U.S. patent number RE34,961 [Application Number 07/888,148] was granted by the patent office on 1995-06-06 for method and apparatus for determining acoustic parameters of an auditory prosthesis using software model.
This patent grant is currently assigned to The Minnesota Mining and Manufacturing Company. Invention is credited to Mats B. Dotevall, Gregory P. Widin.
United States Patent |
RE34,961 |
Widin , et al. |
June 6, 1995 |
Method and apparatus for determining acoustic parameters of an
auditory prosthesis using software model
Abstract
A software model of the auditory characteristics of an auditory
prosthesis is stored independently of the actual auditory
prosthesis being fitted to determine the acoustic parameters to be
utilized. A transfer function of the auditory characterictics of
the individual auditory prosthesis to be fitted, or of an exemplary
model of such an auditory prosthesis, is created, transformed into
a table, or other usable form, and stored in software usable by the
automated fitting program. The automated fitting program may then
"test" or try by iterative process, the various settings for the
acoustic parameters of the auditory prosthesis and determine
accurately the results without actual resort the physical auditory
prosthesis itself.
Inventors: |
Widin; Gregory P. (Lakeland
Township, Washington County, MN), Dotevall; Mats B.
(Gothenburg, SE) |
Assignee: |
The Minnesota Mining and
Manufacturing Company (St. Paul, MN)
|
Family
ID: |
22708721 |
Appl.
No.: |
07/888,148 |
Filed: |
May 26, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
192214 |
May 10, 1988 |
04953112 |
Aug 28, 1990 |
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Current U.S.
Class: |
703/6; 73/585;
381/320; 381/60; 600/559 |
Current CPC
Class: |
H04R
25/70 (20130101); H04R 2225/61 (20130101) |
Current International
Class: |
H04R
25/00 (20060101); H04R 025/02 () |
Field of
Search: |
;364/578,149,150,151
;381/68.2,68.4,158 ;73/585 ;128/746 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Adby et al; "Introduction to optimization method"; Chapman and Hall
(1974). .
Green, D. S. "Pure Tone Air Conduction Testing." In: Katz, J.,
Handbook of Clinical Audiology. (Baltimore, Williams & Wilkins,
1978) pp. 98-109. .
Skinner; "Hearing Aid Evaluation"; Prentice Hall (1988). .
Briskey; "Instrument fitting Techniques" NIHI (1985). .
Sandlin; "Hearing Instrument Science and Fitting Practices" NIHI
(1985). .
Engebretson et al; "A Digital Hearing Aid and Computer-Based
Fitting Procedure"; Hearing Instruments, vol. 37, No. 2, 1986.
.
Cole; "Present and Future developments in hearing aid design"; May
1979. .
Engebretson et al., "A Computer Program for Fitting a Master
Hearing Aid to the Residual Hearing Characteristics of Individual
Patients", Journal of the Acoustical Society of America, 72, No. 2,
pp. 426-430 (1982). .
Engebretson et al., "Development of an Ear-Level Digital Hearing
Aid and Computer-Assisted Fitting Procedure: An Interim Report",
Journal of Rehabilitation Research and Development, vol. 24, No. 4,
pp. 55-64 (1987). .
Bade et al., "Use of a Personal Computer to Model the
Electroacoustics of Hearing Aids", Journal of the Acounstical
Society of America, vol. 75, No. 2, pp. 617-620 (1983). .
Katz, Jack, Editor, Handbook of Clinical Audiology, Williams &
Wilkins, Baltimore, Md. (1978)..
|
Primary Examiner: Ramirez; Ellis B.
Attorney, Agent or Firm: Griswold; Gary L. Kirn; Walter N.
Bauer; William D.
Claims
What is claimed is:
1. For use with a auditory prothesis having acoustic parameters
which at least in part determine at least one of the auditory
characteristics of said auditory prosthesis, said acoustic
parameters being adjustable, a method of determining said acoustic
parameters of said auditory prosthesis which will provide a user of
said auditory prosthesis with a target auditory response,
comprising the steps of:
determining said target auditory response of said user;
determining said auditory characteristics of said auditory
prosthesis operating in conjunction with said user .Iadd.and based
upon a software model.Iaddend.; and
optimizing said acoustic parameters of said auditory prosthesis by
comparing the auditory response of said auditory characteristics
with said target auditory response and by adjusting said acoustic
parameters to minimize the error of said comparison.
2. A method as in claim 1 wherein said determining said .[.acoustic
function.]. .Iadd.auditory characteristics .Iaddend.step further
comprises determining said .[.acoustic fitting function.].
