Sound-processing strategy for cochlear implants

Abstract

A sound processing method for auditory prostheses, such as cochlear implants, which is adapted to improve the perception of loudness by users, and to improve speech perception. The overall contribution of stimuli to simulated loudness is compared with an estimate of acoustic loudness for a normally hearing listener based on the input sound signal. A weighting is applied to the filter channels to emphasize those frequencies which are most important to speech perception for normal hearing listeners when selecting channels as a basis for stimulation.

Description

TECHNICAL FIELD [0001] The present invention relates to a sound processing strategy for use in hearing prosthesis systems, with particular application to cochlear implant systems. BACKGROUND ART [0002] In cases where individuals have experienced sensorineural deafness, the restoration of hearing sensations to such individuals has been achieved through the use of hearing aids and cochlear implants. Cochlear implants in particular have been in clinical use for many years. A wide variety of different speech processing strategies have been employed in order to process a sound signal into a basis for electrical stimulation via implanted electrode arrays. Some systems have focused upon extracting particular acoustic components of the detected sound signal, which are important to the user's understanding of speech, for example the amplitudes and frequencies of formants, and using these as a basis for generating stimuli. Other approaches have also attempted to utilise the generally tonotopi...

AI Technical Summary

Benefits of technology

The present invention relates to improving the control of loudness and providing additional information about sound signals for users of cochlear implants. It uses models of sound perception for normal hearing to process the sound signals. The invention applies shaping algorithms to the amplitudes of the channels after initial analysis to further process the signals. The overall loudness perceived by the implant user is estimated based on the parameters determined and relevant characteristics of the patient's auditory perception. The invention also attempts to improve the control of the relative loudness of signals and the distribution of loudness contributions across frequency or across cochlear position. This is important for ensuring the full benefits of stimulation with a cochlear implant. The invention is particularly useful with more complex stimulation environments, such as provided by multiple simultaneous or near simultaneous stimuli or continuous in time waveforms.

Problems solved by technology

The problem with this method of loudness-mapping is that is does not take into consideration the effects of loudness summation when multiple electrodes are activated in quick succession, as they generally are in the output of speech processors.

This loudness summation leads to the situation that the output of the processor is too loud, even though the individual levels on each electrode do not exceed a comfortable loudness.

These methods, although alleviating the discomfort of implant users for loud sounds, do not address a second important issue, and that is the impact of loudness summation on speech perception.

The present loudness coding methods, whereby the acoustic output of a filter is mapped to a fixed range of electrical levels (however determined) on its corresponding electrode, lead inevitably to a perceptual distortion of the amplitude envelope shape because these methods do not take into account the variations from moment to moment of important aspects such as the number of electrodes activated in each stimulus cycle, and the relative loudness contributions from these other electrodes.

In summary, the relative loudness of electrically stimulated hearing using present approaches does not accurately convey the relative loudness that a normally-hearing person would hear for the same acoustic input.

As well as distorting the perception of the amplitude envelope of the acoustic signal, this effect will lead to narrow-band signals being masked by lower-level broad-band noise, thus disrupting the ability of implantees to understand speech in background noise.

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