U.S. patent application number 13/609877 was filed with the patent office on 2013-01-03 for stochastic stimulation in a hearing prosthesis.
Invention is credited to Sean Lineaweaver.
Application Number | 20130006329 13/609877 |
Document ID | / |
Family ID | 41432012 |
Filed Date | 2013-01-03 |
United States Patent
Application |
20130006329 |
Kind Code |
A1 |
Lineaweaver; Sean |
January 3, 2013 |
STOCHASTIC STIMULATION IN A HEARING PROSTHESIS
Abstract
A method, for inducing a hearing percept to a recipient of a
cochlear implant, includes: building a sequence of electrical
stimulation pulses having first and second inter-pulse intervals;
and making stochastic the sequence including randomly selecting
either the first or the second inter-pulse interval for insertion
between consecutive pulses in the sequence.
Inventors: |
Lineaweaver; Sean; (Parker,
CO) |
Family ID: |
41432012 |
Appl. No.: |
13/609877 |
Filed: |
September 11, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12403949 |
Mar 13, 2009 |
8265767 |
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13609877 |
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61036318 |
Mar 13, 2008 |
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Current U.S.
Class: |
607/57 |
Current CPC
Class: |
A61N 1/36038
20170801 |
Class at
Publication: |
607/57 |
International
Class: |
A61F 11/04 20060101
A61F011/04; A61N 1/36 20060101 A61N001/36 |
Claims
1. A method for inducing a hearing percept to a recipient of a
cochlear implant comprising: building a sequence of electrical
stimulation pulses having first and second inter-pulse intervals;
and making stochastic the sequence including: randomly selecting
either the first or the second inter-pulse interval for insertion
between consecutive pulses in the sequence.
2. The method of claim 1, wherein the revising includes at least
one of: limiting the number of consecutive instances of the same
inter-pulse interval; selectively changing instances of one of the
first and second inter-pulse intervals for the other thereof in
order to substantially balance the distribution of the first and
second inter-pulse intervals within the stochastic sequence; and
selectively changing instances of one of the first and second
inter-pulse intervals for the other thereof in order to weight the
ratio of the number of the first inter-pulse intervals to the
number of second inter-pulse intervals and thereby adjust the
induced hearing percept.
3. The method of claim 1, further comprising: receiving a sound
signal; wherein the sequence of electrical stimulation pulses is
based on the sound signal.
4. The method of claim 1, wherein: the sound signal includes at
least a first pitch; and the first inter-pulse interval is based at
least on the first pitch.
5. The method of claim 4, wherein: the second inter-pulse interval
is based at least on a sequence of conditioning pulses.
6. The method of claim 4, wherein: the sound signal includes at
least a second pitch; and the second inter-pulse interval is based
at least on the second pitch.
7. The method of claim 1, wherein: the first interval is
substantially constant; and the second interval is substantially
constant.
8. The method of claim 1, further comprising: delivering the
stochastic sequence to the recipient via a single stimulation
channel of the cochlear implant.
9. A method for providing a hearing percept to a recipient of a
cochlear implant comprising: generating a stochastic first sequence
of electrical stimulation pulses having inter-pulse intervals
distributed stochastically throughout the first sequence, at least
some of the inter-pulse intervals being based on a second sequence
of conditioning pulses.
10. The method of claim 9, further comprising: encoding the second
sequence of conditioning pulses within a third sequence of pulses
representing at least a first pitch of a received sound signal to
form the first sequence of electrical stimulation pulses.
11. The method of claim 10, wherein: the inter-pulse intervals
based on the second sequence of conditioning pulses are second
inter-pulse intervals; and the inter-pulse intervals further
include: a first inter-pulse interval based on a pitch of the
received sound signal.
12. The method of claim 9, wherein the generating a stochastic
first sequence includes at least one of: constraining the
stochasticity of the first sequence of electrical stimulation
pulses to be within controlled limits.
13. The method of claim 12, wherein the constraining includes:
limiting the number of consecutive instances of the same
inter-pulse interval; selectively changing instances of one of the
first and second inter-pulse intervals for the other thereof in
order to substantially balance the distribution of the first and
second inter-pulse intervals within the stochastic first sequence;
and selectively changing instances of one of the first and second
inter-pulse intervals for the other thereof in order to
substantially balance the distribution of the first and second
inter-pulse intervals within the stochastic first sequence.
14. The method of claim 9, wherein: the inter-pulse intervals
include at least first inter-pulse intervals and second inter-pulse
intervals; the first intervals are substantially constant; and the
second intervals are substantially constant.
15. The method of claim 9, further comprising: receiving a sound
signal; wherein the first sequence of electrical stimulation pulses
is based on the sound signal.
16. The method of claim 9, further comprising: delivering the first
sequence of electrical stimulation pulses to the recipient via a
single stimulation channel of the cochlear implant.
17. A hearing prosthesis for providing a hearing percept to a
recipient of a cochlear implant, the prosthesis comprising: a sound
pickup component configured to receive a sound signal having at
least one pitch; and a stochastic stimulation generator configured
to generate a stochastic first sequence of electrical stimulation
pulses based on the sound signal, inter-pulse intervals being
distributed stochastically throughout the first sequence, at least
some of the inter-pulse intervals being based on a second sequence
of conditioning pulses.
18. The prosthesis of claim 17, wherein: the stochastic stimulation
generator is further configured to encode the second sequence of
conditioning pulses within a third sequence of pulses representing
at least a first pitch of a received sound signal to form the first
sequence of electrical stimulation pulses.
19. The prosthesis of claim 18, wherein: the inter-pulse intervals
based on the second sequence of conditioning pulses are second
inter-pulse intervals; and the inter-pulse intervals further
include: a first inter-pulse interval based on a pitch of the
received sound signal.
20. The prosthesis of claim 17, wherein: the stochastic stimulation
generator is further configured to constrain the stochasticity of
the first sequence of electrical stimulation pulses to be within
controlled limit by doing at least one of: limiting the number of
consecutive instances of the same inter-pulse interval; selectively
changing instances of one of the first and second inter-pulse
intervals for the other thereof in order to substantially balance
the distribution of the first and second inter-pulse intervals
within the stochastic first sequence; and selectively changing
instances of one of the first and second inter-pulse intervals for
the other thereof in order to substantially balance the
distribution of the first and second inter-pulse intervals within
the stochastic first sequence.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/403,949, entitled "Stochastic Stimulation
in a Hearing Prosthesis," filed Mar. 13, 2009, now U.S. Pat. No.
8,265,767 issued Sep. 11, 2012, which is a non-provisional of U.S.
Provisional Patent Application 61/036,318; filed Mar. 13, 2008,
each of which is hereby incorporated by reference herein.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention is generally directed to a hearing
prosthesis, and more particularly, to stochastic stimulation in a
hearing prosthesis.
