Effects of channel-to-electrode mappings on speech reception with the ineraid cochlear implant

Research was conducted to assess multichannel saliency with the Ineraid cochlear prosthesis. The goal was to determine whether tonotopically ordered stimulation benefits speech reception.

In a single high-performing subject, changes in speech reception were studied during two dramatic alterations to the normal (tonotopic) mapping between the sound-processors's four filter channels and the intracochlear electrode array: In one alteration, the four filter outputs were summed and delivered to one electrode; this single-channel mapping was worn for 7 days. In another alteration, the four filter outputs were connected in reverse tonotopic order to four intracochlear electrodes; this reversed mapping was worn for 3 days.

When using the implant in conjunction with speechreading, all three mappings provided large gains over speechreading alone on the recognition of words in sentences. When using the implant alone (without speechreading), tests of consonant and vowel recognition, and the recognition of words in isolation and in sentences all showed substantial decreases in performance across the three mapping conditions: normal > single-channel > reversed. The patterns of segmental confusions and the relations among scores on different tests were highly consistent. Finally, the performance with the altered mappings was, in some ways, remarkably good. With single-channel mapping, 15% word recognition was obtained, much less than the 54% obtained with the normal mapping, but demonstrative of some open-set speech reception. With the reversed mapping, high levels of consonantal voicing and manner information were received, indicating good reception of time-intensity cues, but open-set word recognition was near zero.

Despite the extensive spread of current associated with monopolar intracochlear stimulation, the Ineraid electrode array affords a degree of perceptual selectivity that substantially aids speech reception.