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

Abstract

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. 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. In normal-hearing subjects the discrimination threshold for ITD was 83-117 µs. Localization ability in a free sound field was below the limit of resolution. Asignificant MMN was measured. CI users showed amean angle detection error of more than 30° and adiscrimination threshold between 1100 and 2100 µs. Due to artifacts, no clear MMN component could be recorded. 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.