[0004] 2. Related Art
[0005] Hearing loss, which may be due to many different causes, is
generally of two types, conductive and sensorineural. In some
cases, a person suffers from hearing loss of both types. Conductive
hearing loss occurs when the normal mechanical pathways for sound
to reach the cochlea, and thus the sensory hair cells therein, are
impeded, for example, by damage to the ossicles. Individuals who
suffer from conductive hearing loss typically have some form of
residual hearing because the hair cells in the cochlea are
undamaged. As a result, individuals suffering from conductive
hearing loss typically receive an acoustic hearing aid. Acoustic
hearing aids stimulate an individual's cochlea by providing an
amplified sound to the cochlea that causes mechanical motion of the
cochlear fluid.
[0006] In many people who are profoundly deaf, however, the reason
for their deafness is sensorineural hearing loss. Sensorineural
hearing loss occurs when there is damage to the inner ear, or to
the nerve pathways from the inner ear to the brain. As such, those
suffering from some forms of sensorineural hearing loss are thus
unable to derive suitable benefit from conventional acoustic
hearing aids. As a result, hearing prostheses that deliver
electrical stimulation to nerve cells of the recipient's auditory
system have been developed to provide the sensations of hearing to
persons whom do not derive adequate benefit from conventional
hearing aids. Such electrically-stimulating hearing prostheses
deliver electrical stimulation to nerve cells of the recipient's
auditory system thereby providing the recipient with a hearing
percept.
[0007] As used herein, the recipient's auditory system includes all
sensory system components used to perceive a sound signal, such as
hearing sensation receptors, neural pathways, including the
auditory nerve and spiral ganglion, and parts of the brain used to
sense sounds. Electrically-stimulating hearing prostheses include,
for example, auditory brain stimulators and Cochlear.TM. prostheses
(commonly referred to as Cochlear.TM. prosthetic devices,
Cochlear.TM. implants, Cochlear.TM. devices, and the like; simply
"cochlear implants" herein.)
[0008] Oftentimes, sensorineural hearing loss is due to the absence
or destruction of the cochlear hair cells which transduce acoustic
signals into nerve impulses. It is for this purpose that cochlear
implants have been developed. Cochlear implants provide a recipient
with a hearing percept by delivering electrical stimulation signals
directly to the auditory nerve cells, thereby bypassing absent or
defective hair cells that normally transduce acoustic vibrations
into neural activity. Such devices generally use an electrode array
implanted in the cochlea so that the electrodes may differentially
activate auditory neurons that normally encode differential pitches
of sound.
[0009] Both cochlear implants and hearing aids provide a recipient
with a hearing percept by stimulating the cochlea of an individual
or patient (collectively referred to as recipient herein) with
digital stimulation signals. These stimulation signals may be, for
example, electrical pulses delivered directly to the cochlea via
the electrode assembly of the cochlear implant, or acoustic
information delivered indirectly to the cochlea via the outer and
middle ear of the recipient from the output transducer of the
hearing aid.
SUMMARY
[0010] In one aspect of the present invention, a method for
inducing a hearing percept to a recipient of a cochlear implant is
provided. The method comprises: building a sequence of electrical
stimulation pulses having first and second inter-pulse intervals;
and making stochastic the sequence including randomly selecting
either the first or the second inter-pulse interval for insertion
between consecutive pulses in the sequence.
[0011] In another aspect of the present invention, a method for
providing a hearing percept to a recipient of a cochlear implant is
provided. The method comprises: generating a stochastic first
sequence of electrical stimulation pulses having inter-pulse
intervals distributed stochastically throughout the first sequence,
at least some of the inter-pulse intervals being based on a second
sequence of conditioning pulses.
[0012] In yet another aspect of the present invention, a hearing
prosthesis for providing a hearing percept to a recipient of a
cochlear implant is provided. The hearing prosthesis comprises: a
sound pickup component configured to receive a sound signal having
at least one pitch; and a stochastic stimulation generator
configured to generate a stochastic first sequence of electrical
stimulation pulses based on the sound signal, inter-pulse intervals
being distributed stochastically throughout the first sequence, at
least some of the inter-pulse intervals being based on a second
sequence of conditioning pulses.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Illustrative embodiments of the present invention are
described herein with reference to the accompanying drawings, in
which:
[0014] FIG. 1 is a perspective view of an exemplary hearing
prosthesis, a cochlear implant, in which embodiments of the present
invention may be advantageously implemented;
[0015] FIG. 2A is a functional block diagram of a cochlear implant
in accordance with embodiments of the present invention;
[0016] FIG. 2B is a detailed functional block diagram of the
cochlear implant of FIG. 2A;
[0017] FIG. 3A is a high level flowchart illustrating the
operations performed by a hearing prosthesis in accordance with
embodiments of the present invention;
[0018] FIG. 3B is a detailed flowchart illustrated the operations
performed by a hearing prosthesis in accordance with one embodiment
of FIG. 3B;
[0019] FIG. 3C is a detailed flowchart illustrated the operations
performed by a hearing prosthesis in accordance with another
embodiment of FIG. 3B;
[0020] FIG. 4A is a graph of stimulation current versus time that
illustrate the timing of pulses in stimulation signals generated in
a cochlear implant in accordance with embodiments of the present
invention;
[0021] FIG. 4B is a graph of stimulation current versus time that
illustrate the timing of pulses in stimulation signals generated in
a cochlear implant in accordance with embodiments of the present
invention;
[0022] FIG. 4C is a graph of stimulation current versus time that
illustrates the timing of pulses within a stochastic stimulation
signal generated based on the signals of FIGS. 4A and 4B, in
accordance with embodiments of the present invention;
[0023] FIG. 5 is a graph of stimulation current versus time that
illustrates the delivery of a stimulation signal to a cochlea of a
recipient via four electrodes of a cochlear implant in accordance
with embodiments of the present invention;
[0024] FIG. 6A is a graph of stimulation current versus time that
illustrate the delivery of a synchronized stochastic stimulation
signal to a cochlea of a recipient via four electrodes of a
cochlear implant in accordance with embodiments of FIG. 2B;
[0025] FIG. 6B is a graph of stimulation current versus time that
illustrate the delivery of a synchronized stochastic stimulation
signal to a cochlea of a recipient via four electrodes of a
cochlear implant in accordance with embodiments of FIG. 2B;
[0026] FIG. 7A is a schematic diagram illustrating sound signal
pairs delivered to a recipient in accordance with embodiments of
the present invention; and
[0027] FIG. 7B is a schematic diagram illustrating sound signal
pairs delivered to a recipient in accordance with embodiments of
the present invention; and
[0028] FIG. 8 is a flowchart illustrating a method for determining
a recipient's ability to perceive differences in pitch between
delivered sound signals in accordance with embodiments of the
present invention.
