Matching Automatic Gain Control Across Devices in Bimodal Cochlear Implant Users

Area of Science:

• Audiology
• Biomedical Engineering
• Signal Processing

Background:

• Bimodal hearing, combining a cochlear implant (CI) and a hearing aid (HA), aims to leverage residual hearing in the non-implanted ear.
• Automatic Gain Control (AGC) in hearing devices manages sound loudness dynamically, but mismatches between CI and HA can hinder bimodal benefit.
• Optimizing AGC parameters in HAs to match those of a contralateral CI is a potential strategy to improve speech perception for bimodal users.

Purpose of the Study:

• To enhance bimodal benefit in individuals using a CI and a HA by aligning the AGC time constants and compression channels of the HA with the CI.
• To investigate if equivalent AGC settings can lead to balanced loudness perception for dynamic signals like speech.
• To determine if matched AGC improves speech understanding in quiet and noisy conditions with various noise sources and spatial configurations.

Main Methods:

• Fifteen participants with a CI and HA underwent a 3-visit crossover study comparing a standard HA AGC with a CI-matched AGC.
• The matched AGC featured dual broadband compression with specific attack and release times, while the standard AGC used syllabic multichannel compression.
• Speech understanding was assessed in quiet and noise (single-talker, stationary noise from various directions), alongside subjective questionnaires and preference tests.

Main Results:

• The AGC-matched HA significantly improved speech understanding in single-talker noise by 1.9 dB when noise originated from the HA side, compared to the standard HA.
• While less pronounced, AGC matching showed smaller, insignificant improvements in other noise conditions and spatial configurations.
• Participants rated the AGC-matched HA higher for speech clarity in quiet and noise, sound quality, and listening comfort, with 9 out of 15 preferring the matched HA.

Conclusions:

• The AGC-matched HA demonstrated superior performance over the standard HA in speech understanding tasks involving competing single-talker noise.
• Matched AGC settings were favored in subjective questionnaires and preference tests, indicating improved user experience and perceived benefit.
• These findings suggest that aligning AGC characteristics between CI and HA devices can enhance binaural processing and improve outcomes for bimodal hearing users.