The study will involve the comparison of three groups with severe-profound hearing loss. Patients with a Cochlear Implant only, patients with a cochlear implant and Hearing Aid, and finally patients with two hearing aids.

This will enable a comparison of standard fitting protocols against the new rationale using the same devices. Devices used for patients in all 3 groups are now available in standard of care, and can be kept afterwards should the patients wish.

The study will involve three groups of 20 patients per group. This first is experienced adult bimodal users of the AB system who have usable contralateral residual hearing. A clinical baseline and three research conditions will be evaluated.

The Naida CI Link HA (Link) will be fitted, tested and then optimised using a special bimodal fitting formula. Subjects will be allowed three months to acclimatize and will then be retested. The second research condition will evaluate the fully integrated bimodal system, where the microphone signals from CI and HA are shared and a bilateral beamformer is formed. A third intervention will involve modifying the CI settings to minimize the mis-match between frequencies delivered via the CI.

A second group with no aidable hearing on their non-implanted ear will also be studied. A contralateral routing of signal (CROS) device will send sounds on the non-implanted side. Tests will be made with and without CROS, as well as with directional microphone settings.

Finally as a control group, bilateral HA users will be tested with the similar HA fitting as used for the bimodal group.

This will enable a comparison of standard fitting protocols against the new rationale using the same devices.

Inclusion Criteria:

• Participant is willing and able to give informed consent for participation in the study.
• Male or Female, aged 18 years or above.
• Consistent unilateral user of an Advanced Bionics cochlear implant and a contralateral hearing aid for at least 6 months, ideally 12 months, and Bilateral severe to profound hearing loss (meeting NICE criteria for implantation-2009). (group 1)
• Consistent unilateral user of an Advanced Bionics cochlear implant for at least 6 months and ideally 12 months, with no useful contralateral hearing (group 2)
• Consistent user of bilateral hearing aids for at least six months (group 3) and bilateral severe profound hearing loss (80dB or worse at 2000 and 4000 Hz with speech discrimination of at least 50% IHR sentences live voice at 60dBA)
• First language English
• Post-lingual onset of severe to profound hearing loss
• No other handicaps that would interfere with participation in the study in the opinion of the Principle Investigator

Exclusion Criteria:

• Unstable cochlear implant or hearing aid fitting
• Using medication in an intermittent manner that might influence hearing levels
• Cognitive or psychological challenges that might lead to variations in attention