Cochlear Implants

1. Introduction

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).

2. Cochlear Implant Research

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.

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 publications.

3. Links

  1. Cochlear Implant Manufacturers (alphabetically)

  2. A few Cochlear Implant Research Centers in Germany, Austria, the U.S. and UK (sorry, highly selected)

© Bernhard Seeber - b_seabear (at) gmx (dot) de 
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