DETAILED DESCRIPTION
[0029] Aspects of the present invention are generally directed to
stochastic stimulation in a hearing prosthesis. Specifically, a
stochastic sequence of stimulation signals is generated and
delivered to the recipient. The sequence of signals comprises
electrical, mechanical or acoustical pulses generated and delivered
to the inner, middle, or outer ear of cochlea of the recipient. The
pulses within the sequence have controlled randomness in the pulse
timing. That is, the time intervals between immediately adjacent
pulses (referred to as inter-pulse intervals herein) are selected
stochastically within controlled limits.
[0030] Embodiments of the present invention may be implemented in
various types of hearing prostheses such as a Cochlear.TM.
prosthesis (commonly referred to as a Cochlear.TM. prosthetic
device, Cochlear.TM. implant, Cochlear.TM. device, and the like;
simply "cochlear implants" herein), middle ear transducers or
acoustic hearing aids. For ease of illustration, the present
invention will be described herein primarily in connection with
cochlear implants. FIG. 1 is a perspective view of an exemplary
cochlear implant 120 in which embodiments of the present invention
may be implemented. The relevant components of the recipient's ear
are described below, followed by a description of cochlear implant
120.
[0031] In fully functional human hearing anatomy, outer ear 101
comprises an auricle 105 and an ear canal 106. A sound wave or
acoustic pressure 107 is collected by auricle 105 and channeled
into and through ear canal 106. Disposed across the distal end of
ear canal 106 is a tympanic membrane 104 which vibrates in response
to acoustic wave 107. This vibration is coupled to oval window or
fenestra ovalis 110 through three bones of middle ear 102,
collectively referred to as the ossicles 111 and comprising the
malleus 112, the incus 113 and the stapes 114. Bones 112, 113 and
114 of middle ear 102 serve to filter and amplify acoustic wave
107, causing oval window 110 to articulate, or vibrate. Such
vibration sets up waves of fluid motion within cochlea 115. Such
fluid motion, in turn, activates tiny hair cells (not shown) that
line the inside of cochlea 115. Activation of the hair cells causes
appropriate nerve impulses to be transferred through the spiral
ganglion cells and auditory nerve 116 to the brain (not shown),
where they are perceived as sound. In certain profoundly deaf
persons, there is an absence or destruction of the hair cells.
Cochlear implants such a cochlear implant 120 are utilized to
stimulate the ganglion cells to cause a hearing percept.
[0032] Cochlear implant 120 comprises external component 122 which
is directly or indirectly attached to the body of the recipient,
and an internal component 124 which is temporarily or permanently
implanted in the recipient. External component 122 comprises a
sound pickup component, such as microphone 125, for detecting
sound. The sound detected by microphone 125 is output to a
behind-the-ear (BTE) speech processing unit 126 that generates
coded signals which are provided to an external transmitter unit
128, along with power from a power source 129 such as a battery.
External transmitter unit 128 comprises an external coil 130 and,
preferably, a magnet (not shown) secured directly or indirectly in
external coil 130.
[0033] Internal component 124 comprise an internal coil 132 of a
stimulator unit 134 that receives and transmits power and coded
signals received from external component 122 to other elements of
stimulator unit 134 which apply the coded signal to cochlea 115 via
an implanted electrode assembly 140. Elongate electrode assembly
140 has a proximal end connected to stimulator unit 134, and a
distal end implanted in cochlea 115. In some embodiments electrode
assembly 140 may be implanted at least in basal region 116, and
sometimes further. For example, electrode assembly 140 may extend
towards apical end of cochlea 115, referred to as cochlea apex 134.
In certain circumstances, electrode assembly 140 may be inserted
into cochlea 115 via a cochleostomy 152. In other circumstances, a
cochleostomy may be formed through round window 121, oval window
110, the promontory 123 or through an apical turn of cochlea
115.
[0034] Electrode assembly 140 comprises a longitudinally aligned
and distally extending array 144 of electrodes 150, sometimes
referred to as electrode array 144 herein, disposed along a length
thereof. Although electrode array 144 may be disposed on electrode
assembly 140, in most practical applications, electrode array 144
is integrated into electrode assembly 140. As such, electrode array
144 is referred to herein as being disposed in electrode assembly
140. Stimulator unit 134 generates stimulation signals which are
applied by electrodes 150 to cochlea 115, thereby stimulating
auditory nerve 116.
[0035] Although FIG. 1 illustrates a cochlear implant 120 having an
external component 122, it should be appreciated that embodiments
of the present invention may be implemented in other cochlear
implant embodiments, such as a totally implantable cochlear
implant.
[0036] As noted, aspects of the present invention are generally
directed to generating and delivering a discrete stochastic
sequence of stimulation signals to a recipient. In cochlear
implants, the sequence comprises electrical stimulation pulses
delivered to cochlea 115 via a single implanted electrode. The
intervals between immediately adjacent pulses (referred to as
inter-pulse intervals herein) are selected stochastically within
controlled limits. The distribution of inter-pulse intervals within
a stochastic sequence of the present invention is discussed in
greater detail below.
[0037] Delivering a stochastic sequence of electrical stimulation
signals to a recipient via a single electrode may provide various
benefits that are not possible in conventional systems. As is well
known in the art, a recipient's cochlea is "tonotopically mapped."
In other words, basal region 116 of cochlea 115 is responsive to
high frequency signals, while regions of the recipient's cochlea
115 closer to cochlear apex 134 are responsive to low frequency
signals. To enhance perception of sounds, conventional cochlear
implants exploit these tonotopical properties of cochlea 115 by
delivering stimulation signals within a predetermined frequency
range to a region of the cochlea that is most sensitive to that
particular frequency range. For example, the frequency of a sound,
sometimes referred to as pitch herein, is perceivable to the
recipient by delivering stimulation signals representing the pitch
via an electrode positioned at the location of cochlea 115 that is
most sensitive to the selected pitch.
[0038] In certain conventional cochlear implants, multiple pitches
may be perceived by a recipient by delivering stimulation signals
to the recipient via spatially separated electrodes. That is, a
first set of one or more stimulation signals is delivered to the
recipient via a first electrode, while a second set of stimulation
signals is delivered to the recipient via a second electrode that
is spatially separated from the first electrode. The signals may be
delivered simultaneous or sequentially to cause perception of the
two different pitches. As would be appreciated, a drawback of such
conventional systems is that different electrodes must be used for
each desired pitch.
[0039] Embodiments of the present invention avoid the above and
other drawbacks of conventional systems by exploiting the ability
of cochlea 115 to temporally segregate pitches. Specifically, as
noted above, a stochastic sequence of electrical stimulation pulses
is generated and delivered to the recipient via a single electrode.
The sequence comprises pulses separated by two or more inter-pulse
intervals that are distributed stochastically throughout the
sequence within controlled limits. This controlled randomness in
the pulse timing exploits the temporal pitch perception properties
of the cochlea so that multiple pitches may be perceived as a
result of the single stochastic pulse sequence. This ability may
enhance speech processing and/or sound coding strategies
implemented by a cochlear implant.
