Abstract
Objective: In sound processors of cochlear implant (CI) users, input sound signals are analysed in multiple frequency channels. The amplitude mapping function (AMF) is the output compression function dictating the conversion from (acoustical) channel output levels to (electrical) current levels used for electrode stimulation. This study focused on the detectability of AMF adjustments by CI users and the effects of detectable AMF adjustments on subjective preference and performance. Design: Just noticeable differences (JNDs) for AMF settings were measured for pre-processed sentences at 60 dB SPL in quiet and noise. Three AMF settings, ranging twice the JND, were used during a take-home trial period of 12 days. Subjective ratings were collected and speech recognition in quiet and noise was measured. Study sample: JND measurements: 17 CI users. Field experiment: 15 CI users. Results: JNDs for AMF settings varied among subjects and were similar in quiet and noise. A steeper AMF in the lower part was advantageous for speech recognition in quiet at soft levels. Subjective ratings showed limited agreement with speech recognition, both in quiet and noise. Conclusions: CI users may benefit from different AMF settings in different listening situations regarding subjective preference and speech perception, especially for speech in quiet.
Highlights
cochlear implant (CI) systems analyse input sound signals in multiple frequency channels that correspond to electrodes on the electrode array that is implanted in the cochlea
The default Q-parameter setting (Q20), with which the subjects had the most listening experience, was not always the Q-parameter setting that received the highest rating in the different listening environments. These results indicate that CI users differ in their subjective ratings of Q-parameter settings that are perceptually distinct from each other and that these subjective ratings depend on the listening situation for some CI users
Sensitivity of CI users to amplitude mapping function (AMF) differences For the majority of the subjects, the mean Just noticeable differences (JNDs) for AMF differences was well within the range of AMF adjustments provided in the fitting software that was used
Summary
CI systems analyse input sound signals in multiple frequency channels that correspond to electrodes on the electrode array that is implanted in the cochlea. In the case of the commonly used advanced combination encoder (ACEÔ) processing strategy, during each analysis cycle, a subset of the electrodes is selected for sequential stimulation. This stimulation is restricted to the dynamic ranges (DRs) of the individual electrodes as set by the clinician during the fitting session. The DR of each electrode is defined as the electrical current range between ‘just audible’ and ‘loud but acceptable’ levels.. The electrical DR of the electrodes i The DR of each electrode is defined as the electrical current range between ‘just audible’ and ‘loud but acceptable’ levels. In general, the electrical DR of the electrodes i
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