This is a two-phase study that compares performance growth pre-implant with current hearing aid (HA) technology versus post-implant with a cochlear implant (CI) in children with either asymmetric hearing loss (AHL) or single-sided deafness (SSD). Post-implant performance with a CI alone is expected to outperform pre-implant performance with a HA. The study also evaluates the effectiveness of bimodal hearing defined as a CI in the poor ear and a HA in the better ear for AHL or a CI in the poor ear and normal hearing in the better ear for SSD compared to pre-implant performance. The study examines factors contributing to CI outcomes.

The study is conducted as a multicenter, prospective, two-phase clinical trial, evaluating the efficacy and safety of cochlear implantation in children with asymmetric hearing loss (AHL) or single-sided deafness (SSD). A hearing aid (HA) phase occurs over a minimum of 4 mos prior to obtaining a cochlear implant (CI). A CI phase occurs over the 15-month period after initial activation of the CI. The AHL/SSD groups are tested for change in performance pre- to post-implant. Investigators also collect longitudinal data over 12 months (matching the 3 to 15 month post-implant timeframe) from normal hearing (NH) participants to provide additional information about outcome trajectory due to development alone. The NH participants are matched to AHL/SSD participants on age, gender and parent education. Post-implant performance with a CI alone is expected to outperform pre-implant performance with a HA. The study evaluates the effectiveness of bimodal hearing defined as a CI in the poor ear and a HA in the better ear for AHL or a CI in the poor ear and normal hearing in the better ear for SSD compared to pre-implant performance. The study examines factors contributing to CI outcomes.

Inclusion Criteria:

• At least 4 ys of age and up to 14 yrs, 11 mos of age and able to complete all investigational procedures.
• Parents and child fluent in English. Parents desire bilateral hearing for their child, are willing to comply with study requirements, including the pre-implant HA phase, and are able to provide informed consent.
• Poor ear (AHL/SSD): PTA at .5, 1, 2 kHz > 70 dB HL; Aided CNC word recognition score at 60 dB SPL < 40%; SPHL duration ≥ 6 mos and ≤ 10 yrs at time of CI surgery; If > 5 yrs of age, evidence of non-congenital SPHL onset (e.g., passed newborn hearing screening); If ≤ 5 yrs of age, no restrictions on SPHL onset.
• Better ear
• AHL: PTA at .5, 1, 2, 4 kHz > 25 and ≤ 60 dB HL; Aided CNC word score at 60 dB SPL ≥ 55%; Currently using a HA; Stable hearing for the past 6-mo period. "Stable" is defined as thresholds that have not declined by more than 20 dB at three or more octave-interval audiometric frequencies.
• SSD: PTA at .5, 1, 2, 4 kHz ≤ 25 dB HL; CNC word score at 60 dB SPL ≥ 70%; Stable hearing for the past 6-mo period.
• Both ears of NH participants: PTA at .5, 1, 2, 4 kHz ≤ 25 dB HL.
• To continue with cochlear implantation and into the CI phase of the study: Indication, via imaging, of a normal cochlear nerve and of cochlear anatomy in the ear to be implanted that allows full insertion of the electrode array. Imaging modality is at the discretion of the surgeon. In addition, better ear hearing must be stable throughout the HA phase.

Exclusion Criteria for AHL/SSD Participants:

• Medical condition that contraindicates surgery; Actively using an implantable device in the ear to be implanted; Inability to complete study procedures; Unrealistic expectations related to the benefits and limitations of implantation; Unwillingness or inability to comply with all investigational requirements.
• Exclusions for cochlear implantation and the CI phase of the study: Cochlear malformation or obstruction that would preclude full insertion of the electrode array in the ear to be implanted; Abnormal cochlear nerve in the ear to be implanted; Hearing loss of neural or central origin.

Data will be shared through presentations at relevant scientific meetings and through publication(s) in peer-reviewed journals. As required by the NIH Public Access Policy, an electronic version of final manuscripts resulting from this study will be submitted to the NIH National Library of Medicine PubMed Central (PMC) upon acceptance for publication. The few numbers of children at each study site who meet the inclusion criteria and receive a cochlear implant puts participant's privacy at risk if individual data are shared.