HK1142018A - Electrical nerve stimulation with broad band low frequency filter - Google Patents

Description

Electrical nerve stimulation with broadband low frequency filter

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from US provisional patent application 60/949,649 filed on 13/7/2007, which application is incorporated herein by reference.

Technical Field

The present invention relates to electrical nerve stimulation, and more particularly, to a cochlear implant system including a broadband low frequency filter associated with a stimulation electrode.

Background

Cochlear implants and other inner ear prostheses are one option to help profoundly deaf or severely hearing impaired people. Unlike conventional hearing aids that only apply an amplified and modified sound signal, cochlear implants are based on direct electrical stimulation of the auditory nerve. Typically, cochlear implants electrically stimulate neural structures in the inner ear in a way that can achieve a hearing impression most similar to normal hearing.

Fig. 1 shows a cross-sectional view of an ear with a typical cochlear implant system. The normal ear transmits sound through outer ear 101 to tympanic membrane 102, which tympanic membrane 102 in turn moves the bones of middle ear 103, which in turn excites cochlea 104. The cochlea 104 includes an upper channel known as the scala vestibuli 105 and a lower channel known as the scala tympani 106, which are connected by the cochlear duct 107. In response to receiving sounds transmitted by the middle ear 103, the fluid-filled scala vestibuli 105 and scala tympani 106 function as transducers for transmitting waves to generate electrical pulses that are transmitted to the cochlear nerve 113, and ultimately to the brain. Frequency processing appears to change in nature from the basal region of the cochlea, where the highest frequency components of sound are processed, to the apical region of the cochlea, where the lowest frequencies are analyzed.

Some people have partial or complete loss of normal sensory neurohearing. Cochlear implant systems have been developed to overcome this drawback by directly stimulating the cochlea 104 of the user. A typical cochlear prosthesis consists essentially of two parts: a speech processor and an implanted stimulator 108. The speech processor (not shown in fig. 1) typically includes a microphone, a power supply (battery) for the entire system, and a processor for performing signal processing of the acoustic signal to extract the stimulation parameters. In prior art prostheses, the speech processor is a behind-the-ear (BTE-) device. The implanted stimulator generates stimulation patterns and conducts them to neural tissue through an electrode array 110, which electrode array 110 is typically disposed in the scala tympani in the inner ear. The connection between the speech processor and the stimulator is typically established by a radio frequency (RF-) link. Note that stimulation energy and stimulation information is conveyed via the RF link. Typically, digital data transmission protocols are used that employ bit rates of several hundred kBit/s.

One example of a standard stimulation strategy for cochlear implants is known as the "sequential interleaved sampling strategy" (CIS), which was developed by b.wilson (see, e.g., nature (352), 236-. In a speech processor, the signal processing of the CIS typically comprises the following steps:

1. the audio frequency range is divided into spectral bands by a filter bank,

2. the envelope detection of the output signal of each filter,

3. the instantaneous non-linear compression of the envelope signal (map law), and,

4. adaptive adjustment for Threshold (THR) and Most Comfortable Loudness (MCL) level.

Each stimulation electrode in the scala tympani is associated with a band pass filter of an external filter bank, according to the tonotopic organization of the cochlea. Symmetrical biphasic current pulses were used for stimulation. The amplitude of the stimulation pulses is directly obtained from the compressed envelope signal (step (3) above). These signals are sampled sequentially and the stimulation pulses are applied in a strictly non-overlapping sequence. Thus, as a typical CIS feature, only one stimulation channel is active at a time. The overall stimulation rate is relatively high. For example, assuming a total stimulation rate of 18kpps, and using a 12-channel filter bank, the stimulation rate per channel is 1.5 kpps. Such a stimulation rate per channel is usually sufficient for a suitable time domain representation of the envelope signal.

The maximum overall stimulation rate is limited by the minimum phase duration of each pulse. The phase duration cannot be chosen arbitrarily short, because the shorter the pulse, the higher the current amplitude required to induce an action potential in the neuron, and for various practical reasons, the current amplitude is limited. For a 12-channel system with a total stimulation rate of 18kpps, the phase duration is 27 μ s at the lower limit.

