Objective and Methods:

Spectral peaks and notches are important cues that normal hearing listeners use to localize sounds in the vertical planes (the front/back and up/down dimensions). This study investigates to what extent cochlear implant (CI) listeners are sensitive to spectral peaks and notches imposed upon a constant-loudness background.

Results:

Listeners could always detect peaks, but not always notches. Increasing the bandwidth beyond two electrodes showed no improvement in thresholds. The high-frequency place was significantly worse than the low and middle places; although, listeners had highly-individual tendencies. Thresholds decreased with an increase in the height of the peak. Thresholds for detecting a change in the frequency of a peak or notch were approximately one electrode. Level roving significantly increased thresholds. Thus, there is currently no indication that CI listeners can perform a "true" profile analysis. Future studies will explore if adding temporal cues or roving the level in equal loudness steps, instead of equal-current steps (as in the present study), is relevant for profile analysis.

Application:

Data on the sensitivity to spectral peaks and notches are required to encode spectral localization cues in future CI stimulation strategies.

Funding:

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

Publications:

Objective:

In this project, results from previous steps of the project-cluster CI-HRTF are combined to develop and evaluate a new stimulation strategy for cochlear implants (CI). The new strategy attempts to encode spectral localization cues that are required for vertical-plane sound localization.

Methods and Results:

This project will start approximately in Dec. 2008.

Funding:

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

Objective and Methods:

This study investigates the effect of the number of frequency channels on vertical place sound localization, especially front/back discrimination. This is important to determine how many of the basal-most channels/electrodes of a cochlear implant (CI) are needed to encode spectral localization cues. Normal hearing subjects listening to a CI simulation (the newly developed GET vocoder) will perform the experiment using the localization method developed in the subproject "Loca Methods". Learning effects will be studied by obtaining visual feedback.

Results:

Experiments are underway.

Application:

Knowing the number of channels required to encode spectral cues for localization in the vertical planes is an important step in the development of a 3-D localization strategy for CIs.

Funding:

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

Publications:

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., 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