Cochlear implant patients' localization using interaural level differences exceeds that of untrained normal hearing listeners

Abstract

Bilateral cochlear implant patients are unable to localize as well as normal hearing listeners. Although poor sensitivity to interaural time differences clearly contributes to this deficit, it is unclear whether deficits in terms of interaural level differences are also a contributing factor. In this study, localization was tested while manipulating interaural time and level cues using head-related transfer functions. The results indicate that bilateral cochlear implant users' ability to localize based on interaural level differences is actually greater than that of untrained normal hearing listeners.

Figure 1

In the top left panel, localization scores in terms of RMS error are provided for CI listeners and NH listeners. Each data point represents the trimmed mean for the CI users and the weighted trimmed mean for the NH listeners. Error bars indicate 95% confidence intervals for the trimmed means based on bootstrap analyses. Lower scores indicate better performance. Response patterns are shown in the top right panel. In the bottom panel, performance for each CI user is presented. Participants are ordered based on performance using the ITD + ILD HRTFs. To facilitate comparison across different processors, scores are presented as percentiles based on a normal distribution with a mean and standard deviation matching the processor-specific NH data presented in Table Table 2.. Lower scores indicate better performance. Results suggest that CI users’ binaural localization deficit largely reflects a deficit for using ITD cues, alongside exceptional performance using ILD cues.