The CIS essentially represents envelope information in the respective channels. To some extent, time domain information is present, such as the variation of the envelope signal with pitch frequency. Using the concept of Channel Specific Sampling Sequences (CSSS) (see, for example, U.S. Pat. No.6,594,525, entitled "Electrical channel dependent on channel specific sampling sequences," which is fully incorporated herein by reference), the amount of time domain information is significantly increased. The time-domain variations of the band-pass output signal (sometimes referred to as "time-domain fine structure information") are represented in a low frequency range typically up to about 1 kHz. A typical stimulation setup may therefore comprise a mixture of low frequency CSSS channels and high frequency CIS channels. For each CSSS channel, a specific standardized sequence of ultra-high rate stimulation pulses is defined. For stimulation, zero crossings of the associated band pass filter output are detected, and each zero crossing triggers such a predetermined sequence, whereby the sequence is weighted with a factor derived from the instantaneous envelope of the band pass output. Thus, both envelope and temporal fine temporal information are represented in the CSSS stimulation sequence.

To achieve sufficiently high temporal resolution of the CSSS, support principles such as "Channel interaction compensation" (CIC) for simultaneous Stimulation (see, e.g., US patent No.6594525 entitled "Electrical new Stimulation Based on Channel Specific sampling sequences," which is fully incorporated by reference herein) or "choice group (SG)" algorithms (see, e.g., US patent application publication No.20050203589 entitled "Electrical Stimulation of the active new Based on Selected Groups," which is fully incorporated by reference herein) may be used.

However, spatial channel interaction (interaction) may result in a distribution of electrical potentials, which may result in an unintentional hearing impression. For example, let two adjacent stimulation electrodes 1 and 2 generate sequences with CSSS repetition rates of 100Hz and 200Hz, respectively. Due to spatial channel interaction, a 200Hz sequence will distort a 100Hz sequence at a position close to the electrode 1 and may for example lead to a 200Hz hearing impression (octave failure). Conversely, a 100Hz sequence will distort a 200Hz sequence near the electrode 2 and will result in an additional 100Hz tone being audible. The amount of mutual distortion may depend on the exact phase relationship between the two sequences and the channel interaction.

Disclosure of Invention

According to one embodiment of the invention, a method for generating electrode stimulation signals for a multi-channel electrode array implanted by a cochlear implant is provided. The method includes processing an audio signal with a filter bank. Each filter in the filter bank is associated with at least one channel having an electrode. The filter bank comprises a first band-pass filter which generates a wideband signal b (t) having a frequency: the frequency substantially covers at least one of a pitch frequency range of 100Hz to 400Hz and a first formant (format) range of 400Hz-1000 Hz. Energizing at least one electrode associated with the first band pass filter with an electrode stimulation signal based at least in part on the broadband signal b (t).

According to a related embodiment of the invention, the at least one electrode may be disposed in a apical region of the cochlea. Only one electrode may be associated with the first band pass filter. Alternatively, the at least two electrodes may be associated with a first band pass filter. The at least two electrodes may be excited simultaneously, for example, using sign-correlated pulses. The at least two electrodes may be simultaneously stimulated using the same electrode stimulation signal. Energizing the at least two electrodes may include stimulating the entire apical area within the cochlea.

According to other related embodiments of the invention, the method may further include exciting at least one electrode associated with one or more filters other than the first band pass filter, said one or more filters producing signals having a higher frequency than the broadband signal b (t). The one or more filters may produce signals having only higher frequencies than the wideband signal b (t). Exciting at least one electrode associated with one or more filters other than the first band pass filter may comprise: using a continuous interleaved sampling strategy (CIS) and/or using Channel Interaction Compensation (CIC).

According to further related embodiments of the present invention, the method may further include using a Select Group (SG) algorithm. At least one electrode associated with the first band pass filter may be disposed at a predetermined spatial distance from other electrodes in the multi-channel electrode array, thereby substantially avoiding channel interaction. The broadband signal b (t) may be substantially limited to frequencies below 400 Hz. The broadband signal b (t) may be substantially limited to frequencies below 1000 Hz.

