Towards quantifying cochlear implant localization performance in complex acoustic environments

Abstract

Cochlear implant (CI) users frequently report listening difficulties in reverberant and noisy spaces. While it is common to assess speech understanding with implants in background noise, binaural hearing performance has rarely been quantified in the presence of other sources, although the binaural system is a major contributor to the robustness of speech understanding in noisy situations with normal hearing. Here, a pointing task was used to measure horizontal localization ability of a bilateral CI user in quiet and in a continuous diffuse noise interferer at a signal-to-noise ratio of 0 dB. Results were compared to localization performance of six normal hearing listeners. The average localization error of the normal hearing listeners was within normal ranges reported previously and only increased by 1.8° when the interfering noise was introduced. In contrast, the bilateral CI user showed a localization error of 22° in quiet which rose to 31° in noise. This increase was partly due to target sounds being inaudible when presented from frontal locations between −20° and +20°. With the noise present, the implant user was only able to reliably hear target sounds presented from locations well off the median plane. The results give support to the informal complaints raised by CI users and can help to define targets for the design of, e.g., noise reduction algorithms for implant processors.

Keywords:

• Localization
• Cochlear implant
• Background noise
• Cocktail Party

Acknowledgements

This study was sponsored by the Intramural Programme of the MRC and Cochlear Europe Ltd. We are thankful for the support received from Paula Greenham and Brendan Murray. We are very grateful to our participants for their time and to the following centres for their help with recruitment: The South of England Cochlear Implant Centre, the Birmingham Adult Cochlear Implant Programme, the University Department of Otolaryngology – Head and Neck Surgery at Manchester Royal Infirmary and the Hearing Services Ropewalk House, Nottingham.