In bimodal cochlear implant (CI) / hearing aid (HA) users a constant interaural time delay in the order of several milliseconds occurs due to differences in signal processing of the devices. For MED-EL CI systems in combination with different HA types, we have quantified the respective device delay mismatch (Zirn et al. 2015). In the current study, we investigate the effect of the device delay mismatch in simulated and actual bimodal listeners on sound localization accuracy.
To deal with the device delay mismatch in actual bimodal listeners we designed and assembled a battery-powered, portable and programmable delay system that was given to bimodal listeners for one hour. After this acclimatization period a highly significant decrease of the rms error in the localization task was observed (mean improvement: 11%; p<.01, Wilcoxon Signed Rank Test) compared to the test without the delay system. Tests in simulated bimodal listeners revealed similar outcomes. Thus, the implementation of a programmable delay system in CI processors seems to be a promising way how to improve localization accuracy in bimodal listeners.