In search of the best possible outcome for the severe hearing impaired who have regained the ability to hear by means of a cochlear implant (CI), electrical stimulation and the information it carries should match as closely as possible to what the human brain naturally has evolved to cope with and learned to process instead of relying on plasticity to adapt to an induced mismatch. At the moment, however, CI's are fitted with a 'one size fits all' principle. This is known to cause a mismatch between the frequencies presented by the CI electrode array and the frequencies represented at the corresponding natural acoustic location in an individual cochlea. In this study it is hypothesized that an individual imaged based fitting that pursues natural hearing alignment and is implemented from the start of the rehabilitation process, will improve the individual outcomes of electric hearing. The natural fitting strategy is thought to give rise to a steeper learning curve, result in a better performance in challenging listening situations, improve sound quality, complement better with residual acoustic hearing in the contralateral ear and win the preference of CI-recipients.

Inclusion Criteria:

• Adult (18y or older) and meeting the conventional Dutch CI criteria;
• Proficient speaker of Dutch language;
• Post-lingual onset of profound deafness (> 4 years of age);
• Subject receives an Advanced Bionics implant with Midscala electrode and an Advanced Bionics sound processor;
• Prepared to use study specific hearing aid (Phonak) for the duration of the study;
• Rehabilitation at MUMC+ for the first year after surgery regarding CI as well as HA;
• Active participation in trial related procedures such as daily randomization and regular testing.

Exclusion Criteria:

• Physical or non-physical contraindications for MRI or CT imaging;
• Additional disabilities that may prevent active participation and testing as per protocol. If there are indications that the mental abilities to comply with the study procedures are insufficient, additional screening will be performed with the Mini-Mental State Examination. Patients will be excluded from the study when the resulting score is lower than 24;
• Cochlear or neural abnormalities that could affect outcome measures and/or compromise the placement of the electrode as assessed by the CI surgeon;
• Active participation in another prospective clinical trial;
• Pregnancy at time of imaging;
• Requirement for electric-acoustic activation prior to the first year follow-up;
• Having received a cochlear implant earlier (e.g. explantation or bilateral implantation).