U.S. patent application number 15/079126 was filed with the patent office on 2016-09-29 for frequency specific stimulation sequences.
The applicant listed for this patent is MED-EL Elektromedizinische Geraete GmbH. Invention is credited to Dirk Meister, Reinhold Schatzer, Peter Schleich.
Application Number | 20160279413 15/079126 |
Document ID | / |
Family ID | 55589900 |
Filed Date | 2016-09-29 |
United States Patent
Application |
20160279413 |
Kind Code |
A1 |
Schleich; Peter ; et
al. |
September 29, 2016 |
Frequency Specific Stimulation Sequences
Abstract
A signal processing arrangement generates electrical stimulation
signals to electrode contacts in an implanted cochlear implant
array. An input sound signal is analyzed to determine
characteristic frequency components. One or more stimulation events
are requested based on the timing and amplitude of the frequency
component. A frequency-specific stimulation sequence (FSSS) is
generated for stimulation of a plurality of adjacent electrode
contacts. The FSSS starts with a stimulation pulse to the
highest-frequency, most-basal electrode contact of the adjacent
electrode contacts, ends with a stimulation pulse to the
lowest-frequency, most-apical electrode contact of the adjacent
electrode contacts, and reaches a maximum stimulation amplitude at
a frequency-specific location within the cochlea corresponding to a
natural traveling wave maximum. The electrode stimulation signals
are then generated from the FSSS for delivery by the electrode
contacts to adjacent auditory neural tissue.
Inventors: |
Schleich; Peter; (Telfs,
AT) ; Meister; Dirk; (Innsbruck, AT) ;
Schatzer; Reinhold; (Birgitz, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MED-EL Elektromedizinische Geraete GmbH |
Innsbruck |
|
AT |
|
|
Family ID: |
55589900 |
Appl. No.: |
15/079126 |
Filed: |
March 24, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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62212642 |
Sep 1, 2015 |
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62212643 |
Sep 1, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N 1/36038 20170801;
H04R 25/48 20130101; H04R 25/502 20130101; A61N 1/025 20130101;
H04R 25/70 20130101; A61N 1/36039 20170801; A61N 1/0541
20130101 |
International
Class: |
A61N 1/36 20060101
A61N001/36; A61N 1/05 20060101 A61N001/05 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 2015 |
DE |
102015104614 |
Claims
1. A method for generating electrode stimulation signals to
electrode contacts in an implanted cochlear implant electrode
array, the method comprising: analyzing an input sound signal to
determine a plurality of characteristic frequency components, each
frequency component having a characteristic timing and amplitude;
for each frequency component, requesting one or more stimulation
events based on the timing and amplitude of the frequency
component; for each requested stimulation event, generating a
frequency-specific stimulation sequence (FSSS) for stimulation of a
plurality of adjacent electrode contacts, wherein the FSSS: i.
starts with a stimulation pulse to the highest-frequency,
most-basal electrode contact of the adjacent electrode contacts,
ii. ends with a stimulation pulse to the lowest-frequency,
most-apical electrode contact of the adjacent electrode contacts,
and iii. reaches a maximum stimulation amplitude at a
frequency-specific location within the cochlea corresponding to a
natural traveling wave maximum; and generating the electrode
stimulation signals from the FSSS for delivery by the electrode
contacts to adjacent auditory neural tissue.
2. The method according to claim 1, wherein each stimulation pulse
within the FSSS activates either a single electrode contact, or a
plurality of adjacent electrode contacts simultaneously and
in-phase.
3. The method according to claim 2, wherein simultaneous
stimulation pulses are amplitude corrected based on Channel
Interaction Compensation (CIC).
4. The method according to claim 1, wherein the FSSS is shorter in
time for higher frequency components and longer in time for lower
frequency components.
5. The method according to claim 1, wherein for each electrode
contact, the FSSS is a Channel Specific Sampling Sequence
(CSSS).
6. The method according to claim 1, wherein the timing of each
frequency component reflects a phase characteristic of the
frequency component.
7. The method according to claim 1, wherein the timing of each
frequency component reflects a frequency-specific latency
characteristic of the frequency component.
8. The method according to claim 1, wherein the FSSS is at least
partially simultaneous on two or more electrode contacts.
