Output compression in cochlear implants The added value of subject-specific parameter optimization

A cochlear implant (CI) is an electronic device that can provide a sense of hearing to deaf or profoundly hearing impaired listeners by directly activating auditory nerve fibers. Optimal auditory performance with a CI requires subject-specific adjustments of several system parameters, i.e. the CI needs to be “fitted” to the individual user. A large number of system parameters is available to the clinician in the fitting software. For some of these parameters it is essential that they are individualized prior to switching on the device, since they ensure that sounds are audible without making sounds uncomfortably loud. For other parameters subject-specific optimization is less essential and a one-size-fits-all approach of using default settings results in good performance for the majority of CI users. However, these default settings may not always result in optimal settings for individual CI users and subject-specific fine-tuning of these parameter settings may further improve performance and/or user satisfaction. Unfortunately, for more advanced parameters the literature provides limited information about the added value of subject-specific parameter optimization and/or well-structured approaches to do so.
This thesis includes several studies that have been conducted to gain insight in the added value of optimizing one specific system parameter for individual CI users. This system parameter affects the amplitude mapping function (AMF) which dictates the conversion from acoustical sound levels into electrical current levels and thereby influences the loudness perception of sounds by CI users.