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:

  • Goupell, M., Laback, B., Majdak, P., and Baumgartner, W. D. (2008). Current-level discrimination and spectral profile analysis in multi-channel electrical stimulation, J. Acoust. Soc. Am. 124, 3142-57.
  • Goupell, M. J., Laback, B., Majdak, P., and Baumgartner, W-D. (2007). Sensitivity to spectral peaks and notches in cochlear implant listeners, presented at Conference on Implantable Auditory Prostheses (CIAP), Lake Tahoe.