Influence of microphone soiling on syllable recognition in cochlear implants: simulation and recognition in noise

The microphone is the first link of the sound processing chain and if there is dirt on the membrane or in the input port, the frequency response is modified.

The effect of microphone cleaning in cochlear implants (CI) was studied by measuring speech perception scores in the noise of CI users and of normal hearing (NH) subjects with a CI simulator.

Sixty-one adult CI users and 20 NH were tested. In CI subjects, speech comprehension scores in noise were compared before and after cleaning microphone ports with one of two different cleaning procedures. NH listeners were tested using a vocoder that simulated soiled microphones. Two main coding schemes were considered, channel-picking (CP) and fixed-channel (FC).

With NH subjects, the effect of the coding strategy and degree of soiling was statistically significant (p < 10^-4); for the intermediate signal to noise ratios (SNRs), the recognition percentages were clearly affected. With CI users, cleaning the microphones significantly improved the recognition scores (p < 10^-4). The two cleaning procedures considered turned out to be significantly different (p < 10^-4).

It is suggested to perform a regular microphone port cleaning to avoid deep soiling which leads to a decrease in speech understanding.