Spectral and temporal processing by prelingually deafened adult CI users: focus on electrode discrimination and amplitude modulation detection

Prelingually deafened cochlear implant users mostly do not achieve a high level
of speech understanding with their CI. We hypothesize that the information
these patients are getting from their CI is often too complex for them to
process, given their compromised auditory processing abilities due to the long
duration of deafness. A simplified auditory signal, containing only
discriminable spectral channels, might improve speech understanding with the CI
specifically for this group of patients. Also, the influence of the longterm
deafness on temporal processing abilities and whether temporal processing
skills are related to speech understanding performance with the CI, is yet
unknown. More knowledge on these topics is important for the development and
adjustment of speech processing strategies for this group of patients.

For more detailed background information we refer to chapter 1 (introduction
and rationale) of the research protocol.

There are four main objectives in this research project, belonging to two
different parts of the study.

Part 1 comprises objectives 1 and 2:
1. Determine the electrode discrimination abilities of prelingually deafened
adult CI users in order to adjust the speech processing strategy with respect
to the number of active electrodes.
2. Determine whether the adjusted speech processing strategy leads to improved
speech understanding.

Part 2 comprises objectives 3 and 4:
3. Determine the amplitude modulation detection thresholds of 5 different
modulation frequencies by means of a listening task in a group of prelingually
deafened adult CI users and to obtain a reference value for these detection
thresholds in a group of postlingually deafened adults, measured under the same
testing conditions as the prelingually deaf.
4. Investigate the correlation between temporal resolution (as determined via
the amplidute modulation detection thresholds) and speech understanding.

The study comprises two major parts, with part 1 comprising objectives 1 and 2
and part 2 comprising objectives 3 and 4. Part 1 can be divided into 1A and 1B.

Part 1A is related to objective 1 and is an observational cohort study,
studying the effects of long-term deafness on the electrode discrimination
abilities with a cochlear implant.
Part 1B is related to objective 2 and is an interventional prospective cohort
study with one single group of participants who form their own controls. In
part 1B a specific cochlear implant setting is altered (this is the
intervention), and the effect of the change on speech understanding and on the
subjects* subjective appreciation of the sound is measured. These results are
then compared to baseline measurements (before the intervention) of speech
understanding and subjective scores.
In part 2, objectives 3 and 4 form an observational cohort study, measuring
temporal resolution in a group of prelingually deafened CI-users (with long
duration of deafness) and determining reference values for the same testing
conditions in a postlingually deafened group with short duration of deafness.
Furthermore we will investigate the correlation between temporal resolution and
speech understanding scores.

Part 1
Part 1A will be completed during three visits. Each visit will last for about 2
hours. In the following table the content of each session is described. Time
between subsequent visits is maximally two weeks.

Visit 1 * Remeasurement of the clinical T- and C-levels according to the test
protocol
* Initiate the loudness balancing procedure according to
the test protocol
Visit 2 * Loudness balancing procedure according to the test protocol
Visit 3 * Electrode discrimination testing according to the test protocol


Part 1B will be completed during two additional patient visits. Each visit will
last about 2 hours. Time between both visits is four weeks. If necessary, an
additional short visit can be planned intermediary to optimize the fitting if
the subject has certain complaints or has difficulties getting used to the new
programme. Therefore, the subject will be contacted by the researcher after one
week to see how he or she is adjusting. If a subject experiences more serious
problems to understand speech with the new programme and this causes practical
problems in for instance a working situation, the standard clinical programme
can be added to the processor in the additional visit. The subject will then be
advised to wear the new programme as much as possible, but is allowed to wear
the standard clinical programme in certain work-related situations. If this
situation were to occur, the subject will be asked to note per day how many
hours he or she has been wearing both the new and the standard programme.

Visit 1 * Baseline speech testing with subjects* standard clinical
programme
* Subjective evaluation of the standard clinical programme
* Programming the new, adapted programme (according to the
results of part 1) in the speech processor
Optional visit * CI Fitting: optimizing the adapted programme according
to subjects* experiences or adding the standard clinical programme
(when necessary)
Visit 3 * Speech testing with the adapted programme
* Subjective evaluation of the adapted programme
* Reprogramming the processor in accordance with subject's
preference
Part 2

For objectives 3 and 4 there is a small difference in duration of the study
between the postlingually and the prelingually deafened CI users. For the
latter, 2 additional tests of speech understanding are required, since the
standard speech test that is clinically used often is too difficult for this
patient group, resulting in a bottom-effect. This leads to 2 visits of 1 to1,5
hours for the postlingual CI users. For the prelingual CI users 2 visits of
1,5 to 2 hours per session are required, breaks included.

Visit 1 * Determine amplitude modulation detection thresholds for 5 modulation
frequencies according to the test protocol (pre- and
postlingual group)
Visit 2 * Determine amplitude modulation detection thresholds for 5 modulation
frequencies according to the test protocol
(continuation, pre- and postlingual group)
* Speech tests (prelingual group only)

The intervention in part 1B consists of an adaptation in the listening
programme the subject uses with his cochlear implant, thus a change in the
setting of the medical device that the subject already uses. The new programme
is made with the standard clinical fitting software. This new programme is
based on the results for the individual subject of part 1A and will comprise
the switching off of non-discriminable electrodes. A comparison is made between
this new programme (in terms of subjective preference and objective speech
understanding sores) and the standard clinical programme that the subject has
used until then.

Participation mainly requires a time investment of the subjects. However, the
subjects participating in part 1 are generally not the same as the subjects of
part 2, thus reducing testing time per subject.

In part 1 there is no division into groups; in part 2 the division is based on
the onset of deafness (pre-existing) because our interest lies within the
possibly different perceptual abilities of both groups.

For part 1, the time investment per subject includes 5 visits and a period of
4 weeks during which the subject has to wear an adapted programme in his speech
processor. During these visits speech perception tests will be performed at two
different moments and a small questionnaire will also have to be completed two
times.
The potential risks of the electrode discrimination test of part 1 are
qualified as low (NIC V2 Hazards analysis) and a number of additional safety
measures are incorporated in the test protocol to basically eliminate the risk
of stimulating too loud. The potential risk of the adapted programme in part 1B
is that the subject has to wear * for maximally 4 weeks - a speech programme
with a lesser sound quality. However, the potential benefit for a subject is
receiving a cochlear implant programme that allows for better speech
understanding or which is subjectively more pleasant to wear.

For part 2 the time investment is considerably less, with 2 visits per
subject. There are no risks associated with the testing procedure and no
alterations are made to the clinical programme of the subjects. Although there
are no direct practical advantages for the individual subjects, this new
information is useful for future developments in cochlear implant processing
strategies.