Fundamental frequency and the intelligibility of competing sentences with cochlear implant processing

Abstract

Speech perception in the presence of another competing voice is one of the most challenging tasks for cochlear implant users. Several studies have shown (1) that the fundamental frequency (F0) is a useful cue for segregating competing speech sounds and (2) the F0 is better represented by the temporal fine structure than the temporal envelope. However, current cochlear implant speech processing algorithms emphasize the temporal envelope information and discard the temporal fine structure. In this study, speech recognition was measured as a function of the F0 separation of the target and competing sentence in normal-hearing and cochlear implant listeners. For the normal-hearing listeners, the combined sentences were processed through either a traditional cochlear implant simulation or a new algorithm which additionally extracts a slowed-down version of the temporal fine structure. The results showed no benefit of increasing F0 separation for the cochlear implant or traditional simulation groups. However, as found with unprocessed sentences presented to normal-hearing listeners, the new algorithm resulted in gradual improvements with increasing F0 separations. These results demonstrate that inadequate coding of the temporal fine structure in current speech processing algorithms may complicate the segregation of competing speech sounds. [Work supported by NIDCD F32DC05900 and R01DC02267.]