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OCR for page 32
Measurement Procedures
For both theoretical and practical reasons, it is impor-
tant to obtain characterizations of tinnitus--spectral
location, degree of spectral complexity, magnitude, etc.--
that are as accurate as possible. Unfortunately, little
basic research has gone into the important psychophysical
questions of: (1) comparability of the various existing
measurement procedures, (2) their test-retest reliabili-
ties, (3) their relative efficiencies with different types
of patients, etc. Such research may be unexciting, but
it is necessary as a basis for establishing a standardized
test procedure.
The reader should keep in mind throughout this section
on tinnitus measurement that for many people tinnitus is
not constant in character, either within a day or across
days. This raises two problems: (1) the psychophysical
procedures, which are already unusual and troublesome for
many naive subjects, can be made additionally difficult
and frustrating by short-term fluctuations in the tinni-
tus; and (2) these short-term and long-term fluctuations
necessarily create an uncertainty as to whether what is
measured on a given day is truly representative of the
tinnitus experienced by the sufferer.
Basically, there are three questions one might ask
about a tinnitus: What is its quality? What is its
spectral location? What is its magnitude? We consider
these questions in turn.
QUALITY OF THE TINtIITUS
What is the perceived quality of the tinnitus? This ques-
tion pertains to both its temporal and its spectral char-
acteristics. Does it sound continuous, fluctuating,
32
OCR for page 33
33
interrupted, etc.? Is it spectrally simple--tonal or
reasonably narrowband--or is it spectrally complex--
wideband, multiple but relatively discrete frequency
regions, etc.? From where does it seem to emanate--one
ear, both ears, somewhere inside the head, etc.? It is
intuitive that different tinnitus qualities would be
associated with different sites of origin and, thus, that
information about quality would be important in diagnosis.
Unfortunately, tinnitus quality is rarely an accurate
guide to site of origin. Some exceptions are the pulsa-
tile tinnitus of objective vascular origin and the low-
frequency roaring tinnitus of Meniere's Disease and
otosclerosis.
Most of what we know about the quality of tinnitus
comes from patients' self-reports, a procedure that is
fraught with problems. For example, we cannot be sure
that when two patients use the same word to describe their
tinnitus--(say) "chirping" or "chuggingn--they mean the
same thing. Different people have had different acoustic
experiences and, as a consequence, may use words differ-
ently. What a "high-pitched squeal" is to a piccolo
player and to a nonmusician who has considerable high-
frequency hearing loss obviously could be very differ-
ent. Further, the words chosen by a tinnitus sufferer as
best describing his or her experience may or may not touch
upon all of the dimensions of interest to the scientist,
and, unfortunately, the questioner may not always ask the
follow-up question(s) necessary to discover the omitted
information. Standardized procedures for gathering infor-
mation on tinnitus quality would be welcome and valuable.
With the various problems of self-report procedures in
mind, let us consider some results.
Heller and Bergman (1953) supplied a list of 39 words
used by 80 normal-hearing and 100 hearing-impaired sub-
jects to describe their tinnitus. For those with normal
hearing, "hum, "buzz, n nring, n and "pulse" were used by
18 percent, 15 percent, 12 percent, and 8 percent, respec-
tively. For the hearing-impaired, "ring," nbuzz,n "hum,"
and "whistle" were used by 30 percent, 11 percent, 10 per-
cent, and 9 percent, respectively. Reed (1960) reported
that about 70 percent of his 200 patients used "steam,"
"ring, n or "buzz"; he also noted that the patients' de-
scriptions were not predictive of site of lesion--an un-
fortunate but common finding.
Some attempts have been made to acquire more objective
information about the quality of tinnitus. Goodhill
(1952) supplied patients with recordings of 27 different
OCR for page 34
34
sounds created to mimic previous descriptions of tinnitus.
Patients were asked to indicate which sound was the most
like their tinnitus, but only a few cases were reported.
Hazell (1979b, 1981c) has developed a procedure that has
much appeal. He uses a commercially available music syn-
thesizer to create imitations of the patient's tinnitus.
The procedure is said to be time-consuming--sometimes tak-
ing as long as 2 hours--but rewarding to the patient and
informative to the experimenter. The patient is pleased
to finally have a nonverbal way of communicating his ex-
perience to family, friends, and the clinician, and the
experimenter discovers the wide range and richness of
tinnitus experiences. One finding particularly worthy of
note here is that tinnitus described as tonal by many
patients is much more complex than a tone--a common
product was a single frequency embedded in a less-intense
narrow band of noise. To date about 200 patients have
been studied in this way. Only preliminary findings are
yet available, but these indicate that about 83 percent
of the synthesized waveforms are nonpulsatile, about 52
percent involve a narrowband noise, and about 39 percent
a tone, singly or in combination. Correlations of tin-
nitus quality with presumed site of origin have yet to be
reported.
Related to this question of quality is the matter of
the characteristics of the tinnitus in the two ears.
Logically, there are multiple possibilities. The tin-
nitus might be strictly monaural. It might be binaural
and very similar in the two ears. It might be binaural
and of similar spectral and temporal characteristics but
not of equal magnitudes in the two ears (see "Is the Tin-
nitus Monaural or Binaural? n in this chapter). It might
be binaural and of quite different spectral and/or tem-
poral characteristics in the two ears--(say) tonal in one
ear at one frequency and rather broadband in the other
ear at a different frequency. m is issue of possible
binaural differences in tinnitus has not been extensively
studied, but clearly it is important (and may explain
some of the failures of (monaural) devices like tinnitus
maskers/instruments to alleviate tinnitus). Until more
is known, it should be clear that the pitch-matching and
masking procedures described below should be done with
headphones, not free-field presentations, so that there
is at least the opportunity for the patient and the
examiner to detect different origins for different
aspects of the tinnitus.