9. A system for generating electrode stimulation signals to
electrode contacts in an implanted cochlear implant electrode
array, the arrangement comprising: a signal filter bank configured
to analyze an input sound signal to determine a plurality of
characteristic frequency components, each frequency component
having a characteristic timing and amplitude; a signal processing
module configured to: i. request one or more stimulation events for
each frequency component based on the timing and amplitude of the
frequency component, and ii. generate a frequency-specific
stimulation sequence (FSSS) for each requested stimulation event
for at least partially simultaneous stimulation of a plurality of
adjacent electrode contacts, wherein the FSSS: a) starts with a
stimulation pulse to the highest-frequency, most-basal electrode
contact of the adjacent electrode contacts, b) ends with a
stimulation pulse to the lowest-frequency, most-apical electrode
contact of the adjacent electrode contacts, and c) reaches a
maximum stimulation amplitude at a frequency-specific location
within the cochlea corresponding to a natural traveling wave
maximum; and a pulse generator configured to generating the
electrode stimulation signals from the FSSS for delivery by the
electrode contacts to adjacent auditory neural tissue.
10. The system according to claim 9, wherein the signal processing
module is configured so that each stimulation pulse within the FSSS
activates either a single electrode contact, or a plurality of
adjacent electrode contacts simultaneously and in-phase.
11. The system according to claim 10, wherein the signal processing
module is configured so that simultaneous stimulation pulses are
amplitude corrected based on Channel Interaction Compensation
(CIC).
12. The system according to claim 9, wherein the signal processing
module is configured so that the FSSS is shorter in time for higher
frequency components and longer in time for lower frequency
components.
13. The system according to claim 9, wherein the signal processing
module is configured so that for each electrode contact, the FSSS
is a Channel Specific Sampling Sequence (CSSS).
14. The system according to claim 9, wherein the signal processing
module is configured so that the timing of each frequency component
reflects a phase characteristic of the frequency component.
15. The system according to claim 9, wherein the signal processing
module is configured so that the timing of each frequency component
reflects a frequency-specific latency characteristic of the
frequency component.
16. The system according to claim 9, wherein the signal processing
module is configured so that the FSSS is at least partially
simultaneous on two or more electrode contacts.
17. A non-transitory tangible computer-readable medium having
instructions thereon for generating electrode stimulation signals
to electrode contacts in an implanted cochlear implant electrode
array, the instructions comprising: analyzing an input sound signal
to determine a plurality of characteristic frequency components,
each frequency component having a characteristic timing and
amplitude; for each frequency component, requesting one or more
stimulation events based on the timing and amplitude of the
frequency component; for each requested stimulation event,
generating a frequency-specific stimulation sequence (FSSS) for at
least partially simultaneous stimulation of a plurality of adjacent
electrode contacts, wherein the FSSS: starts with a stimulation
pulse to the highest-frequency, most-basal electrode contact of the
adjacent electrode contacts, ends with a stimulation pulse to the
lowest-frequency, most-apical electrode contact of the adjacent
electrode contacts, and reaches a maximum stimulation amplitude at
a frequency-specific location within the cochlea corresponding to a
natural traveling wave maximum; and generating the electrode
stimulation signals from the FSSS for delivery by the electrode
contacts to adjacent auditory neural tissue.
Description
[0001] This application claims priority from German Patent
Application DE 102015104614, filed Mar. 26, 2015, from U.S.
Provisional Patent Application 62/212,642, filed Sep. 1, 2015, and
from U.S. Provisional Patent Application 62/212,643, filed Sep. 1,
2015, all of which are incorporated herein by reference in their
entireties.
FIELD OF THE INVENTION
[0002] The present invention relates to hearing implant systems,
and more specifically, to techniques for producing electrical
stimulation signals in such systems.
BACKGROUND ART
[0003] A normal ear transmits sounds as shown in FIG. 1 through the
outer ear 101 to the tympanic membrane 102, which moves the bones
of the middle ear 103 (malleus, incus, and stapes) that vibrate the
oval window and round window openings of the cochlea 104. The
cochlea 104 is a long narrow duct wound spirally about its axis for
approximately two and a half turns. It includes an upper channel
known as the scala vestibuli and a lower channel known as the scala
tympani, which are connected by the cochlear duct. The cochlea 104
forms an upright spiraling cone with a center called the modiolar
where the spiral ganglion cells of the acoustic nerve 113 reside.
In response to received sounds transmitted by the middle ear 103,
the fluid-filled cochlea 104 functions as a transducer to generate
electric pulses which are transmitted to the cochlear nerve 113,
and ultimately to the brain.
[0004] Hearing is impaired when there are problems in the ability
to transduce external sounds into meaningful action potentials
along the neural substrate of the cochlea 104. To improve impaired
hearing, hearing prostheses have been developed. For example, when
the impairment is related to operation of the middle ear 103, a
conventional hearing aid may be used to provide mechanical
stimulation to the auditory system in the form of amplified sound.
