Asynchronous bilateral CI stimulation impairs the development of interaural time difference sensitivity

Early deafened cochlear implanted (CI) patients exhibit poor sensitivity for interaural time differences (ITD), which play a major role in sound localisation and speech understanding. Current CI processors lack bilateral synchronisation. This results in inconsistent and uninformative ITD presentation when stimulating the auditory system electrically due to an offset between the two clock times. Here, we investigate whether the development of ITD sensitivity is impaired in the hearing inexperienced auditory system when subjected to asynchronous ITD stimulation.

Four neonatally deafened (kanamycin, P9-20) Wistar rats were bilaterally implanted with CIs as young adults. A 2-alternative forced choice task was used to train the animals to detect amplitude modulation (AM) while additionally receiving ITD and ILD (interaural level difference) information within the stimuli. While two animals were exclusively presented with informative ITDs, the other two animals solely received randomly chosen, uninformative ITDs in the range of +/-0.5 ms. The degree to which the animals relied on each of the cues, AM, ITD, and ILD, was then assessed after 4 weeks permutatively and analysed using a probit analysis.

CI animals who received uninformative ITDs almost exclusively used AM and ILD information to lateralise. However, for animals who received useful ITD information all three cues were similarly weighted in importance for decision making during the behavioural task.

The results suggest that ITD sensitivity does not rely on early auditory experience but rather can be perturbed with the absence of synchronised stimulation. It remains to be determined whether this perturbation is reversible under optimal synchronised stimulation currently absent in clinical speech processors.

Poster-PDF A-1201.pdf

MED-EL

Publication History

Article published online:
13 May 2021