Towards objective measures of speech intelligibility for Cochlear Implant users in reverberant environments

Abstract

This study validates a novel approach to predict speech intelligibility for Cochlear Implant users (CIs) in reverberant environments. More specifically, we explore the use of existing objective quality and intelligibility metrics, applied directly to vocoded speech degraded by room reverberation, here assessed at ten different reverberation time (RT60) values: 0 s, 0.4 s – 1.0 s (0.1 s increments), 1.5 s and 2 s. Eight objective speech intelligibility predictors (SIPs) were investigated in this study. Of these, two were non-intrusive (i.e. did not require a reference signal) audio quality measures, four were intrusive, and two were intrusive speech intelligibility indexes. Three types of vocoders were implemented to examine how speech intelligibility predictions depended on the vocoder type. These were: noise-excited vocoder, tone-excited vocoder and a FFT-based N-of-M vocoder. Experimental results show that several intrusive quality and intelligibility measures were highly correlated with exponentially fit CI intelligibility data. On the other hand, only a recently - developed non-intrusive measure showed high correlations. These evaluations suggest that CI intelligibility may be accurately assessed via objective metrics applied to vocoded speech, thus may reduce the need for expensive and time-consuming listening tests.