Delay-Kompensationen verbessern die neuronale Kodierung interauraler Zeitdifferenzen bei binaural-bimodaler Stimulation

Unilateral cochlear implants (CIs) allow the functional restoration of binaural hearing in subjects with single-sided deafness (SSD-CI users). Nevertheless, directional hearing in SSD-CI users is typically poorer than that in normal hearing subjects and in subjects using bilateral CIs. This finding indicates suboptimal neural integration of binaural-bimodal (acoustic/electric) stimulation.

To identify deficits of binaural-bimodal processing, we compared neural interaural time difference (ITD) coding in response to bimodal stimulation and two kinds of unimodal stimulation, namely bilateral acoustic and bilateral electric stimulation, in auditory midbrain of normal-hearing gerbils. To maintain acoustic sensitivity of the implanted ears and, thus, to allow within-neuron comparisons of responses across the three kinds of stimulation, electric stimuli were delivered to the round window.

ITD discrimination thresholds and ITD coding efficacy (Fisher information) were similar for both unimodal electric and acoustic stimulation, but were significantly degraded in response to bimodal stimulation. ITD tuning metrics (e.g., best ITD, maximum slope) were widely dispersed in response to bimodal stimulation. Delay compensations between bimodal and unimodal ITD functions increased the Fisher information for ITD coding in neuronal populations. However, despite such compensations, maximum Fisher information in response to bimodal ITDs remained lower than that to unimodal acoustic or unimodal electric ITDs.

Our results suggest that compensating the latency differences between electric and acoustic stimulation can improve neural ITD coding efficacy in auditory midbrain and might thus be a suitable strategy for improving directional hearing in SSD-CI users.

Supported by DFG VO 640/2-2

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