[0040] For example, in certain embodiments, the cochlear implant
may receive a sound signal generated by first and second sound
sources having first and second pitches, respectively. In these
embodiments, a stochastic sequence of electrical stimulation pulses
in accordance with embodiments of the present invention is
generated. The sequence comprises pulses separated by a first
inter-pulse interval based on the first pitch, and pulses separated
by a second inter-pulse interval based on the second pitch. As
noted, the first and second inter-pulse intervals are
stochastically distributed throughout the sequence within
controlled limits. Upon delivery of the stochastic stimulation
sequence, the recipient may differentiate sounds from the first and
second sources.
[0041] In alternative embodiments, the first and second pitches are
not necessarily obtained from two sources. For example, the first
and second pitches may comprise different pitch components of a
sound signal, regardless of the source of the signal.
[0042] In other embodiments of the present invention, the cochlear
implant is configured to deliver a conditioning stimulus to the
recipient. The conditioning stimulus comprises a sequence of pulses
delivered to the recipient at a high rate. A cochlear implant in
accordance with embodiments of the present invention may encode a
conditioning sequence within a pulse sequence representing a pitch
of a received sound signal. Specifically, in such embodiments, a
stochastic sequence of electrical stimulation pulses having a first
inter-pulse interval based on the pitch of a received sound signal,
and a second inter-pulse interval based on a conditioning sequence
is generated. As noted, the first and second inter-pulse intervals
are stochastically distributed throughout the sequence within
controlled limits. Thus, the generated sequence permits
conditioning and sound perception at a single electrode.
[0043] FIG. 2A is a functional block diagram illustrating
embodiments of cochlear implant 120 of FIG. 1, referred to as
cochlear implant 200 herein. Cochlear implant 200 comprises a sound
pickup component 202, a processing module 204, a stimulator unit
206 and an electrode assembly 250. Sound pickup component 202 is
configured to receive a sound signal 207. Sound pickup component
202 may comprise, for example, one or more microphones, a telecoil,
or an electrical input which connects cochlear implant 200 to FM
hearing systems, MP3 players, musical instruments, computers,
televisions, mobile phones, etc. As such, sound signal 207 may
comprise a sound wave or an electrical audio signal. In the
embodiment of FIG. 2A, sound pickup component 202 comprises a
microphone 202 which may be a directional microphone and/or an
omni-directional microphone. Sound pickup component 202 outputs
signals 209 representing received sound signal 207 to processing
module 204.
[0044] As shown, processing module 204 comprises a pre-processor
252, a sound processor 254, and a conditioner 256. Pre-processor
252 converts signals 209 output by sound pickup component 202 into
digital signals 211 representing the received sound. Digital
signals 211 are provided to sound processor 254. Pre-processor 252
is shown in FIG. 2A as an element of processing module 204. As
would be appreciated, in certain embodiments of the present
invention, pre-processor 252 may be implemented by sound pickup
module 202. In these embodiments, sound pickup module 202 would
output digital signals directly to sound processor 254.
[0045] Signals 211 are converted by processing module 254 into data
signals 213. As described in greater detail below, data signals 213
may be utilized by stimulator unit 206 to generate a stochastic
sequence of electrical stimulation pulses that are delivered to the
recipient's cochlea via electrode assembly 250.
[0046] As noted, processing module further includes conditioner
256. As described in greater detail below, in certain embodiments
conditioner 256 generates conditioning signals 217 which are
utilized by stimulator unit 206 to generate a stochastic sequence
of electrical stimulation pulses.
[0047] FIG. 2B is a detailed functional block diagram illustrating
the components of cochlear implant 200 in accordance with one
embodiment of the present invention. As noted above, cochlear
implant 200 comprises sound pickup component 202, processing module
204, stimulator 206 and electrode assembly 250.
[0048] As noted, signals 209 from sound pickup component 202 are
provided to pre-processor 252. As noted above, embodiments of the
present invention are configured to generate a stochastic sequence
of electrical stimulation pulses resulting in the perception of two
or more pitches by the recipient. In such embodiments,
pre-processor 252 comprises a segregation module 260 which
separates signals 209 into components 223A corresponding to a first
pitch within sound signal 207, and components 223B corresponding to
a second pitch within sound signal 207. As noted above, the first
and second pitches may correspond to different sources, different
pitch components of a sound signal regardless of the source,
etc.
[0049] Pre-processor 252 also comprises two each of
preamplifiers/automatic gain controllers 210 and Analog-to
Digital-Converters (ADCs) 212. Electrical signal components 223A,
223B are provided to preamplifiers/automatic gain controllers 210
which amplify and control the level of the electrical signals. The
electrical signals modified by preamplifiers/automatic gain
controllers 210 are provided to ADCs 212. ADCs 212 convert the
modified electrical signal into a stream of digital pulses 211A,
211B.
[0050] In the embodiment shown in FIG. 2B, segregation module 260,
preamplifiers/automatic gain controllers 210 and ADCs 212 have been
shown separated for ease of illustration. However, it should be
appreciated that these components may be implemented in a single
element. FIG. 2B has been described in reference to an illustrative
embodiment comprising two each of preamplifiers/automatic gain
controllers 210 and ADCs 212. It should be appreciated that more or
less of these components may be provided and the embodiments of
FIG. 2B are provided for illustrative purposes only. Furthermore,
as noted above, in certain embodiments of the present invention,
pre-processor 252 may be implemented as a component of sound pickup
component 202.
[0051] It should also be appreciated that in certain embodiments,
one or more components of pre-processor module 252 may not be
necessary. For example, in certain embodiments, sound signal 207
received by sound pickup component may comprise a digitized signal
received from, for example, a FM hearing system, MP3 player,
television, mobile phones, etc. In these embodiments, the received
signal may be processed by segregation module and provided to sound
processor 254, or under certain circumstances, the signals may be
provided directly to sound processor 254.
[0052] As shown in FIG. 2B, digital signals 211 are provided to
sound processor 254 which comprises a digital sound processor.
Sound processor 254 converts digital signals 211 into one or more
data signals 213. In the embodiments of FIG. 2B, data signals 213
may be utilized by stimulator unit 206 to generate a stochastic
sequence of electrical stimulation pulses. For example, in the
illustrative embodiments, a first data signal 213A is generated
based on components 223A of sound signal 207 corresponding to a
first pitch. Data signal 213A is usable by stimulator unit 206 to
generate a sequence of electrical stimulation pulses having a
substantially constant inter-pulse interval that is based on the
first pitch. Similarly, a second data signal 213B is generated
based on components 223B of sound signal 207 corresponding to a
second pitch. Data signal 213B is usable by stimulator unit 206 to
generate a sequence of electrical stimulation pulses having a
substantially constant inter-pulse interval that is based on the
second pitch.