OCR for page 35
35
SPECTRAL LOCATION OF THE TINNITU S
If the tinnitus is reasonably narrowband or tonal, where
is it located spectrally? Two basic procedures--with
numerous major and minor variations on each--have been
used to obtain measures of the spectral location of a
tinnitus.
Pitch Matching
As the name implies, in pitch-matching procedures the
objective is to obtain from the subject a match in pitch
between the tinnitus and a sound supplied by the experi-
menter. Fowler (1928) and Josephson (1931) were among
the first to use pitch-matching procedures. In the most
common procedure, the matching sound is tonal; it is pre-
sented to the ear contralateral to the one the patient
believes contains the tinnitus (see "Is the Tinnitus
Monaural or Binaural?" in this chapter); it is interrupted
at a regular rate; and it is not adjusted by the patient,
but by the experimenter on the basis of responses made by
the patient.
While pitch matching is perhaps the most intuitive pro-
cedure for ascertaining the spectral locus of a tinnitus,
it is, unfortunately, subject to major problems. For one
thing, tinnitus is often not strictly tonal in quality
(see "Quality of the Tinnitus" in this chapter), which
makes matching to tonal stimuli both very difficult and
of questionable value once accomplished. Further, in the
best of circumstances, pitch matching is a difficult task
even for highly practiced subjects, let alone for rela-
tively inexperienced patients. In both populations, it
is common to see so-called octave errors--settings for a
match that are actually twice or one-half the frequency
of the sound being matched (see Vernon, 1977). Pitch-
matching procedures have their place in tinnitus diag-
nosis, but the results must be interpreted with special
care.
The problem of octave errors is particularly bother-
some when interpreting pitch-matching data obtained from
tinnitus patients. One reason is that tinnitus patients
are often given only the sounds available from a standard
audiometer for use in matching their tinnitus. That is,
frequencies above about 6-8 kHz are often not available
to the patient. Among the problems raised by this equip-
ment limitation is the possibility that the tinnitus
OCR for page 36
36
frequency is being greatly underestimated in many cases
of high-frequency tinnitus. As noted above, about 64
percent of tinnitus sufferers match their tinnitus to
frequencies in the range 3-8 kHz.
But, since the fre-
quencies available on audiometers are rarely higher than
about 8 kHz, it would be impossible for a patient with
tinnitus at (say) 12 kHz to reveal that fact; his "best
match might be a 6-kHz tone or noise band. The use of
standard audio oscillators or of the recently introduced
tinnitus-measuring devices (e.g., Voroba, 1979a) would
reduce this problem of underestimating tinnitus frequency.
Furthermore, all tinnitus examination protocols should
include a procedure to verify that any pitch match pro-
duced by a patient is not in error by one or more octaves
in one direction or the other (Vernon and Meikle, 1981).
Penner (personal communication) has recently completed
an extensive study using a pitch-matching procedure.
Three sensorineural subjects with a history of noise ex-
posure made approximately 80 matches over the course of 4
weeks. m e surprising finding was that for all subjects
the frequencies chosen as matches to the tinnitus had a
tremendous range across sessions--from 2 to 5 kHz for
A similar effect was briefly noted
different subjects.
by Voroba (1979b). If this finding is confirmed, it will
have great theoretical and practical importance. Nearly
all tinnitus sufferers comment on the fluctuating nature
of their perception, but it seems safe to assert that few
investigators realized that it varied so much in fre-
quency. If it does, it has obvious implications for the
design of tinnitus maskers/instruments (see "Tinnitus
Maskers/Instruments" in Chapter 4).
Masking
m e second basic procedure for estimating the spectral
locus of tinnitus, masking, has the appearance of being
free from some of the problems of the pitch-matching pro-
cedure. In masking, a relatively narrowband (octave or
one-third octave) stimulus is swept across the spectrum
in successive steps and at each is adjusted in intensity
until the tinnitus is just masked. me spectral location
at which the least masker intensity is needed is taken as
the locus of the tinnitus. This procedure is attractive
because it appears to be more accurate than, and to lack
some of the problems of, the pitch-matching procedure--
the task seems to require less sophistication and prac
OCR for page 37
37
Lice than pitch matching, and octave errors are less
likely to occur. One problem noted with pitch matching
applies to masking as well: if the tinnitus lies beyond
the range of the equipment, such as a standard audiometer,
it may be maskable, since lower frequencies can mask
higher ones, but inferences drawn about the spectral locus
(and the magnitude) of the tinnitus will be in error.
There is another problem that is not so much pro-
cedural as it is evidence of the great variety of maladies
that can underlie tinnitus: in some patients the tinnitus
cannot be masked, and in some others it can be masked by
nearly any weak tone or noise band. Feldmann (1971) re-
ported that the tinnitus in about 11 percent of his 200
patients was completely refractory to masking; they tended
to be the patients with the most severe sensorineural
losses. At the other extreme, about 32 percent of Feld-
mann's patients reported masking of their tinnitus when
any weak sound was presented; these tended to be patients
having flat hearing losses due to Meniere's Disease, sud-
den deafness, or otosclerosis. One must assume that, for
this latter group, tinnitus must not have been much of an
everyday problem, since environmental noise would pre-
sumably be adequate to mask the tinnitus. Vernon et al.
(1980) confirm Feldmann's observations that masking of
tinnitus is different from masking of real sounds in a
number of ways. This issue is addressed in the section
"Some Ways Tinnitus Is Not Like an External Sound" in
this chapter.
