Defining & stimulating residual hearing ability

 The limiting historical concept of
hearing instrument fitting has been
that all we really needed to do was to
replace the intensity at frequencies
damaged or destroyed by pathology
in each ear.

 Clearly, if that was all it took to return
a person to “normal” hearing, we
would have been making perfect
fittings for the past 40 years.
 Today, though it is not that simple, it is
possible!

 Many fitting formulae have been
theorized and researched in an
attempt to “correct” hearing loss as
defined audiometrically in decibels
relative to hearing level (dB HL).

 Most hearing instrument fitting
formulae modify the audiometric
results into an “appropriate
correction” for the patient/client.
 This concept of “appropriate
correction” as a HI fitting “target”
should be considered as a starting
point--not a prescriptive requirement.

 Rather than applying a conceptual
target for “appropriate correction”,
what we really need to do is define
and then fully stimulate the patient’s
residual auditory function.
 The correct approach is to maximize
the patient’s residual hearing!

 We must identify the parameters of the
patient/client’s residual auditory area.
 Specifically, pure tone thresholds and
loudness discomfort levels (LDLs) at
discreet frequencies.
 By defining the residual auditory area
parameters, the hearing instrument
will provide the most benefit to the
patient/client.

 Figure 1 depicts the auditory area of a
normal hearing person. The shadowed
area represents average
conversational speech.
 The range between just audible and
uncomfortably loud is called the
auditory area or the dynamic range of
hearing.

 As seen in Figure 1, speech is audible
and comfortable across a wide
frequency range for a normal hearing
person.
 Because of the large range of hearing
available to them, normal hearing
people can experience all the
dynamics of speech; that is, its peaks
and valleys and soft, average and
loud levels.

 Most prescriptive methods utilize
insertion gain targets.
 The gain suggested by a prescriptive
fitting method only gets you to
audibility.
 Prescriptive gain targets do not always
allow patient/clients to enjoy the full
benefits of their residual auditory area
and the dynamics of conversational
speech.

 Hearing instrument fitting methods
must be described, so that we may
achieve hearing instrument
electroacoustic performance which
may be adapted to the
psychoacoustic parameters of each
patient/client’s residual auditory
ability/capacity.
 Fitting methods should include not
only audiometric pure tone thresholds
but LDLs by frequency, as well.

 After all, our goal is to ensure
audibility of important sounds,
especially speech, while limiting loud
sounds to below the patient’s UCL.
 Today’s digital electroacoustic
technology enables us to do just that!

 Figure 2, is a display of unaided results
as a function of frequency.
 The dotted line at the lower part of the
figure represents normal hearing defined
in dB SPL measured near the eardrum as
a function of frequency (in Hz).
 The pink circles joined by a line
represent the individual’s hearing
threshold levels, in dB SPL, as a function
of frequency.

 In figure 2, the asterisks represent average
UCL values for this individual’s hearing
threshold levels.
 The green line represents average
unamplified conversational speech
generally associated with average
conversational speech (representing
peaks and valleys of speech). Speech
sounds associated with average
unamplified conversational speech lying
BELOW the pink circles, will not be audible.

 Fitting wide dynamic range
compression (WDRC) instruments to
meet gain targets helps patients hear
better.
 Most current fitting formulae generate
targets based on frequency-specific
insertion gain.
 These frequency specific data are
easily obtained utilizing probe
microphone real-ear measurements.

 In figure 3, aided test results are
displayed as a function of frequency.
 The circles joined by lines indicate
hearing threshold levels (eardrum dB
SPL) as a function of frequency (in Hz).
 The asterisks indicate UCL.

 The orange line at the top of the graph
running close to, but not exceeding
the asterisks, is the probe microphone
measured real-ear maximum output
of the hearing instrument fitted for the
individual (the real-ear saturation
response [RESR]—usually measured at
85dB input).

 The bars show the dynamics of an
amplified average conversational
speech signal relative to the targets
for aided average conversational
speech.
 If no compression were occurring for a
speech-like signal, then the bars
would extend about 30dB (similar to
the dynamic range of speech
displayed within Figure 1).

 A patient/client’s residual auditory
area is defined as the difference
between their air conduction
thresholds and their loudness
discomfort levels as measured at
each octave and half-octave
frequencies from 250 to 6k Hz.

 The goal for fitting amplification is to
adjust the parameters available on
the hearing instrument to amplify soft,
average and loud speech within the
reduced auditory area across the
broadest relevant frequency range
while ensuring that loud sounds do not
exceed the patient/client’s LDLs.

 Loudness discomfort levels should be
especially evaluated at 1k, 2k, 3k and
4k Hz, because most of today’s
amplification systems possess their
peak output responses at those
frequencies.
 Also, many hearing loss pathologies
exhibit significant recruitment at those
very same frequencies.

 In figure 4, the pink circles joined by a
line represent the individual’s
threshold levels (dB SPL eardrum) as a
function of frequency.
 The asterisks represent average UCL
values for this individual’s hearing
threshold levels.
 The blue shaded region outlines the
individual’s residual auditory area.

The goal for fitting amplification to this
individual would be to adjust the
parameters available on the hearing
instrument to fit amplified soft, average
and loud speech within the reduced
auditory area across the broadest
relevant frequency range; and to ensure
that loud sounds do not exceed the
recommended loudness discomfort
levels.

 In 1988, Dr. Skinner provided a table of
estimates for most comfortable loudness
(MCL) and UCL data that were derived
from air conduction threshold results by
frequency. This table was obtained from
the study by Kamm, Dirks and Mickey
(1978).
 Further research found this estimated
“normative data” to have a disparity
among individuals by as much as
seventeen decibels!

 Despite the slight variability in
frequency specific LDL measurement
results, today’s hearing instrument
technology demands that each
patient/client’s LDLs be known for
each ear.
 These results define the residual
auditory area, and are most crucial to
comfortable and successful auditory
stimulation.

 Today’s digital hearing instrument
technology provides a variety of
adjustable response bands and
compression ratios so that our custom
fitting efforts are no longer
compromised with reduced gain or
excessive output.

 The major and most exciting
electroacoustic difference between
analog and digital hearing instrument
technology is that the hearing instrument
gain of digital instruments is no longer
directly correlated to its output.
 Old custom electroacoustic fitting
methods often compromised the
required gain relative to the output for
patient comfort.

We will learn more tomorrow
regarding: 1)residual hearing
ability, 2)patient/client counseling
and 3)patient/client realistic
expectations for hearing instrument
use.

Defining & stimulating residual hearing ability

More Related Content

What's hot (19)

Viewers also liked (9)

Similar to Defining & stimulating residual hearing ability (20)

More from Lynn Royer (10)

Recently uploaded (20)

Defining & stimulating residual hearing ability