Or when the impairment is associated with the cochlea 104, a
cochlear implant with an implanted stimulation electrode can
electrically stimulate auditory nerve tissue with small currents
delivered by multiple electrode contacts distributed along the
electrode.
[0005] FIG. 1 also shows some components of a typical cochlear
implant system, including an external microphone that provides an
audio signal input to an external signal processor 111 where
various signal processing schemes can be implemented. The processed
signal is then converted into a digital data format, such as a
sequence of data frames, for transmission into the implant 108.
Besides receiving the processed audio information, the implant 108
also performs additional signal processing such as error
correction, pulse formation, etc., and produces a stimulation
pattern (based on the extracted audio information) that is sent
through an electrode lead 109 to an implanted electrode array
110.
[0006] Typically, the electrode array 110 includes multiple
electrode contacts 112 on its surface that provide selective
stimulation of the cochlea 104. Depending on context, the electrode
contacts 112 are also referred to as electrode channels. In
cochlear implants today, a relatively small number of electrode
channels are each associated with relatively broad frequency bands,
with each electrode contact 112 addressing a group of neurons with
an electric stimulation pulse having a charge that is derived from
the instantaneous amplitude of the signal envelope within that
frequency band.
[0007] In some coding strategies, stimulation pulses are applied at
a constant rate across all electrode channels, whereas in other
coding strategies, stimulation pulses are applied at a
channel-specific rate. Various specific signal processing schemes
can be implemented to produce the electrical stimulation signals.
Signal processing approaches that are well-known in the field of
cochlear implants include continuous interleaved sampling (CIS),
channel specific sampling sequences (CSSS) (as described in U.S.
Pat. No. 6,348,070, incorporated herein by reference), spectral
peak (SPEAK), and compressed analog (CA) processing.
[0008] FIG. 2 shows the major functional blocks in a typical
cochlear implant signal processing system wherein band pass signals
are processed and coding to generate electrode stimulation signals
to stimulation electrodes in an implanted cochlear implant
electrode array. For example, commercially available Digital Signal
Processors (DSP) can be used to perform speech processing according
to a 12-channel CIS approach. The initial acoustic audio signal
input is produced by one or more sensing microphones, which may be
omnidirectional and/or directional. Preprocessor Filter Bank 201
pre-processes the initial acoustic audio signal with a bank of
multiple band pass filters, each of which is associated with a
specific band of audio frequencies--for example, a digital filter
bank having 12 digital Butterworth band pass filters of 6th order,
Infinite Impulse Response (IIR) type--so that the acoustic audio
signal is filtered into some M band pass signals, B.sub.1 to
B.sub.M where each signal corresponds to the band of frequencies
for one of the band pass filters. Each output of the CIS band pass
filters can roughly be regarded as a sinusoid at the center
frequency of the band pass filter which is modulated by the
envelope signal. This is due to the quality factor (Q.apprxeq.3) of
the filters. In case of a voiced speech segment, this envelope is
approximately periodic, and the repetition rate is equal to the
pitch frequency. Alternatively and without limitation, the
Preprocessor Filter Bank 201 may be implemented based on use of a
fast Fourier transform (FFT) or a short-time Fourier transform
(STFT). Based on the tonotopic organization of the cochlea, each
electrode contact in the scala tympani often is associated with a
specific band pass filter of the external filter bank.
[0009] FIG. 3 shows an example of a short time period of an audio
speech signal from a microphone, and FIG. 4 shows an acoustic
microphone signal decomposed by band-pass filtering by a bank of
filters into a set of signals. An example of pseudocode for an
infinite impulse response (IIR) filter bank based on a direct form
II transposed structure is given by Fontaine et al., Brian Hears:
Online Auditory Processing Using Vectorization Over Channels,
Frontiers in Neuroinformatics, 2011; incorporated herein by
reference in its entirety:
TABLE-US-00001 for j = 0 to number of channels - 1 do for s = 0 to
number of samples - 1 do Y.sub.j(s) = B.sub.0j * X.sub.j (s) +
Z.sub.0j for i = 0 to order - 3 do Z.sub.ij = B.sub.i+1,j *
X.sub.j(s) + Z.sub.i+1,j - A.sub.i+1,j * Y.sub.j(s) end for
Z.sub.order - 2,j = B.sub.order - 1,j * X.sub.j(s) - A.sub.order -
1,j * Y.sub.j(s) end for end for
[0010] The band pass signals B.sub.1 to B.sub.M (which can also be
thought of as frequency channels) are input to a Signal Processor
202 which extracts signal specific stimulation information--e.g.,
envelope information, phase information, timing of requested
stimulation events, etc.--into a set of N stimulation channel
signals S.sub.1 to S.sub.N that represent electrode specific
requested stimulation events. For example, channel specific
sampling sequences (CSSS) may be used as described in U.S. Pat. No.
