Biomedical Engineering Reference
In-Depth Information
However, in case of complete preservation of the audiotory nerve, modiolar electrode
positions could not reduce the spread of excitation.
In experiment 2, different stimulation modes were simulated. The model pre-
dicted that monopolar stimulation produces a wider spread of excitation than bipolar
and that bipolar stimulation produces a wider spread of excitation than tripolar for
non-degenerated auditory nerves. However, for degenerated auditory nerves the dif-
ferences between the three stimulation modes became much smaller. This means
that depending on the electrode-nerve interface of each individual some stimulation
modes can be more beneficial than others.
Experiment 3 investigated the differences in extracellular voltage for different
cochlear anatomies. The model presented here is based on existing models and
although simple, it allows for a relatively easy adaptation to clinical CT images
of CI individuals. An example of two different cochleas has been presented. From
the simulations it was observed that the width of the spread of excitation depends on
the anatomy of the cochlea.
The scope of the manuscript is focused on the development of the model. The
model should serve as a tool in the future such as to understand better the variability
of each individual. The validation of the model, comparing the simulations with real
data is out of the scope of this paper.
Finally, experiment 4 was designed to illustrate the impact of peripheral aspects
(such as the electrical field or the amount of neural degeneration) on the perception
of sounds. The goal was to demonstrate that at least for computers, differences in
the excitation patterns provided to the cochlear implant can have an influence in
sound identification. For example, we could show that stimulation modes causing
a narrower spread of excitation (tripolar stimulation) obtained higher identification
scores than stimulation modes that produce a wider spread of excitation (monopolar
stimulation).
5 Conclusions
A model of the electrically stimulated cochlea has been developed. This model has
been used to assess the impact of electrode position, cochlear anatomy and different
stimulation modes on the spread of excitation. Simulations show variability in the
spread of excitation for all these configurations of the model. An automatic sound
classifier was able to illustrate the effects in correct classification rate for the different
configurations of the CI electrical model.
Acknowledgments
The authors would like to thank the valuable contributions to the development
of the model from Prof. Antoni Ivorra, Marcel Farres and Nikos Papachristou from the Univer-
sitat Pompeu Fabra. This work was supported by the DFG Cluster of Excellence EXC 1077/1
“Hearing4all”.
