Background: Current fitting guidelines from the American Academy of Audiology (Academy) support
the use of objective electroacoustic measures and behavioral testing when fitting
frequency modulation (FM) systems to hearing aids. However, only behavioral testing
is recommended when fitting FM systems to individuals with cochlear implants (CIs)
because a protocol for conducting electroacoustic measures has yet to be developed
for this population.
Purpose: The purpose of this study was to propose and examine the validity of a newly developed,
objective, electroacoustic test protocol for fitting electrically and electromagnetically
coupled FM systems to CI sound processors.
Research Design: Electroacoustic measures were conducted and replicated in the laboratory with three
contemporary CI sound processors and several FM system combinations. A repeated measures
design was used with four participants to examine the validity of the proposed electroacoustic
test protocol.
Study Sample: Three contemporary CI sound processors were tested electroacoustically in the laboratory
while coupled to combinations of five FM receivers and four FM transmitters. Two adolescents
using Cochlear Nucleus 5 sound processors and two adult participants using MED-EL
OPUS 2 sound processors completed behavioral and subjective measures.
Data Collection and Analysis: Using current hearing aid practice guidelines from the Academy, electroacoustic measurements
were conducted in the laboratory with the CIs and FM systems to determine transparency,
where equivalent inputs to the CI and FM microphones result in equivalent outputs.
Using a hearing aid analyzer, acoustic output from the CI sound processor was measured
via monitor earphones and specialized equipment from CI manufacturers with 65 dB SPL
speech inputs (1) to the sound processor and (2) to the FM transmitter microphones.
The FM gain or volume was adjusted to attempt to achieve transparency for outputs
from the two input devices. The four participants completed some or all of the following
measures: speech recognition in noise without and with two FM systems in a classroom,
loudness ratings without and with two FM systems measures in a quiet condition in
a classroom, and questionnaires.
Results: Transparency was achieved for most CI and FM combinations, but most systems required
adjustments to FM gain or volume relative to the manufacturer default setting. Despite
adjustments to the systems, transparency was not attainable for some FM receiver and
transmitter combinations. Behavioral testing in four participants provided preliminary
support to the proposed electroacoustic test protocol.
Conclusions: Valid and reliable electroacoustic test measures may be feasible with CIs coupled
to FM systems with specialized equipment from the CI manufacturer. Advances in equipment
available for electroacoustic testing with these devices as well as additional research
will lend further support to this objective approach to fitting FM systems to CIs.
Key Words
Cochlear implant - electroacoustic - FM system