.Iadd.auditory characteristics .Iaddend.based upon a software
lookup table.
3. A method as in claim 1 wherein said determining said .[.acoustic
function.]. .Iadd.auditory characteristics .Iaddend.steps further
comprises determining said .Iadd.auditory characteristics
.Iaddend.based upon a set of mathematical equations to serve as
said .[.acoustic fitting functions.]. .Iadd.auditory
characteristics.Iaddend..
4. A method as in claim 3 wherein said optimizing step further
comprises solving said set of mathematical equations for said
acoustic parameters based upon said target auditory response.
5. For use with an auditory prosthesis having acoustic parameters
which at least in part determine the .[.acoustic fitting
function.]. .Iadd.auditory characteristics .Iaddend.of said
auditory prosthesis, said acoustic parameters being adjustable, a
method of determining said acoustic parameters of said auditory
prosthesis which will provide a user of said auditory prosthesis
with a target auditory response, comprising the steps of:
determining said target auditory response of said user;
determining said .[.acoustic fitting function.]. .Iadd.auditory
characteristics .Iaddend.of said auditory prosthesis operating in
conjunction with said user;
storing a software model of said .[.acoustic fitting function.].
.Iadd.auditory characteristics.Iaddend.;
optimizing said acoustic parameters of auditory prosthesis by
comparing the auditory response of said software model with said
target auditory response and by adjusting said acoustic parameters
to minimize the error of said comparison.
6. A method as in claim 5 wherein said software model of said
auditory characteristics comprises a software look-up
.Iadd.table.Iaddend..
7. A method as in claim 5 wherein said software model of said
.[.acoustic fitting function.]. .Iadd.auditory characteristics
.Iaddend.comprises a set of mathematical equations to serve as said
.[.acoustic fitting function.]. .Iadd.auditory
characteristics.Iaddend..
8. A method as in claim 7 wherein said optimizing step further
comprises solving said set of mathematical equations for said
acoustic parameters based upon said target auditory response.
.Iadd.
9. For use with an auditory prosthesis having acoustic parameters
which at least in part determine at least one of the auditory
characteristics of said auditory prosthesis, said acoustic
parameters being adjustable, a method of determining said acoustic
parameters of said auditory prosthesis which will provide a user of
said auditory prosthesis with a target auditory response,
comprising the steps of:
determining said target auditory response of said user;
determining said auditory characteristics of said auditory
prosthesis based upon a software model; and
optimizing said acoustic parameters of said auditory prosthesis by
comparing the auditory response of said auditory characteristics
with said target auditory response and by adjusting said acoustic
parameters to minimize the error of said comparison. .Iaddend.
.Iadd.
10. A method as in claim 9 wherein said determining said auditory
characteristics step further comprises determining said auditory
characteristics based upon a software look-up table. .Iaddend.
.Iadd.11. A method as in claim 9 wherein said determining said
auditory characteristics step further comprises determining said
auditory characteristics based upon a set of mathematical equations
to serve as
said auditory characteristics. .Iaddend. .Iadd.12. A method as in
claim 11 wherein said optimizing step further comprises solving
said set of mathematical equations for said acoustic parameters
based upon said target
auditory response. .Iaddend. .Iadd.13. For use with an auditory
prosthesis having acoustic parameters which at least in part
determine the auditory characteristics of said auditory prosthesis,
said acoustic parameters being adjustable, a method of determining
said acoustic parameters of said auditory prosthesis which will
provide a user of said auditory prosthesis with a target auditory
response, comprising the steps of:
determining said target auditory response of said user;
determining said auditory characteristics of said auditory
prosthesis;
storing a software model of said auditory characteristics;
optimizing said acoustic parameters of auditory prosthesis by
comparing the auditory response of said software model with said
target auditory response and by adjusting said acoustic parameters
to minimize the error of said comparison. .Iaddend. .Iadd.14. A
method as in claim 13 wherein said software model of said auditory
characteristics comprises a software look-up table. .Iaddend.
.Iadd.15. A method as in claim 13 wherein said software model of
said auditory characteristics comprises a set of mathematical
equations to serve as said auditory characteristics.
.Iaddend. .Iadd.16. A method as in claim 15 wherein said optimizing
step further comprises solving said set of mathematical equations
for said acoustic parameters based upon said target auditory
response. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to auditory prostheses and
more particularly to auditory prostheses having adjustable acoustic
parameters.
