Factors affecting binaural fusion in cochlear implant users

Area of Science:

• Audiology
• Neuroscience
• Biomedical Engineering

Background:

• Differences in auditory input between ears can impair binaural fusion in cochlear implant (CI) users, limiting binaural perception.
• Binaural fusion is crucial for effective speech segregation, especially in noisy environments.

Purpose of the Study:

• To investigate factors influencing binaural fusion for speech segregation in bilateral CI (BiCI) users and acoustic-electric hearing (AEH) CI users.
• To assess the impact of implantation strategy (simultaneous vs. sequential) and hearing modality on binaural fusion.

Main Methods:

• Speech recognition thresholds (SRTs) were measured adaptively in simultaneously implanted (SIM) and sequentially implanted (SEQ) BiCI users, and AEH CI users.
• Target sentences were presented with same-sex or different-sex maskers under monaural and bilateral listening conditions.
• The bilateral-monaural difference (BMD) in SRTs was calculated to estimate binaural fusion.

Main Results:

• SEQ-BiCI users exhibited poorer SRTs in bilateral compared to monaural listening, unlike SIM-BiCI users.
• A negative correlation was found between BMD and inter-implant interval across BiCI users.
• AEH CI users showed better bilateral than monaural SRTs when target speech was in the acoustic hearing ear, but poorer when in the CI ear.

Conclusions:

• Binaural fusion for speech segregation is affected by implantation timing in BiCI users, with sequential implantation potentially disrupting this ability.
• The benefits of binaural fusion are asymmetric in SEQ-BiCI and AEH CI users, favoring the first-implanted or acoustic hearing ear, respectively.
• Findings highlight the importance of considering individual hearing characteristics and implantation history for optimizing auditory rehabilitation.