Related Masking Results
Another interesting finding by Feldmann (1971, 1981)
deserves note and further study. In some patients with
monaural tinnitus, he claims to have been able to mask it
with tones and noise bands delivered to the opposite ear
(also noted by Josephson, 1931). Feldmann argues that
the obvious interpretation of cross-conduction can be
excluded; in fact, the intensity necessary to mask the
tinnitus was often less when presented to the contra-
lateral ear than to the ipsilateral ear.
Apparently he
saw this contralateral masking effect most regularly with
Meniere's and sudden deafness patients, but it was also
present in presbycusic and noise trauma patients.
Note that a contralateral masking effect can be ex-
plained in a least two ways:
OCR for page 38
38
1. The contralateral masker in some way produces a
reduction in the tinnitus signal at its source. By way
of an example. the efferent mechanism might be activated,
, _ _ ,
thereby causing a change in the hair cells or primary
fibers in the contralateral (tinnitus-producing) ear.
This alternative is meant to encompass Feldmann's own
suggestion of a "neural mechanism of contralateral
inhibition."
2. m e contralateral masker accomplishes a n true"
masking at some neural level where information from the
two ears is combined (the tinnitus might be originating
at this neural level or at a more peripheral level and
Just passing through"). m is alternative shares some
features with so-called central masking (Zwislocki et
al., 1968), but the latter is typically smaller in mag-
nitude than is contralateral masking of tinnitus. Cur-
iously, the possibility of contralateral control of tin-
nitus has not been extensively explored by the advocates
of tinnitus maskers/instruments (see "Tinnitus Maskers/
Instruments" in Chapter 4; CIBA Foundation, 1981:174-175).
... . .
An important finding recently rediscovered by Feldmann
(1971) is that for some patients the tinnitus does not re-
turn immediately upon termination of the masker. Rather,
termination is followed by a silent period and then a
period of gradually returning tinnitus. (This effect was
·
previously noted by Spaulding [1903] and by Josephson
[1931].) In an example shown by Feldmann, a 500-msec
masker produced anywhere from about 1.0 to about 2.5
seconds of posttermination silence, depending upon the
masker's intensity and the ear to which the masker was
delivered. He indicates that in other patients the
silent period was much longer than this, and he raises
the prospect of trying to n train" the mechanism ',nder-
lying the effect. m is period of silence or diminished
tinnitus magnitude has since been named residual inhi-
bition (Vernon, 1977). It is a topic to which we return
in "Residual Inhibition" in Chapter 4.
Formby and Gjerdingen (1980) studied masking in a
single tinnitus sufferer using a procedure similar to
that widely used in experiments on the so-called psy-
chophysical tuning curve. The tinnitus was viewed as a
signal, and each of a set of pure-tone maskers was ad-
justed in turn until it "just masked" the tinnitus. When
the signal is an external tone, the pattern of masker
intensities obtained with such a procedure has a charac-
teristic shape (see Small, 1959); relatively little
. _ .
. _ ~_
OCR for page 39
39
intensity is needed when the masker frequency equals or
is close to that of the signal, and increasingly greater
masker intensity is necessary for masker frequencies
increasingly distant from the signal, with the slope
being steeper on the high side than on the low side of
the signal. Formby and Gjerdingen obtained this same
general pattern when the signal to be masked was a tin-
nitus. m is masking procedure has the virtue of providing
a relatively precise estimate of the spectral locus of
the tinnitus--be it tonal or narrowband--but it has the
drawback of being relatively time-consuming and thus may
not see wide application clinically. Relevant to the come
mon assertion that tinnitus magnitude fluctuates greatly
is the observation by Formby and Gjerdingen that substan-
tially different masker levels were necessary in differ-
ent sessions to mask the tinnitus. The range was about
40 dB in the most extreme case, and 15-20 dB was not
uncommon.
One finding by FormbY and Gierdingen (1980) deserves
_ _ _
further study, for it has important theoretical ana prac-
tical implications. They found that when the tonal mask-
ers were binaural, they had to be between 8 and 15 dB more
intense in order to mask the tinnitus than when they were
monaural. Such an outcome is reminiscent of a phenomenon
obtained with external sounds, known as the masking-level
difference or MLD (reviewed by McFadden, 1975). If veri-
fied to exist in some forms of tinnitus, the MLD might
eventually prove useful in diagnosing the site of origin
of the tinnitus.
Penner (personal communication) used both pitch match-
ing and tonal masking (psychophysical tuning curves)
across a number of sessions with the same subjects and
found that the intersession variability for pitch match-
ing was much higher than that for masking. There are a
number of possible explanations for this outcome. One is
that pitch matching is a less reliable procedure than
masking for determining the spectral locus of tinnitus.
Another is that the procedure is accurate but that tinni-
tus can somehow fluctuate in pitch without a concomitant
fluctuation in its maskability. m is matter deserves
further attention.
Another intriguing feature of the relationship between
masking and tinnitus has been discovered by Penner et al.
(1981). Twenty patients were studied, all having tonal
tinnitus and all diagnosed as having sensorineural hearing
loss as a consequence of noise trauma or exposure (recall
that, by Feldmann's [1971] account, such patients consti
OCR for page 40
40
tute about 34 percent of tinnitus sufferers). m e task
was to continuously adjust the intensity of a broadband
noise so as to keep masked either the tinnitus, in some
runs, or, in other runs, a real tone of about 10 dB sensa-
tion level (SL)--decibels above the patient's own absolute
threshold at a given frequency. As expected, for the real
tone, 90 percent of the subjects needed essentially the
same intensity throughout the 5-minute test period; that
is, the signal-to-noise ratio remained the same. When
the task was to continuously mask the tinnitus, however,
all of the subjects showed a need for increasing intensity
during the first few minutes of listening. The changes
were considerable, averaging about 30 dB across subjects.
