Masking Release for Speech in Modulated Maskers: Electrophysiological and Behavioral Measures

Objectives: The purpose of this study was to obtain an electrophysiological analog of masking release using speech-evoked cortical potentials in steady and modulated maskers and to relate this masking release to behavioral measures for the same stimuli. The hypothesis was that the evoked potentials can be tracked to a lower stimulus level in a modulated masker than in a steady masker and that the magnitude of this electrophysiological masking release is of the same order as that of the behavioral masking release for the same stimuli. Design: Cortical potentials evoked by an 80-ms /ba/ stimulus were measured in two steady maskers (30 and 65 dB SPL), and in a masker that modulated between these two levels at a rate of 25 Hz. In each masker, a level series was undertaken to determine electrophysiological threshold. Behavioral detection thresholds were determined in the same maskers using an adaptive tracking procedure. Masking release was defined as the difference between signal thresholds measured in the steady 65-dB SPL masker and the modulated masker. A total of 23 normal-hearing adults participated. Results: Electrophysiological thresholds were uniformly elevated relative to behavioral thresholds by about 6.5 dB. However, the magnitude of masking release was about 13.5 dB for both measurement domains. Conclusions: Electrophysiological measures of masking release using speech-evoked cortical auditory evoked potentials correspond closely to behavioral estimates for the same stimuli. This suggests that objective measures based on electrophysiological techniques can be used to reliably gauge aspects of temporal processing ability. ACKNOWLEDGMENTS: All authors contributed to multiple aspects of the study. Broadly, E.R.S. and J.H.G. designed and implemented the experiments, while A.M.T. and J.P.H. performed the experiments and contributed to data analysis. All authors assisted in manuscript preparation. This research was funded by the National Institute on Deafness and other Communication Disorders (NIDCD) 5-R01-DC001507 (J.H.G.). The authors have no conflicts of interest to disclose. Address for correspondence: John H. Grose, Department OHNS, University of North Carolina at Chapel Hill, CB No. 7070, 170 Manning Drive, Chapel Hill, NC 27599. E-mail: john_grose@med.unc.edu Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.

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