[0053] As noted above, generated signals 213 are provided to
stimulator unit 206. Stimulator unit 206 comprises a stochastic
stimulation generator 216 and a synchronization module 218. In the
embodiment of FIG. 2B, signals 213 are provided to stochastic
stimulation generator 216. Stochastic stimulation generator 216
generates a stochastic sequence of electrical stimulating pulses
215 having controlled randomness in the pulse timing. Pulse timing
refers to distribution of inter-pulse intervals within the
sequence. For example, each pulse in stochastic stimulation
sequence 215 is separated in time from an immediately adjacent
pulse by an inter-pulse interval selected stochastically within
controlled limits. The controlled limits on the stochastic
inter-pulse interval distribution are discussed below.
[0054] In the illustrative embodiment of FIG. 2B, stochastic
stimulation generator 216 combines signals 213A and 213B to derive
stochastic stimulation sequence 215. It should be appreciated that
stochastic stimulation generator 216 may use a variety of methods,
algorithms, etc. to derive stochastic stimulation 215 from signals
213. In one alternative embodiment of the present invention, a
single set of signals 213 may be provided to stochastic stimulation
generator 216. In this embodiment, stochastic stimulation sequence
215 may be derived from this single stimulation signal 213.
[0055] In certain embodiments of the present invention, stochastic
stimulation sequence 215 is delivered to the recipient via a single
electrode 240 of electrode assembly 250. Upon delivery of
stochastic stimulation sequence 250, the recipient is able to
perceive two pitches. For ease of illustration, electrode assembly
250 is shown schematically in FIG. 2B.
[0056] In certain embodiments of FIG. 2B, prior to delivery of
stochastic stimulation sequence 215, synchronization module 218
synchronizes the delivery of sequence 215 across a plurality of
electrodes 240. In other words, synchronization module 218 is
configured to deliver the entirety of sequence 215 to each of a
plurality of electrodes. This may enhance the perception of the two
pitches. The delivery of the sequences to the plurality of
electrodes may occur simultaneously or sequentially.
[0057] In the illustrated embodiment, stochastic stimulation
generator 216 and synchronization module 218 have been shown
separated from sound processor 254 as being integrated in
stimulator unit 206. It should be appreciated that in certain
embodiments of the present invention, stochastic stimulation
generator 216 may be integrated with sound processor 254.
[0058] Electrode assembly 250 has been shown with four electrodes
240. However, it should be appreciated that more or less electrodes
may be provided. For example, in certain embodiments, 22 electrodes
may be provided to deliver stimulation to the recipient's
cochlea.
[0059] As noted, processing module 204 also comprises conditioner
256. Conditioner 256 is configured to provide an instruction signal
217 to stochastic stimulation generator 216 indicating that a
conditioning stimulus is desired or necessary. In these embodiments
of the present invention, stochastic stimulation sequence 215 may
be generated based on one or more signals 213 and signal 217. In
such embodiments, stochastic stimulation 215 comprises a set of
signals representing one or more pitches of a received sound, and a
set of pulses which provide the desired conditioning
stimulation.
[0060] As noted, the embodiments of the present invention have been
discussed with reference to a received sound signal 207. As noted
sound signal 207 may be received by sound pickup component which
comprises one or more microphones, an electrical input, music
instrument digital interface (MIDI), telecoil, etc. As such, the
sound signal may comprise a sound wave or an electrical audio
signal. In certain embodiments, the sound signal comprises music
provided to the recipient via, for example, an MIDI file. In such
embodiments, the pitches represented by the stochastic stimulation
sequence comprise musical notes. Thus, embodiments of the present
invention may permit a recipient to perceive multiple musical notes
as a result of a single stimulation sequence delivered via a single
electrode. This capability may provide a cochlear implant recipient
with enhanced harmony and melody perception.
[0061] FIG. 3A is a flowchart illustrating a method 300 in
accordance with embodiments of the present invention that may be
implemented by a hearing prostheses to provide a hearing percept to
a recipient of the hearing prosthesis. As shown, at block 302A a
sound signal having at least one pitch is received by the hearing
prosthesis. The sound signal may be received by a sound pickup
component described above with reference to FIGS. 2A and 2B.
[0062] A block 304, a stochastic sequence of stimulation pulses is
generated. The sequence comprises pulses first and second
inter-pulse intervals distributed stochastically throughout the
sequence within controlled or predetermined limits. That is, the
timing of the pulses within the sequence is primarily stochastic,
but fall within specified control parameters described in greater
detail below. The first inter-pulse interval is based on the at
least one pitch of the received sound.
[0063] At block 306, the generated sequence of stimulation pulses
is delivered to the recipient via a single stimulation channel. As
noted, embodiments of the present invention may be implemented in a
variety of hearing prosthesis now known or later developed such as
cochlear implants, acoustic hearing aids, etc. In the case of
cochlear implants, the single stimulation channel terminates in a
single electrode implanted in the recipient's cochlea. In the case
of other types of hearing prosthesis, a single stimulation channel
refers to a single output acoustic or mechanical transducer.
[0064] FIG. 3B is a detail level flowchart illustrating the
operations performed at block 304 in accordance with one embodiment
of FIG. 3A. As noted above, a sound signal is first received at
block 302. In this embodiment, the sound signal has two or more
pitches rather than at least one pitch, thus block 302 is referred
to as block 302B.
[0065] As noted above, at block 304 a stochastic sequence of
stimulation pulses is generated. In this illustrative embodiment,
at block 308 a first electrical signal based on a first pitch of
the received sound signal is generated. The first electrical signal
is usable by the hearing prosthesis to generate a first sequence of
stimulation pulses that have a substantially constant inter-pulse
interval associated with the first pitch of the sound signal. At
block 310, a second electrical signal based on a second pitch of
the received sound signal is generated. The second electrical
signal is usable by the hearing prosthesis to generate a second
sequence of stimulation pulses that have a substantially constant
inter-pulse interval associated with the second pitch of the sound
signal.
[0066] At block 312, the first and second electrical signals
generated at blocks 308, 310, respectively, are used to generate a
stochastic sequence of stimulation pulses having first and second
inter-pulse intervals. In this illustrative embodiment, the first
inter-pulse interval is substantially the same as the inter-pulse
interval of the first sequence of pulses corresponding to the first
electrical signal, while the second inter-pulse interval is
substantially the same as the inter-pulse interval of the second
sequence of pulses corresponding to the second electrical signal.
At block 306, the generated sequence of stimulation pulses is
delivered to the recipient via a single stimulation channel.
[0067] FIG. 3C is a detail level flowchart illustrating the
operations performed at block 304 in accordance with one embodiment
of FIG. 3A. In these embodiments, the hearing prosthesis is
configured to provide sequences of conditioning pulses to the
recipient. As noted above, a sound signal having at least one pitch
is first received at block 302A. As noted above, at block 304 a
discrete sequence of stimulation pulses is generated.