The typical trend was for a rapid change in the necessary
intensity over the first 10-15 minutes, followed by a
flattening of the function. Penner et al. (1981) explain
this curious outcome by noting that throughout the presen-
tation of the masking noise and real tone, the firing
rates of primary auditory neurons (and thus, perhaps, the
rates of neurons throughout the auditory system) would de-
cline with time, but because both masker and signal were
being about equally affected, the noise intensity for
equal masking would stay about the same. mat the inten-
sity does not remain the same when masking the tinnitus
implies either that external sounds and peripheral tinni-
tus do not affect primary fibers in the same way or that
in these subjects the tinnitus is originating at a site
beyond the (adapting) primary fibers being activated by
the masker.
As Penner et al. (1981) note, their outcome has impor-
tant implications for one of the most puzzling problems
of tinnitus--why its annoyance seems so out of proportion
to its loudness. It may be that, for some patients, real-
world sounds "fade" under continuous presentation, but
the tinnitus does not and thus continues to annoy even in
relatively high-noise backgrounds. The Penner et al.
finding may also prove to be of great practical signifi-
cance. Clearly, those tinnitus sufferers for whom con-
tinuous maskers lose effectiveness through time should
not be treated with continuous maskers, but with inter-
mittent maskers so that masker level--and, thereby, the
risk of additional hearing loss--can be minimized.
(Parenthetically, Penner [personal communication] finds
that only about one-third of her (highly selected) tin-
nitus patients experiences residual inhibition following
presentation of her maskers.)
OCR for page 41
41
Penner (1980) has introduced a variant on the basic
masking procedure that is attractive because it offers
the twin prospects of being more accurate and more infor-
mative about the tinnitus. The experimenter begins with
a broadband noise, adjusts it to just mask the tinnitus,
.. . . . , ~ .. .
e
and then begins to (say) low-pass the noise in successive
steps until the patient again hears the tinnitus. mi s
value is noted, the noise is again made broadband and is
now high-passed in successive steps until the tinnitus is
again heard. The resulting pair of cutoff frequencies--
the "masking interval"--is taken as the bandwidth of the
tinnitus.
As noted above, the possibility of binaural tinnitus
that is not spectrally or Qualitatively similar in the
two ears points out the need for masking measurements to
be made using headphones, with monaural presentations made
first to one ear and then the other, while the contralat-
eral ear receives a broadband masker of reasonable inten-
sity. This may, for the first time, allow the patient to
identify the respective origins of a complex, binaural
tinnitus.
Finally, a comment is necessary about people suffering
from tinnitus who hear about masking as a treatment and
wish to learn whether their tinnitus is of the maskable
type. People may have heard about the common use of
interstation FM noise
as a masking source for tinnitus
and may attempt to use it in a self-conducted maskability
test. If people choose a small, inexpensive pocket radio
for this test, however, they run the risk of reaching the
wrong conclusion about the maskability of their tinnitus,
because the speaker system on such a radio will not ordi-
narily be able to transduce the high frequencies at high
levels. Emus, there may be failure to mask a high-
frequency tinnitus, not because it is inherently unmask-
able, but because sufficient high-frequency energy is not
present. Tinnitus sufferers wishing to use ~nterstat~on
FM noise to test themselves for masking effectiveness
should be encouraged to use a speaker system of reasonably
high fidelity.
. . . · . . .
,
Either for the purposes of this test or
for the purposes of relief, use of a standard home stereo
system is to be further preferred over a cheap radio,
because a stereo system will allow the sufferer to selec-
tively emphasize the high- or low-frequency regions to
some extent, and thus it offers the prospects of
effective masking at lower overall sound levels.
OCR for page 42
42
MAGNITUDE OF THE TINNITU S
What is the magnitude of the tinnitus? The masking
procedures described above for estimating the spectral
locus of the tinnitus might also be thought of as measures
of tinnitus magnitude--the greater the intensity necessary
for masking (at the frequency requiring the least mask-
ing), the greater the tinnitus strength must have been.
Without denying this view, it must be noted that measures
of tinnitus magnitude based upon masking procedures should
be regarded as indirect at best, for a number of relevant
factors are necessarily uncontrolled across patients, and
these make conclusions and comparisons difficult. For
example, the intensity necessary for masking will be
affected by the relative widths of the noise band used
for masking and the patient's critical band at the tin-
nitus frequency. Also, using a masking procedure to esti-
mate tinnitus magnitude is questionable in those patients
for whom maskers at any frequency are equally effective,
and, of course, it is impossible in patients whose tinni-
tus cannot be masked.
Many auditory scientists believe that a more direct
measure of tinnitus magnitude is obtained from loudness-
matching procedures (see Scharf, 1983) than from masking
procedures. Loudness matching is similar in concept to
pitch matching, and, as shall be seen, they have some
mutual problems. Minton (1923) and Fowler (1928) were
among the first to use loudness-matching procedures.
In its purest and simplest form, loudness matching
would proceed as follows. The tinnitus would be strictly
monaural and either tonal or relatively restricted spec-
trally. A sound that is the best match possible to the
quality and pitch of the tinnitus would be periodically
presented to the ear opposite the tinnitus, and the pa-
tient would adjust its intensity (directly or indirectly
by responses to the tester) until it matched the loudness
of the tinnitus. There are several obstacles to this
ideal case:
1. Quality, pitch, and loudness judgments are clearly
all mutually interdependent--the best pitch match cannot
be achieved until the loudness is known, etc. The solu-
tion would appear to be to first get rough measures of
all three characteristics and then to use this informa-
tion when getting more precise measures (see below).