Auditory prostheses have been utilized to modify the auditory
characteristics of sound received by a user or wearer of that
auditory prosthesis. Usually the intent of the prosthesis is, at
least partially, to compensate for a hearing impairment of the user
or wearer. Hearing aids which provide an acoustic signal in the
audible range to a wearer have been well known and are an example
of an auditory prosthesis. More recently, cochlear implants which
stimulate the auditory nerve with an electrical stimulus signal
have been used to compensate for the hearing impairment of a
wearer. Other examples of auditory prostheses are implanted hearing
aids which stimulate the auditory response of the wearer by a
mechanical stimulation of the middle ear and prostheses which
otherwise electromechanically stimulate the user.
Hearing impairments are quite variable from one individual to
another individual. An auditory prosthesis which properly
compensates for the hearing impairment of one individual may not be
beneficial or may be disruptive to another individual. Thus,
auditory prostheses must be adjustable to serve the needs of an
individual user or patient.
The process by which an individual auditory prosthesis is adjusted
to be of optimum benefit to the user or patient is typically called
"fitting". Stated another way, the auditory prosthesis must be
"fit" to the individual user of that auditory prosthesis in order
to provide a maximum benefit to that user, or patient. The
"fitting" of the auditory prosthesis provides the auditory
prosthesis with the appropriate auditory characteristics to be of
benefit to the user.
This fitting process involves measuring the auditory
characteristics of the individual's hearing, calculating the nature
of the acoustic characteristics, e.g., acoustic amplification in
specified frequency bands, needed to compensate for the particular
auditory deficiency measured, adjusting the auditory
characteristics of the auditory prosthesis to enable the prosthesis
to deliver the appropriate acoustic characteristic, e.g., acoustic
amplification is specified frequency bands, and verifying that this
particular auditory characteristic does compensate for the hearing
deficiency found by operating the auditory prosthesis in
conjunction with the individual. In practice with conventional
hearing aids, the adjustment of the auditory characteristics is
accomplished by selection of components during the manufacturing
process, so called "custom" hearing aids, or by adjusting
potentiometers available to the fitter, typically an audiologist,
hearing aid dispenser, otologist, otolaryngologist or other doctor
or medical specialist.
Some hearing aids are programmable in addition to being adjustable.
Programmable hearing aids have some memory device which store the
acoustic parameters which the hearing aid can utilize to provide a
particular auditory characteristic. The memory device may be
changed or modified to provide a new or modified auditory parameter
or set of auditory parameters which in turn will provide the
hearing aid with a modified auditory characteristic. Typically, the
memory device will be an electronic memory, such as a register or
randomly addressable memory, but may also be other types of memory
devices such as programmed cards, switch settings or other
alterable mechanism having retention capability. An example of a
programmable hearing aid which utilizes electronic memory is
described in U.S. Pat. No. 4,425,481, Mangold et al. With a
programmable hearing aid which utilizes electronic memory, a new
auditory characteristic, or a new set of acoustic parameters, may
be provided to the hearing aid by a host computer or other
programming device which includes a mechanism for communicating
with the hearing aid being programmed.
In order to achieve an acceptable fitting for an individual,
changes or modifications in the acoustic parameters may need to be
made, either initially to achieve an initial setting or value for
the acoustic parameters or to revise such settings or valuations
after the hearing aid has been used by the user. Known mechanisms
for providing settings or valuations for the acoustic parameters
usually involve measuring the hearing impairment of an individual
and determining the setting or value necessary for an individual
acoustic parameter in order to compensate for the hearing
impairment so measured.
A persistent problem in such fitting procedures is that the
measuring and the adjustments in the acoustic parameters during
fitting must be made using the auditory prosthesis itself which
provides some practical difficulties. If the fitting procedure is
automated, as is sometimes the case, the automatic features of the
fitting process must be stopped and a physical, usually mechanical,
adjustment of the acoustic parameters must be made while the
auditory prosthesis is operated or utilized in conjunction with the
user. Such manual, physical processes not only consume a lot of
time but also involve the user, patient, of the auditory prosthesis
and, thus, makes the fitting process long and arduous for the
patient.
SUMMARY OF THE INVENTION
The present invention provides a method and an apparatus for
determining the acoustic parameters for an auditory prosthesis
without the manual, arduous, time consuming steps required in the
past.
The present invention utilizes a software model of the auditory
prosthesis which may be stored independently of the actual auditory
prosthesis being fitted to determine the acoustic parameters to be
utilized. A transfer function of the auditory characteristics of
the individual auditory prosthesis to be fitted, or of an exemplary
model of such an auditory prosthesis, is created, transformed into
a table, or other usable form, and stored in software usable by an
automated fitting program. The automated fitting program may then
"test" or try by iterative process, the various settings for the
acoustic parameters of the auditory prosthesis and accurately
determine the results without actual resort to the physical
auditory prosthesis itself. Since the transfer function of the
auditory prosthesis is stored in software, it is no longer
necessary to halt the automated fitting process to physically
adjust the auditory prosthesis. The automated fitting process,
thus, remains automated and the fitting process is greatly
accelerated and enhanced. Further, since less time is required for
each step in the fitting process, a greater accuracy may be
obtained in the same amount of fitting time. Alternatively, since
less time is required to each step, the fitting process may be
accelerated and more patients may be treated by the technician in
the same mount of time.
