PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Towards a model of electric-acoustic stimulation in cochlear implant
subjects with residual hearing
Daniel ALRUTZ1; Waldo NOGUEIRA2
1,2

Department of Otolaryngology, Hannover Medical School (MHH),
Cluster of Excellence Hearing4all, Germany

ABSTRACT
When provided with electric-acoustic stimulation (EAS), cochlear implant (CI) users with residual acoustic
low-frequency hearing in the same ear show enhanced speech perception compared to subjects withconventional CIs. However, when electric and acoustic stimulation is presented at the same time, masking
between both modalities occurs. To date, it remains unclear at which stage of the auditory pathway thesemasking effects arise (i.e. at the level of hair cells, the auditory nerve or more centrally).
In order to investigate the underlying mechanisms of electric-acoustic stimulation, we develop acomputational model of the spiking activity in auditory nerve fibers (ANFs) triggered by combined
electric-acoustic stimulation. We present our approaches to couple existing state-of-the-art models, each ofwhich simulates spiking responses to either electric or acoustic stimuli.
Keywords: cochlear implants, auditory nerve fibers, modelling

OVERVIEW
Thanks to recent improvements in surgical technique and electrode design, it is now often possible
to preserve residual acoustic hearing in the low frequencies during the insertion of a cochlear implant(CI) in the same ear. Compared to users of conventional CIs, these subjects receiving combined
electric-acoustic stimulation (EAS) show enhanced speech perception, especially in noisy situations(1). However, impeding interactions between both modalities are possible when the cochlea issimultaneously stimulated acoustically and electrically. Masking between electric and acoustic
stimulation has been observed in auditory nerve fiber (ANF) spike trains in animals (2) as well as inelectrocochleographic (ECochG) responses (3) and psychophysical experiments with humans (4–6),
but it is unknown at which stage of the auditory pathway these interactions take place and how they canbe taken into account in future CI stimulation strategies.
Here, computational models can be used to improve the understanding of the underlying interaction
mechanisms in EAS users. Existing models either simulate ECochG responses phenomenologically (7,8) or
calculate ANF spiking for sole acoustic (9,10) or electric (11–13) stimulation. We present a new model,
where we coupled the acoustic model of Bruce et al. (2018) with a model of electrically induced spikes inANFs. Our model shows appropriate responses to acoustic stimulation of remaining hair cells as well as todirect electric stimulation of ANFs.

ACKNOWLEDGEMENTS
This work was supported by the DFG Cluster of Excellence EXC 2177/1 Hearing4all and funded by
the German Research Foundation (DFG) - Project number: 396932747 (PI: Waldo Nogueira).

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