6,594,525, which is incorporated herein by reference in its
entirety. For example, the envelope extraction may be performed
using 12 rectifiers and 12 digital Butterworth low pass filters of
2nd order, IIR-type.
[0011] A Pulse Generator 205 includes a Pulse Mapping Module 203
that applies a non-linear mapping function (typically logarithmic)
to the amplitude of each band-pass envelope. This mapping
function--for example, using instantaneous nonlinear compression of
the envelope signal (map law)--typically is adapted to the needs of
the individual cochlear implant user during fitting of the implant
in order to achieve natural loudness growth. This may be in the
specific form of functions that are applied to each requested
stimulation event signal S.sub.1 to S.sub.N that reflect
patient-specific perceptual characteristics to produce a set of
electrode stimulation signals A.sub.1 to A.sub.M that provide an
optimal electric representation of the acoustic signal. A
logarithmic function with a form-factor C typically may be applied
as a loudness mapping function, which typically is identical across
all the band pass analysis channels. In different systems,
different specific loudness mapping functions other than a
logarithmic function may be used, with just one identical function
is applied to all channels or one individual function for each
channel to produce the electrode stimulation signals A.sub.1 to
A.sub.M outputs from the Pulse Mapping Module 203.
[0012] The Pulse Generator 205 also includes a Pulse Shaper 204
that develops the set of electrode stimulation signals A.sub.1 to
A.sub.M into a set of output electrode pulses E.sub.1 to E.sub.M
for the electrode contacts in the implanted electrode array which
stimulate the adjacent nerve tissue. The electrode stimulation
signals A.sub.1 to A.sub.M may be symmetrical biphasic current
pulses with amplitudes that are directly obtained from the
compressed envelope signals.
[0013] In the specific case of a CIS system, the stimulation pulses
are applied in a strictly non-overlapping sequence. Thus, as a
typical CIS-feature, only one electrode channel is active at a time
and the overall stimulation rate is comparatively high. For
example, assuming an overall stimulation rate of 18 kpps and a 12
channel filter bank, the stimulation rate per channel is 1.5 kpps.
Such a stimulation rate per channel usually is sufficient for
adequate temporal representation of the envelope signal. The
maximum overall stimulation rate is limited by the minimum phase
duration per pulse. The phase duration cannot be arbitrarily short
because, the shorter the pulses, the higher the current amplitudes
have to be to elicit action potentials in neurons, and current
amplitudes are limited for various practical reasons. For an
overall stimulation rate of 18 kpps, the phase duration is 27
.mu.s, which is near the lower limit.
[0014] In the CIS strategy, the signal processor only uses the band
pass signal envelopes for further processing, i.e., they contain
the entire stimulation information. For each electrode channel, the
signal envelope is represented as a sequence of biphasic pulses at
a constant repetition rate. A characteristic feature of CIS is that
the stimulation rate is equal for all electrode channels and there
is no relation to the center frequencies of the individual
channels. It is intended that the pulse repetition rate is not a
temporal cue for the patient (i.e., it should be sufficiently high
so that the patient does not perceive tones with a frequency equal
to the pulse repetition rate). The pulse repetition rate is usually
chosen at greater than twice the bandwidth of the envelope signals
(based on the Nyquist theorem).
[0015] Another cochlear implant stimulation strategy that does
transmit fine time structure information is the Fine Structure
Processing (FSP) strategy by Med-El. Zero crossings of the band
pass filtered time signals are tracked, and at each negative to
positive zero crossing, a Channel Specific Sampling Sequence (CSSS)
is started. Typically CSSS sequences are only applied on the first
one or two most apical electrode channels, covering the frequency
range up to 200 or 330 Hz. The FSP arrangement is described further
in Hochmair I, Nopp P, Jolly C, Schmidt M, Scho.beta.er H, Garnham
C, Anderson I, MED-EL Cochlear Implants: State of the Art and a
Glimpse into the Future, Trends in Amplification, vol. 10, 201-219,
2006, which is incorporated herein by reference.
[0016] Many cochlear implant coding strategies use what is referred
to as an N-of-M approach where only some number n electrode
channels with the greatest amplitude are stimulated in a given
sampling time frame. If, for a given time frame, the amplitude of a
specific electrode channel remains higher than the amplitudes of
other channels, then that channel will be selected for the whole
time frame. Subsequently, the number of electrode channels that are
available for coding information is reduced by one, which results
in a clustering of stimulation pulses. Thus, fewer electrode
channels are available for coding important temporal and spectral
properties of the sound signal such as speech onset.
