Take your pick: Channel selection and noise reduction in Cochlear implants

Abstract:
Signal processing in the Nucleus(TM) cochlear implant system traditionally uses a stimulation strategy where a subset of spectral channels is selected in each stimulation frame based on maximum amplitude (for instance 8 largest out of 22). Recent evidence suggests that other criteria than maximum amplitude may be better for channel selection in terms of speech understanding, subjective preference and power consumption. This evidence is reviewed and discussed in this paper. We also describe a new noise reduction strategy that uses a real-time SNR estimator to apply a gain reduction on channels having low SNR prior to the amplitude-based channel selection stage. This new noise reduction scheme was tested in 13 Cochlear implant users using an adaptive speech-in-noise test to find the 50% speech reception threshold (SRT). The average improvement using the new scheme was 2.2 dB in speech weigthed noise, 0.9 dB in party noise and 1.3 dB in city noise. All these improvements were statistically significant.