Event:

The normal-hearing human auditory system is able to perceive interaural time differences (ITD) as small as 10 us. The largest ITD occurring physiologically is about 700 us. In bimodal users differences in processing latencies of digital hearing aids (HA) and cochlear implants (CI) up to 9 ms superpose these tiny ITD resulting in an interaural stimulation timing mismatch.

Our hypothesis in the present study is that this interaural stimulation timing mismatch impairs sound localization in the horizontal plane in bimodal HA/CI users. To investigate, we conducted localization tests in bimodal users with and without differences in processing latencies. To compensate for individual processing latency differences we designed a wearable, battery powered and programmable delay line based on a circular buffer implemented on a microcontroller in order to delay the faster device (the CI system).

In each subject, an initial localization test with the delay line deactivated was conducted. Afterwards the delay line was activated followed by a 1 hour familiarization period. Finally, the localization test was repeated.

Results showed an improvement in sound localization of 10% averaged across 8 bimodal users after compensation. The effect was significant (p under .05, Wilcoxon signed rank test).