The present invention is designed for use with an auditory
prosthesis having acoustic parameters which at least in part
determine at least one of the acoustic fitting functions of the
auditory prosthesis, the acoustic parameters being adjustable, and
provides a method of determining the acoustic parameters of the
auditory prosthesis which will provide a user of the auditory
prosthesis with a target auditory response by following the steps
of determining the target auditory response of the user,
determining the acoustic fitting function of the auditory
prosthesis operating in conjunction with the user, and optimizing
the acoustic parameters of auditory prosthesis by comparing the
auditory response of the acoustic fitting function with the target
auditory response and by adjusting the acoustic parameters to
minimize the error of the comparison.
The present invention is also designed for use with an auditory
prosthesis having acoustic parameters which at least in part
determine the acoustic fitting function of the auditory prosthesis,
the acoustic parameters being adjustable, and provides a method of
determining the acoustic parameters of the auditory prosthesis
which will provide a user of the auditory prosthesis with a target
auditory response, by following the steps of determining the target
auditory response of the user, determining the acoustic fitting
function of the auditory prosthesis operating in conjunction with
the user, storing a software model of the acoustic fitting
function, and optimizing the acoustic parameters of auditory
prosthesis by comparing the auditory response of the software model
with the target auditory response and by adjusting the acoustic
parameters to minimize the error of the comparison.
The present invention is also designed for use with an auditory
prosthesis having acoustic parameters which at least in part
determine the acoustic fitting function of the auditory prosthesis,
the acoustic parameters being adjustable, and provides an apparatus
for determining the acoustic parameters of the auditory prosthesis
which will provide a user of the auditory prosthesis with a target
auditory response. A first mechanism determines the target auditory
response of the user. A second mechanism is adapted to be operably
coupled to the user and determines the acoustic fitting function of
the auditory prosthesis operating in conjunction with the user. An
optimization mechanism is operably coupled to the trust mechanism
and the second mechanism and optimizes the acoustic parameters of
auditory prosthesis by comparing the auditory response of the
acoustic fitting function with the target auditory response and
adjusting the acoustic parameters to minimize the error of the
comparison.
The present invention is also designed for use with an auditory
prosthesis having acoustic parameters which at least in part
determine the acoustic fitting function of the auditory prosthesis,
the acoustic parameters being adjustable, and provides an apparatus
for determining the acoustic parameters of the auditory prosthesis
which will provide a user of the auditory prosthesis with a target
auditory response. A first mechanism determines the target auditory
response of the user. A second mechanism is adapted to be operably
coupled to the user and determines the acoustic fitting function of
the auditory prosthesis operating in conjunction with the user. A
storage mechanism is operably coupled to the second mechanism and
stores a software model of the acoustic fitting function. An
optimization mechanism is operably coupled to the first mechanism
and the second mechanism and optimizes the acoustic parameters of
auditory prosthesis by comparing the auditory response of the
software model with the target auditory response and for adjusting
the acoustic parameters to minimize the error of the
comparison.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing advantages, construction and operation of the present
invention will become more readily apparent from the following
description and accompanying drawings in which:
FIG. 1 is a block diagram of a prior art fitting system operating
in conjunction with an auditory prosthesis;
FIG. 2 is a schematic illustration of a prior art fitting system
operating during the fitting process;
FIG. 3 is a flow chart illustrating the prior art fitting
system;
FIG. 4 is a schematic illustration of the fitting system of the
present invention operating during the fitting process;
FIG. 5 is a flow diagram of the fitting system utilizing the
present invention;
FIG. 6 is a block diagram illustration of a fitting system
utilizing the present invention;
FIG. 7 is a block diagram illustration of the flow chart of the
real ear measurement step of the fitting system utilizing the
present invention; and
FIG. 8 illustrates an "error surface" encountered by an
optimization technique;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a prior art auditory prosthesis 10, which in
this description is described as being a hearing aid. The auditory
prosthesis has a microphone 12 for receiving an acoustic signal 14
and converting the acoustic signal 14 into an electrical signal 16
for transmission to a signal processor 18. The signal processor 18
operates on the electrical input signal 16 and provides a processed
electrical signal 20 which is transmitted to a receiver 22 to be
transformed into a signal which is perceptible to the user of the
auditory prosthesis 10. The auditory prosthesis 10 illustrated in
FIG. 1 is adjustable in its auditory characteristics. The auditory
characteristic of the auditory prosthesis 10 is determined by a set
of acoustic parameters 24 stored within the auditory prosthesis 10,
preferably, or in any other convenient retrievable location. The
signal processor 18 modifies the electrical input signal 16 in
accordance with a set of acoustic parameters 24 to provide the
processed electrical signal 20. The set of acoustic parameters 24
define the auditory characteristic of the auditory prosthesis 10.
