Bilateral cochlear implantation and directional multi-microphone systems

Abstract

Better speech understanding in noise is a common goal of bilateral cochlear implantation and directional multi-microphone systems. In this study, the performance of five signal processing/presentation strategies is compared: (1) monaural presentation using a single omnidirectional microphone, (2) monaural presentation using a simple two-microphone beamformer in a behind-the-ear (BTE) housing, (3) monaural presentation using a complex four-microphone adaptive beamformer, (4) binaural presentation using two omnidirectional microphones and (5) binaural presentation using two simple two-microphone beamformers in separate behind-the-ear units. Speech reception thresholds (SRT) in noise were measured in four adults implanted bilaterally with MED-EL cochlear implant systems. Speech was presented from the front and speech spectrum noise from an azimuth of 90°. For all conditions involving microphones at only one ear, the noise source was placed at the contralateral side. Average speech reception threshold (SRT) improvements over the single omnidirectional microphone (condition 1) were 3.0 dB for the simple two-microphone BTE beamformer, 1.8 dB for bilateral cochlear implants and 3.6 dB for the combination of both. The largest mean improvement (13.0 dB) was achieved by the complex four-microphone beamformer. Bilateral cochlear implants and multi-microphone beamforming seem to complement each other but are outperformed by complex signal processing strategies in this laboratory setting.