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Detection, Adaptation and Integration of auditory information: Applications for cochlear implants – DAIMA

Electrical stimulation of the auditory nerve

Cochlear implants (CIs) are the only way to restore hearing to profoundly deaf people. CIs directly stimulate the auditory nerve with electrical pulses via electrodes surgically implanted inside the cochlea. The DAIMA project aims to better understand the functioning of the peripheral auditory system in order to optimize stimulation parameters in CIs.

Understanding and fighting against electrode interactions

Although most CI users show scores of speech recognition in quiet close to normal, a large majority of them also struggle in more complex acoustical environments such as when listening to speech in noise or to music. <br /><br />One reason for this drop in performance lies in the complex interactions occurring within and between electrodes. Each electrode transmits information about a specific frequency region of the incoming sounds. The electrodes are stimulated one at a time, thereby minimising unwanted interactions that would occur between electrodes if they were stimulated simultaneously. However, because electrical charge is integrated (smoothed over time) by the neural membrane and because neurons are constrained by refractoriness, non-simultaneous interactions are particularly large when, as is the case in modern implants, the delay between pulses is very small. We think that these interactions can have unintentional and deleterious effects on both the loudness and the quality of the sounds heard by CI users. <br /><br />The DAIMA project aims to understand several aspects of these interactions by combining psychophysical experiments in CI and in normally-hearing listeners, electrophysiological measures at the level of the auditory nerve and phenomenological modelling. <br /><br />This will allow us (1) to refine our understanding of the basic principles of electrical stimulation of the auditory nerve, (2) to use this knowledge to optimize the stimulation parameters of existing implants, and (3) to develop innovative strategies to improve the coding of sounds transmitted by future generations of CIs.

Our approach combines:
- psychoacoustical tests with normal-hearing listeners using stimuli that simulate certain aspects of CI perception
- psychophysical tests with CI listeners
- electrophysiological recordings with CI listeners (particularly the electrically-evoked compound action potentials)

The results of these tests will be used to develop our computational model of electrical stimulation of the auditory nerve as well as to propose novel ways of optimizing sound coding in CIs. These new strategies will finally be evaluated using speech perception tests.

Given the delay taken by our research proposal to be accepted by the ethical comitee, we have focused on:
- the development of test interfaces
- the study of perceptual effects of stimulation rate using simulations of CIs with normal-hearing listeners
- the study of perceptual effects of electrode configuration, also using simulations and normal-hearing listeners

Psychophysical tests with CI listeners are starting. A post-doctoral research is also going to be recruited on a 2-year contract.

Although the following publications do not result from data collected within the present ANR, they are related to our present research questions. We have published two papers since the beginning of this project:

- Macherey O, Carlyon RP. Place-pitch manipulations with cochlear implants. J. Acoust Soc Am. 2012 Mar;131(3):2225-36.

- Undurraga JA, Carlyon RP, Macherey O, Wouters J, van Wieringen A. Spread of excitation varies for different electrical pulse shapes and stimulation modes in cochlear implants. Hear Res. 2012 May 11.

We also have two other papers submitted to Ear and Hearing (2nd revision) and to the Journal of the Acoustical Society of America.

Cochlear implants (CIs) have restored hearing to more than 180,000 deaf people worldwide. They work by bypassing the damaged receptor cells in the inner ear and by directly stimulating the auditory nerve using an array of surgically-implanted electrodes. Although most CI users show scores of speech recognition in quiet close to normal, a large majority of them also struggle in more complex acoustical environments such as when listening to speech in noise or to music.

One reason for this drop in performance lies in the complex interactions occurring within and between electrodes. Each electrode transmits information about a specific frequency region of the incoming sounds. The electrodes are stimulated one at a time, thereby minimising unwanted interactions that would occur if they were stimulated simultaneously. However, because electrical charge is integrated (smoothed over time) by the neural membrane and because neurons are constrained by refractoriness, non-simultaneous interactions are particularly large when, as is the case in modern implants, the delay between pulses is very small. We think that these interactions can have unintentional and deleterious effects on both the loudness and the quality of the sounds heard by CI users.

The DAIMA project aims to understand several aspects of these interactions by combining psychophysical experiments in CI and in normally-hearing listeners, electrophysiological measures at the level of the auditory nerve and phenomenological modelling. This will allow us (1) to refine our understanding of the basic principles of electrical stimulation of the auditory nerve, (2) to use this knowledge to optimize the stimulation parameters of existing implants, and (3) to develop innovative strategies to improve the coding of sounds transmitted by future generations of CIs.

Project coordination

Olivier Macherey (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE PROVENCE ET CORSE) – macherey@lma.cnrs-mrs.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CNRS DR 12 _ LMA CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE PROVENCE ET CORSE

Help of the ANR 295,200 euros
Beginning and duration of the scientific project: December 2011 - 36 Months

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