Synchronizing Automatic Gain Control in Bilateral Cochlear Implants Mitigates Dynamic Localization Deficits...

Area of Science:

• Audiology
• Neuroscience
• Biomedical Engineering

Background:

• Independent left and right automatic gain controls (AGCs) in cochlear implants can distort interaural level differences.
• This distortion compromises dynamic sound source localization and can lead to front-back reversals (FBRs).

Purpose of the Study:

• To assess if synchronizing left and right AGCs mitigates localization difficulties.
• To determine if synchronized AGCs improve listeners' ability to use head movements to avoid FBRs.

Main Methods:

• 10 bilateral cochlear implant patients listened to broadband noise from six loudspeakers.
• Tests were conducted with synchronized and independent AGCs at 70 dBA (above threshold) and 50 dBA (below threshold).
• Listeners' ability to localize sound was tested under stationary and free head movement conditions.

Main Results:

• Independent AGCs at 70 dBA increased FBRs compared to 50 dBA baseline.
• Synchronizing AGCs with head movements reduced FBRs to baseline levels.
• Synchronized AGCs significantly improved listeners' overall percent correct localization.

Conclusions:

• Synchronizing AGCs helps mitigate FBRs caused by independent AGCs when head motion is permitted.
• Synchronization restored performance to baseline levels, independent of AGC compression.
• Synchronization did not address localization issues unrelated to AGC compression.