According to another embodiment of the present invention, a method of generating electrode stimulation signals for an implanted electrode array is provided. The method includes providing a filter bank. Each filter is associated with at least one channel having an electrode. In addition, each filter is associated with an audio frequency band, thereby generating a set of band pass signals. The audio signal is processed using the set of filters. For each channel of electrodes, stimulation information is extracted from their associated band pass signals to generate a set of stimulation event signals defining electrode stimulation signals. The electrode stimulation signals are converted into a set of output electrode pulses for the electrodes implanted in the electrode array. Providing the set of filters includes determining filters and associated band pass signals to thereby avoid low frequency channel interaction between the electrodes.

According to a related embodiment of the invention, the pitch frequency range of 100Hz to 400Hz may be covered by a single band pass filter in the set of filters. The first formant range of 400Hz to 1000Hz may be covered by a single band pass filter in the bank of filters. A single band pass filter in the set of filters may cover a pitch frequency range of 100Hz to 1000 Hz.

In accordance with another embodiment of the present invention, a cochlear implant system includes a multi-channel electrode array having a plurality of stimulation electrodes for stimulating audio neural tissue with an electrode stimulation signal. The preprocessor processes an audio signal, the processor including a filter bank. Each filter in the set of filters is associated with at least one channel having an electrode. The filter bank comprises a first band-pass filter which generates a wideband signal b (t) having a frequency: the frequency substantially covers at least one of a pitch frequency range of 100Hz to 400Hz and a first formant range of 400Hz-1000 Hz. A stimulation module excites at least one electrode associated with the first band pass filter with an electrode stimulation signal based at least in part on the broadband signal b (t).

According to a related embodiment of the invention, only one electrode may be associated with the first band pass filter. Alternatively, the at least two electrodes may be associated with a first band pass filter. The stimulation module may simultaneously energize the at least two electrodes using the same electrode stimulation signal.

According to a further related embodiment of the present invention, the filter bank may include at least one electrode associated with one or more filters other than the first band pass filter, and the one or more filters generate signals having a higher frequency than the broadband signal b (t). The one or more filters may produce signals having only higher frequencies than the wideband signal b (t).

According to other related embodiments of the invention, the stimulation module may excite at least one electrode associated with one or more filters other than the first band pass filter using a continuous interleaved sampling strategy (CIS) or using Channel Interaction Compensation (CIC).

According to further related embodiments of the present invention, a Select Group (SG) algorithm may be used. At least one electrode associated with the first band pass filter may be disposed at a spatial distance from other electrodes in the multi-channel electrode array, thereby substantially avoiding channel interaction. The broadband signal b (t) may be substantially limited to frequencies below 400 Hz. The broadband signal b (t) may be substantially limited to frequencies below 1000 Hz.

Drawings

The above-mentioned features of the present invention will be more readily understood by reference to the following detailed description, taken in conjunction with the accompanying drawings, in which:

fig. 1 shows a cross-sectional view of an ear with a typical cochlear implant system;

fig. 2 shows a cochlear implant system 201 according to one embodiment of the present invention;

FIG. 3A shows a wideband signal filtered in the range [100Hz-400Hz ] according to one embodiment of the present invention;

FIG. 3B illustrates a half-wave rectification version of the wideband signal of FIG. 3A according to one embodiment of the invention; and

FIG. 3C shows a half-wave rectified version of a wideband signal sampled at a rate of approximately 5kHz, in accordance with one embodiment of the present invention.

Detailed Description

In an exemplary embodiment, a cochlear implant system and method provides a single or minimal number of (wideband) signals that include temporal fine structure information, thereby avoiding distortion between competing adjacent channels containing temporal fine structure information. As described in detail below.

Fig. 2 shows a cochlear implant system 201 according to one embodiment of the present invention. As described above, the cochlear implant system 201 may have two parts: an external speech processor and an implanted stimulator 105 (see fig. 1). The system 201 may be implemented, at least in part, using a controller integrated into the speech processor and/or stimulator 105. The controller may, without limitation, include circuitry and/or a processor that may be preprogrammed or configured to be loaded with an appropriate software program.

