Interaural level differences and sound source localization for bilateral cochlear implant patients

Area of Science:

• Auditory Neuroscience
• Biomedical Engineering
• Signal Processing

Background:

• Cochlear implants (CIs) aim to restore hearing but can alter sound localization cues.
• Interaural level differences (ILDs) are crucial for horizontal plane sound localization.

Purpose of the Study:

• To quantify remaining ILDs after CI signal processing.
• To correlate these ILDs with sound source localization errors in CI users.

Main Methods:

• MED-EL CIs and head-related transfer functions (HRTFs) were simulated in MATLAB.
• Wideband, high-pass, and low-pass noise stimuli were used.
• ILDs and localization accuracy were measured in 16 CI users and 34 normal-hearing listeners.

Main Results:

• CI processing reduced maximum ILDs from 15-17 dB to 1-4 dB depending on signal type.
• CI patients exhibited significantly poorer localization than normal-hearing listeners.
• Localization accuracy was best with wideband/high-pass signals and worst with low-pass signals.

Conclusions:

• Localization accuracy in CI users is linked to the magnitude of available ILD cues.
• Error patterns suggest CI users divide the horizontal plane into broad sectors.
• Limited ILD resolution within sectors results in poor localization acuity.