2. Tinnitus is often binaural and not intermurally
identical in magnitude or spectral locus, so the choice
OCR for page 44
44
With these comments in mind, let us examine some of
the available data on tinnitus magnitude. After finding
the best-quality matches and pitch matches that he could,
Reed (1960) used a binaural matching procedure to estimate
the magnitude of tinnitus. He found that about 69 percent
of his patients needed 10 dB SL (sensation level) or less
to match the loudness of their tinnitus, and only 5 per-
cent needed more than 30 dB SL. While this widely cited
survey is informative, interpretation of the data is
hampered by obstacle 5 noted above; namely, when there
are intermural differences in audibility in the spectral
region of the tinnitus and the match is reported in terms
of SL in the contralateral ear, there is necessarily un-
certainty about the actual intensity needed for the match.
Graham's (1960) data are similar to Reed' se-about 75 per-
cent of the patients needed 10 dB SL or less, and only
about 4 percent needed more than 20 dB SL. Vernon et al.
(1980) have asserted that patients are "inordinately
reliable" in making loudness matches to their tinnitus;
they claimed that test-retest comparisons rarely reveal
differences of more than about 1 dB (also see Goodwin and
Johnson, 1980b). This claim is remarkable and worthy of
additional study, for highly practiced normal listeners
show much greater variability than this in alternate
binaural loudness balance (ABLB) tasks (e.g., McFadden
and Plattsmier, 1982b). It is difficult to attribute
this high reliability to the presence of recruitment, for
even if small increment thresholds did accompany recruit-
ment (see McFadden and Plattsmier, 1982a), Vernon and his
colleagues see patients having tinnitus of various eti-
ologies, and not all of these patients have recruitment.
For the sake of completeness, it should be noted that
psychophysical methods other than masking and loudness
matching might be adapted for use in estimating tinnitus
magnitude. For example, with cross-modality matching
(Stevens, 1966; Scharf, 1983), the subject would adjust
the intensity of a stimulus presented to another modal-
ity--a light or a vibrator, say--until its magnitude
equaled that of the tinnitus. To our knowledge, this has
never been attempted with tinnitus. In other tasks reli-
able data have been obtained with this procedure; however,
those subjects were typically rather well educated and
sophisticated, and it is unclear whether cross-modality
data from average people suffering from tinnitus would
accurately represent tinnitus magnitude. One virtue of
the procedure is that data can be obtained rapidly, so a
simple test of the usefulness of the method should be easy
OCR for page 45
45
to implement. As another example, Goodwin and Johnson
(1980a) have suggested reaction time as a measure of tin-
nitus magnitude.
ANNOYANCE OF THE TINNITUS
As we have seen, typical measures of tinnitus magnitude
indicate that it is rarely matched to sounds greater than
about 30 dB SL, and it is often difficult for the nonsuf-
ferer to understand how such apparently weak sensations
can cause such great annoyance and distress to some tinni
tus sufferers. At the root of this misunderstanding are
two errors--presuming that near-threshold intensities
cannot be perceived as loud and equating loudness with
annoyance. Let us first consider the latter issue.
Numerous everyday examples testify to the lack of a
simple relationship between loudness and annoyance. A
buzzing fluorescent light can be extraordinarily irritat-
ing even though its level is below 30 dB SPL, while an
air conditioner or heater bringing relief from the weather
goes unnoticed at 50-60 dB SPL. A passing motorcycle
that masks a segment of the evening news broadcast is
more annoying than is the kitchen appliance being used to
prepare the evening meal, even though the latter masks
the same news segment. A neighbor's stereo system is more
annoying than one's own even when 40 dB less intense. The
barely audible crinkling of a cellophane candy wrapper can
be highly distracting and annoying even during the loudest
segment of a concerto with full orchestra.
Beyond everyday examples, the noncorrespondence between
physical and psychophysical measures of sound and its
capacity to annoy has long plagued scientists interested
in quantifying annoyance (see, for example, Fidell, 1978;
Schultz, 1978). The so-called "message of the noise~--
while frequently difficult to measure beforehand--is far
more predictive of annoyance than are physical measures
of the sound involved. For example, airline employees or
military dependents living at the foot of a jet runway
are far less likely to complain about the aircraft noise
than are neighbors whose livelihoods derive from other
activities. And the noise from delivery trucks is far
more annoying to neighbors than it is to the recipient of
the delivery. There is evidence that in some situations
annoyance is nearly synonymous with speech interference
(Fidel!, 1978), but this finding probably has little rele-
vance to most tinnitus cases, where speech intelligibility
is essentially unaffected by the tinnitus. Interference
-
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46
with sleep is a common source of annoyance, but, somewhat
surprisingly, tinnitus produces sleep difficulties for
only about one-half of tinnitus sufferers (CIBA Founda-
tion, 1981:27).
Various writers have revealed a misunderstanding about
the loudness/annoyance relationship when discussing tin-
nitus. Fowler (1942, 1943) was among the first to note
the poor correlation between annoyance and psychophysical
measures of tinnitus magnitude. He talked of the "illu-
sion of loudness" of tinnitus and claimed that through
conscientious effort the clinician could eventually di-
minish or abolish the illusion. One suggested step was
to have the patient perform a loudness match--which would
invariably be achieved with a relatively weak sound--and
then to present this sound while emphasizing to the pa-
tient that it obviously did "not correspond to his state-
ments as to the severity of the symptom" (p. 397). The
clear implication is that Fowler did not accept the pos-
sibility that a tinnitus could behave differently from a
weak external sound in its ability to produce annoyance,
an attitude that is not uncommon today.