An example of such an auditory prosthesis includes a signal
processor such as is described in U.S. Pat. No. 4,425,481, Mangold
et al which is hereby incorporated by reference. Receiver 22, which
in hearing aid parlance is a miniature speaker, which produce a
signal which is adapted to be perceptible to the user of the
auditory prosthesis 10 as sound. Since the set of acoustic
parameters 24 is modifiable, or in one embodiment my be selected
from a plurality of sets of acoustic parameters 24, the auditory
characteristic of a particular auditory prosthesis 10 is adjustable
and is determined, at least in part, by the set of acoustic
parameters 24.
In order to provide the user of the auditory prosthesis 10 with an
appropriate auditory characteristic, as specified by the set of
acoustic parameters 24, the auditory prosthesis 10 must be "fit" to
the individual's hearing impairment. The fitting process involves
measuring the auditory characteristic of the individual's hearing,
calculating the nature of the amplification or other signal
processing characteristics needed to compensate for a particular
hearing impairment, determining the individual acoustic parameters
24 which are to be utilized by the auditory prosthesis 10 and
verifying that these acoustic parameters do operate in conjunction
with the individual's hearing to obtain the compensation desired
With the programmable auditory prosthesis 10 as illustrated in FIG.
1, the adjustment of the set of acoustic parameters 24 occurs by
electronic control from a fitting apparatus 26 which communicates
with the auditory prosthesis 10 via communication link 28. Usually,
fitting apparatus 26 is a host computer which may be programmed to
provide an initial "fitting", i.e., to determine the initial values
for the set of acoustic parameters 24 in order to compensate for a
particular hearing impairment for a particular individual with
which the auditory prosthesis 10 is intended to be utilized. Such
an initial "fitting" process is well known in the art. Examples of
techniques which can be utilized for such a fitting process may be
obtained by following the technique described in Skinner, Margaret
W., Hearing Aid Evaluation, Prentice Hall, Englewood Cliffs, N.J.
(1988), the entire content of which is hereby incorporated by
reference, especially Chapters 6-9. Similar techniques can be found
in Briskey, Robert J., "Instrument Fitting Techniques", in Sandlin,
Robert E., Hearing Instrument Science and Fitting Practices;
National Institute for Hearing Instruments Studies, Livonia, Mich.
(1985), pp. 439-494, which are hereby incorporated by
reference.
FIG. 2 illustrates such a prior art fitting system 26 being
operated in conjunction with a programmable auditory prosthesis 10
which is being fit to an individual or patient 30. In operation,
the fitting system 26 is used in conjunction with the auditory
prosthesis 10 coupled to the individual 30 in order to determine
and adjust the auditory prosthesis 10 to properly compensate for
the individual's 30 hearing impairment.
This prior art process is illustrated in FIG. 3. First, an audio
gram 110 is made of the individual's 30 hearing impairment by
standard well known techniques. Such as is described Green, David
S., "Pure Tone Air Conduction Testing", Chapter 9, in Katz, Jack,
editor, Handbook of Clinical Audiology, Williams & Wilkins,
Baltimore, Md. (1978). The audiogram 110 represents the actual
auditory ability of the individual 30 and, hence, illustrates or
represents the hearing impairment of the individual 30. From the
hearing impairment of the individual 30, as represented by the
audiogram 110, the prescriptive method, or compensation of the
hearing impairment, 112 can be developed, also by well known
techniques. From the prescriptive method 112 an insertion gain 114
is determined. That is, once the prescriptive method 112, or the
compensation needed for this individual's 30 hearing impairment has
been determined, the settings of the acoustic parameters 24 of the
auditory prosthesis 10 can be determined at step 114. Once the
insertion gain 114 is determined, a particular auditory prosthesis
is selected 116 and adjusted 118 according to that insertion gain
114. With the auditory prosthesis 10 adjusted as in step 118, the
actual response of the individual 30 is measured 120. From the
measured response 120, it can be determined whether the auditory
prosthesis 10 is adjusted properly (step 122). If the auditory
prosthesis, at this point, is adjusted properly, the process ends
(step 124). If, however, the auditory prothesis is not adjusted
properly (step 122), the process must revert back to step 118 where
the auditory prosthesis 10 is readjusted to a new or better
approximation of an auditory characteristics and the response is
again measured at block 120. Again, it is determined whether or not
the auditory prosthesis is adjusted properly at step 122. Thus, an
interative adjustment and measurement of the response of the
individual 30 occurs This well known adjustment/fitting technique
is represented in the prior art fitting system as illustrated by
block 26 in FIGS. 1 and 2. It can be seen that the entire process
for fitting system 26, as illustrated in FIG. 3 must be done with
the auditory prosthesis 10 operating in conjunction with the
individual 30. Thus, depending upon the length of the iterative
process, the individual 30 is subjected to a long and arduous
fitting process with the auditory prosthesis being utilized in
conjunction with the individual's 30 ear. Since much time is spent
for each fitting step, a fewer number of iterative processes can be
performed in the same amount of time, resulting in potentially high
in accuracy in the fitting process.