[0017] One method to reduce the spectral clustering of stimulation
per time frame is the MP3000.TM. coding strategy by Cochlear Ltd,
which uses a spectral masking model on the electrode channels.
Another method that inherently enhances coding of speech onsets is
the ClearVoice.TM. coding strategy used by Advanced Bionics Corp,
which selects electrode channels having a high signal to noise
ratio. U.S. Patent Publication 2005/0203589 (which is incorporated
herein by reference in its entirety) describes how to organize
electrode channels into two or more groups per time frame. The
decision which electrode channels to select is based on the
amplitude of the signal envelopes.
[0018] In addition to the specific processing and coding approaches
discussed above, different specific pulse stimulation modes are
possible to deliver the stimulation pulses with specific
electrodes--i.e. mono-polar, bi-polar, tri-polar, multi-polar, and
phased-array stimulation. And there also are different stimulation
pulse shapes--i.e. biphasic, symmetric triphasic, asymmetric
triphasic pulses, or asymmetric pulse shapes. These various pulse
stimulation modes and pulse shapes each provide different benefits;
for example, higher tonotopic selectivity, smaller electrical
thresholds, higher electric dynamic range, less unwanted
side-effects such as facial nerve stimulation, etc. But some
stimulation arrangements are quite power consuming, especially when
neighboring electrodes are used as current sinks. Up to 10 dB more
charge might be required than with simple mono-polar stimulation
concepts (if the power-consuming pulse shapes or stimulation modes
are used continuously).
[0019] It is well-known in the field that electric stimulation at
different locations within the cochlea produce different frequency
percepts. The underlying mechanism in normal acoustic hearing is
referred to as the tonotopic principle. In cochlear implant users,
the tonotopic organization of the cochlea has been extensively
investigated; for example, see Vermeire et al., Neural tonotopy in
cochlear implants: An evaluation in unilateral cochlear implant
patients with unilateral deafness and tinnitus, Hear Res, 245(1-2),
2008 Sep. 12 p. 98-106; and Schatzer et al., Electric-acoustic
pitch comparisons in single-sided-deaf cochlear implant users:
Frequency-place functions and rate pitch, Hear Res, 309, 2014
March, p. 26-35 (both of which are incorporated herein by reference
in their entireties).
[0020] In a normal hearing ear, one frequency component
consecutively stimulates multiple neural populations. This
phenomenon was described as the "travelling wave" as shown in FIG.
5 from Von Bekesy, Georg. Experiments in hearing. Ed. Ernest Glen
Wever. Vol. 8. New York: McGraw-Hill, 1960 (incorporated herein by
reference in its entirety). That is, in response to a pure tone,
the basilar membrane resonates in a travelling wave (the ascending
numbers within FIG. 5) which gradually grows in amplitude (the
dashed lines in FIG. 5) as it moves along the cochlear duct from
the stapes (base) toward the helicotrema (apex).
[0021] One quality of the travelling wave that is partly reflected
in modern cochlear implant systems is that each frequency component
reaches a peak amplitude at a specific spot within the cochlea (the
tonotopic principle discussed above). These spectro-temporal
properties can also be observed in the activity of cat's cochlear
nerve fibres shown in FIG. 6 from Secker Walker et al, Time domain
analysis of auditory nerve fiber firing rates, J Acoust Soc Am,
88(3), 1990, p. 1427-1436 (incorporated herein by reference in its
entirety). FIG. 6 shows neural activity in the cochlear nerve over
time at nerve fibres with different characteristic frequencies in
response to synthetic vowels. One dominant frequency component in
the synthetic vowel stimuli is the fundamental frequency (F0),
which in FIG. 6 can be clearly identified as a regular pattern
starting at high frequencies and ending several milliseconds later
at low frequencies. The black curve in the shaded box in FIG. 6
indicates the frequency-specific time delays or the neural
responses. Higher frequency components also can be observed between
the F0 structures; for example, harmonics that are visible between
1800 and 1000 Hz. Similar to the F0 structures, they start at high
frequency fibers and end some milliseconds later at low frequency
fibers. This spectro-temporal excitation behaviour is not currently
explicitly implemented in cochlear implant systems.
[0022] Loeb G., Are cochlear implant patients suffering from
perceptual dissonance? Ear Hear, 26, 2005, p. 435-450 (incorporated
herein by reference in its entirety) describes that phase-locking
occurs over a substantial length of the cochlea. Furthermore, the
action potentials exhibit a coherent spatial gradient with the
steepest and most rapidly changing gradient of the phase occurring
next to the place of the resonant frequency. At this point, the
travelling wave starts to significantly slow down and dissipates.