[0068] In this illustrative embodiment, at block 314 a first
electrical signal based on the at least one pitch of the received
sound signal is generated. The first electrical signal is usable by
the hearing prosthesis to generate a first sequence of stimulation
pulses that have a substantially constant inter-pulse interval that
is associated with the at least one pitch of the sound signal. At
block 316, a second electrical signal usable to generate a desired
sequence of conditioning pulses is generated.
[0069] At block 318, the first and second electrical signals
generated at blocks 314, 316, respectively, are used to generate a
sequence of stimulation pulses having first and second inter-pulse
intervals. In this illustrative embodiment, the first inter-pulse
interval is substantially the same as the inter-pulse interval of
the first sequence of pulses corresponding to the first electrical
signal. Furthermore, the second inter-pulse interval is
substantially the same as the inter-pulse interval of the sequence
of conditioning pulses corresponding to the second electrical
signal. At block 306, the generated sequence of stimulation pulses
is delivered to the recipient via a single stimulation channel.
[0070] As would be appreciated, the above and other operations of
the present invention may be implemented an application-specific
integrated circuit (ASIC), or other hardware or combination of
hardware and software, or software as deemed appropriate for the
particular application. For example, operations in accordance with
certain embodiments of the present invention may be implemented as
software executing on a cochlear implant or other hearing
prosthesis. In such embodiments, the program code and any other
necessary information may be stored in any manner suitable for the
particular application, including programmed in an ASIC or other
computer hardware or as software code stored in computer or machine
readable medium such as any non-volatile storage device well known
to those skilled in the art. In such embodiments, the program code
is executed by the hearing prosthesis to perform the desired
operations.
[0071] As noted above, sound signal 207 is received by cochlear
implant 200 and converted to one or more data signals 213. As
noted, data signals 213 may be utilized by stimulator unit to
generate sequences of electrical pulses. For example, a first data
signal 213A is generated based on components 223A of sound signal
207 corresponding to a first pitch. Data signal 213A is usable by
stimulator unit 206 to generate a sequence of electrical
stimulation pulses having a substantially constant inter-pulse
interval that is based on the first pitch. Similarly, a second data
signal 213B is generated based on components 223B of sound signal
207 corresponding to a second pitch. Data signal 213B is usable by
stimulator unit 206 to generate a sequence of electrical
stimulation pulses having a substantially constant inter-pulse
interval that is based on the second pitch. FIG. 4A is a graph of
stimulation current versus time illustrating the timing of pulses
in an exemplary pulse sequence that is generated using signal 213A.
Furthermore, FIG. 4B is a graph of stimulation current versus time
illustrating the timing of pulses in an exemplary pulse sequence
that is generated using signal 213B.
[0072] In FIG. 4A, stimulation signal 420 corresponding to signal
213A comprises a sequence of digital pulses each spaced in time
from adjacent pulses by an inter-pulse interval 422 of
approximately 2 ms. The substantially constant inter-pulse interval
is based on a first pitch of sound signal 207. The pulses each
comprise a bi-phasic pulse of stimulation current. However, in
other embodiments, additional pulse types may be used.
[0073] In FIG. 4B, stimulation signal 440 corresponding to signal
213B comprises a sequence of digital pulses each spaced in time
from adjacent pulses by an inter-pulse interval 432 of
approximately 3 ms. The substantially constant inter-pulse interval
is based on a second pitch of sound signal 207. The pulses each
comprise a bi-phasic pulse of stimulation current. However, in
other embodiments, additional pulse types may be used.
[0074] FIG. 4C is a graph of stimulation current versus time that
illustrates the timing of pulses within a stochastic stimulation
sequence 460 generated by stochastic stimulation generator 216 of
FIG. 2B. In this embodiment, stochastic stimulation sequence 460 is
generated by combining stimulation signals 420 and 440. Stimulation
signals 420 and 440 are combined in a manner such that inter-pulse
intervals 422, 432 are distributed stochastically throughout
stimulation sequence 460. For example, in the embodiment of FIG.
4C, the inter-pulse intervals between pulses of stochastic
stimulation sequence 460 vary between 2 ms and 3 ms. In the
exemplary embodiment of FIG. 4C, a first pulse occurs at time 2 ms,
followed by pulses at 5 ms (inter-pulse interval of 3 ms), 7 ms
(inter-pulse interval of 2 ms), 10 ms (inter-pulse interval of 3
ms), 12 ms (inter-pulse interval of 2 ms), 14 ms (inter-pulse
interval of 2 ms), 16 ms (inter-pulse interval of 2 ms), etc. This
random variation of inter-pulse intervals between pulses continues
throughout the entirety of stochastic stimulation sequence 460.
[0075] As noted above, the pulse timing within stochastic
stimulation sequence 460 varies at random between inter-pulse
intervals 422 and 432 within controlled limits. For example, in
certain embodiments, the number of consecutive pulses having the
same inter-pulse interval there between may be limited. In other
embodiments, the distribution of inter-pulse intervals within
stochastic stimulation sequence 460 may need to be substantially
balanced throughout the signal, or alternatively, the number of
inter-pulse intervals 422 or 432 may weighted to adjust the
resulting hearing perception. In certain embodiments, such as the
embodiment described above, first and second inter-pulse intervals
are present in a stochastic stimulation signal. In these
embodiments, the inter-pulse intervals between pulses may not
continually alternate between the first and second inter-pulse
intervals.
[0076] As noted above, delivery of a stochastic stimulation signal
460 to a recipient causes a recipient to perceive multiple pitches
within a single stimulation sequence. For example, in FIG. 4C,
stochastic stimulation sequence 460 corresponds to signals 213A,
213B used to generate stimulation signals 420 and 440. Due to the
fact that multiple pitches may be perceived by the recipient, one
sound source from which signal 420 was generated may be associated
with a first perceived pitch and a second source from which signal
440 was generated may be associated with a second perceived pitch.
In these embodiments, upon delivery of stochastic stimulation
sequence 460, the perception of the multiple pitches each
associated with a particular source by the recipient may result in
the recipient's ability to differentiate between the two
sources.
[0077] In alternative embodiments of the present invention, a
conditioning stimulus and a sound signal corresponding to a
received sound may be encoded within a single stochastic
stimulation sequence so as to cause sound perception and rate
conditioning within a single sequence.
[0078] A cochlear implant may deliver electrical stimulation
signals to a recipient via a plurality of electrodes. FIG. 5 is a
graph of stimulation current versus time that illustrates the
delivery of a stimulation signal 500 to a recipient's cochlea via
four electrodes of a cochlear implant, illustrated as electrodes
E1, E2, E3 and E4.
