In recent years cochlear implants became the most successful neuronal prothesis. Cochlear implants
circumvent the natural way of spectral decomposition in the human cochlea by replacing their function
with digital signal processing. Sounds are picked up by a microphone and processed in a filterbank with
successive envelope processing. The processed band-pass signals are mapped to an electrical current at electrodes.
The electrodes are inserted in the cochlea in order to stimulate the auditory nerve.
Compared to the high number of nerve fibers there are very few electrodes which additionally stimulate each a wide
place region at the nerve. It is obvious that this kind of processing and stimulation reduces strongly the information
content present in the nerve. Nevertheless, surprising results have been reported:
Many patients regain the ability to understand fluent speech and even to talk on the telephone.
An overview of the signal processing in cochlear implants from past to present as well as some thoughts
on future developments are presented in a talk which I held at an IEEE-meeting in Stanford, CA, in 2004.
The slides can be found here:
Talk on Cochlear Implants (861 kB, Adobe Acrobat pdf).
As speech understanding was the first main goal with cochlear implants my research aims at further benefits for
everyday life situations: the ability to localize sounds. Our first experiments tested the localization ability with
a cochlear implant on one ear and a hearing aid on the other as well as with bilateral cochlear implants.
We could find that selected subjects in both groups were able to localize sounds to some extend, whereas in each
group one subject showed superior localization ability.
2. Cochlear Implant Research
My next research interest was to explain the localization ability. What localization cues can these people use?
Localization with normal hearing persons is based on interaural time differences for most except high frequency
sounds. With one bilateral cochlear implant subject I was able to show that interaural level differences are used
instead. Interaural time differences did not contribute to form the localized position.
We are now working on the ability to segregate one sound from another which is particularly impaired with cochlear
implants. This is our ongoing research – more information about it can be found in the abstracts of my
Cochlear Implant Manufacturers (alphabetically)
A few Cochlear Implant Research Centers in Germany, Austria, the U.S. and UK (sorry, highly selected)