Early-deafened patients with bilateral cochlear implants (biCI) show impaired sensitivity to interaural time differences (ITD). However, we have recently shown that neonatally-deafened (ND) rats, supplied with biCI in young adulthood, can develop excellent ITD sensitivity if the CIs are synchronized resulting in the presentation of informative, microsecond precise ITD. Limitations in the temporal accuracy of clinical biCI, which try to encode temporal features of sound in pulse timing, can lead to small deviations (jitter) in the pulse timing pattern. Here we investigate how much jitter the inexperienced auditory system can tolerate in order to develop good ITD sensitivity.

ND biCI rats were trained to lateralize pulse trains with jittered ITD. Baseline ITD were drawn independently from a set of ±120 μs in 20 μs steps. Binaural jitter values changed per pulse and were randomly drawn from a distribution ranging from ±60 μs in 20 μs steps or ±120 μs in 40 μs steps. After five weeks of training, rats were tested on ITD sensitivity with and without jitter on each pulse.

Under both jitter conditions, all biCI rats showed very good ITD sensitivities. Training with ±60 µs jitter resulted in a significantly better sensitivity than without jitter (≙microsecond precise ITD) or with ±120 µs jitter.

The results show that the early-deafened auditory system develops good ITD sensitivity under both jitter conditions. Interestingly, the auditory system seems to retrieve better ITD sensitivity with small binaural jitter than under binaural stimulation with microsecond precise ITD (≙without jitter). Therefore, we recommend fine structure stimulation strategies for biCI patients to improve their spatial hearing, although these do not necessarily have to provide microsecond-precise ITD.

Das Projekt ist gefördert durch Gelder der Firma MED-EL GmbH aus Innsbruck, Österreich.