Transmission of Binaural Cues by Bilateral Cochlear Implants: Examining the Impacts of Bilaterally Independent Spectral Peak-Picking, Pulse Timing, and Compression.
William O Gray, Paul G Mayo, Matthew J Goupell and 1 others
PMID 34293981WHAT IT FOUND
Bilateral cochlear implants distort sound location cues because each ear picks different frequencies independently, not because their internal clocks are unsynchronized.
For patients struggling to locate sounds, check if the processor settings are reducing level differences or if the strategy is causing asymmetric pulse allocation.
Key findings
01Independent spectral peak-picking in bilateral processors causes asymmetric pulse allocation, which degrades the transmission of interaural time differences (ITDs) and level differences (ILDs).
02Unsynced processor clocks are not the primary cause of poor ITD transmission; envelope ITDs can be conveyed effectively if pulse counts are symmetric between ears.
03Higher sound levels reduce transmitted ILDs due to compression, and dynamic gain control features can cause large, spurious fluctuations in ILD over time.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The study used a manikin, so it cannot account for individual patient auditory processing or perceptual outcomes. Measurements were taken in a simple, anechoic environment without background noise or reverberation. The study only evaluated the ACE strategy; other strategies like CIS were not tested. Acoustic and electrical ILDs are measured in different units (dB SPL vs. current levels), making direct comparison complex.
Declared interests
The authors declared no potential conflicts of interest. The work was supported by the National Institute on Deafness and Other Communication Disorders and a Top Scholar Award from the University of Washington.
The easy way to misread this
Do not conclude that bilateral cochlear implants cannot transmit any useful binaural information. The study found that envelope ITDs can be transmitted effectively despite unsynchronized clocks, provided that pulse allocation is symmetric between the ears. The distortion is primarily due to independent spectral peak-picking and compression, not just clock drift.