Binaural Enhancement for Bilateral Cochlear Implant Users

In Brief Objectives: Bilateral cochlear implant (BCI) users receive limited binaural cues and, thus, show little improvement to speech intelligibility from spatial cues. The feasibility of a method for enhancing the binaural cues available to BCI users is investigated. This involved extending interaural differences of levels, which typically are restricted to high frequencies, into the low-frequency region. Design: Speech intelligibility was measured in BCI users listening over headphones and with direct stimulation, with a target talker presented to one side of the head in the presence of a masker talker on the other side. Spatial separation was achieved by applying either naturally occurring binaural cues or enhanced cues. Results: In this listening configuration, BCI patients showed greater speech intelligibility with the enhanced binaural cues than with naturally occurring binaural cues. Conclusions: In some situations, it is possible for BCI users to achieve greater speech intelligibility when binaural cues are enhanced by applying interaural differences of levels in the low-frequency region. Bilateral cochlear implant (BCI) users have shown reduced binaural abilities as compared to listeners with normal hearing. Although BCI users have been shown to be sensitive to interaural differences of levels, their sensitivity to interaural time differences is poorer, and this is likely the reason that as a group they have shown limited benefit to speech intelligibility from spatial cues, as listeners with normal hearing do. A method for enhancing the binaural cues available to BCI users is investigated, which involved computing instantaneous interaural time differences in the low-frequency region (which are present naturally in a BCI configuration, although not typically available to BCI users due to the signal processing of the devices), and converting them to low-frequency interaural differences of levels (which are not present naturally, but are useable by normal-hearing listeners). The efficacy of such manipulation on the speech intelligibility of a target talker presented to one side of the head, in the presence of a masker talker on the other is evaluated. BCI patients showed greater speech intelligibility with enhanced than with naturally occurring binaural cues. Thus, improved speech intelligibility under some listening configurations is possible using the binaural cues available to BCI users.