The cochlear implant system 201 includes a set of filters 203, and these filters 203 may be implemented in, but are not limited to, a speech processor. Each filter 203 is associated with an audio frequency band, thereby generating a set of band pass signals, and each band pass signal corresponds to a frequency band associated with one of the filters.

Each filter is associated with at least one channel 205 having an electrode 207. Each channel 205 may, without limitation, further include a half-wave rectifier 209, a sampling module 211, an envelope detector, and/or a compressor. By way of example and not limitation, the acoustic audio signal 202 passing through each channel may thus be filtered to produce a band pass signal, rectified and sampled to produce, at least in part, an electrode stimulation signal, which is then provided to the channel's associated electrode 210. Typically, but not by way of limitation, the basic stimulation waveform is a symmetric, biphasic pulse. The electrodes may be arranged in a monopolar configuration, in which a remote ground electrode is used, or in a bipolar configuration, in which each active electrode has a corresponding reference electrode.

In an exemplary embodiment of the invention, the set of filters 203 comprises a band-pass filter 212, the band-pass filter 212 providing a broadband signal b (t) covering a predetermined low frequency range. In various embodiments, this wideband signal b (t) is the only signal in the filter array associated with the time-domain fine structure information (typically associated with frequencies ≦ 1000 Hz), and has the minimum amount of filter roll-off from the other filters in the bank that is generally acceptable in various embodiments. The wideband frequency range may, but is not limited to, cover a pitch frequency range of typically 100Hz to 400 Hz. In another embodiment, the wideband frequency range may cover a range of first resonance peaks (formants) of typically 400Hz to 1000 Hz. In yet another embodiment, the wideband frequency range covers a range of pitch plus first resonance peak typically 100Hz to 1000 Hz.

The half-wave rectified version of b (t) is sampled at a rate typically between 5-10 kHz. Similar to CIS, each sample is used, at least in part, to define the amplitude of the stimulation pulse. Typically, each sampled value may be compressed (non-linear instantaneous compression, mapping rule) and then adjusted to accommodate the threshold and the most comfortable loudness requirements of the patient. By introducing (presenting) only one wideband signal comprising time domain fine structure information, distortion between competing adjacent channels containing time domain fine structure information is avoided.

The wideband signal b (t) may be used, without limitation, in conjunction with other CIS channels. In order to achieve a representation of the broadband signal b (t) in combination with, for example, a CIS channel with a sufficiently high time resolution, supporting principles such as "channel interaction compensation" (CIC) or "selection group" algorithms can be used. Using CIC, the amplitude of the electrode stimulation pulses (which may be, but are not limited to, simultaneously activated, sign-correlated pulses) is calculated by considering parameters of spatial channel interaction that reflect the geometric overlap of the electric fields from each electrode. Generally, using the SG algorithm, electrodes with high spatial channel interaction are typically selected to establish a "selection group". Within the "selection group", stimulation pulses masked by spatial channel interaction are detected based on a simple "maximum amplitude" criterion, and are not applied. Thus for each stimulation cycle, a number of electrodes (programmable) with the highest amplitudes within the "selection group" is detected before stimulation. Stimulation is performed only on these electrodes during a particular stimulation cycle, and this stimulation can be sequential or simultaneous. The members of the selected group should have sufficient spatial channel interaction so that the cochlear region is adequately stimulated. The algorithm for providing the electrode stimulation signals may be implemented using circuitry and/or a processor that is pre-programmable or configured to be loaded with an appropriate software program.

An exemplary example of the processing associated with the wideband signal is presented in fig. 3A-3C, according to one embodiment of the invention. FIG. 3A shows a filtered broadband signal in the range of [100Hz-400Hz ]. Fig. 3B shows a half-wave rectified version of the broadband signal. Fig. 3C shows a half-wave rectified version of the broadband signal sampled at a rate of about 5kHz, where each vertical line represents a stimulation pulse. Note that here, for example, temporal compression and adjustments to accommodate the Threshold (THR) and Most Comfortable Loudness (MCL) levels are omitted.

