Die Relevanz zeitlicher Kodierung für das Richtungshören mit Cochlea-Implantaten

Although cochlear implants (CIs) have revolutionized hearing restoration, they still exhibit limitations. While efforts have focused on optimizing the delivery of spectral information, relatively little attention has been paid to replicating the precise temporal firing patterns of the auditory nerve observed in normal hearing. Our research explores factors contributing to the poor spatial hearing with CIs by investigating the sensitivity to interaural time differences (ITDs) in cochlear implanted rats. The use of this animal model allows us to circumvent confounds arising from patient needs and clinical practice that plague research on human volunteers. We trained and tested neonatally deafened rats with bilateral CIs delivering exclusively informative pulse timing ITDs throughout, and found that their ITD discrimination thresholds were as good as those of normally hearing individuals even at clinical stimulation rates. Furthermore, we observed that delivering ITDs via pulse timing is much more effective than delivering ITDs via pulse train envelopes, and that even small conflicting ITDs can confound sizeable interaural level differences (ILDs). Our findings thus demonstrate that much better outcomes with bilateral CIs should be achievable in principle if patients were given useful and precise pulse timing cues throughout. Our results indicate that uninformative pulse timing delivered by the majority of current clinical CI processors may hinder spatial hearing in CI patients.