Cochlear Implant Microphone Location Affects Speech Recognition in Diffuse Noise
Cochlear Implant Microphone Location Affects Speech Recognition in Diffuse Noise
Background: Despite improvements in cochlear implants (CIs), CI recipients continue to experience
significant communicative difficulty in background noise. Many potential solutions have been proposed
to help increase signal-to-noise ratio in noisy environments, including signal processing and external
accessories. To date, however, the effect of microphone location on speech recognition in noise has
focused primarily on hearing aid users.
Purpose: The purpose of this study was to (1) measure physical output for the T-Mic as compared with
the integrated behind-the-ear (BTE) processor mic for various source azimuths, and (2) to investigate the
effect of CI processor mic location for speech recognition in semi-diffuse noise with speech originating
from various source azimuths as encountered in everyday communicative environments.
Research Design: A repeated-measures, within-participant design was used to compare performance
across listening conditions.
Study Sample: A total of 11 adults with Advanced Bionics CIs were recruited for this study.
Data Collection and Analysis: Physical acoustic output was measured on a Knowles Experimental
Mannequin for Acoustic Research (KEMAR) for the T-Mic and BTE mic, with broadband noise presented
at 0 and 90 (directed toward the implant processor). In addition to physical acousticmeasurements, we also
assessed recognition of sentences constructed by researchers at Texas Instruments, the Massachusetts
Institute of Technology, and the Stanford Research Institute (TIMIT sentences) at 60 dBA for speech source
azimuths of 0, 90, and 270. Sentences were presented in a semi-diffuse restaurant noise originating from
the R-SPACE 8-loudspeaker array. Signal-to-noise ratio was determined individually to achieve approximately
50%correct in the unilateral implanted listening condition with speech at 0. Performance was compared
across the T-Mic, 50/50, and the integrated BTE processor mic.
Results: The integrated BTE mic provided approximately 5 dB attenuation from 1500–4500 Hz for signals
presented at 0 as compared with 90 (directed toward the processor). The T-Mic output was essentially
equivalent for sources originating from 0 and 90. Mic location also significantly affected sentence recognition
as a function of source azimuth,with the T-Mic yielding the highest performance for speech originating
from 0.
Conclusions: These results have clinical implications for (1) future implant processor design with
respect to mic location, (2) mic settings for implant recipients, and (3) execution of advanced speech
testing in the clinic.
Cochlear implants, microphone location, R-SPACE, restaurant noise, T-Mic, SNR, speech recognition
Background: Despite improvements in cochlear implants (CIs), CI recipients continue to experience
significant communicative difficulty in background noise. Many potential solutions have been proposed
to help increase signal-to-noise ratio in noisy environments, including signal processing and external
accessories. To date, however, the effect of microphone location on speech recognition in noise has
focused primarily on hearing aid users.
Purpose: The purpose of this study was to (1) measure physical output for the T-Mic as compared with
the integrated behind-the-ear (BTE) processor mic for various source azimuths, and (2) to investigate the
effect of CI processor mic location for speech recognition in semi-diffuse noise with speech originating
from various source azimuths as encountered in everyday communicative environments.
Research Design: A repeated-measures, within-participant design was used to compare performance
across listening conditions.
Study Sample: A total of 11 adults with Advanced Bionics CIs were recruited for this study.
Data Collection and Analysis: Physical acoustic output was measured on a Knowles Experimental
Mannequin for Acoustic Research (KEMAR) for the T-Mic and BTE mic, with broadband noise presented
at 0 and 90 (directed toward the implant processor). In addition to physical acousticmeasurements, we also
assessed recognition of sentences constructed by researchers at Texas Instruments, the Massachusetts
Institute of Technology, and the Stanford Research Institute (TIMIT sentences) at 60 dBA for speech source
azimuths of 0, 90, and 270. Sentences were presented in a semi-diffuse restaurant noise originating from
the R-SPACE 8-loudspeaker array. Signal-to-noise ratio was determined individually to achieve approximately
50%correct in the unilateral implanted listening condition with speech at 0. Performance was compared
across the T-Mic, 50/50, and the integrated BTE processor mic.
Results: The integrated BTE mic provided approximately 5 dB attenuation from 1500–4500 Hz for signals
presented at 0 as compared with 90 (directed toward the processor). The T-Mic output was essentially
equivalent for sources originating from 0 and 90. Mic location also significantly affected sentence recognition
as a function of source azimuth,with the T-Mic yielding the highest performance for speech originating
from 0.
Conclusions: These results have clinical implications for (1) future implant processor design with
respect to mic location, (2) mic settings for implant recipients, and (3) execution of advanced speech
testing in the clinic.
Cochlear implants, microphone location, R-SPACE, restaurant noise, T-Mic, SNR, speech recognition