More recent discussions of the discrepancy between the
apparent magnitude and the annoyance of tinnitus have
tried to emphasize the possibility of a basis for the
effect other than a "psychological" one. The reader
should recall here that tinnitus magnitude is typically
reported in units of SL--decibels above the subject's own
absolute threshold at that frequency.
So, if hearing
loss is substantial, a small value of SL will correspond
to a large SPL. Appreciating this fact, Vernon (1976)
suggested that the small tinnitus magnitudes reported
might somehow be under the influence of a mechanism like
the one functioning in certain pathological conditions to
produce recruitment of loudness. Recruitment is defined
as an abnormally rapid rate of growth of loudness; its
effect is to render sounds well above (a pathology-
elevated) threshold to be essentially normal in loudness
even though weak sounds only 20-30 dB above threshold are
depressed in loudness. Vernon (1976) suggested a "super-
recruitment" might be operating on some forms of tinnitus
to make them more loud, and thus more annoying, than they
might seem. This explanation is unlikely to be univer-
sally applicable, for recruitment is present in only some
of the pathological conditions that are routinely accom-
panied by annoying tinnitus, but the proposal is worthy
of study.
Goodwin and Johnson (1980b) attempted a test of the
Vernon proposal using a small sample of tinnitus suffer
. .
-
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47
ers of different types. They compared loudness matches
obtained with two procedures: a standard alternate
binaural loudness balance (ABLB) and a monaural method
that used a matching tone whose threshold was in the nor-
mal range (and thus was presumably free from recruitment
even if the tinnitus frequency was not). The result was
that the estimated magnitudes of tinnitus were, in every
case, greater with the monaural than with the binaural
procedure, and the conclusion was that tinnitus magnitude
is frequently underestimated due to the contribution of
recruitment. (While this may be a correct conclusion, it
is also possible that for some subjects the results are
complicated by the fact that, in order to find a matching
frequency having a normal threshold, frequencies below
about 1000 Hz had to be used, and these frequencies are
known to have steeper loudness functions than tones
between 1000 and 4000 Hz [Scharf, 19781--that is, they
have a Normal recruitment.n) The Goodwin and Johnson
results imply that the apparent discrepancy between the
magnitude and the annoyance of tinnitus may be due in
part to underestimation of the magnitude. Tyler and
Conrad-Armes (no date) arrived at a similar conclusion
using similar procedures.
Penner et al. (1981) have suggested that the high an-
noyance of tinnitus may in some cases be due to its fail-
ure to behave like an external sound once it gets into
the central nervous system. In particular, Penner et al.
point to their demonstration that a constant external
sound can gradually lose its masking power over a tinni-
tus through the course of about 30 minutes of continuous
listening, while it does not over a second external
sound. Whatever the eventual neurophysiological explana-
tion of this effect it is clear that the tinnitus is be-
having aberrantly.
Expanding on the comment of Penner et al., it may be
that this and other aberrant behaviors "bring the tinni-
tus to the attention" of certain neural mechanisms that
persist in unsuccessful attempts to force the tinnitus to
conform to the behavior of external sounds and that their
ongoing failure reaches consciousness as annoyance. It
is difficult to make this idea any more concrete at this
time, but an analogy to sound localization comes to mind.
When dichotic sounds are presented to a person's ears over
headphones instead of in the normal, free-field manner,
the sounds are not perceived as originating from external
sources, but are perceived as having an intracranial
origin. Various explanations of this phenomenon exist,
but a long-standing one points to the fact that with head
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48
phones the waveforms are not altered as they ought to be
by normal head movements. The "expectations" of certain
neural networks are not met following certain motor ac-
tions, and this gives rise to a unique perceptual experi-
ence--not annoyance, to be sure, but the analogy neverthe-
less appears relevant.
Finally, we return to "psychological" explanations of
the apparently disproportionate annoyance of some tinni-
tus. Glass and Singer (1972) have studied the stress-
inducing properties of noise exposure and have found
evidence of much greater cognitive, emotional, and phy-
siological effects when the schedule of noise presenta-
tions was perceived as being beyond the control of the
subject. Perception of control greatly reduced the aver-
siveness and the aftereffects of the situation. This out
come is reminiscent of the comments made by some success-
ful users of tinnitus maskers/instruments when attempting
to explain their apparently paradoxical preference for one
continuous sound (the masker) over another (the tinnitus).
These patients often comment on the control they have over
the masker. m ey can turn it on and off, change its in-
tensitY etc.. while their tinnitus is nearly totally out
, ,
of their control--whatever changes it undergoes bear no
immediately apparent relation to anything the patient has
factor of tinnitus, it is necessary to consider several
facts. First of all, since the loudness of real-world
sounds is not a good predictor of their annoyance, it is
not reasonable to expect that it would be for tinnitus
either. Second, the low sensation level of most tinnitus
does not mean it is not unpleasantly loud. Finally, tin-
nitus does not behave like external sounds in a number of
ways, and this aberrant behavior may have various neuro-
physiological and psychological consequences capable of
producing high annoyance, directly or indirectly.
done. It is believable that the feeling of helplessness
induced by this lack of control over their tinnitus is an
important contributor to the annoyance reported by many
tinnitus sufferers.
In summary, when attempting to comprehend the annoyance
I S THE TINNITUS MONAURAL OR BINAURAL ?