According to one embodiment of the invention, the resulting wideband sequence may be applied to one top low frequency channel and associated electrodes. The overall stimulation configuration thus consists of this low-frequency broadband channel and CIS channels in the higher frequency range. The CIS channel can substantially handle only higher frequencies than those associated with the wideband sequence.

According to another embodiment of the invention, the resulting wideband sequence may be applied to one top low frequency channel and associated electrode, and a specific spatial distance from the first adjacent CIS channel is maintained to substantially reduce the effects due to channel interaction between the wideband channel and the CIS channel. For example, one or more electrodes may be switched inactive.

According to yet another embodiment of the invention, the broadband sequence may be applied to several apical low frequency channels and associated electrodes simultaneously, stimulating the entire apical area within the cochlea with only one sequence.

According to another embodiment of the present invention, the wideband sequence may be applied to several top low frequency channels simultaneously and maintain a certain spatial distance from the first adjacent CIS channel. For example, one or more electrodes may be switched inactive.

Embodiments of the present invention may be implemented using any conventional computer programming language. For example, the preferred embodiments may be implemented using a procedural programming language (e.g., "C") or an object-oriented programming language (e.g., "C + +", Python). Alternative embodiments of the invention may be implemented as pre-programmed hardware elements, other related components, or as a combination of hardware and software components.

Embodiments can be implemented as a computer program product for use with a computer system. Such an embodiment may comprise a series of computer instructions either mounted on a tangible medium, such as a computer readable medium (e.g., a diskette, CD-ROM, or fixed disk) or transmittable to a computer system, via a modem or other interface device, such as a communications adapter connected to a network over a medium. The medium may be either a tangible medium (e.g., optical or analog communications lines) or a medium implemented with wireless techniques (e.g., microwave, infrared or other transmission techniques). The series of computer instructions embodies all or part of the functionality previously described herein with respect to the system. Those skilled in the art will appreciate that such computer instructions can be written in a number of programming languages for use with many computer architectures or operating systems. Further, such instructions may be stored in any memory device, such as semiconductor, magnetic, optical, or other memory devices, and may be transmitted using any communications technology, such as optical, infrared, microwave, or other transmission technologies. It is contemplated that such a computer program product may be distributed as a removable medium with accompanying printed or electronic documentation (e.g., shrink wrapped software), preloaded with a computer system (e.g., on system ROM or fixed disk), or distributed from a server or electronic bulletin board over the network (e.g., the Internet or world wide web). Of course, some embodiments of the invention may be implemented as a combination of software (e.g., a computer program product) and hardware. Still other embodiments of the invention are implemented as entirely hardware, or entirely software (e.g., a computer program product).

The above-described embodiments of the invention are intended to be merely exemplary and numerous variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to fall within the scope of the present invention as defined in the appended claims.

Claims (30)

1. A method for generating electrode stimulation signals for an implanted multi-channel electrode array of a cochlear implant, the method comprising:

processing an audio signal with a filter bank, each filter of the filter bank being associated with at least one channel having electrodes, the filter bank comprising a first band-pass filter, the first band-pass filter producing a wideband signal b (t) having frequencies such that: the frequency substantially covers at least one of a pitch frequency range of 100Hz to 400Hz and a first formant range of 400Hz-1000 Hz; and

based at least in part on the broadband signal b (t), at least one electrode associated with the first band pass filter is excited with an electrode stimulation signal.

2. The method of claim 1, wherein only one electrode is associated with the first band pass filter.

3. The method of claim 1, wherein energizing at least one electrode comprises energizing at least two electrodes.

4. The method of claim 3, wherein stimulating the at least two electrodes includes stimulating the entire apical area within the cochlea.

5. The method of claim 3, wherein energizing the at least two electrodes comprises simultaneously energizing the at least two electrodes using the same electrode stimulation signal.

6. The method of claim 1, wherein the at least one electrode is disposed in a apical region of a cochlea.

7. The method of claim 1, further comprising energizing at least one electrode associated with one or more filters other than the first band pass filter, the one or more filters producing signals having a higher frequency than broadband signal b (t).