FIG. 4 illustrates a fitting system 32 of the present invention
operating in conjunction with an auditory prosthesis 10, again
being fitted to individual 30. Fitting system 32 contains an
automated fitting program 34 which may operate either in
conjunction with the auditory prosthesis 10 or with a software
model 36 of the auditory prosthesis 10 which is stored in, or
retrievable by, fitting system 32.
The procedures involved in the fitting system 32 are illustrated in
FIG. 5. As in the prior art fitting systems 26, fitting system 32
starts with an audiogram 110 of the individual's 30 hearing. This
technique is well known and exactly the same as it is performed in
the prior art fitting system 26 illustrated in FIG. 3.
Again as in FIG. 3, the procedure in FIG. 5 develops a prescriptive
method 112 from the audiogram 110. From the prescriptive method 112
an insertion gain that is the desired auditory characteristic of
the auditory prosthesis 10 is determined. The determination of the
prescriptive method 112 and the development of the insertion gain
are exactly the same as they occur in the prior art fitting system
26 illustrated in FIG. 3. With fitting system 32, a real ear
measurement 126 of the auditory prosthesis 10 operating in
conjunction with the individual 30 is obtained by the automated
fitting program 34. The technique used to perform the real ear
measure 126 will be described later. From the real ear measure 126
and the insertion gain 116 determined previously, a target response
of the auditory response is computed 128. The computed target
response 128 simply takes the insertion gain as determined by 116
and it modifies that insertion gain according to the real ear
measured 126 corrections. Thus, the computed target response 128
simply represents a combination of the insertion gain 116 and the
real ear measure corrections 126. The fitting system 32 then
"adjusts" 130 the acoustic parameters which would determine the
auditory characteristics of the auditory prosthesis. This
"adjustment" is performed utilizing a software model 36 of the
auditory prosthesis contained in the fitting system 32. Thus, the
adjustment 130 need not be performed with the fitting system 32
coupled to the auditory prosthesis 10. The adjustment 130 can be
performed independently and separately from any connection to the
auditory prosthesis 10 and, hence, the individual 30 is not
encumbered at this point. From the software model 36, the presumed
response 132 of the auditory prosthesis 10 is computed. Since the
fitting system 32 contains a software model 36, it is not necessary
to actually operate the auditory prosthesis 10 with the calculated
acoustic parameters 24, but it is merely necessary to utilize the
software model 36 to compute the projected response 132. Step 134
determines whether the presumably properly "adjusted" auditory
prosthesis 10 has the proper values of acoustic parameters 24 to
provide the auditory characteristic as determined by the computed
target response 128. If the adjustment determination at step 134
indicates, based upon the software model 36, that the presumed
auditory prosthesis 10 will not operate properly, then the process
reverts to the "adjustment" 130 step and the acoustic parameters of
the auditory prosthesis 10 are readjusted, based upon known
techniques, to new values where a new computed response 132 may be
obtained and a new determination as to the proper adjustment of the
presumed auditory prosthesis 10 may be performed (step 134). If the
adjustment, however, is proper, then the process optionally ends or
(as shown) the auditory prosthesis is adjusted 118 with that set of
acoustic parameters 24 and the actual response of the auditory
prosthesis 10 is measured 120. If this adjustment of the auditory
prosthesis 10 is proper (step 122), then the process is ended (step
124). If at step 122, after actually measuring the auditory
prosthesis 10 in conjunction with the individual 30, it is
determined that the adjustment is not proper, the process returns
to recompute the target response at step 128 or to readjust the
control settings at step 130 in order to revise and obtain a new
computed response 132 and the process is again accomplished from
that point forward.
