The aim of this study was to investigate the effects on speech perception of manipulating
filter gains in a cochlear implant speech processor. Five implantees, who use the
CI22 implant and Spectra processor manufactured by Cochlear Ltd, participated. Four
experimental maps were created that were identical to their clinical map except for
the profile of gains across the filters. Experimental gain profiles had rising or
falling gains across the frequency range, or emphasized or de-emphasized the middle
frequencies, relative to the clinical map. Perception of CNC (consonant-vowel-consonant)
words at 70 dB SPL was significantly better with the clinical map than with all experimental
maps, whereas at the lower level (60 dB SPL) there was minimal difference between
the maps, with the low-frequency emphasis map giving significantly better scores than
the high-frequency emphasis map. Perception of sentences at 70 dB SPL with a signal-to-noise
ratio of +10 dB was better with the high-frequency emphasis map than with the low-frequency
emphasis map. None of these best-conditions, however, were statistically better than
the clinical map. The results highlighted the importance of signal audibility for
speech perception with cochlear implants.
Key Words
Cochlear implants - frequency response - speech perception
