Processing of interaural time differences in normal-hearing subjects and cochlear implant users with FSP and HDCIS coding strategy

Background Sound localization is necessary for social interaction and remains challenging for bilateral cochlear implant (CI) users. This study investigated the influence of fine structure processing (FSP) coding strategies on temporal accuracy and source localization. The ability to discriminate between different interaural time differences (ITD) was measured objectively and compared. Materials and methods Fifteen normal-hearing subjects and five CI users participated in this study. Electrophysiological recording of mismatch negativity (MMN) and psychoacoustic tests with headphones and loudspeakers were conducted to measure and compare the discrimination of ITDs. Results In normal-hearing subjects the discrimination threshold for ITD was 83-117 mu s. Localization ability in a free sound field was below the limit of resolution. A significant MMN was measured. CI users showed a mean angle detection error of more than 30 degrees and a discrimination threshold between 1100 and 2100 mu s. Due to artifacts, no clear MMN component could be recorded. Conclusion This study shows that MMN can be used as an objective measure of ITD discrimination in normal-hearing participants. An indication that improvements in directional hearing can be achieved with the transfer of fine structure could not be provided by this study.