Speech recognition in noise for cochlear implantees with a two-microphone monaural adaptive noise reduction system

In this study the performance of a noise reduction strategy applied to cochlear implants is evaluated. The noise reduction strategy is based on a 2-channel adaptive filtering strategy using two microphones in a single behind-the-ear hearing aid.

Four adult LAURA cochlear implant users (Peeters et al., 1993) took part in the experiments. The tests included identification of monosyllabic CVC (consonant-vowel-consonant) words and measurements of the speech reception threshold (SRT) of lists of numbers, in background noise presented at 90 degrees relative to the 0 degrees frontal direction of the speech. Percent correct phoneme scores for the CVC words at signal to noise ratios (SNRs) of -5, 0, and +5 dB in steady speech-weighted noise at 60 dB SPL and SRTs for numbers in speech-weighted steady and nonsteady ICRA noise were both obtained in conditions with and without the noise reduction pre-processing. Physical SNR improvements of the noise reduction system are evaluated as well, as a function of the direction of the noise source.

Highly significant improvements in speech understanding, corresponding on average to an SNR improvement of about 10 dB, were observed with this 2-channel adaptive filtering noise reduction strategy using both types of speech-noise test materials. These perceptual evaluations agree with physical evaluations and simulations of this noise reduction strategy. Taken together, these data demonstrate that cochlear implantees may increase their speech intelligibility in noisy environments with the use of multimicrophone noise reduction systems.