[0079] As shown in FIG. 5, a sequence of pulses 562 is delivered to
a portion of the cochlea via electrode E1. Pulses within sequence
562 are spaced in time from adjacent pulses by a substantially
constant inter-pulse interval of 4 ms. A first pulse 552 in
sequence 562 occurs at time 2 ms.
[0080] Stimulation signal 500 further comprises a sequence 564 of
pulses delivered to a portion of the cochlea via electrode E2.
Similar to sequence 562, pulses within sequence 564 are spaced in
time from adjacent pulses by a substantially constant inter-pulse
interval of 4 ms. As shown, the delivery of a first pulse 554 in
sequence 564 is delayed by a time interval 572 from the delivery of
first pulse 552 of sequence 562. In the embodiment of FIG. 5, this
delay comprises approximately 1 ms.
[0081] Stimulation signal 500 also comprises sequences 566 and 568
of pulses delivered to portions of the cochlea via electrodes E3,
34 respectively. Similar to sequences 562 and 564, pulses within
sequences 566 and 568 are spaced in time by a substantially
constant inter-pulse interval of 4 ms. The delivery of a first
pulse 556 of sequence 566 is delayed by 1 ms from the delivery of
pulse 554. Likewise, the delivery of a first pulse 558 of sequence
568 is delayed by 1 ms from the delivery of pulse 556. Following
delivery of pulse 556, a second pulse 550 is delivered at electrode
E1. The delivery of pulse 550 is also delayed by 1 ms from the
delivery of pulse 558.
[0082] The above procedure of sequentially delivering delayed
pulses at electrodes E1-E4 continues until all pulses within
stimulation signal 500 have been delivered. Following delivery of
stimulation signal 500, a next stimulation signal may be delivered
to the cochlea.
[0083] As would appreciated by one of ordinary skill in the art,
the perceived pitch of a sound refers to the cochlea's response to
the frequency of a sound. The perception of pitch by an individual
generally depends on place pitch perception. Place pitch perception
refers to the cochlea's spatial sensitivity to frequency.
Specifically, in a fully functional ear, high frequency sounds
selectively vibrate the basilar membrane near the oval window, and
lower frequency sounds travel further along the membrane before
excitation of the membrane. Thus, the basic pitch determining
mechanism of the cochlea is based on the location along the
membrane where the hairs cells are stimulated.
[0084] Conventional cochlear implants have been designed to take
advantage of this place pitch phenomenon of the cochlea. In these
cochlear implants, the location at which stimulation is delivered
to the cochlea is used to control the pitch perceived by a
recipient. Stimulation signal 500 of FIG. 5 is an example of this
type of stimulation. The pitch perceived by the recipient as a
result of stimulation 500 depends on which electrodes E1-E4 are
used. For example, a first pitch may be perceived when stimulation
is delivered via all four electrodes, while an alternative pitch
may be perceived when stimulation is delivered, for example, via
electrodes E1 and E3 only. In contrast, as noted above, embodiments
of the present invent exploit the ability of the cochlea to
temporally segregate pitches. Specifically, as noted above, a
stochastic sequence of electrical stimulation pulses is generated
and delivered to the recipient via a single electrode. The sequence
comprises pulses separated by two or more inter-pulse intervals
that are distributed stochastically throughout the sequence within
controlled limits. This controlled randomness in the pulse timing
exploits the temporal pitch perception properties of the cochlea so
that multiple pitches may be perceived as a result of the single
stochastic pulse sequence. This ability may enhance speech
processing and/or sound coding strategies implemented by a cochlear
implant.
[0085] In certain embodiments of the present invention, a
stochastic sequence of electrical stimulation pulses may be
synchronized for delivery via a plurality of electrodes. FIGS. 6A
and 6B are graphs of stimulation current versus time that
illustrate the delivery of synchronized stochastic stimulation
sequences to a recipient's cochlea via four electrodes E1-E4.
[0086] In the embodiments illustrated in FIG. 6A stochastic
stimulation sequences 662 are applied to each of electrodes E1-E4.
Similarly, in the embodiments illustrated in FIG. 6B stochastic
stimulation sequences 664 are applied to each of electrodes E1-E4.
Stochastic sequences 662 and 664 are substantially the same as
sequence 460 of FIG. 4C. Thus, the inter-pulse intervals and
interval distribution within each sequence 662, 664 correspond
directly to the inter-pulse intervals and pulse distribution of
stochastic stimulation sequence 460. For example, as described
above with reference to FIG. 4C, stochastic stimulation sequence
460 comprises a sequence of pulses each spaced in time from
adjacent pulses by a controllably random inter-pulse interval. As
noted, the inter-pulse intervals of stochastic stimulation sequence
460 are stochastically varied, within controlled limits, between 2
ms and 3 ms. In the embodiments of FIGS. 6A and 6B, the inter-pulse
intervals between pulses within a given sequence are also varied
between 2 ms and 3 ms in the same manner as in stochastic
stimulation sequence 460.
[0087] In the embodiment of FIG. 6A, the pulse sequences are
delivered to the cochlea via electrodes E1-E4 simultaneously. As
shown in FIG. 6A, a first pulse is applied to electrodes E1-E4 at 2
ms. After a time interval 670, a second pulse is delivered
simultaneously to electrodes E1-E4. Simultaneous pulse delivery
continues until all pulses in the sequences have been
delivered.
[0088] FIG. 6B illustrates alternative embodiments in which
sequential pulse delivery is utilized for pulse sequences 664. As
shown in FIG. 6B, a sequences of pulses 664 is delivered via
electrodes E1-E4 sequentially. Pulses within sequences 664 are
spaced in time by inter-pulse intervals directly corresponding to
the inter-pulse intervals of stochastic stimulation sequence 460.
The first pulse in sequence 664A occurs at time 2 ms.
[0089] The above embodiments illustrated in FIGS. 6A and 6B provide
examples of synchronized stochastic stimulation. It should be
appreciated that other embodiments are within the scope of the
present invention. For example, in certain embodiments, cochlear
implant 200 may include more or less than four electrodes. For
example, in specific embodiments, cochlear implant 200 may include
22 electrodes. In these embodiments, the stochastic stimulation
sequence may be applied via any number of electrodes.
[0090] FIGS. 7A and 7B are schematic diagrams illustrating sound
signal pairs delivered to a recipient in accordance with
embodiments of a method described below with reference to FIGS. 8A
and 8B. FIG. 7A illustrates a first version 782 of a sound signal
pair, while FIG. 7B illustrates a second version 784 of a sound
signal pair. For ease of illustration, the following discusses
sound pairs based on a first signal A, a second signal B and a
third signal N. Presentation of first signal A to the recipient
results in the perception of pitch A, while presentation of second
signal B to the recipient results in the perception of pitch B by
the recipient. Signal N comprises a noise signal causing a
perception of a pitch N by the recipient.
