The effect of pulse rate on temporal resolution and speech intelligibility in cochlear implant users

Rationale:

Spectral and temporal resolution are thought to be key contributors to understanding speech by cochlear implant (CI) users. In theory, increasing temporal resolution would enhance discrimination of fast intensity fluctuations in speech. However, clinical studies seem to indicate the opposite; they show a better speech understanding at reduced pulse rates, although the majority of these studies do not mimic real-life situations. In most cases, the pulse rates of only 1 or 2 electrodes are altered whereas other electrodes are deactivated. Therefore, additional information is required on the effects of pulse rate on speech intelligibility in a more real-life test environment.



Objectives:

To determine the (in)direct effect of CI pulse rate on speech intelligibility by means of (1) a standard test for temporal resolution: amplitude modulation detection (AMD) at two different modulation frequencies, (2) speech intelligibility tests (words in quiet and sentences in noise) and (3) investigate the reproducibility of the measurements.



Study design:

Interventional prospective cohort study to investigate correlations between pulse rate and speech intelligibility in post-lingually hearing impaired adult CI users.



Study population:

The study population consists of adult cochlear implant users from the CI-team South-East Netherlands patient population with an onset of deafness/severe hearing loss after the age of 4 years (post-lingual). No upper age limit is defined, since the participation depends on their willingness and ability to participate. Participants should have at least 1 year of experience with the uni- or bilateral cochlear implant(s) from the brand Cochlear.



Main study parameters/endpoints

The main study parameters are the temporal resolution capabilities – expressed as amplitude modulation detection threshold (AMDT) - and speech intelligibility – expressed as phoneme score (words in quiet) and speech recognition threshold (sentences in noise) - as a function of CI pulse rate in post-lingually hearing impaired CI users.



Nature and extent of the burden and risks associated with participation, benefit and group relatedness:

The intervention, i.e. replacement of the subjects’ speech processor with our own speech processor with preprogrammed MAPs during the tests, is equal for all subjects. This will increase time efficiency and ensure proper functioning of the speech processor during experiments. Associated risks are therefore considered minor to negligible. Participation does require time and effort from the subjects. Although we expect no direct benefits noticeable by the subjects when altering the pulse rate, the obtained results may contribute to optimized speech processing strategies in the future.

CI pulse rate is known to affect temporal resolution and speech intelligibility. Based on literature it is hypothesized that low pulse rates decrease temporal resolution, but increase speech intelligibility.

N/A

The patients that comply to the in- and exclusion criteria have specific types of speech processors, each of which is able to carry a maximum of 4 programs (MAPs, which drive the implant electrodes). To minimize risk for the patients CI, increase time efficiency and ensure proper functioning of the speech processor during experiments, we will not use the patient speech processor, but our own processors (same type as used by patient) that carry preprogrammed MAPs. The processors are programmed using the standard clinical fitting software Custom Sound™ from Cochlear, with 3 different pulse rates. These preprogrammed MAPs will be based on the MAP that the patient uses the most. A comparison will be made between the various MAPs in terms of amplitude modulation detection thresholds and objective speech understanding scores.