Coherent Coding of Enhanced Interaural Cues Improves Sound Localization in Noise With Bilateral Cochlear Implants

Area of Science:

• Auditory Neuroscience
• Signal Processing
• Audiology

Background:

• Bilateral cochlear implant (BCI) users exhibit limited spatial hearing due to distorted interaural level differences (ILDs) and restricted interaural time difference (ITD) transmission.
• Current BCI technology offers coarse sound localization in quiet, but performance degrades significantly in noisy environments.

Purpose of the Study:

• To develop and evaluate a novel signal processing algorithm for BCIs aimed at enhancing sound localization, particularly in noisy conditions.
• To investigate the efficacy of transmitting interaural cues (ITDs and ILDs) for improving spatial hearing in BCI users.

Main Methods:

• A new BCI algorithm was developed, duplicating monophonic electrode patterns and applying natural or artificial ITDs/ILDs based on estimated source direction.
• Three experiments were conducted: Experiment 1 assessed speech lateralization using ITDs alone; Experiments 2 and 3 evaluated azimuthal angle discrimination in noise with various ITD/ILD configurations.

Main Results:

• Six out of nine BCI subjects successfully lateralized intelligible speech in quiet using only ITDs.
• Azimuthal angle discrimination was possible for frontal sound sources with all tested algorithm variants, including pure ITD.
• Effective discrimination of lateral sound sources required a linearized ILD mapping, while pure ITD was insufficient.

Conclusions:

• Transmitting ITDs alone can enable basic speech lateralization in BCI users.
• The developed algorithm shows promise for improving sound localization in noise for BCI users, with linearized ILD mapping being crucial for lateral sound identification.
• Further modifications are suggested to enhance speech intelligibility and overcome limitations of interaural cue transmission in BCI devices.