Effect of reducing the static interaural time difference in bimodal listeners

Previous work has shown that the ability to localize sound signals in the horizontal plane can be improved in listeners provided with a cochlear implant (CI) in one ear and a hearing aid (HA) in the contralateral ear (bimodal listeners) when the static interaural time delay between the modalities is technically reduced.The timing mismatch is caused by differences in the processing latencies of CI and HA and by different stimulation sites (CI: auditory nerve; HA: external auditory canal).In 2020 the CI manufacturer MED-EL has made the technical reduction of the timing mismatch available by a programmable across-frequency CI stimulation delay.To reduce the timing mismatch even further, we now use frequency-dependent delays to minimize the timing mismatch in every frequency band.Results show that the rms and the signed bias of sound localization can be further reduced in most bimodal study participants when using frequency-specific delays compared to an across-frequency delay.However, it is methodically complex to determine appropriate delays for different frequency bands.It is therefore questionable whether frequency-specific delays are useful in clinical practice.