Factors for speech intelligibility in the symmetric and anti-symmetric speech-masker conditions

Date
2013
DOI
Authors
Spencer, Nathaniel John
Version
OA Version
Citation
Abstract
The goal of this work is to better understand why it is easier for some than others to understand an in-front target talker presented amid two spatially-distributed interfering talkers. Speech reception thresholds (SRTs) of young listeners (normal-hearing and hearing-impaired) were measured, with the maskers arranged in the following spatial configurations: 1) "colocated", both in-front, 2) "symmetric", at ± 60° azimuth, and 3) "anti-symmetric", both at either +60°, or -60°, azimuth. SRTs were measured both binaurally and monaurally, with monaural stimuli presented to the "better-ear." Binaural benefits were calculated as the decrease in threshold when the second ear was added to the better-ear. Sensitivity to interaural time differences, interaural level differences and interaural cross-correlation were measured in the same listeners, using narrow-band noises centered at a low frequency (500Hz) and at a high frequency (2 or 4kHz). Large inter-subject differences were found for both listener groups among both interaural difference sensitivity thresholds and binaural benefits for the spatially-separated conditions. No correlations, for either of the listener groups, were observed between symmetric binaural benefit and any of the interaural difference sensitivity measures. Anti-symmetric binaural benefit significantly correlated with interaural difference sensitivity for many of the tasks, both for the normal-hearing group and among the set of hearing-impaired listeners with severe-amd-less hearing-loss. SRTs were predicted using the short-time Equalization-Cancellation (EC) model, in which two types of parameters were varied: first, the standard deviations of time-and intensity-jitters at the inputs of the binaural processing mechanism (analogous to changes in interaural sensitivity) and second, the temporal window in the binaural processing mechanism (affecting benefit from short-time binaural advantages). EC-window length was most important for predicting changes in symmetric SRTs. Changes in jitter standard deviations were most important for predicting changes in anti-symmetric SRTs. These results suggest some key differences in the mechanisms related to individual differences for the two speechmasker conditions. Both interaural difference sensitivity and a mechanism suggested by the importance of the EC-window length might be important for the symmetric condition, while interaural difference sensitivity is a key factor for the anti-symmetric condition.
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Thesis (Ph.D.)--Boston University
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