - Dates: 16th International Symposium on Hearing, Cambridge, United Kingdom, 2012-07-22 - 2012-07-26

Identifiers

Local EPrints ID: 417290
URI: http://eprints.soton.ac.uk/id/eprint/417290
PURE UUID: 2d5086c8-d4a6-4095-bcbf-44cabcd2b848

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Date deposited: 29 Jan 2018 17:30
Last modified: 08 Jan 2022 16:19

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Contributors

Author: Mark Fletcher
Author: Jessica de Boer
Author: Katrin Krumbholz

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