It is to be noted that only step 110 (determining the audiogram)
and steps 118-124 (actually measuring the output) need be performed
in conjunction with the individual 30. The remainder of the
iterative adjustment technique contained in steps 128-134 may be
performed by the fitting system 32 with the automated fitting
program 34 operating in direct conjunction with the software model
36 and without utilization, of or connection with, the actual
auditory prosthesis 10 or any encumbrance of the individual 30.
Thus, individual 30 avoids the long, arduous, iterative adjustment
techniques involved in processing the fitting system 32.
The use of the software model 36 can be also illustrated with
reference to the block diagram shown in FIG. 6. In this diagram,
the individual's 30 target auditory characteristic is determined at
block 210 (embodying blocks 110, 112 & 114 in FIG. 5). This
target auditory response can be developed by known techniques.
Further, the acoustic characteristics of the individual's 30 ear,
i.e., a real ear measurement, is accomplished at block 212. This
real ear measurement is similar to block 126 illustrated in FIG. 5.
The electrical response of the actual auditory prosthesis 10 is
determined in block 214. This can be accomplished by measuring the
auditory characteristics of an auditory prosthesis 10, i.e., its
acoustic input to output characteristics, with the auditory
prosthesis 10 being operated separately from the individual 30.
Thus, block 210 determines the target auditory characteristic of
the individual, e.g., by the performance of an audiogram and
subsequent calculation, and the acoustic real ear measurement 212
of the auditory prosthesis 10 on individual 30 is determined. In
addition, actual measurements are taken of the electro-acoustic
response to 14 of the auditory prosthesis 10 but this need not be
done in conjunction with the individual 30 nor at the same time.
From the acoustic characteristics of the real ear measurement from
block 212 and the electrical response of the auditory prosthesis
10, a software model 36 of the auditory prosthesis 10 may be
constructed. Using known optimization techniques at block 216, the
target auditory characteristics from block 212 can be compared with
the characteristics of the software model of the auditory
prosthesis 10 from block 36 to adjust the values of the software
model's parameters so as to minimize any error between the target
auditory response from block 212 and the response of the software
model 36. Using these known optimization techniques, the best fit
for the auditory prosthesis 10 can be obtained at block 218.
The technique to obtain the real ear measurements as discussed in
block 126 of FIG. 5 and block 212 of FIG. 6, may be had by
reference to FIG. 7. The purpose of the real ear measurement is to
obtain the acoustic characteristics of the auditory prosthesis 10
in combination with the individual's 30 external ear canal and any
associated "plumbing", e.g., the ear mold, tubing, etc. These real
ear measurements are commonly taken and utilized in conjunction
with individuals. However, the usual technique is to insert a
functioning auditory prosthesis 10 into the external ear canal or
near the external ear canal of the individual 30 with the auditory
prosthesis 10 "programmed" to provide the prescribed auditory
characteristic to correct the individual's hearing impairment. The
"real ear measurement" then obtains the actual response of the
prescribed auditory characteristics correcting the hearing
impairment of the individual. The real ear measurement technique
illustrated in FIG. 7 utilizes the same real ear measurement
technique except that first the unoccluded ear canal response is
measured at block 310 across the entire frequency range with which
the auditory prosthesis 10 is designed to be operated. Next, the
auditory prosthesis 10, or in a less preferred embodiment a replica
thereof dedicated to the fitting system 32, is set to a known
standard configuration, which is not dependent upon the individual
hearing impairment of the individual 30, and is operated in
conjunction with the individual 30 and his external ear canal. This
is illustrated by block 312. Without presenting a sound stimulus to
the auditory prosthesis 10, the sound level is measured with a real
ear measurement with the auditory prosthesis in the ear and
operating as illustrated at block 314. An auditory stimulus is then
presented to the auditory prosthesis 10, at block 316, and the real
ear response is measured. At block 318, it is determined whether
the measurement obtained in block 316 is at least 10 dB more than
the measurement obtained in block 314. If not, the gain of the
auditory prosthesis 10 is increased at block 320 and the process
returns to step 314 where a new nonsound stimulus real ear
measurement is obtained and then at block 316 where a sound
stimulus response is measured and a new determination is made of
whether the measurement at block 316 is at least 10 dB greater than
the measurement made at block 314. This process is repeated until
the auditory prosthesis 10 provides a response at block 316 which
is at least 10 dB greater than the response measured in block 314
or until a present maximum allowable level is reached and operator
intervention is required. The process, then at block 322, using the
software model 36, predicts what the measurement at block 316
should have been based on the sound stimulus presented. Block 324
then computes the difference between the result from block 322 and
the result obtained in block 316. The difference between these
values becomes the real ear measurement correction discussed at
block 126 in FIG. 5. Thus, the technique illustrated in FIG. 7
measures the appropriate "real ear" acoustics and the amount of
compensation needed to supplement the software model 36 to apply to
the particular individual 30.