As noted above, about 37 percent of all tinnitus is
believed to be monaural--a statistic based primarily upon
patients' self-reports (Vernon, 1978a). It is possible
that such reliance on self-reports is producing an under-
estimate of the incidence of binaural tinnitus, which may
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49
in turn be leading to depressed success rates with treat-
ments such as tinnitus maskers. The possibility of this
error lies in the perceptual experience aroused by bin-
aural stimulation. When external sounds that are similar
spectrally and equal in intensity are presented to the two
ears, the phenomenological experience is of a single fused
image located in the center of the head. (In everyday
listening, of course, sounds correctly appear to originate
outside the head from locations in auditory space, but,
with headphone listening and with self-generated sounds
such as tinnitus, the sounds appear to originate from a
location somewhere within the head; this difference be-
tween localization and lateralization, respectively, has
never been fully explained--but see Schroeder [1975].)
If an intermural difference in intensity is now intro-
duced, the fused image appears to move in the head toward
the ear receiving the more intense sound. The larger the
intermural intensity difference, the more lateralized the
acoustic image appears to be. Once the interaural dif-
ference gets to be about 15-20 dB, most listeners report
the image to be so strongly lateralized toward the more
-
~, ~
intense ear that it is unclear whether the stimulus is
binaural or monaural, and sometimes the presentation of a
truly monaural stimulus is required to convince the
listener that the previous stimulus was binaural but
highly asymmetric.
The relevance of these facts to tinnitus should be
clear. There is the danger that when a patient indicates
that his tinnitus is present in one ear only, he may be
in error: it may be originating at both ears, but more
intensely at one of them, thereby producing a strongly
lateralized image that misleads the patient into believing
the problem is monaural. Note that the tinnitus need not
be spectrally identical in the two ears for this to be a
possible problem; real sounds that are several hundred
Hertz apart can be fused and lateralized, and, in fact,
the frequency limits for dichotic fusion grow with center
. . . .
frequency (Scharf, 1969, 1974; however, these experiments
used brief stimuli and thus may not be relevant to the
binaural tinnitus situation).
If the spectral regions of tinnitus origin are widely
different in the two ears, or if the quality or com-
plexity of the tinnitus is different in the two ears, the
monaural/binaural question will be less of a worry than
in patients whose configuration of hearing loss is similar
in the two ears and whose tinnitus might thereby be ex-
pected to be spectrally similar in the two ears. There
is also less concern when the matched intensity of the
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50
tinnitus is about 10 dB SL or less (and the audibility is
approximately equal in that frequency region in the two
ears), for then the maximum possible intermural intensity
difference would not be adequate to produce an acoustic
image strongly lateralized to one side.
For completeness, it should be noted here that an
effect not known for external sounds does occur with tin-
nitus. Some patients report their tinnitus to be similar
or identical in the two ears but not fused--there is a
(similar) image localized to each ear (Vernon, 1978a).
In the laboratory a simple test is available to a
listener trying to decide whether an input is monaural or
binaural--pulling the plug to one of the two earphones
and observing any change in locus of the acoustic image--
and while this option is obviously not available to a
tinnitus sufferer, fortunately the means are available to
test psychophysically for the possible binaural origin of
tinnitus that is perceived to be monaural. Once a subject
has matched his or her tinnitus for center frequency, com-
plexity, and intensity, a similar waveform--but located
in a spectral region adjacent to the tinnitus--could be
presented binaurally and the subject asked to adjust the
intensity in the ear opposite the perceived tinnitus until
the image of this external sound appeared to originate
from the same intracranial location as the tinnitus. If
the intensity difference required for this match is small,
it would be evidence for a binaural origin of the tinni-
tus; if it is relatively large, or if the patient is sat-
isfied with a match to a monaural stimulus, it would argue
for a monaural origin.
It is possible that some of the patients who have found
tinnitus maskers to be of little long-term value might
have been better satisfied had they been fitted binaur-
ally. Similarly, at least some of the reports of tinni-
tus persisting after sectioning of the auditory nerve may
be traceable to unrecognized binaural origin of the tinni-
tus prior to surgery.
Finally, there is a misunderstanding about the locali-
zation (lateralization is the correct term) of the tinni-
tus that must be corrected. Some authorities seem to
believe that the locus of the source of a tinnitus is
revealed by where the patient hears it. Reed (1960) and
Goodhill (1979), for example, seem to believe that a tin-
nitus that sounds as if it originates at the ear(s) does
so and that one that appears to be inside the head has a
central rigin. This simply does not follow.
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51
THE ISSUE OF BEATS WITH TINNITUS
If some forms of tonal tinnitus were identical to an
external tone in all ways but their origins, one might
expect to be able to produce the experience of beats by
introducing an external tone slightly different in fre-
quency and similar in intensity to the tinnitus. In fact,
reports of such beats are few. Wegel (1931) claimed to be
able to hear an irregular, "mushy" beat when some single
tones were introduced, but it is clear that Wegel appre-
ciated how different his experience was from the normal
beat heard when two external tones interact. For example,
he found combinations of frequency and intensity of the
external tone that should have produced beats but that
instead produced "complete silence. n Over the years,
Wegel's report has been widely cited, but it has gen-
erally been viewed with skepticism and dismissed; how-
ever, recent developments have brought new attention and
credibility to it.
Specifically, the spontaneous otoacoustic emissions
(OAKS) discovered by Kemp (1979b) and studied by Wilson
(1979, 1980) and Zurek (1981) have several features in
common with Wegel's report, as well as with the reports
on monaural diplacusis by Flottorp (1953) and Ward (1955).
