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HEARING EVALUATION IN THE DISPENSING PRACTICE, PART I
By Max Stanley Chartrand
“Fine-tuning of the psychological and sociological
infrastructure of the hearing evaluation is a hallmark
of the professional hearing instrument specialist.”
INTRODUCTION
Without "the facts" in front of all concerned, the
debate concerning hearing loss and recommended
amplification often becomes a pitting of wills and
opinions, an exercise in futility. The psychological and
sociological importance of the hearing evaluation is to
provide that objective backdrop from which all
discussions emanate. Furthermore, validation of the
fitted hearing instrument may also be weighted against a
set of measurable parameters and outcomes that should be
understood by both the specialist and the patient. The
process through which these factors are communicated,
when carefully planned and utilized, become a form of
instructional counseling.
Also important to our discussion is the crucial role the
instructional counseling approach plays in extracting
more accurate thresholds and responses in the evaluation
and validation. Indeed, the accomplished specialist will
develop tried and tested means of describing, probing,
and instructing the patient. In other words, precision
in communication may effectively be achieved in a field
otherwise fraught with communication breakdowns.
Difficulty in finding threshold: Important
considerations
Throughout the hearing aid evaluation the specialist
must train the patient to sharpen their perception of
threshold. ANSI refers to threshold as “the minimum
effective sound pressure of the signal that is capable
of evoking an auditory sensation in a specified fraction
of the trials” (ANSI, 1973). In this case, we recording
two out of three responses at a given sensation level,
or better than 50% of the time. The line between
imagining a tone and actually perceiving it as an
acoustic sensation can be difficult many individuals,
especially when the presentation is pulsed or
predictable.
Ability to discern threshold is significantly affected
by age and maturity. At the extremes of biological age,
we find that threshold discernment can be somewhat
difficult. Think, for a moment, the last time you were
given a truly objective threshold test administered by
another professional. For even the most astute and
trained individual, it can be a frustrating
experience…is it my imagination or do I actually hear
the tone, you ask yourself. Perhaps if you stop
breathing for a second you can improve your thresholds
another 5 decibels. This presents an even more enormous
challenge to the untrained ear, which fact is too often
taken for granted by those sitting at the other end of
the audiometer. Indeed, ambient sound levels that meet
the latest ANSI standards have evoked patient reports of
“hearing my heart beat”, “a deafening silence”---sounds
and sensations that, in themselves, can contaminate true
threshold measurements. And the question has been asked,
over and over in hearings, debates, and rebuttals: Is it
really that important to find such absolute thresholds?
After all, we’re measuring hearing impaired cases.”
But let’s back up for a minute. First, the fact remains
that MOST adults with aidable hearing loss exhibit
normal thresholds in the low frequencies, the evidence
of which can only be ascertained in an ambient
environment that attenuates low frequencies near ANSI
(ANSI, 1985). Secondly, by ignoring sound levels of the
test environment, the specialist will experience many
more occlusion and over-amplification-in-lows
complaints. This alone should be incentive enough for
the specialist to carefully select and/or modify the
testing environment to a suitable level. Certainly, it
can be safely assumed that those who exhibit a mild loss
in the lows when tested in an uncontrolled environment
will probably exhibit normal low frequency thresholds in
a controlled environment. Without accommodating this
problem, the specialist is setting up more patients for
failure, as this group constitutes the single largest
group for failed trials and credit returns. But not to
belabor the point: Yes, it is vital to evoke the best
possible thresholds in the best possible test
environment. They may not normally listen in such an
environment, but it is the only way we can ascertain
accurate thresholds.
In cases of children, it often takes a great deal of
patience to train their listening ability to produce
reliable and repeatable threshold responses. Indeed,
very young children need multiple sittings before the
specialist may feel confident with the results (Matkin,
1988). Furthermore, it behooves the specialist who
handles the testing of children to become thoroughly
familiar with play audiometry and other behavioral
methods of testing (Ross et al, 1991). Indeed,
oftentimes one must develop visual evoked responses from
the child, which, coupled with the usual modes of
voluntary response may provide greater indication of
actual threshold versus perceived threshold (Allen,
1967). As the child matures, their ability to
communicate threshold should also improve. This
sometimes presents the false conclusion that the child’s
hearing acuity has actually improved. But, in actuality,
the child’s ability to discern and communicate threshold
has improved. The recognition of this phenomena can be
particularly confusing for parents and other casual
observers to understand if one of the sources of
auditory deficit resulted from an undeveloped or
underdeveloped Eustachian tube. But the resolution of
that difficulty would merely affect the low frequencies.
The critical speech range would still be unaffected.
An important side-note: No longer the exclusive domain
of the clinical audiologist, the testing of children by
hearing instrument specialists has dramatically
increased in recent years, as interdisciplinary hearing
health care teams continue to be formed in communities
all over the world. In many dispensing settings,
traditional dispensers and dispensing audiologists work
side-by-side while working with all age groups, except
perhaps the very young children. The need to include
children as hearing instrument patients in the private
dispensing practice also arises from the fact that over
14,000 school districts in the U.S. today still do not
have a staff audiologist, or anyone as well trained as
their local specialist. As a result, millions of
children go their entire school years without adequate
testing or care for their hearing loss (Chartrand,
1997). This has brought about an almost universal call
to specialists in under-served areas to help supplement
the work of the local schools, and to open up their
practices to serve the needs of children, in conjunction
with other appropriate professionals.
Training for threshold in adults, on the other hand,
generally requires more verbally-based approaches
(Wilber, 1991). For young adults through middle age
adults (i.e., 22-64 years of age) training for threshold
detection may not require more than the simplest
explanations, which will be given further in this
chapter. Older adults may require more explicit
instructions with more assessment checks (i.e.: “Did you
barely hear the tone, or was it easily heard?”), with
repeated instructions as needed. In cases of central
auditory processing problems or dementia, the challenge
may be particularly difficult, especially so as not to
fatigue the patient. Special care and training are
required to serve this group, usually in tandem with
other hearing health professionals.
The author has found that the best way to evoke accurate
thresholds for all age groups is to make the patient a
partner in the process. In other words, to explain what
is being measured and why, every step of the way. An
informed patient will more likely be cooperative, and
make the specialist’s job easier. In fact, they can
assist in making the test one of discovery and
anticipation, at the same time helping to overcome
psychosocial artifacts, such as denial, or lack of
recognition of the effects of hearing impairment.
