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DOI: 10.1055/s-0040-1711165
Within-Ear Balancing of Response Strength Between Acoustic and Electric Stimulation Improves Interaural Time Difference Coding in an Animal Model of Single-Sided Deafness
Subjects with single-sided deafness increasingly receive unilateral cochlear implants to benefit from binaural hearing (‘SSD-CI users’). However, improvements in directional hearing are mainly based on interaural-level differences, not on interaural-time differences (ITDs). Possible explanations for these deficits include deafness-induced degradations in neural ITD sensitivity and between-ear mismatches in activation sites.
To identify the limitations of bimodal ITD coding, the present study compared neural ITD coding to bilateral bimodal and bilateral acoustic-only stimulation in auditory midbrain of normal hearing (NH) gerbils. Animals received a unilateral round window electrode to maintain sensitivity to both electric and acoustic stimulation in the implanted ear. This approach excluded the possibility of deafness-induced degradations.
We adjusted delay differences to acoustic and electric stimulation in the implanted ear. To balance the response strength between stimulus modes, we adjusted the electric stimulus level in the implanted ear to match the spike-rate of the same ear to acoustic stimulation. This in turn balanced the binaural level cues between the two ears and increased the shape similarity of rate-ITD functions to bimodal and bilateral acoustic stimulation obtained from the same neuron. Moreover, within-neuron comparisons showed no differences in ITD sensitivity or ITD discrimination thresholds between bimodal and bilateral acoustic stimulation.
Our results in the NH system reveal widespread similarities of neural ITD coding to bimodal and unimodal-acoustic stimulation. However, results suggest that balancing the relative delay and binaural level cues between the two modes of stimulation is important to improve binaural hearing in SSD-CI users.
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Publication History
Article published online:
10 June 2020
© 2020. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial-License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/).
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