The acoustic change complex in cochlear implant users

Cochlear implantation (CI) is the preferred treatment option for both adult and
paediatric patients with profound sensorineural hearing loss. In the
rehabilitation period after implantation, CI users develop the interpretation
of CI induced activity as sounds. A large variability in auditory performance
occurs in this first period, and a certain variability persists after several
years of CI use. The available objective measurements assessing auditory
performance in CI patients are limited. This study aims at an objective
measurement possibly related to speech intelligibility. Intelligibility of
speech, which is a complex sound consisting of various frequency and amplitude
changes, is related to the ability to perceive these subtle changes in
frequency and intensity. CI users may experience difficulties recognizing these
subtle changes, in particular when they adapting to CI induced 'hearing'. An
electrophysiological measurement, such as the acoustic change complex (ACC),
recorded from the auditory cortex, might be an appropriate objective tool to
test whether tone changes are perceived. To date, little is known about the
relation between the ACC and the perception of small tone changes in CI users.
In this study we aim to assess the level of agreement between ACC parameters
and frequency discrimination ability, assessed with Frequency Discrimination
Tresholds (FDTs), in the same CI users. This level of agreement could increase
with CI hearing experience, which could imply that the ACC has predictive value
for an individual*s maximum expected auditory performance.

Primary Objective:

To assess the level of agreement between ACC variables (amplitude, latency) in
CI users and the FDT perceived by the same CI users.

Secondary Objectives:

• To assess correlations between speech perception and ACC variables, and
between speech perception and FDT.
• To explore development of ACC and FDT with CI use.
• To compare ACC and FDT between short and long term CI users, and between
unilateral deaf and bilateral deaf CI users.
• To compare ACC and FDT between the CI ear and the normal ear within
unilateral deaf CI users.

This study concerns an explorative pilot study with adult CI users as subjects.
The study will be performed at the department of Otorhinolaryngology in the
University Medical Center Utrecht.

All participants will undergo a test session with frequency discrimination
tests and a speech perception test. Two frequency discrimination tests are
used, the electrophysiological ACC and the FDT test. In order to assess speech
perception, the speech reception threshold (SRT) is measured with the Digits In
Noise (DIN) test.
This study will include a total of 30 subjects, 18 CI users with long term
experience and 12 with short term CI experience. The 18 long term CI users will
undergo one test session, the 12 short term CI users are followed
longitudinally during their rehabilitation period with repeated test sessions.
After the first test session in their first month of CI use the test session
will repeated 3 times; after 3, 6 and 12 months of CI hearing experience.
Both the 'long term experience' group and the 'short term experience' group are
further divided in 2 subgroups: Bilateral deaf and unilateral CI users.
All frequency discrimination tests for the unilateral CI users will take more
time because their normal hearing ear is tested in addition to their CI ear.
Only the subgroup of 6 unilateral deaf subjects with short term CI experience
will undergo one additional baseline measurement prior to activation of their
CI to assess frequency discrimination and speech perception of their normal
hearing ear only.

The ACC recording and the just noticeable difference tests are considered as
non-risk investigations.
The procedure of ACC recording is principally the same as the recording
procedure for the clinically applied ABR, CAEP and EEG recordings.
The expected burden due to participation for all subjects consists of
approximately 3 to 4.5 hours per session. The tests will be performed during
one visit to the outpatient clinic. These sessions will be scheduled in
consultation with the subject and if possible, during the subjects clinically
scheduled visits to the department of Otorhinolaryngology, so that no
additional visits to the outpatient clinic are necessary.
Subjects will not have a direct benefit of this study, but the results of this
study will contribute to the scientific knowledge of how frequency and
intensity changes in stimuli are perceived in the auditory cortex of CI users.
Furthermore, this explorative study will gain knowledge on the level of
agreement between the ACC and FDT in short and long term CI users, which can be
used for future studies.