Improved Neural Coding of ITD with Bilateral Cochlear Implants by Introducing Short Inter-pulse Intervals.

Area of Science:

• Neuroscience
• Biomedical Engineering
• Auditory Perception

Background:

• Bilateral cochlear implant (CI) users exhibit diminished sensitivity to interaural time differences (ITDs), impairing sound localization and speech comprehension in noise.
• High-rate periodic pulse trains used in CI processors exacerbate this limitation, particularly for speech processing.

Purpose of the Study:

• To investigate a novel stimulation strategy using short inter-pulse intervals (SIPIs) to enhance neural ITD sensitivity in bilateral CI users.
• To determine if SIPIs can improve ITD perception similarly to random inter-pulse interval (IPI) jittering.

Main Methods:

• Single-unit recordings were conducted in the inferior colliculus (IC) of unanesthetized rabbits with bilateral CIs.
• SIPIs were introduced into high-rate periodic pulse trains, and ITD sensitivity was measured.
• Coincidence detection analysis was employed to reveal ITD sensitivity masked by high spontaneous firing rates.

Main Results:

• Introducing SIPIs significantly increased firing rates in approximately 60% of IC neurons, with extra spikes synchronized to the SIPIs.
• SIPIs uncovered latent ITD sensitivity comparable to low-rate pulse trains.
• Coincidence detection analysis revealed ITD sensitivity in neurons where it was previously masked by high spontaneous firing rates.

Conclusions:

• SIPIs enhance neural ITD sensitivity in a manner consistent with jittered pulse trains, offering controlled timing and quantity.
• A novel CI processing strategy incorporating SIPIs could improve ITD perception and speech intelligibility for bilateral CI users.
• This approach holds potential for improving auditory outcomes in individuals with bilateral cochlear implants.