The Intelligibility of Interrupted Speech: Cochlear Implant Users and Normal Hearing Listeners.

Pranesh Bhargava,Deniz Başkent,Etienne Gaudrain

doi:10.1007/s10162-016-0565-9

Abstract

Compared with normal-hearing listeners, cochlear implant (CI) users display a loss of intelligibility of speech interrupted by silence or noise, possibly due to reduced ability to integrate and restore speech glimpses across silence or noise intervals. The present study was conducted to establish the extent of the deficit typical CI users have in understanding interrupted high-context sentences as a function of a range of interruption rates (1.5 to 24 Hz) and duty cycles (50 and 75 %). Further, factors such as reduced signal quality of CI signal transmission and advanced age, as well as potentially lower speech intelligibility of CI users even in the lack of interruption manipulation, were explored by presenting young, as well as age-matched, normal-hearing (NH) listeners with full-spectrum and vocoded speech (eight-channel and speech intelligibility baseline performance matched). While the actual CI users had more difficulties in understanding interrupted speech and taking advantage of faster interruption rates and increased duty cycle than the eight-channel noise-band vocoded listeners, their performance was similar to the matched noise-band vocoded listeners. These results suggest that while loss of spectro-temporal resolution indeed plays an important role in reduced intelligibility of interrupted speech, these factors alone cannot entirely explain the deficit. Other factors associated with real CIs, such as aging or failure in transmission of essential speech cues, seem to additionally contribute to poor intelligibility of interrupted speech.

Highlights

In everyday listening scenarios, when the target speech is masked by fluctuating background noise or competing speech, normal-hearing (NH) listeners are able to employ top-down mechanisms to perceptually restore the masked speech information
The first research question is BHow does the interrupted-speech perception of cochlear implant (CI) users differ from the interrupted-speech perception of NH listeners?^ In this regard, in experiment 1, we aimed to systematically characterize the extent of potential deficits in perception of periodically interrupted speech that the CI users have as compared to the NH listeners presented with normal speech (NHnorm)
The third research question was BCould the disparity in interrupted-speech perception between CI users and NH listeners be contingent on more factors than only the loss of spectro-temporal details?^ To answer this, in experiment 3, we aimed to test the factors of aging and baseline intelligibility

Summary

Introduction

In everyday listening scenarios, when the target speech is masked by fluctuating background noise or competing speech, normal-hearing (NH) listeners are able to employ top-down mechanisms to perceptually restore the masked speech information This phenomenon, variously referred to as ‘glimpsing’, ‘diplistening’ or ‘listening-in-the-valleys’, implies that the listeners are able to track and integrate the glimpses of unmasked target speech portions into a speech stream using the spectro-temporal cues and additional linguistic and contextual information from the unmasked segments (Miller and Licklider 1950; Buus 1985; Moore 2003; Srinivasan and Wang 2005; Wang and Humes 2010; Başkent and Chatterjee 2010; Başkent 2012). This could cause a difficulty in employing the top-down mechanisms in restoring and understanding degraded speech

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