Background: Use of personal frequency modulated (FM) systems significantly improves speech recognition
in noise for users of cochlear implants (CI). There are, however, a number of adjustable
parameters of the cochlear implant and FM receiver that may affect performance and
benefit, and there is limited evidence to guide audiologists in optimizing these parameters.
Purpose: This study examined the effect of two sound processor audio-mixing ratios (30/70
and 50/50) on speech recognition and functional benefit for adults with CIs using
the Advanced Bionics Auria® sound processors.
Research Design: Fully-repeated repeated measures experimental design. Each subject participated in
every speech-recognition condition in the study, and qualitative data was collected
with subject questionnaires.
Study Sample: Twelve adults using Advanced Bionics Auria sound processors. Participants had greater
than 20% correct speech recognition on consonant-nucleus-consonant (CNC) monosyllabic
words in quiet and had used their CIs for at least six months.
Intervention: Performance was assessed at two audio-mixing ratios (30/70 and 50/50). For the 50/50
mixing ratio, equal emphasis is placed on the signals from the sound processor and
the FM system. For the 30/70 mixing ratio, the signal from the microphone of the sound
processor is attenuated by 10 dB.
Data Collection and Analysis: Speech recognition was assessed at two audio-mixing ratios (30/70 and 50/50) in quiet
(35 and 50 dB HL) and in noise (+5 signal-to-noise ratio) with and without the personal
FM system. After two weeks of using each audio-mixing ratio, the participants completed
subjective questionnaires.
Results: Study results suggested that use of a personal FM system resulted in significant
improvements in speech recognition in quiet at low-presentation levels, speech recognition
in noise, and perceived benefit in noise. Use of the 30/70 mixing ratio resulted in
significantly poorer speech recognition for low-level speech that was not directed
to the FM transmitter. There was no significant difference in speech recognition in
noise or functional benefit between the two audio-mixing ratios.
Conclusions: Use of a 50/50 audio-mixing ratio is recommended for optimal performance with an
FM system in quiet and noisy listening situations.
Key Words
FM system - speech recognition