The phase gradient is believed to substantially contribute to pitch
perception, especially in loud situations where harmonics are not
resolved.
[0023] Existing coding approaches take into account some of the
temporal properties of the acoustic signal. CIS determines
frequency-specific envelopes which inherently contain a certain
amount of information about individual low frequency components
such as the fundamental frequency. More advanced approaches for
calculating band specific envelopes also have been described; for
example, U.S. Patent Publication 2006/0235486 (which is
incorporated herein by reference in its entirety). The latter and
CIS both sample the band pass envelopes with fixed rate stimulation
pulses to resemble rudimentary properties of the basilar membrane
movement. Other advanced systems as described in U.S. Patent
Publication 2011/0230934 (which is incorporated herein by reference
in its entirety) explicitly extract temporal characteristics of a
band pass signal by identifying phase characteristics such as zero
crossings. The described system triggers channel-specific sequences
of stimulation pulses at each detected zero crossing. Each of the
foregoing arrangements attributes certain frequency components to
certain stimulation places. U.S. Patent Publication 2011/0230934
also explicitly takes into account the timing of certain frequency
components.
[0024] Vocoder-based cochlear implant stimulation arrangements such
as CIS and N-of-M do not take into account the travelling wave
properties of normal acoustic hearing. The acoustic signal is
analysed by filter banks or FFT and assigned either to single
intracochlear electrodes, or to simultaneous stimulation of
multiple adjacent electrodes. While filter banks can mimic the
latencies of single frequency components at the place of
stimulation, they are not able to mimic other aspects of the
travelling wave behaviour such as the spectro-temporal distribution
of this component to neighbouring stimulation sites, starting at a
more basal site with low amplitude and ending at a more apical
stimulation site with a maximum of stimulation at a site in
between. An FFT, also used for mimicking the tonotopic principle in
a cochlear implant is no better able to replicate the general
latency differences between the frequency components (at the place
of stimulation) nor does it provide the spectro-temporal behaviour
described above.
SUMMARY OF THE INVENTION
[0025] Embodiments of the present invention are directed to a
signal processing arrangement and corresponding method that
generates electrode stimulation signals to electrode contacts in an
implanted cochlear implant array. An input sound signal is analyzed
to determine characteristic frequency components. For each
frequency component, one or more stimulation events are requested
based on the timing and amplitude of the frequency component. For
each requested stimulation event, a frequency-specific stimulation
sequence (FSSS) is generated for stimulation of adjacent electrode
contacts. The FSSS starts with a stimulation pulse to the
highest-frequency, most-basal electrode contact of the adjacent
electrode contacts, ends with a stimulation pulse to the
lowest-frequency, most-apical electrode contact of the adjacent
electrode contacts, and reaches a maximum stimulation amplitude at
a frequency-specific location within the cochlea corresponding to a
natural traveling wave maximum. The electrode stimulation signals
are then generated from the FSSS for delivery by the electrode
contacts to adjacent auditory neural tissue.
[0026] In further specific embodiments, each stimulation pulse
within the FSSS activates either a single electrode contact, or a
plurality of adjacent electrode contacts simultaneously and
in-phase. Simultaneous stimulation pulses may be amplitude
corrected based on Channel Interaction Compensation (CIC). The FSSS
may be shorter in time for higher frequency components and longer
in time for lower frequency components. The FSSS may be at least
partially simultaneous on two or more electrode contacts. For each
electrode contact, the FSSS may be a Channel Specific Sampling
Sequence (CSSS). The timing of each frequency component may reflect
a phase characteristic and/or frequency-specific latency
characteristic of the frequency component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 shows a section view of a human ear with a typical
cochlear implant system designed to deliver electrical stimulation
to the inner ear.
[0028] FIG. 2 shows various functional blocks in a continuous
interleaved sampling (CIS) processing system.
[0029] FIG. 3 shows an example of a short time period of an audio
speech signal from a microphone.
[0030] FIG. 4 shows an acoustic microphone signal decomposed by
band-pass filtering by a bank of filters into a set of band pass
signals.
[0031] FIG. 5 shows the concept of the travelling wave within the
cochlea.
[0032] FIG. 6 shows an example neurogram of auditory nerve fibers
of a cat over time.
[0033] FIG. 7 shows various logical steps in developing electrode
stimulation signals according to an embodiment of the present
invention.
[0034] FIG. 8 shows various waveforms related to producing
frequency-specific stimulation sequences for a low frequency
component according to an embodiment of the present invention.
[0035] FIG. 9 shows various waveforms related to producing
frequency-specific stimulation sequences for a high frequency
component according to an embodiment of the present invention.
[0036] FIG. 10 shows different shapes of frequency-specific
stimulation sequences.