But there are several dimensions that we are attempting
to measure in a thorough hearing assessment. Measurement
of acoustic performance parameters give us different,
but important, views of a given hearing system. Taken
together we are able to make more precise prognosis and
render better counseling. Some of the dimensions being
measured in pure-tone and speech audiometry are:
· Threshold detection (with or without masking)
· Discrete tone identification
· Octave resolution
· Ear lateralization discernment
· Intensity Difference Limens (DLs)
· Critical bandwidth sensitivity (also, DLs)
· Maximum tolerance of discrete and broad band (speech)
sound
· Comfort level sensation
· Localization/spatial mapping ability
· Binaural loudness summation
· Aided monosyllabic speech discrimination
· Speech-in-Noise (SiN) ability
These are indications that must be explained and trained
into the patient, by verbal instruction, demonstration,
periodic assessment, repetition, and age-appropriate
strategies. So remember, it is important to enlist the
patient as a partner in this journey of discovery. To do
so will yield far more repeatable and accurate results
than leaving them in the dark.
Counseling considerations in pure-tone testing
From a counseling context the specialist will find
several considerations that may affect the validity of
pure-tone thresholds. Alertness and motivation of both
the client and third party are essential to continue the
"journey of discovery" began earlier in the case
history. Furthermore, we are now embarking upon what
needs to be the most "objective" or abstract section of
the evaluation, the one part that may be proven or
disputed by another professional because of the relative
repeatability of the results. There are two main
considerations: involvement and accuracy. Following are
some observations that may enhance both of these
considerations:
The Acoustic Testing Environment. Ideally, ANSI
standards will be observed in all test settings.
Certainly, it is incumbent of all professional
dispensers to observe maximum permissible ambient noise
standards, of say, <50 dBC for purposes of fitting
hearing instruments. It is not the purpose of this
chapter to debate what the maximum permissible sound
level standard or appropriate test environment should
be. There are myriad settings in which hearing impaired
patients are tested---sound suite, sound chair, ordinary
office, at home, service center, school, etc.---but one
should be acutely aware of the psychological impact each
test setting can have on the patient, including its
relationship to accuracy. If there are extraneous
noises, such as people conversing in the other room,
traffic noise outside, or air conditioner fans, the
patient (and third party) may rightfully suspect that
the evaluator is not evoking accurate threshold
responses. When they begin to experience difficulty
separating those noises from the extraneous signals in
the environment, they may completely lose faith in the
judgment of the specialist. Often this concern is
reported to the specialist, but, at least, at a
subconscious level it is occurring. Indeed, experience
has shown that many patients will privately predetermine
not to proceed with a fitting, while waiting for the
moment to leave the test. Perhaps their stated
explanation is "I want to think about it for awhile."
or, a more candid "I really don't believe my hearing is
as bad as you say it is." If extraneous noises are
interfering with the hearing test, it behooves the
specialist to go to great lengths to accommodate the
situation, such as:
· Waiting for the cessation of such disturbances
· Verification with a sound level meter (not with the
volume units (vu) meter of the audiometer)
· Moving to a more appropriate acoustic environment
· Switching to calibrated insert earphones
In cases where it is obvious that the patient or third
party are distracted by inadvertent noises it is vital
that they see the specialist openly address the problem,
whether by leaving the testing room to bring the noise
situation under control, or by offering verbal
explanation. Either or both actions may be necessary to
appease apprehensions, and assure professionalism. A
very important consideration in cases of intermittent
noise is the phenomena of backward and/or forward
masking (Preves and Curran, 1985). Especially near the
point of threshold, this can cause serious temporal
shift and confusion. Also, in situations where low
frequency background (60-250Hz >45dBC) the upward spread
of masking may cause excitation of the cochlear hair
cells throughout the mid and some of the high
frequencies (Pickles, 1988).
Indeed, the U.S. Occupational Safety and Health
Administration (OSHA), in conjunction with numerous
audiological studies, has determined that the ambient
noise level at 125-500Hz must be no greater than 45dBC
for proper pure-tone threshold testing at the industrial
site. It is arguable that such a standard, especially
the ANSI uncovered ear standard for sound suites, may
present an element of "overkill" to that needed in the
typical dispensing situation. However, in recent years
there have been tremendous strides made in the
development of equipment for adequate sound control in a
wide array of dispensing settings, from noise-occluding
headphones and insert earphones to anechoic sound chairs
and portable sound booths (Chartrand, 1993). In fact, it
is advisable that all testing areas are lined with at
least a minimal amount of anechoic material or surface.
The acoustic environment must be adequate not only for
accuracy, but also to maintain client and third party
confidence. It is an absolute necessity that the
specialist have an accurate Sound Level Meter with both
"A" and "C" weightings and "Slow" and "Fast" responses.
Without this vital piece of equipment, the accuracy of
the evaluative environment is merely guesswork.
Several considerations pertaining to the acoustic
qualities of the test room will include the following:
· Surfaces of the testing room should be as anechoic as
possible, with little sound reflection or reverberation.
That means open-cell anechoic foam, acoustic tile,
carpeting, or other sound-absorbent surface on the
walls, floor, and ceiling.
· The size of the test site should be no larger than
necessary. Usually a room of 10' x 10' or smaller will
easily accommodate a three-person test-site.
· Outside doors should be airtight and insulated, as
well as anechoic and solid.
· Ventilation should be filtered and redirected so as
not to contribute to the ambient noise levels. Keep in
mind that reducing ventilation openings, while possibly
reducing sound from other rooms, also increases the
velocity of air coming into the testing room, creating
yet another ambient disturbance.
· Lighting should be bright, not contribute to the
ambient sound level (i.e., incandescent).
The Physical Setting of the Test Site. Perception of
professionalism is often inseparable from appearances.
The quality and sophistication of the test equipment,
upkeep of the premises, cleanliness and visual
coordination, psychosocial seating arrangement are all
important considerations that must be observed. For
example, a most effective seating arrangement is to have
both the patient and third party seated in such a way
that they are both facing the specialist, while not
directly facing each other. This presents a better
"control" arrangement and minimizes conscious and
subliminal "body language" between the client and third
party which would normally create a "two-to-one"
arrangement. With the absence of direct visual contact
between patient and third party a one-on-one arrangement
may be effectively achieved. See figure 5.1a for an
example of an ideal seating/equipment arrangement in the
multi-occupant testing site, which will accomplish the
"one-on-one objective". Figure 5.1b will show the ideal
seating arrangement with a test booth situation
(Chartrand, 1998). Added to the mental picture should
also be the placement of new equipment available to
today's dispenser.
While some might perceive the consideration of equipment
sophistication as only a cosmetic consideration, the
fact remains that there is powerful psychological
validity to the visual concept. Patients often marvel at
the complex and intricate equipment in the dentist’s
office. In the doctor’s office they notice an array of
examining tools and charts on the wall. In the
optometrist's office a patient may have increased
confidence because of sophisticated modern equipment.
Likewise, when the hearing impaired patient is seated in
the auditory testing room they cannot help but make
comparisons with environments of other health
professionals they’ve visited. For this and other
reasons, proper attention to equipment and condition is
of utmost importance in eliciting patient confidence.
Instead of putting away equipment after each use, or
haphazardly distributing equipment throughout the room,
place it out on display in a functionally organized
manner. The examination and impression tools should be
laid out on a clean, white towel or cloth in plain view.
The audiometer, video otoscope, tympanometer,
electroacoustic analyzer, real ear measurement and
digital programming equipment, soundfield speakers, all
should be out in open view. Furthermore, a substantial
testing chair, along with third party seating, and
audiometer/audiometric equipment counters should be
first class. The investments made and the open placement
of these items will 1) assure their easy and frequent
use, and 2) increase patient and third party confidence
in the specialist's professionalism. Sit in the
patient’s chair, and observe through their eyes. Think
in terms of how the visual appearance would affect you
if you were a patient entering your office for the first
time. Does the appearance of the room evoke confidence,
professionalism, capability, current technology?
Figure 5.1a Suggested seating arrangement for multiple
occupant test room.
Figure 1b. Suggested seating arrangement when testing
with a sound suite setting.
Adequate lighting is also important to maintain a
positive mental attitude, and to assure alertness. Poor
lighting will not only impair vision, it will cause an
atmosphere of depression, lethargy, or
uncooperativeness. The best type of lighting is that
closest to "outdoor light". Ordinary fluorescent lights,
by themselves fatigue the eyes over time. Where possible
indirect incandescent lighting, possibly in combination
with florescent lighting, is the best choice for the
testing room. To enhance this theme, furthermore, colors
of the surfaces should be medium or light, projecting a
conservative or neutral aesthetic visual impact.
Cleanliness should be obvious to the observer. Paper
towels and/or tissue should be used as needed. Alcohol
and other antiseptics/disinfectants should be readily
available. Deodorizing mists will help maintain a clean
odor in the room. Smoking should never be permitted in
the testing room, or even in the inside premises of the
practice. All of the above considerations, if met, will
surely contribute significantly to a feeling of
confidence on the part of the patient, and alertness
during the testing. And, hence, the specialist who
accomplishes the proper planning and investment in the
testing environment may achieve greater success.
Achieving the best thresholds
Most often, those receiving hearing tests simply reflect
the attitude and thoroughness of the specialist giving
the test. For instance, if the specialist treats the
test scores as routine or hurriedly obtains thresholds,
the patient will perceive that this is not an important
part of the evaluation. Therefore, the thresholds may
not be "barely discernible" indications, but may be
instead "comfortable" responses, waiting until the
inattentive ear's attention is demanded. This could be
as much as 10 or 15dB above threshold, essentially
invalidating the threshold scores---the reader will
notice the test-retest variability presented later in
this chapter relative to arriving at the most
comfortable level (MCL). The same degree of
"subjectivity" could occur with cursory threshold
responses, if the specialist does not give proper
attention to reliability of presentation and responses.
Furthermore, where low frequency ambients are present,
this could present a very substantial threshold "shift"
for the low frequency test tones (Martin, 1985). Indeed,
some hearing instrument manufacturers have been known to
automatically adjust the low-frequency design of hearing
aid circuits for some dispensers because of an ongoing
pattern of remake/redesign orders. Those who test in
questionable acoustic environments are especially at
risk for such design adjustments. Even more important,
however, is the cost of time and frustration experienced
by the hearing aid user when threshold inaccuracies
complicate post-fitting adjustments. Therefore, it is
crucial that proper thresholds be obtained during
pure-tone testing.
An example of verbal instructions, which may be used for
obtaining true thresholds, is as follows:
"Now, I am going to give you a series of tones. When you
barely hear a tone, please (raise your hand)(push the
button), even if you barely hear the tone. Are you
ready?"
Notice the emphasis on the word “barely”. The repetition
of this word will make a definite subconscious
impression on the test subject from which semi-conscious
(semi-evoked) threshold responses may be provided. If
the evaluator is in doubt as to the validity of a given
response, he/she may stop and ask, "Did you barely hear
that tone?", to which the reply may indicate that they
responded at a suprathreshold level, such as, "Oh, I
could hear it pretty good." In that case, the above
instructions must be repeated, ending with, "Do you
understand?"
Of course, it goes without saying that physical
movements of the evaluator, such as pressing buttons,
etc., should be kept from view of the patient.
Furthermore, it is imperative that presentation
frequency be varied so that the patient does not
memorize or anticipate the tone at a level below their
ability to hear it, especially in descending
presentations. Another phenomena that can occur,
although not common, is echoacousia, or a psychological
reconstruction of the tone (or echo), causing the
listener to believe the tone is still being given.
Therefore, I strongly caution against using pulsated
presentation of pure-tones, as it does not provide the
needed variation, and can evoke a degree of echoacousia
in the unsuspected patient (Chartrand, 1999).
Psychological importance of masking
Just as any elementary text on audiometric testing will
assert, effective masking is a prime concern in
pure-tone testing asymmetrical ears so as not to involve
interaural attenuation or cross-hearing
(Larson-Donaldson, 1988). Looking at the practice of
masking from a counseling standpoint, however, one must
be alert to the confusion or, worse, loss of confidence
on the part of the patient when masking is needed but
not used. During pure-tone testing, an alert patient
will notice a stimulus shift from one ear to another in
"mid stream", and, if nothing is said, he/she may wonder
about the accuracy or validity of the entire test, or
the competence of the specialist. On the other hand, it
may be difficult for the specialist to detect an
interaural shift during testing, because interaural
attenuation values can vary significantly from one
individual to another. In addition, there are a number
of situations in which masking confusion can ensue.
Therefore, it is of both diagnostic value as well as
psychological value for the specialist to inquire which
ear a given stimulus was heard. This will not only
provide another needed clue in the need for or
modification in masking, but will also increase the
patient’s confidence in the evaluation and in the
professionalism of the specialist.
It is especially of value to take the time to utilize
proper methods of masking. Undermasking and overmasking
can be equally detrimental to the confidence of an
evaluation. Effective masking is essentially that point
where its only function is to isolate the ears from one
another. When it becomes part of the test, by causing
threshold shifts in the test ear or by exceeding
loudness discomfort in the non-test ear, it will serve
only as an impedance in building a good
patient/professional relationship that is necessary for
effectively counseling in the other aspects of
rehabilitation. To minimize the risk of exceeding
discomfort levels narrow band masking is much preferred
over white noise masking. When applying masking, the
patient should be asked, “Is the masking noise becoming
uncomfortable?”. Any inadequacies or special procedures
made in the masking sequence should be noted on the
audiometric report for future reference. Be sure to note
on the audiogram the amount of masking used, and to
which ear. More than a few state board complaints and
civil lawsuits has been filed and lost because of this
oversight. Therefore, it is of significant value to
receive training and to develop needed skills in masking
technique.
Involving the Third Party
Involving the third party in the pure-tone test will
prove beneficial from several vantage points. Let's
suppose the third party is only nominally interested,
one who would like to "wait outside". In this case,
they’ve adjusted their life to accommodate the patient’s
hearing loss, or may refuse to believe it is indeed a
hearing loss that has affected their relationship (Oja
and Schow, 1984). Let’s also suppose that the test is
being given in a multiple occupant testing room where a
given pure-tone signal is above, say, 70dB, and can be
easily heard by non-test subjects, even a normal hearing
third-party who is present at the testing. Once a
substantial threshold at any frequency (particularly 2K,
4K, or 6KHz) is found, just before the final crossing of
the threshold is about to take place (65-70dB, for
instance), the specialist may ask the third party, "Do
you hear that tone?"
If the third party nods affirmatively, the specialist
may follow up with, "He can't hear it...how long has he
been suffering with his hearing loss?" The third’s
party’s awakening as to the severity of the patient’s
loss may be enough to evoke empathy, possibly even
sympathy toward the patient’s rehabilitative outcome. In
the event that the third party has a partial hearing
loss where they cannot hear the tone (in free field),
the evaluator may then say something to the effect, "You
can't hear that? That is quite loud and near the limits
of my audiometer." The third party, thereafter, will sit
up, take notice, and likely give the evaluator a
dramatic response when a tone is given which they can
hear---as if he or she is the one being tested! We will
now have an alert and, hopefully, interested third party
on our team for the remainder of the evaluation.
Needless to say, because of often prevalent psychosocial
barriers, the third party is often the most important
factor and can make the difference between success and
failure in motivating an otherwise hesitant patient to
move forward.
Moreover, throughout the evaluation, the third party
needs to be involved in every facet of the evaluation,
from hearing health history and otoscopy, to pure-tone
and speech testing, to circuit demonstration and
decision-making. If at all possible, never leave the
spouse out of the final decision of hearing correction,
for they too have a stake in the outcomes and benefits
about to realized by the patient. They are part of the
rehabilitative process and may also need to go through a
mimicked version of the stages of mourning (Bowlby and
Parkes, 1970). The reader may see the appendix on
utilizing third party psychology at the end of this text
for a more complete treatment on this topic.
Explanations through drawings of ear, audiogram
Many specialists utilize the excellent practice of
drawing or showing pictures of how the ear works, how we
transmit sound, and what happens when we lose
sensitivity in hearing (see figure 5.2). A drawing,
drawn impromptu during the evaluation either on paper or
on a board, may be more effective than an actual picture
because of the "word-picture" association and mental
steps involved. Thereby, the parts of the ear are drawn
out as they are explained. Many people are surprised to
find that there is a difference between sensorineural
and conductive impairments, and that it is customary to
address the issue of “nerve deafness”, per se, as too
many have been told that “nothing can be done” about
sensorineural loss by their family doctor and others.
Furthermore, specialists should teach the patient and
third party about the audiogram, what it means, and how
we use it to determine hearing acuity and the need for
correction. Particularly important is an explanation of
the differentiation and paradox of having near normal
thresholds in the low frequencies, while having a
serious or severe loss in the more important high
frequencies, and how that relates to “hearing without
understanding”. In this way, the critical speech range
is shown, and a brief description about loudness growth
problems that may need to be addressed to bring the most
deteriorated frequency thresholds back to as near normal
function as possible. At this point, it would be
advisable to explain loudness growth in this manner:
“When one has a serious loss of sensitivity at any given
frequency, say 2KHz, it is not a simple matter of just
increasing loudness to bring hearing back to optimal
correction. In many cases, loudness at that frequency is
growing several times faster than it is at the
frequencies where one’s hearing thresholds are more
normal. The phenomena of abnormally fast loudness growth
is called “recruitment”. Therefore, where we find
significant recruitment we will need to try to slow the
growth of loudness, to be able to bring you as close to
normal function as possible.”
Fgure 5.2 Depiction of a hand-drawn ear used as a tool
to explain how the ear works.
Drawing the ear as one explains it is a most effective
way to bring both the patient and third party into the
circle of knowledge about their hearing impairment.
Furthermore, they become informed participants in that
"journey of discovery", anxiously awaiting the results
of the test. It is important to point out that when
employing this method, and after obtaining pure-tone
thresholds for air and bone, to go back to the audiogram
and show them the results of the completed test. Draw
lines or lightly mark the areas of concern, explaining
what auditory information is being missed, and what they
may expect in amplified correction.
Furthermore, this is an excellent time to review some of
the limitations of amplification correction, for in many
cases it may be said, "Even after we correct your loss
with amplification as best as possible, you will still
have some hearing loss. But without correction, you have
even more of a hearing loss." The foregoing is supposing
that we are talking about a sensorineural or presbycusis
case, not one needing medical attention. Indeed, nearly
all medically treatable cases should be exposed by the
end of the air-bone tests.
Bone conduction test considerations
Considerations in bone conduction testing involve those
used in air conduction with the exception that:
1) Ambient noise will surely affect outcomes even more
than with ear- covered testing
2) Masking (even at low levels) is crucial in nearly all
cases to avoid interaural attenuation or cross-hearing
artifact.
3) Variations in oscillator placement requires more
skill and sensitivity than does earphone placement.
4) The lack of observing these considerations is likely
to shake the patient’s confidence in the validity or
objectivity of the hearing test.
In cases of asymmetrical thresholds, it advisable for
the specialist to utilize both screening tympanometry
and the Weber test (@256Hz and/or 512Hz with tuning
forks, or @250Hz and/or 500Hz on the bone oscillator) in
conjunction with the bone conduction test. This will
also ascertain whether masking was used properly, and
provide a better picture of the actual conductive
involvement in the hearing loss.
Finding Recruitment: A Counseling-based approach
Searching out recruitment or abnormal suprathreshold
sensitivity will be another primary consideration of the
specialist. In a nutshell, this phenomena can be
described where the intensity of sound is perceived to
grow more rapidly than is actually occurring, and is
measured as difference limens (Jerger, 1952). In other
words, intensity at a given frequency or band may
increase 5dB, but to the hearing impaired listener, the
sensation of loudness grows at a rate of 10dB, 15dB,
20dB, or more. Some investigators report that up to 80%
of sensorineural cases have some recruitment involvement
(Libby, 1993). Certainly, this is one of the auditory
dimensions that causes many hearing aid trials to fail,
and one that the specialist should carefully consider in
arriving at the most appropriate amplification solution
for those with sensorineural loss. We will be covering
this subject in greater detail in the next chapter.
Here, however, it must be pointed out that discovering
bandwidth specific recruitment is a pure-tone,
warble-tone or narrow-band test propriety, while
broadband recruitment is primarily a speech test
propriety.
A fast and effective method of arriving at relative
suprathreshold sensitivity growth (or relative
difference limens)involves establishing loudness growth
immediately above threshold at various pure-tones,
particularly where thresholds are greater than 70dB. By
using their index finger and thumb in the shape of a
"C", the patient should be instructed to indicate by
proportionate "spreading" of the finger and thumb to
indicate relative loudness increases immediately above
threshold. An example of instructions for this "Loudness
Growth Test" is as follows:
"I would now like you to put your index finger and thumb
together like this (demonstrating, with finger and thumb
together in closed position). I will then give you a
tone, which you can barely hear (at threshold). As I
increase the loudness of this tone, I would like you to
indicate how much of an increase seems to be taking
place, a small amount like this (demonstrating a ¼”
spread) or a larger amount like this (demonstrating a
wider 2-3” spread). Continue to open the distance
between the forefinger and thumb in proportion to the
increase of loudness thereafter. Do you understand?”
Then the specialist may start at an already-established
threshold level of a pure-tone, ascertaining that the
client can detect the tone at that level. Thereafter, as
the intensity is increased by 5dB increments, the
patient may indicate the subjectively perceived rate of
growth by indicating same by gradually (or rapidly)
opening the space between forefinger and thumb. By
comparison to a more normally perceived tone, the
evaluator may determine where a significantly
exaggerated rate of loudness growth occurs, making
appropriate notations on the audiogram for reference in
the hearing aid circuit prescription. A near-normal or
consistent loudness growth is indicated by a small
parting of the finger and thumb (1/2 - 1" distance),
while an abnormal growth is evidenced with a wide spread
of the finger and thumb (2" - 4"). This test is simply a
quick test for selective recruitment, and is useful only
for dispensing purposes. A more clinical approach would
involve the Alternate Binaural or Monaural Loudness
Balance tests (ABLB, MLBT), or other variations on these
techniques (Dix, Hallpike, and Hood, 1948)(Hall, 1991).
The above is not meant to be a textbook instruction on
the mechanics or techniques of pure-tone testing; only a
counseling viewpoint. Fine-tuning of the psychological
and sociological infrastructure of the hearing
evaluation is a hallmark of the professional hearing
instrument specialist. Consequently, the observance of
these principles will inherently result in near
automatic patient compliance in achieving objective
outcomes in pure-tone audiometry.
Speech Testing: A counseling approach
Speech testing for the purposes of adapting
amplification to the impaired ear has long been
recognized as an area of great debate. The purpose of
speech tests in hearing aid testing is both quantitative
and qualitative, and often represents a validation or in
collaboration with pure-tone audiometry. In this section
of the text we'll discuss not only some of the
psychoacoustic considerations as they apply to
counseling, but also some insights into possible
application of the test scores derived from audiometric
speech testing. These observations are intended more for
stimulating thought and increased interest of the
student than for actually providing a comprehensive or
complete review of the materials and techniques
involved.
From a psychological and "ear training" standpoint,
however, there are some important considerations for the
specialist during speech testing. Because of the ear
training aspects needed to properly quantify speech
testing, the author suggests following a specific order
in speech testing (see fig. 5.3):
1) The speech reception threshold (SRT) test to train
for the “floor” or lowest possible functional level of
hearing.
2) Then, the uncomfortable listening level (UCL) or
threshold of discomfort (TD), to establish (and stretch)
the “ceiling” or highest possible functional level of
hearing, before degradation or discomfort.
3) Then, establish the most comfortable listening level
(MCL), now having a good representation of the floor and
ceiling, which will allow the happy medium.
4) Finally, utilizing MCL as the presentation level, the
monosyllabic speech discrimination (SD) tests may be
applied.
Counseling for an accurate SRT
The Speech Reception Threshold or SRT provides a
relative correlation with the pure-tone audiogram, and
is expected to come out at about +or- 5-10dB of the
pure-tone average (PTA). A short-cut method of checking
SRT accuracy is to note if the SRT is within 5dB of the
threshold at 1KHz. This measurement will also act as
calibration standard or reference point for the comfort
and discomfort levels. In totality, the SRT represents
the “floor” of the dynamic range in hearing complex
(i.e., speech) sounds (Martin, 1985). Consequently, if
the SRT does not correlate with the pure-tone scores,
the other speech scores cannot be trusted.
The SRT demands the absolute "attention" of the patient.
The patient begins consciously "training" their ear to
listen for discernible speech sounds at threshold
levels. The word lists used are Spondaic or two syllable
CID/W-1 & W-2 spondee words, which provide evenly
presented familiar words. These words also provide
fairly redundant speech context and inflectional cues
for ease of understanding at the lowest intensity
possible. As stated above, when compared to the
pure-tone air-conduction thresholds, the SRT should
occur within 5-10dB of the pure-tone average (PTA @
.5KHz, 1KHz and 2KHz) of the audiogram (Conn, Ventry, &
Woods, 1972). On the other hand, an accurate SRT can
help expose a patient that did not clearly understand
pure-tone threshold instructions earlier in the test, or
one that would deliberately exaggerate their hearing
loss on the pure tone test, but show considerably better
thresholds on their SRT (Carhart, 1960). When the SRT
comes out 10dB better than the PTA of the pure-tone
test, it behooves the specialist to go back and retest
pure-tones, repeating instructions, before going any
further.
Exceptions to the above rule would include ski-slope,
corner, or reverse slope audiograms. In cases of central
auditory processing disorder (CAPD) such as in phonemic
regression (temporary) or auditory agnosia or aphasia
(which coincidentally require clinical
therapy)(Schuknecht, 1974) the SRT score may be
significantly more elevated than the PTA, or may be
entirely impossible to measure (marked “N/A” or “CNT”).
In difficult-to-test cases, you may instead administer a
Speech Detection Threshold or SDT, also known as the
Speech Awareness Threshold or SAT (ASHA, 1988). The SDT
may also be used where language or vocabulary
limitations interfere with familiarity of the standard
spondaic word lists used for SRT. In either event, it is
important to make appropriate notations on the
evaluation form, with further updated notations in
subsequent post-fitting results. The dialogue for test
SDT is one asking for the subject to simply raise their
hand when they begin to hear speech. You may simply
record that point of dBHL where they indicate hearing
speech, either recorded or monitored live-voice. The SDT
will usually correlate closer to 500Hz or the best
pure-tone threshold, while the SRT generally correlates
closely with the PTA and 1KHz.
To administer the SRT from the Spondaic word list, a
suggested dialog would be as follows:
"Now, you will hear a list of words. Please, repeat the
words the best you can. I will reduce the volume to a
very low level, which will eventually fall below the
level you will need to understand. Don't let this
frustrate you. Just do the best you can by repeating
that which you do hear. For example, I will say, 'Say
the word BASEBALL' and you will repeat BASEBALL back to
me. Do you have any questions?"
As a side-note: The specialist must also ascertain that
there are no visual clues during this test, and to use
the proper level of masking as indicated. While the
objective is to establish the 50% response level, or
threshold, attention should also be given to any
consistent pattern of missed consonantal sounds (such as
“s” or “v”, etc.). This may help later in counseling in
expectations and limitations with amplification, and the
need for added assistive devices or strategies.
Also, the author recommends that when live voice testing
is utilized, that the evaluator consistently use the
carrier phrase "Say the word...." before each word
(Gelfand, 1975). Without a technical discussion about
the use of the carrier phrase, its purpose is two-fold:
1) for consistent modulation and control of the
evaluator's voice, and 2) for psychological preparation
of the patient for a more accurate response to each
individual word. The carrier phrase should be
approximately 5dB louder than the presented spondaic
word. Practice with a sound level meter is of utmost
importance when giving speech tests in live-voice. After
ascertaining over-all loudness with the SL meter, the
evaluator may then rely upon the calibrated vu
(volume-unit) meter on their audiometer to maintain
consistency. To avoid these steps can make live-voice
speech testing into sheer guesswork, and invalidate the
results.
Again, one must observe considerations for masking when
it is indicated. Some professionals maintain that
masking is always needed for an objective SRT, although
it is generally unclear what level of masking is
appropriate when there is no significant difference in
pure-tone thresholds. The author’s feeling is that 60dB
of white noise masking is nearly always a safe level,
without causing undue threshold shifts in the ear under
test. Otherwise, one should use the same basic rules of
masking utilized in pure-tone testing. One rule of thumb
is that when testing outside the sound booth with live
voice, the non-test ear needs always to be isolated with
masking to obtain a more objective result.
When indicated, it cannot be emphasized enough the
importance of proper masking during the SRT. Since we
are seeking threshold levels, masking can make it
possible to achieve true thresholds. In many of the new
digital programmable circuits today, the SRT established
the needed input sensitivity or “floor” for amplified
loudness growth. Even in cases of symmetrical
sensorineural loss, a masking level of 60-65dB in the
non-test ear can further "isolate" the non-test ear from
the ear under test in open, live-voice settings while
administering the SRT.
The SRT should always be derived by using spondaic or
phonetically-balanced words that are in common use. In a
language other than English, it can be a challenge, if
the evaluator is not intimately familiar with that
language. When a list is used that is outside the
everyday vocabulary of the patient the result may be
invalid. For in many cases, we use the SRT to establish
the Minimum Use-Gain Level (MUL), from which we can
predict the bottom-side parameter of tapered gain in the
hearing aid. Furthermore, a proportional relationship
between SRT and gain expectation (which theoretically
becomes the MCL) may shed further light on the loudness
growth picture. For instance, if a patient with
presbycusis exhibits an SRT of 55dB and an MCL of 60dB,
we may safely assume that loudness grows very quickly at
just above threshold. Also, this may be an indication of
reduced gain expectation, such as for a patient who
lives alone in quiet surroundings. This observation can
significantly affect target gain prescription, or the
use of a BILL/TILL type amplification strategy. On the
other hand, in the case of a younger client, who---with
an identical pure-tone audiogram---may exhibit an SRT of
55dB and an MCL of 85dB. In this case, we may assume a
higher gain expectation OR a slower loudness growth
logarithm above threshold.
Stretching expectations with a more realistic UCL
Following the SRT, the UCL is taken, enabling the
patient to establish the loudness end of their auditory
spectrum. Considered the "ceiling" of the dynamic range
of hearing, the UCL provides a most important parameter
for the appropriate fitting of amplification. The
speech-based UCL generally correlates closely with the
SSPL90 HFA in the hearing aid prescription (McCandless,
1983)(Kamm, Dirks, and Mickey, 1978). Ideally, the
circuit output will be no higher, or, possibly, slightly
below the UCL score---usually taken on the
HL-scale---which is taken on the SPL-scale. For speech,
the translation from the HL reading to SPL is
accomplished by adding 20dB to the HL result of the UCL.
Today, with the use of multichannel instrumentation,
UCLs no longer correlate quite so simply, for what would
be considered a fair correlation in a single band device
now appears to be overstated for a multichannel device
(Chartrand, 1999). This is due to the fact that loudness
discomfort levels vary significantly across the range of
hearing, and multiband instruments can be more
discretely adjusted to accommodate the areas of greatest
concern.
There are a number of acceptable approaches to determine
UCL (Stabb, 1997). When utilizing a traditional
dispensing approach, the author strongly suggests the
use of "cold running speech" sentences to determine
broad band (speech band) levels of discomfort
(Chartrand, 1988). The spondaic word list does not
provide enough stimulus running time to allow the
patient’s objective determination of loudness sensation;
whereas running speech allows adequate time for the
patient to determine broadband discomfort level.
Although it is not common practice, pure-tones, warble
tones, or, more preferably, narrow-band masking noise
can also be utilized to determine band-selective UCLs.
