Neural ITD coding with bilateral cochlear implants: effect of binaurally coherent jitter

Area of Science:

• Neuroscience
• Auditory Neuroscience
• Cochlear Implants

Background:

• Bilateral cochlear implant users exhibit poor interaural time difference (ITD) sensitivity, limiting their ability to process sound in noisy environments.
• ITD sensitivity to periodic pulse trains declines with increasing pulse rate, but binaurally coherent jittering can restore this sensitivity.

Purpose of the Study:

• To investigate the neural mechanisms underlying the binaural jitter effect in the inferior colliculus (IC).
• To determine how jittering interpulse intervals impacts neural responses to high-rate pulse trains in the context of ITD processing.

Main Methods:

• Single inferior colliculus (IC) neurons were recorded in bilaterally implanted, anesthetized cats.
• Neural responses to biphasic pulse trains were analyzed as a function of pulse rate, jitter, and ITD.

Main Results:

• The jitter effect was most pronounced at pulse rates above 300 pulses/s.
• Jittering increased ongoing firing rates in approximately half of the IC neurons that only showed onset responses to high-rate periodic trains.
• Neurons responding robustly to jittered trains exhibited ITD tuning comparable to low-rate periodic pulse trains.

Conclusions:

• Binaural jittering enhances neural ITD sensitivity by promoting sustained neural firing in IC neurons.
• The observed neural effects of jitter are consistent with human psychophysical findings.
• The findings suggest that strategic insertion of short interpulse intervals may restore ITD sensitivity for periodic carriers.