Speech intelligibility as a function of the number of channels of stimulation for normal-hearing listeners and patients with cochlear implants

Objective: One goal was to determine for normal-hearing listeners the number of channels of stimulation necessary to achieve a high level of speech understanding. The second goal was to determine whether patients with a six- channel cochlear implant could achieve the same level of speech understanding as normal-hearing subjects listening to speech processed through six channels. Method: Speech signals were processed, for normal-hearing listeners, either in the manner of cochlear-implant processors with 2-9 fixed channels, or in the manner of a processor which picked, on each update cycle, 6 of 16 channels. Results: For the most difficult test material eight fixed channels were necessary to achieve the level of performance achieved with the 'n of m' processor. Some cochlear implant patients with a six-channel continuous interleaved sampling processor achieved the same level of performance as normal-hearing subjects listening to speech via six channels. Conclusions: A signal processor for cochlear implants with eight channels should produce the same level of intelligibility as a processor with many more channels. Processors using continuous interleaved sampling technology can provide a signal which results in the same level of speech understanding as normal, acoustic stimulation.