The optimization technique illustrated in block 216 of FIG. 6,
while being applied to the software model and the present
invention, may be one of the many well known techniques for
determining the proper values with a set of unknowns which can not
be solved analytically. A preferred optimization technique involves
a "constrained modified method of steepest descent" (sometimes
referred to as a "gradient method"), using Newton accelerators. The
constraints are the values of the set of acoustic parameters 24,
e.g., a center frequency of between 500 and 4,000 Hertz and maximum
power output which is not greater than the uncomfortable loudness
level. The optimization criteria include centering, i.e., the
center frequency being as close as possible to 1500 Hertz; the
inband average error in both the high pass and low pass frequency
bands and the absolute error of the entire amplitude over the
entire frequency response of the auditory prosthesis 10, i.e., the
dB difference between the model and the target auditory response.
Successful optimization depends upon a good initial estimate of the
values of the acoustic parameters which can be done with known
auditory techniques. These initial estimate techniques are well
understood in the art. As an example, the initial estimate for the
crossover frequency is chosen as a weighted average of the
frequencies f.sub.i at which the model response is calculated
according to the formula: ##EQU1## Where In is the Naperian
logarithm, t.sub.i is the target response at the i.sup.th
frequency, and e=2.718281828. The summations are taken over the
range of i which gives frequencies f.sub.i from the lowest to the
highest at which the model is calculated (in this case 125-8000
Hz).
Minimizing the error resulting from specific values of acoustic
parameters 24 involve trying a new value for the acoustic
parameters and comparing the target insertion gain with the
predicted response from the model. Through appropriate optimization
techniques, this comparison can be made to find the minimum of the
error function by moving in the proper direction "down" the error
surface. Reference on how to obtain this optimization can be be
found in Adby, P. R. and Dempster, M.A.H., Introduction to
Optimization Methods, Chapman and Hall, London (1974).
FIG. 8 schematically illustrates the general optimization problem
with more than one variable. The two parameters, 1 and 2 may be set
to particular values arbitrarily. In this example, the error,
computed as just described, describes a parabola as a function of
parameters 1 and 2. In general, for a N-dimensional optimization,
the error surface exists in a space of dimension (N +1). The goal
is to find the minimum error. In the example given in FIG. 8, the
initial choice of (P.sub.1, P.sub.2) results in a non-minimum
error, as shown by point A on the error surface. The optimization
algorithm must find the minimum point, point B, by search through
the error space. Note that in general the error surface or function
described analytically is not known. However, there are many
methods developed to cope with this problem which involve, in
general, evaluating equations.
In the software fitting system 32, the programmable parameters are:
1. Microphone attenuation, 2. Crossover frequency between low pass
and high pass channels, 3. Attenuation in the low pass automatic
gain control circuitry, 4. Attenuation in the low pass channel
following the automatic gain control circuitry, 5. Attenuation in
the high pass automatic gain control circuitry and 6. Attenuation
in the high pass channel following the automatic gain control
circuitry. There are two other programmable measures, low pass and
high pass release time but they do not affect the frequency
response and are not among the optimized quantities in the
preferred embodiment. The following equations utilizing these
programmable acoustic parameters 24 provide for the software model
34. The estimated IG(f) [in dB]=the acoustic correction (f)
+microphone response (f) ++ internal amplifiers (f) + receiver
response (f) + microphone attenuation (f) +20 .times.log.sub.10 [LP
(fc -F).times.10.sup.(AGC L)/20 +HP (f-fc).times.10.sup.(AGC
H.sup.+ATT H/.sup.20 ]+ constant. Where the notation X(f) is
intended to indicate that the value of x is a function of frequency
f. These equations describe the software model in the frequency
domain. It is to be recognized and understood that other equations
may also calculate the amplitude response of the auditory
prosthesis when set to acoustic parameters 24.
Thus, it can be seen that there has been shown and described a
novel method and an apparatus for determining the acoustic
parameters of an auditory prosthesis. It is to be recognized and
understood, however, that various changes, modifications and
substitutions in the form and the details of the present invention
may be made by those skilled in the art without departing from the
scope of the invention as defined by the following claims.
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