8. The method of claim 7, wherein the one or more filters produce signals having only higher frequencies than wideband signal b (t).

9. The method of claim 7, wherein exciting at least one electrode associated with one or more filters other than the first band pass filter comprises: a sequential interleaved sampling strategy (CIS) is used.

10. The method of claim 7, further comprising using Channel Interaction Compensation (CIC).

11. The method of claim 1, further comprising using a Select Group (SG) algorithm.

12. The method of claim 1, further comprising arranging the at least one electrode associated with the first band pass filter at a predetermined spatial distance from other electrodes in a multi-channel electrode array, thereby to substantially avoid channel interaction.

13. The method of claim 1, wherein the broadband signal b (t) is substantially limited to frequencies below 400 Hz.

14. The method of claim 1, wherein the wideband signal b (t) is substantially limited to frequencies below 1000 Hz.

15. A method of generating electrode stimulation signals for an implanted electrode array, the method comprising:

providing a bank of filters, each filter being associated with at least one channel having electrodes, each filter being associated with an audio frequency band, thereby to generate a set of band pass signals;

processing the audio signal by using the filter bank;

for each channel of electrodes, extracting stimulation information from their associated band pass signals to generate a set of stimulation event signals defining electrode stimulation signals; and

transforming the electrode stimulation signals into a set of output electrode pulses for the electrodes in the implanted electrode array,

wherein providing the filter bank comprises determining the filters and associated band pass signals, thereby to avoid low frequency channel interaction between electrodes.

16. The method according to claim 15, wherein providing the filter bank comprises providing a single band pass filter in the filter bank covering a pitch frequency range of 100Hz to 400 Hz.

17. The method of claim 15, wherein providing the filter bank comprises providing a single band pass filter in the filter bank, the single band pass filter covering a first resonant peak range of 400Hz to 1000 Hz.

18. The method according to claim 15, wherein providing the filter bank comprises providing a single band pass filter in the filter bank, the single band pass filter covering a frequency range of 100Hz to 1000 Hz.

19. A cochlear implant system comprising:

a multi-channel electrode array having a plurality of stimulation electrodes for stimulating audio neural tissue with electrode stimulation signals,

a pre-processor for processing an audio signal, the processor comprising a filter bank,

each filter of the filter bank is associated with at least one channel having electrodes, the filter bank including a first band-pass filter that produces a wideband signal b (t) having frequencies such that: the frequency substantially covers at least one of a pitch frequency range of 100Hz to 400Hz and a first formant range of 400Hz-1000 Hz;

and

a stimulation module to stimulate at least one electrode associated with the first band pass filter with an electrode stimulation signal based at least in part on the broadband signal b (t).

20. The system of claim 19, wherein only one electrode is associated with the first band pass filter.

21. The system of claim 19, wherein at least two electrodes are associated with the first band pass filter.

22. The system of claim 21, wherein the stimulation module simultaneously excites the at least two electrodes using the same electrode stimulation signal.

23. The system of claim 19, further the filter bank comprising at least one electrode associated with one or more filters other than the first band pass filter, the one or more filters producing signals having a higher frequency than broadband signal b (t).

24. The system of claim 23, wherein the one or more filters produce signals having only higher frequencies than wideband signal b (t).

25. The system of claim 23, wherein the stimulation module excites the at least one electrode associated with one or more filters other than the first band pass filter using a continuous interleaved sampling strategy (CIS).

26. The system of claim 19, wherein the stimulation module uses Channel Interaction Compensation (CIC).

27. The system of claim 19, further comprising using a Select Group (SG) algorithm.

28. The system of claim 19, wherein the at least one electrode associated with the first band pass filter is disposed at a spatial distance from other electrodes in the multi-channel electrode array, thereby to substantially avoid channel interaction.

29. The system of claim 19, wherein the broadband signal b (t) is substantially limited to frequencies below 400 Hz.

30. The system of claim 19, wherein the broadband signal b (t) is substantially limited to frequencies below 1000 Hz.