[0037] FIG. 11 shows different amplitude and phase delay shapes of
frequency-specific stimulation sequences.
[0038] FIG. 12 shows an example of steered multi-polar travelling
wave stimulation.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0039] Embodiments of the present invention add to a cochlear
implant system an emulation of a normal auditory physiological
process which is important for frequency perception in normal
hearing individuals, the travelling wave response of the cochlea.
The added spectro-temporal features reflect the rise and sharp fall
of excitation along the cochlea from the travelling wave, as well
as its slowing down. Embodiments of the invention use arrangements
that detect a number of relevant (i.e. spectrally spread or
psychophysically unmasked) frequency components and translates them
into stimulation sequences which can be super-positioned. This
approach can be configured for the specific number of individual
information channels of a given patient by skipping frequency
components while transmitting distinguishable components in a
highly natural way.
[0040] FIG. 7 is a flow chart showing various logical steps in
producing electrode stimulation signals to electrode contacts in an
implanted cochlear implant array according to an embodiment of the
present invention. A pseudo code example of such a method can be
set forth as:
TABLE-US-00002 Input Frequency and Component Level Estimation:
FilterAnalyze (input_sound, frequency_components) Frequency
Specific Stimulation Sequences: Code (frequency_components,
stim_events) FSSS (stim_events, fsss_seqs) Stimulation Pulse
Generation: Generate (fsss_seqs, output_pulses)
The details of such an arrangement are set forth in the following
discussion.
[0041] As in the arrangement discussed above with respect to FIG.
2, a preprocessor signal filter bank 201 can be configured to
decompose an input sound signal into band pass frequency component
signals B.sub.1 to B.sub.M, step 701, representing an estimate of
instantaneous input frequency/timing and component level/amplitude
such that each band pass frequency component signal B.sub.1 to
B.sub.M changes over time in characteristic timing and amplitude.
The timing of the band pass frequency component signals B.sub.1 to
B.sub.M typically may reflect frequency-specific response latencies
and/or phase characteristics. The signal processing module 202 then
processes the band pass frequency component signals B.sub.1 to
B.sub.M to code each frequency component, step 702, as a sequence
of requested stimulation events based on the frequency component
timing and amplitude.
[0042] For each requested stimulation event, a frequency-specific
stimulation sequence (FSSS) output S.sub.1 to S.sub.N is generated,
step 703, for at least partially simultaneous stimulation of
adjacent electrode contacts. FIG. 8 shows various waveforms related
to the signal processing module 202 producing an FSSS according to
an embodiment of the present invention for a low frequency
component. The top panel A in FIG. 8 shows a low frequency
component where the circles (zero crossings) indicate specific
stimulation events. Each stimulation event triggers an FSSS. The
middle Panel B in FIG. 8 shows the timing of the desired neural
response to the input frequency in terms of location along the
cochlea over time. The thin horizontal lines in Panel B indicate
examples of electrode-specific locations/frequencies. The lower
Panel C in FIG. 8 shows FSSS stimulation sequences on two adjacent
electrode contacts that apply weighted partially simultaneous
stimulation in the specific form of Channel Specific Sampling
Sequences (CSSS as described in U.S. Pat. No. 6,594,525;
incorporated herein by reference in its entirety). Specifically,
Panel C shows that the FSSS starts with the left-most stimulation
pulse to the highest-frequency, most-basal electrode contact (n+1),
ends with the right-most stimulation pulse to the lowest-frequency,
most-apical electrode contact (n). The FSSS is defined so as to
reach a maximum stimulation amplitude at a frequency-specific
location within the cochlea that corresponds to a natural traveling
wave maximum. Each given stimulation pulse within the FSSS
activates either a single electrode contact, or multiple adjacent
electrode contacts simultaneously and in-phase.
[0043] For the low frequency component shown in FIG. 8, there is a
relatively large phase delay and longer duration FSSS. The FSSS is
typically shorter in time for higher frequency components and
longer in time for lower frequency components. Thus, FIG. 9 shows
various waveforms related to producing frequency-specific
stimulation sequences for a high frequency component where the
phase delay is smaller and the FSSS is shorter in duration. And
FIG. 10 shows different potential shapes of frequency-specific
stimulation sequences.
