Channel discrimination along all contacts of the cochlear implant electrode array.

Cochlear implants provide people with severe hearing loss or deafness the
ability to acquire functional hearing by electrically stimulating the auditory
nerve fibres in the cochlea. The most commonly used stimulation strategy
(monopolar stimulation) introduces a lot of current spreading through the
cochlea. Consequently, various electrode contacts excite the same neural
fibres. Several studies have shown that patients are often not able to
discriminate between two neighbouring electrodes (Bierer & Faulkner, 2010;
Bonham & Litvak, 2008). Furthermore, no improvement in speech perception has
been found as the number of active electrodes increase beyond eight (Friesen,
Shannon, Baskent, & Wang, 2001; Shannon, Fu, & Galvin, 2004). These results
indicate that the CI recipients are not able to take full advantage of the
provided spectral information.

In a recent study (METC application registered under P02.106.AB), we tested 30
subjects and the results revealed that the channel discrimination of CI users
is linked to their speech perception (Biesheuvel, Briaire, de Jong, Boehringer
& Frijns, 2019).

The results from the previous study have proven the clinical value of the
discrimination test. Now we want to include the test in clinical routine as a
tool for helping the audiologist with cochlear implant fitting, and possibly
leading to improved speech perception. Before doing this, however, we can
pursue improvements identified in the earlier study, and validate the software
against a control test, such as comparison to psychometric curves (Wichmann &
Hill, 2001) or the Just Noticeable Difference value of the contact, similar to
what we have done before (Snel-Bongers, Briaire, Vanpoucke, & Frijns, 2011).

Validate and improve the new experimental algorithm.

The total duration of the study is estimated to be 2 years (0.5 fte / year).
Each subject will have to come to the ENT-department twice, for two to three
hours, including breaks. The first time the researcher will guide them through
both the tests step-by-step. The data from this test will be used for
validation of the algoritm. We will also evaluate how well the subject would be
able to go through the tests independently, by discussing with them what they
found confusing (about the user interface for example) and how we can improve
on this.

On the second test day, the subject has to go through the tests as
independently as they can (supervised by the researcher). This data can also be
used for validation, but mostly serves the goal of making an accessible test
for in the clinic.

On the test days, the patient will be briefed on the two tests that will be
done. The tests are the experimental algorithm (essentially the same test as in
METC application P02.106.AB) and control algorithm, based on psychometric
curves or the Just Noticable Difference tests (chapter 2). In all cases, the
patient is subjected to electrical stimulation just as is done in normal use of
the CI.

The tests are randomly allocated (every subject has an equal chance to start
with test 1 or 2 respectively). The tests will be separated by a break.

We also use the subjects demographic and retrospective performance data from
their medical records for further evaluation.

There are no known potential risks involved in this study. The subjects are
presented with electrical stimuli just as in normal use of the CI. We are
extensively testing the software before subjecting subjects to the stimuli. A
potential benefit may be that a subject can be better fitted through more
insight into their use of the spectral information provided by the CI.