Criteria

For all Parts A, B and C of the study,

Inclusion criteria:

Written informed consent must be obtained before any assessment is performed. For all Parts A, B and C of the study, male or female patients, 18 to 75 years old, inclusive, with severe-to-profound bilateral hearing loss or unilateral hearing loss with intact vestibular function in the nonoperative ear. Non-fluctuating severe-to-profound hearing loss is required for the study ear and is defined as: PTA within 10 dB of the PTA obtained at least 11 months previously.

Word recognition within 20% of previous test at least 11 months previously Candidate ear ("study ear"): Minimal residual hearing based on the pure tone average of 0.5, 1, 2, and 4 kHz thresholds of ≤110 dB HL Candidate ear ("study ear"): Pure tone audiometric thresholds of ≥50 dB HL for each testable octave frequency of 0.125 and 0.250 kHz, ≥70 dB HL for each testable octave frequency from 0.5 through 8 kHz and sentence recognition scores ≤50% at screening.

6. Patients with intact vestibular function in at least one ear (non-study ear) as measured by vestibular evoked myogenic potential (VEMP) 7. Able to communicate well with the investigator, to understand and comply with the requirements of the study 8. MRI scan within 6 months or at screening to confirm suitability for inner ear surgery 9. Patients must weigh at least 40 kg to participate in the study, and must have a body mass index (BMI) <45 kg/m2. BMI = Body weight (kg) / [Height (m)]2

Exclusion Criteria: