The relative importance of temporal envelope information for intelligibility prediction: A study on cochlear-implant vocoded speech

Vocoder simulation has been long applied as an effective tool to assess factors influencing the intelligibility of cochlear implants listeners. Considering that the temporal envelope information contained in contiguous bands of vocoded speech is correlated and redundant, this study examined the hypothesis that the intelligibility measure evaluating the distortions from a small number of selected envelope cues is sufficient to well predict the intelligibility scores. The speech intelligibility data from 80 conditions was collected from vocoder simulation experiments involving 22 normal-hearing listeners. The relative importance of temporal envelope information in cochlear-implant vocoded speech was modeled by correlating its speech-transmission indices (STIs) with the intelligibility scores. The relative importance pattern was subsequently utilized to determine a binary weight vector for STIs of all envelopes to compute the index predicting the speech intelligibility. A high correlation (r = 0.95) was obtained when selecting a small number (e.g., 4 out of 20) of temporal envelope cues from disjoint bands to predict the intelligibility of cochlear-implant vocoded speech.