These data are called discrete or tonal UCLs, from which
one may more closely determine the proper Maximum SSPL90
parameter of the hearing aid, which in turn will allow
more output headroom for the remaining, less offensive
frequencies. Measuring discrete UCLs will be
particularly important in resolving problem fitting
cases.
To arrive at an accurate speech-based UCL it is
important that instructions be clear and suggestive. The
standard instructions for sentences are:
“You will now listen to a list of sentences to determine
how loud you can tolerate sound intensity before it
becomes uncomfortable for you. I will start at a
moderate loudness and gradually increase the volume.
When it becomes uncomfortably loud, raise your hand to
let me know. We will start with the right ear, and you
will not need to repeat to me. Do you have any
questions?”
In some cases, patients tend to indicate when it’s “too
loud” rather than when it is physically “uncomfortable”.
One of the problems with the UCL is that it can become a
behavioral test rather than one of physical sensation.
In other words, the patient might raise their hand at
only 70dB, which---excepting hyperacusis cases---is very
unlikely to be their true discomfort level. In such
cases you may need to repeat the instructions and add
the phrase, "We will not reach the painful level, but
you may think we are getting close ...". Then, the
patient will be more prepared to "go the limit". On the
other hand, if no mention is made of the possible
top-side expectation of this test, the patient may
instead respond to what they consider is "too loud".
Their conception of what is "too loud" could easily be a
point just above comfortable listening.
An illustration. The older adult may consider the
background music in the restaurant "too loud" when they
are forced to listen because it interferes with an
ongoing conversation or is at a volume higher than they
personally prefer for casual listening. In the same
restaurant sits a teenager who is thinking, “The music’s
too soft. They need to crank it up.” Same music, same
volume, with differing perspectives.
The same variations can exist in determining loudness
discomfort. Therefore, it is easy to arrive at
subjective UCLs, which, if used as a reference for
hearing aid output, may generate unnecessary distortion,
peak-clipping, or an unnecessarily low threshold
kneepoint (TK) below their true UCL. Or, in the other
extreme, if the output is too high (as in the case of
the teenager) it could drive the defective cochlea into
distortion or diplacusis by overloading it, in this case
reaching the hearing aid’s pre-set MPO limit before
reaching or leaving the patient’s PB-Max level. To avoid
evoking a low UCL, it may be best to utilize any of the
available loudness scale charts, such as one described
by Hawkins (1984): very soft; soft; comfortable; but
soft; comfortable; comfortable, but loud; loud, but OK;
uncomfortably loud; extremely uncomfortable; painfully
loud. Placing these incremental designations onto a
rule-type chart, the patient can slide their finger
along the chart to indicate at which level they perceive
the sentences presented in UCL testing.
Where we listen: Finding a more realistic MCL
The most comfortable loudness level or MCL is not a
fixed level of loudness or gain, but rather a range of
loudness (Stabb, 1978). The fact that we typically refer
to the MCL as a singular level sometimes causes
confusion when trying to correlate use-gain levels of a
given hearing aid fitting. The level that meets
“comfort” expectations may not be the same for the
loudness required for maximum speech understanding
(Ullrich and Grimm, 1976)(Clemis and Carver, 1967).
Victoreen and others have long held that MCL ideally
comprises the listener’s preferred level of listening,
and therefore, comprises the happy medium between
comfort and clarity (Victoreen, 1973).
Obtaining MCL may bring a host of other considerations
as well:
· Functional dynamic range: The range from comfort to
discomfort level, or the areas most critical for
determining gain and output. The difference between MCL
and UCL may also assist the specialist in determining by
how much loudness growth will need to be slowed down
when setting compression kneepoint in programmable
instruments.
· Psychoacoustic factors: The acoustical environment in
which the client is accustomed will determine, more than
most other factors, their perception of the level of
comfortable listening above threshold. Those whose
listening tasks are typically within quiet environments
may not exhibit the same practical gain expectation as
one in noisy environments.
· Epithelial atrophy of the stria vascularis:
Presbycusis cases may also exhibit a loss of elasticity
in cochlear tissue, which may have a greater bearing
upon the proximity of MCL to UCL. The same assumption
may hold true for many cases of diabetes, as well.
· Abnormal loudness growth: Recruitment is particularly
a concern when the MCL and UCL are within 15-20 dB of
the other. Ski-slope and corner audiograms may present
the biggest dilemma when attempting to achieve improved
speech understanding by elevation of high frequency
amplification without exceeding discomfort/distortion
levels. Hyper-recruitment at supra-threshold (i.e.,
SRT=65dBHL, MCL=70dBHL) may also be of concern, in that
the rise time or input sensitivity of the hearing aid
circuit may not be sufficient to accommodate head-shadow
effect and distance hearing.
· Central auditory processing problem cases: There have
been reports where slightly elevated MCL (use-gain) has
benefited patients with receptive aphasia. Perhaps the
MCL in these cases is actually set at PB-max rather than
at physiological comfort level. At the other end of the
central lesion spectrum, however, one may experience
reduced selective ability in critical signal-to-noise
situations presumably because of an impaired
neurological system, which may necessitate a reduction
of over-all MCL, particularly in noisy circumstances.
The above factors may have a significant influence on
the patient's perception of what is considered
"comfortable", which possibilities should be noted
during the course of the health assessment/case history
portion of the evaluation. Furthermore, these concerns
may have a substantial effect upon other amplification
parameters, such as output, frequency response, and F1F2
bandwidth. The reader will note the variations of the
test-retest variability of the speech scores for SRT,
MCL, and SRT as illustrated in figure 5.3.
Figure 5.3 Test-retest variables due to subjective
perception during speech tests.
Communicating the nature of the desired response is most
important for obtaining a more objective and
reproducible MCL. Here is one suggested dialog, which
may be used to establish the MCL:
"You will now listen to a list of sentences to determine
a comfortable level of listening. I will start softly,
and gradually increase the loudness. When we reach a
level that sounds most comfortable and easy to
understand, raise your hand to let me know. Are you
ready?"
As the patient responds with raised hand, it is
important that the specialist ascertain that the
response is valid. One way to find out is by speaking
(in monitored live-voice) through the audiometer speech
circuit or master hearing at the indicated level, and
ask, "Is my voice too loud, too soft, or just right for
you?" For this to be a fair comparison, the specialist
will need to be sure that their presentation is of equal
loudness to the just-established MCL reading. Often,
there will be an adjustment or two in achieving a more
objective MCL. If live-voice is used, it is imperative
that the evaluator utilize their audiometer volume unit
(vu) meter to assure peaks at "0". It cannot be
emphasized enough that monitored live-voice speech
testing requires a great deal of practice, and careful
attention to standard practice. Further, it should only
be attempted after meeting the same scientific criteria
as that which has been established for recorded speech
tests.
