Clinical Utility of Residual Hearing in the Cochlear Implant Ear

Inclusion Criteria: 1. Provision of signed and dated informed consent form. 2. Adults, males and females, ages 18 -79 who have a bilateral sensorineural hearing loss with postlingual onset. 3. Minimum of 30 days experience with appropriately fit binaural amplification (standardized National Acoustic Laboratories (NAL) fitting method) verified with real ear measurements within 5 dB SPL of targets. 4. Limited benefit from conventional amplification in the best aided condition as defined by test scores of: 1. The ear to implanted: Consonant-nucleus-consonant (CNC) words ≤ 60% or AzBio sentences (+10, +5 dB SNR ≤ 60% correct) 2. Contralateral ear: ≤ 80% on CNC words or AzBio sentences (+10, +5 dB SNR ≤ 80% correct) 5. Low frequency Pure Tone Average (PTA- 125, 250, 500 Hz) ≤ 55 dB HL in the ear to be implanted. 6. Severe to profound mid to high-frequency sensorineural hearing loss (threshold average of 1000, 2000, 3000, and 4000 Hz ≥75 dB HL) in the ear to be implanted. 7. Low frequency PTA ≤ 55 dB HL sloping to moderately severe to profound mid-to high frequency sensorineural hearing loss (threshold average of 1000, 2000, 3000, 4000 Hz ≥ 60 dB) in the contralateral ear. 8. Proficient in English. 9. Undergoing implantation with a current generation CI device from either Cochlear Limited or Advanced Bionics AG. 1. Cochlear Limited devices include: Nucleus CI612, CI622, CI632, CI624 2. Advanced Bionics AG devices include: HiFocus SlimJ, Mid-Scala 10. Stated willingness and ability to complete testing and all associated study visits. Exclusion Criteria: 1. Previous cochlear implantation. 2. Prelingual onset of hearing loss. 3. Abnormal inner ear anatomy on CT imaging. 4. Auditory neuropathy spectrum disorder. 5. Retrocochlear pathology such as a vestibular schwannoma or stroke. 6. Unwillingness or inability to comply with all investigational requirements including the randomization process. 7. Additional medical, or social barriers that would prevent completion of all study requirements. 8. Medical condition contraindicated for surgery. 9. Device selection of Med El CI (per the patient's selection).