Advanced beamformers for cochlear implant users: acute measurement of speech perception in challenging listening conditions

Abstract

Objective: To investigate the performance of monaural and binaural beamforming technology with an additional noise reduction algorithm, in cochlear implant recipients.

Method: This experimental study was conducted as a single subject repeated measures design within a large German cochlear implant centre. Twelve experienced users of an Advanced Bionics HiRes90K or CII implant with a Harmony speech processor were enrolled. The cochlear implant processor of each subject was connected to one of two bilaterally placed state-of-the-art hearing aids (Phonak Ambra) providing three alternative directional processing options: an omnidirectional setting, an adaptive monaural beamformer, and a binaural beamformer. A further noise reduction algorithm (ClearVoice) was applied to the signal on the cochlear implant processor itself. The speech signal was presented from 0° and speech shaped noise presented from loudspeakers placed at ±70°, ±135° and 180°. The Oldenburg sentence test was used to determine the signal-to-noise ratio at which subjects scored 50% correct.

Results: Both the adaptive and binaural beamformer were significantly better than the omnidirectional condition (5.3 dB±1.2 dB and 7.1 dB±1.6 dB (p<0.001) respectively). The best score was achieved with the binaural beamformer in combination with the ClearVoice noise reduction algorithm, with a significant improvement in SRT of 7.9 dB±2.4 dB (p<0.001) over the omnidirectional alone condition.

Conclusions: The study showed that the binaural beamformer implemented in the Phonak Ambra hearing aid could be used in conjunction with a Harmony speech processor to produce substantial average improvements in SRT of 7.1 dB. The monaural, adaptive beamformer provided an averaged SRT improvement of 5.3 dB.

Conflict of interest statement

Competing Interests: The authors have read the journal's policy and have the following conflicts: One co-author of the manuscript was employed by the MHH using ‘no strings’ funding supplied by Advanced Bionics. Additionally two co-authors hold scientific posts in the Advanced Bionics European Research Centre. The study protocol was developed in close cooperation between MHH and Advanced Bionics. All testing was conducted at MHH by MHH employees and all data were again analyzed in close cooperation between Advanced Bionics and MHH. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials.

Figures

Figure 1. Set-up of hearing aids and cochlear implant processor.

Subjects wearing Ambra behind-the-ear hearing aids on both sides communicating wirelessly; the hearing aid on the implanted side being connected to the cochlear implant speech processor.

Figure 2. Flow-chart of the adaptive beamformer.

The front (F) and back (B) microphone signals are added with a fixed delay to form the static cardioid beamformer. Afterwards, the beamformer outputs are added using a time-varying factor β for the adaptive beamformer. Not shown is the signal processing in different frequency bands.

Figure 3. Flow-chart of the binaural beamformer.

In the left and right device a dual-microphone beamformer is calculated and the audio signal is wirelessly transmitted to the opposite device yielding in the binaural beamformer.

Figure 4. Spatial characteristic of the monaural and binaural beamformer.

The polar plots are showing the microphone response for the omnidirectional microphone as well as monaural and binaural beamformers on a KEMAR dummy. Circles indicate the gain in decibels (dB) relative to the 00 response.

Figure 5. Speaker set up for speech perception testing.

Six loudspeakers were positioned in a circle of 1.20 and noise was presented simultaneously from the other five speaker locations.

Figure 6. Mean and individual speech reception thresholds for the monaural adaptive beamformer test session.

Speech reception thresholds (SRT) as measured for the OLSA sentences for each of the 10 subjects, in the four conditions tested during session A (omni – omnidirectional microphone; omni+CV – omnidirectional microphone with ClearVoice; aBF – monaural adaptive beamformer; aBF+CV – monaural adaptive beamformer mit ClearVoice). Short black lines indicate the mean of the study group; horizontal brackets indicate significant differences (*** at p

Figure 7. Mean and individual speech reception thresholds for the binaural beamformer test session.

Speech reception thresholds (SRT) as measured for the OLSA sentences for each of the 10 subjects, in the four conditions tested during session B (omni – omnidirectional microphone; aBF – monaural adaptive beamformer; bBF – binaural beamformer; bBF+CV – binaural beamformer mit ClearVoice). Short black lines indicate the mean of the study group; horizontal brackets indicate significant differences (*** at p