[0091] As described herein, sound pairs 786, 788, 790 and 792 may
comprise acoustic or electrical representations of signals A, B and
N. For example, in certain embodiments, sound signal 772 may
comprise a sequence of electrical pulses which causes the recipient
to perceive pitch A, while sound signal 774 may comprise a sequence
of electrical pulses which causes the recipient to perceive pitch A
mixed with pitch N.
[0092] In the embodiment of FIG. 7A, sound pair version 782
includes a corresponding sound pair 786 and a non-corresponding
sound pair 788. Corresponding pair 786 comprises a first sound
signal 772 which results in the perception of a pitch A and a
second sound signal 774. Second sound signal 774 comprises a sound
signal resulting in the perception of pitch A and pitch N.
Non-corresponding pair 788 comprises a first sound signal 776
resulting in the perception of pitch B and a second sound signal
778. Second sound signal 778 comprises a sound signal resulting in
the perception of pitch A and pitch N. Details of how these sound
pair versions are used in the present invention are provided below
with reference to FIGS. 8A and 8B.
[0093] In the embodiment of FIG. 7B, sound pair version 784
includes a corresponding sound pair 790 and a non-corresponding
sound pair 792. In this embodiment, corresponding pair 790
comprises a first sound signal 762 resulting in the perception of a
pitch B and a second sound signal 764. Second sound signal 764
comprises a sound signal resulting in the perception of pitch B and
pitch N. Non-corresponding pair 792 comprises a first sound signal
766 resulting in the perception of a pitch A and a second sound
signal 768. Second sound signal 768 comprises a sound signal
resulting in the perception of pitch B and pitch N. Details of how
these sound pair versions are used in the present invention are
provided below with reference to FIG. 8.
[0094] FIG. 8 illustrates one exemplary method for determining a
recipient's ability to perceive differences in pitch between
delivered signals in accordance with embodiments of the present
invention. The method of FIG. 8 is described herein with respect to
a cochlear implant. However, it should be appreciated that the
method of FIG. 8 may also be used with other hearing prosthesis,
such as a hearing aid.
[0095] As shown in FIG. 8, at block 870 either first or second pair
version 782, 784 discussed above is randomly selected for
presentation to a recipient. At block 872, a first sound signal
pair of the selected sound pair version is presented to the
recipient. For ease of illustration, the method of FIG. 8 will be
discussed with reference to presentation of version 782 of FIG. 7A.
However, it should be appreciated that other versions may also be
presented.
[0096] At block 870, corresponding pair 786 is presented to the
recipient. This step comprises presenting sound signal 772 to the
recipient, then separately presenting sound signal 774 to the
recipient. Following presentation of corresponding pair 786, at
block 872, non-corresponding pair 788 is presented to the
recipient. This step comprises presenting sound signal 776 to the
recipient, then separately presenting sound signal 778 to the
recipient.
[0097] Following presentation of both sound signal pairs 786, 788,
at block 876 the recipient must determine, based on the perceived
pitches, if the presented sounds within corresponding sound pair
786, or the presented sounds within non-corresponding sound pair
788 sounded more similar to one another. As noted above, pitch is
the cochlea's response to a frequency of a sound. As such, a
correct identification by the recipient that the sound signals of
corresponding sound pair 786 sounded more similar indicates that
the recipient is able to perceive the frequency difference between
signal A and signal B. An incorrect identification indicates that
the recipient is unable to perceive the frequency difference
between signals A and B.
[0098] If the recipient incorrectly identifies the sound signals of
non-corresponding pair 788 as sounding more similar to one another,
the method continues to block 880 where the sound signal pairs are
adjusted. At block 870, the frequency difference between sound
signals A and B is increased and new sound pair versions are
generated. Following this increase, the method then returns to
block 870 to randomly select a sound signal version and to present
the adjusted sound signal pairs to the recipient. An increase in
the frequency difference between signals A and B increases the
likelihood that the recipient will correctly identify the
corresponding pair.
[0099] Returning to block 876, if the recipient correctly
identifies the corresponding pair, a check is done at block 878 to
determine if the recipient has correctly identified the
corresponding pair twice at a given frequency difference between
signals A and B. If the recipient has not completed two consecutive
identifications in a row, the method returns to block 870 to
randomly select the sound pair version, and to reapply the sounds
of the selected version at blocks 872 and 870.
[0100] If the recipient has completed two consecutive
identifications of corresponding pair 786 at a given frequency
difference between signals A and B, then the method continues to
block 882. At block 882, the frequency difference between signals A
and B are decreased, thereby making it more difficult for a
recipient to perceive differences in the frequency. The utilized
sound pairs may be adjusted to correspond to this new frequency
difference and the above procedure may then be re-performed to
determine if the recipient can perceive the frequency difference
between adjusted signals A and B.
[0101] The above described method may be described as an adaptive
staircase approach for determining a recipient's ability to
perceive frequency differences in two sounds. This method may be
referred to as an adaptive staircase approach because a two up, one
down adjustment is implemented. In other words, as described above,
if a recipient incorrectly identifies the non-corresponding pair a
single time, the frequency difference between sound signals A and B
are increased to make it easier for the recipient to perceive the
frequency difference. However, a recipient must correctly identify
the corresponding sound pair twice prior to decreasing the
frequency difference between signals A and B. This adaptive
staircase increases the accuracy of the above method as compared to
an approach that increases or decreases the frequency difference
between signals A and B based on a single response.
[0102] As noted above, the method described above with reference to
FIG. 8 may be utilized in embodiments of the present invention to
determine an individual recipients' ability to perceive frequencies
differences in two sounds signals. This information may be used,
for example, to fit a cochlear implant implementing embodiments of
the present invention.
[0103] The method of FIG. 8 has been provided for illustration
purposes only. It should be appreciated that other methods may be
used to determine a user's ability to perceive frequency
differences in two sound signals and/or to fit a cochlear implant
implementing embodiments of the present invention to a
recipient.
[0104] Although the present invention is described herein with
respect to the generation of a stochastic stimulation signal by
combining two or more stimulation signals, it should be appreciated
that the above description has been provided for illustration
purposes. Other methods for generating a stochastic stimulation
signal are within the scope of the present invention. For example,
in certain embodiments, a stochastic stimulation signal may be
generated directly from digital signals rather than from
stimulation signals generated by a signal processor.
[0105] Furthermore, while various embodiments of the present
invention have been described above, it should be understood that
they have been presented by way of example only, and not
limitation. It will be apparent to persons skilled in the relevant
art that various changes in form and detail can be made therein
without departing from the spirit and scope of the invention. Thus,
the breadth and scope of the present invention should not be
limited by any of the above-described exemplary embodiments, but
should be defined only in accordance with the following claims and
their equivalents. All patents and publications discussed herein
are incorporated in their entirety by reference thereto.
* * * * *