Objective and Method:

Current cochlear implant (CI) systems are not designed for sound localization in the sagittal planes (front-back and up/down-dimensions). Nevertheless, some of the spectral cues that are important for sagittal plane localization in normal hearing (NH) listeners might be audible for CI listeners. Here, we studied 3-D localization with bilateral CI-listeners using "clinical" CI systems and with NH listeners. Noise sources were filtered with subject-specific head-related transfer functions, and a virtually structured environment was presented via a head-mounted display to provide feedback for learning. 

Results:

The CI listeners performed generally worse than NH listeners, both in the horizontal and vertical dimensions. The localization error decreases with an increase in the duration of training. The front/back confusion rate of trained CI listeners was comparable to that of untrained (naive) NH listeners and two times higher than for the trained NH listeners. 

Application:

The results indicate that some spectral localization cues are available to bilateral CI listeners, even though the localization performance is much worse than for NH listeners. These results clearly show the need for new strategies to encode spectral localization cues for CI listeners, and thus improve sagittal plane localization. Front-back discrimination is particularly important in traffic situations.

Funding:

FWF (Austrian Science Fund): Project # P18401-B15

Publications:

  • Majdak, P., Goupell, M., and Laback, B. (2011). Two-Dimensional Localization of Virtual Sound Sources in Cochlear-Implant Listeners, Ear & Hearing.
  • Majdak, P., Laback, B., and Goupell, M. (2008). 3D-localization of virtual sound sources in normal-hearing and cochlear-implant listeners, presented at Acoustics '08  (ASA-EAA joint) conference, Paris