In the final analysis, the MCL figure is often
considered a subjective correlation of use-gain levels
of amplification in the hearing aid prescription. Hence,
for a custom in-the-ear or canal instrument, an MCL of
60dB may be translated into a use-gain level of
approximately 15dB, subtracting 50dB from the MCL and
adding 5dB for over-all insertion loss, or by
establishing “0” at 45dB on the HL dial. Using the MCL
as a function of gain prediction, in this example, the
prescribed HFA Gain for this instrument (assuming a 2cc
coupler data) would be 25dB with 10dB reserve gain. Most
manufacturers use a similar formula to correlate
predicted HFA or peak gain and the MCL, in which case
the MCL must represent a realistic measure of amplified
speech. Although this measure is considered approximate
and non-frequency-specific, it is otherwise a general
validation of predicted use-gain. The newer target gain
formulae have taken most of these variables into
consideration.
Speech discrimination testing: Measurable outcomes
The reader has probably noted that a great deal more
discussion in this text is being attributed to speech
testing than with pure-tone testing. If that perception
has not already begun to sink in, the section on speech
discrimination will drive home the point! Pure-tone
testing, while basically a behavioral test-battery,
tends to be fairly straightforward and mechanical.
Test-retest variability is relatively small in
comparison to the sometimes-unwieldy considerations in
speech testing. Calibration factors, word and sentence
list efficacy, presentation levels and methods, examiner
involvement, psychosocial dynamics, all contribute to an
immensely more complex process than what is encountered
in pure-tone testing.
Speech discrimination testing tends to be the alter at
which much of the hearing health field worships, for
both cochlear implants or hearing instruments. Arbitrary
candidacy rules based upon speech discrimination
improvements often apply, sometimes in disregard to
other aidable dimensions and outcomes. The most common
monosyllabic word lists used today for speech
discrimination tests in adults are the CID W-22, NU-6,
and CNC lists (Olsen and Matkin, 1991). Indeed, a
perusal of dozens of textbooks and the literature in
general reveal whole books and chapters written on these
speech discrimination tests. With such profound interest
in speech discrimination, it would seem that relevancy
of scoring methodology of discrimination tests to
hearing aid performance would be explored to at least
the same degree as other considerations. But that is not
the case. For purposes of fitting hearing aids, outcomes
have been both variable and incomplete, if not poorly
applicable to the kinds of high frequency audiograms
that comprise the majority of the specialist’s patient
base: mild to moderate and mild to severe sensorineural
losses. To provide an important outcome that measures
amplification benefits, speech discrimination testing
must be sensitive enough so as not to encounter early
ceiling effects, or to be plagued with gross-scoring
artifact.
Instead, specialists too often find themselves having to
defend the need for amplification for a patient that
exhibits such typical sensorineural audiometric scores
as: 250Hz=15dB, 500Hz=20, 1000Hz=35dB, 2000Hz=55dB,
4000Hz=80, and 8000Hz=65. The speech discrimination
score, in our hypothetical case, is a respectable 78% in
quiet. Looked at in the traditional interpretation it is
hardly bad enough to justify the level of motivation it
will require to overcome the psychosocial hurdles
preventing the patient from moving forward. Let’s say
the patient, by chance, is motivated enough to go on a
thirty-day trial. Upon delivery of the new instruments
an aided discrimination score of 86% is found, a mere 8%
improvement in quiet. But then there’s the untold side
of this scenario:
First of all, the patient’s chief complaint was about
hearing in noise and at distances, two situations
repeatedly encountered in a typical day. Indeed, he
claimed to hear “fine” one-on-one and in quiet. The
reason there showed only an “8% improvement” is because
of the all-or-nothing discrim scoring method, which
treats the three phonemes of each monosyllabic word as
one entity. But there were improvements, not measured in
the traditional scoring approach. When we go back and
use a phoneme recognition scoring method, such as that
developed by John K. Duffy, Ph.D. (1988), we find that
aided speech discrimination rises to 96%, for a 18%
improvement in quiet, and that’s before subsequent
post-fitting adjustments and adaptation over the next
60-90 days. Because each corrected phoneme is counted
(as opposed to word-units) we witness substantial speech
discrimination improvements, which would also positively
impact function in both noise and at distances.
In far too many cases the benefits of amplification have
been underexposed and unmeasured because of traditional
methodology. This can present an additional counseling
challenge for the specialist, but not one that cannot be
overcome by a change in methodology. Let’s now review
Duffy’s rationale:
The foundation for hearing rehabilitation is optimum
audibility of the sounds needed for speech perception.
For the hearing-impaired person the audibility of speech
sounds can only be provided through appropriate
selective amplification.
He goes on to observe that many professionals are
awaiting the magical technology that will bring
sophisticated and advanced means of a "hearing aid
selection and evaluation procedure which includes the
entire hearing mechanism from the hearing aid to the
brain." All the while, he says, we already have the
procedures, the equipment, and the understanding to
accomplish the desired goals. He goes on,
To truly evaluate the effectiveness of amplification for
speech communication one must discover the degree to
which the sounds of speech are made audible to the
client. This can be done through phoneme recognition
testing. (Emphasis added).
We will not be able to give adequate space or the needed
precision to describe Dr. Duffy's techniques. However,
we will attempt to whet the reader's appetite for what
this author feels is the most reliable speech
discrimination methodology available today. First of
all, he shatters the age-old practice of "all or
nothing" discrim scoring, treating each phonetically
balanced (PB) word as one entity. Instead, each PB word
becomes three phonemes, with one point assigned to each.
A phoneme is defined by Yule (1990) as
"meaning-distinguishing sounds in a language”. Hence,
when the patient, upon being given the word "c-a-t"
responds with "c-a-p", the score is not "0" correct, but
instead "2" phonemes correct out of "3" possible. In the
comparison of aided and unaided scores the difference
can be dramatic when utilizing Dr. Duffy's method, while
the traditional method often "masks" the true state of
the corrected ear. Since the phoneme scoring method is
frequency specific, the affected components of
deficiency may be identified for remedial purposes. See
figure 5.4 for an illustration of the scoring method. |