[0044] The pulse generator 205 is configured to convert the
requested stimulation events S.sub.1 to S.sub.N to produce a
corresponding sequence of unweighted stimulation signals A.sub.1 to
A.sub.M that provide an optimal electric representation of the
acoustic signal, and then apply a linear mapping function
(typically logarithmic) and pulse shaping to produce weighted
output pulse sequences electrode stimulation signals E.sub.1 to
E.sub.M for delivery by the electrode contacts to adjacent auditory
neural tissue, step 704. Simultaneous stimulation pulses may be
amplitude corrected based on Channel Interaction Compensation
(CIC). The weighted output pulse sequences electrode stimulation
signals E.sub.1 to E.sub.M also are adapted to the needs of the
individual implant user based on a post-surgical fitting process
that determines patient-specific perceptual characteristics.
[0045] The length of the FSSS can vary based on the number of
electrode channels and the number of the CSSS per channel. The
lengths of the electrode channel CSSS per FSSS may be constant,
however, varying CSSS lengths per FSSS also may be possible, such
as longer CSSS at more apical channels or longer/shorter CSSS at
the maximum level of the FSSS, etc. Some embodiments also may apply
a Channel Interaction Compensation (CIC) algorithm (e.g., U.S. Pat.
No. 7,917,224; incorporated herein by reference in its entirety) to
the amplitudes of simultaneous FSSS to provide a desired loudness
level to the user. The onset of the CSSS within a FSSS is
controlled by the phase of the travelling wave. Subthreshold
stimulation on individual electrode channels may be applied within
a single FSSS in order to support and maintain spontaneous action
potentials at the stimulation locations.
[0046] Frequency specific characteristics of the FSSS such as
amplitude shape, spread over electrode positions, and duration (of
entire FSSS and channel specific CSSS per FSSS) can be stored as
templates in system memory that is accessible to the signal
processing module 202. FIG. 11 shows some specific examples of
different amplitude and phase delay shapes of frequency-specific
stimulation sequences, with a low frequency component shown on the
left, and a high frequency component shown on the right. The
vertical lines in FIG. 11 represent time instances at which
simultaneous stimulation is elicited. And an FSSS can be calculated
for any desired frequency component by using interpolation.
[0047] Temporal overlap of an FSSS can be handled by applying
simultaneous stimulation of all necessary electrodes, i.e.
superposition. Spectral overlap of two simultaneously requested
interleaving FSSS can also be omitted.
[0048] The FSSS can be optimized in duration, number of
stimulations, and amplitude shape to produce a the most tone-like
percept in response to an acoustic presentation of a pure tone. The
amplitude shape and timing of the FSSS can reproduce the envelope
of the traveling wave by representing portions of the traveling
wave at consecutive positions along the cochlea (FIG. 11) starting
at the base of the cochlea with low amplitude and rising with a
shallow slope up to the maximum frequency and then falling with a
steep slope towards the apex of the cochlea. Alternatively, in
simplest form, the amplitude shape of the FSSS can consist of a
single stimulation event, occurring simultaneously on two or more
adjacent electrode channels. The various FSSS may overlap in time
so that they can be applied in a superimposed manner. The timing of
the stimulation event reflects the phase delay of the encoded
frequency component as shown in FIGS. 8 and 9. The amplitude
weightings of the simultaneous stimulation events on the adjacent
electrodes reflect the frequency specific place of the component
along the cochlea. And, in some specific embodiments, the
stimulation events may be selected as described in U.S. Patent
Publication 2009/0125082, which is incorporated herein by reference
in its entirety.
[0049] Stimulation positions which are intermediate to physical
electrode positions can be produced by weighted simultaneous
stimulation of one or more adjacent electrodes. Alternatively, a
FSSS can also be compiled from a series of focused stimulation
modes, e.g. tri- or multipolar stimulation such as phased array
stimulation as shown in Bonham et al., Current focusing and
steering: modeling, physiology, and psychophysics, Hear Res,
242(1-2), August 2008, pp. 141-153; incorporated herein by
reference in its entirety. The focus, amplitude and timing of the
stimulation will follow the tempo-spectral shape of the traveling
wave envelope. FIG. 12 shows an example of steered multi-polar
traveling wave stimulation where the focus of stimulation (circles)
follows the temporal course of the traveling wave.
[0050] Embodiments of the invention may be implemented in part in
any conventional computer programming language. For example,
preferred embodiments may be implemented in 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.
[0051] Embodiments can be implemented in part as a computer program
product for use with a computer system. Such implementation may
include a series of computer instructions fixed either on a
tangible medium, such as a computer readable medium (e.g., a
diskette, CD-ROM, 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 should appreciate that such
computer instructions can be written in a number of programming
languages for use with many computer architectures or operating
systems. Furthermore, 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 expected 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 both 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).
[0052] Although various exemplary embodiments of the invention have
been disclosed, it should be apparent to those skilled in the art
that various changes and modifications can be made which will
achieve some of the advantages of the invention without departing
from the true scope of the invention.
* * * * *