For example, in some subjects a heard OAK has been sup-
pressed by an external tone of appropriate frequency and
intensity; this is reminiscent of Wegel's "complete
silence. n OAEs have been observed, both perceptually and
acoustically, to fluctuate in level (beat) when appro-
priate tones are introduced (Wilson, 1980; Zurek, 1981),
and these fluctuations are often irregular, just like the
"mushy" beats reported by Wegel (1931), Flottorp (1953),
and Ward (1955). me fact that Flottorp and Ward did not
have a tinnitus against which to beat, and Wegel did,
appears to be a much-less-important difference since the
discovery of heard and unheard OAEs. It is now possible
to imagine that, in some of those rare instances in which
beats against tinnitus were reported (Wegel, 1931; Wever,
1949; Vernon et al., 1980), what was being heard were
interactions between the external tone and a heard OAK
and that the beatlike effects observed by Flottorp and
Ward were interactions with an unheard (perhaps narrow-
band) OAK. (In this regard, it is sobering to see how
close Flottorp was to discovering OAKS and how modern
both his and Ward's discussions are.)
Some other reports of beats against tinnitus are
apparently not explainable by appeal to OAKS. Stanaway
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52
et al. (1970) reported on a single subject who could hear
beats between an external tone and a tinnitus induced by
exposure to an intense broadband noise, but no such
interactions were reported by Loeb and Smith (1967) or
Atherly et al. (1968). Lackner (1976) claims to have
produced beats in patients whose tinnitus was of central
rather than peripheral origin, but his arguments make no
sense. For one thing, his procedure for producing beats
was to introduce an external tone to the ear contralat-
eral to the one in which the tinnitus was localized. Two
external tones to different ears can produce beats--they
are called binaural beats--but such beats are different
from monaural beats in many ways. Of primary interest
here is the fact that binaural beats cannot be produced
above about 800-1000 Hz using a single pure tone to each
ear (Licklider et al., 1950; Perrott and Nelson, 1969;
but compare McFadden and Pasanen, 1975). Yet Lackner
reports binaural beats at frequencies from about 2500 to
5000 Hz. It is conceivable that his patients were experi-
encing some other form of binaural interaction with their
tinnitus--contralateral masking, for example, or perhaps
the tinnitus had components in both ears and only appeared
to be monaural (see n Is the Tinnitus Monaural or Bin-
aural?" above), and the beat heard was a monaural one--
but whatever the explanation, it is certain that these
patients were not hearing what is ordinarily called a
binaural beat with such high-frequency tones.
m e weight of the evidence, then, favors the conclu-
sion that tonelike tinnitus does not ordinarily behave
like an external tone when it comes to the issue of
beats--monaural or binaural. There is a possibility that
some of the reports of beats against tinnitus could be
traced to an OAK underlying the tinnitus. The rarity of
the reports of beats against tinnitus is in accord with
this interpretation, for the growing belief is that
relatively few cases of tinnitus have an OAK as their
basis.
SOME WAYS TINNITUS I S NOT LIKE AN EXTERNAL SOUND
Some of the facts of tinnitus masking discussed in this
report naturally raise the question of whether tinnitus
masking should really be regarded as masking or whether
it involves mechanisms fundamentally different from those
involved when one external sound obscures another. An
easy decision on this question is prevented by our ignor
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53
ance of the bases of the various forms of tinnitus. That
is, in some instances the tinnitus and the masker may
interact physiologically in much the same way as the
physiological concomitants of two external sounds inter-
act when masking occurs, whereas in other instances tin-
nitus "masking" may be accomplished via quite different
physiological interactions. At this point all that can
be done is to review and emphasize those features of
successful tinnitus "masking" that have led some to ques-
tion whether it is better called by another name in order
to promote its better understanding (e.g., Vernon, 1981).
In what follows it is important for the reader to remember
that not all of these features of tinnitus masking are
present in all patients, and exactly which features clus-
ter as sets is not yet known. Further, some of these
features may be refuted or modified by future research.
Tinnitus masking has shown itself to be unlike ordinary
masking in several ways:
1. Sometimes tones of almost any frequency can ~mask"
tinnitus (Feldmann, 1971, 1981). For external sounds,
masking can only be accomplished by sounds within certain
spectral regions surrounding the signal; those regions do
increase with increasing masker intensity, but they never
reach the point of being several octaves above or below
the signal, as has sometimes been reported for tinnitus
"masking" (Vernon and Meikle, 1981).
2. When tinnitus can be masked, the intensity neces-
sary for masking is often abnormally great or small rela-
tive to the signal-to-noise ratios required by external
signals and maskers.
3. In order to keep some forms of tinnitus masked, it
is necessary to gradually increase the intensity of the
masker over the course of a half-hour listening session;
this increase can amount to 30-45 dB (Penner et al.,
1981). An external sound requires no such increase in
the masker to remain at the same level of detectability.
4. It is claimed that sometimes tinnitus cannot be
masked no matter how intense the masker is made (Vernon
and Meikle, 1981). For external sounds this is never
strictly true, although signals intense enough to be near
the upper intensity limit of audibility--the so-called
threshold of pain--may require maskers that are themselves
dangerous to hearing.
5. In a reasonably large fraction of tinnitus cases,
the tinnitus can be masked with sounds presented to the
ear contralateral to the side of reported origin of the
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54
tinnitus (Feldmann, 1971, 1981). In itself this is not
unlike the behavior of external sounds--an external sound
can mask a contralateral external signal via either cross-
conduction or central masking. m e peculiarity is that
the intensity necessary for masking tinnitus often appears
to be the same ipsilaterally and contralaterally.
6. Following the termination of an effective masker,
ipsilateral or contralateral, there is sometimes a period
of residual inhibition during which the tinnitus is absent
or reduced in magnitude. In contrast, a masked external
signal returns to audibility essentially immediately upon
termination of the masker.
7. If spectrally similar sounds are presented to the
two ears over headphones, they are perceived as a single
fused sound having an apparent intracranial position that
depends upon the relative levels and timing of the wave-
forms at the two ears. In contrast, tinnitus that is
spectrally similar in the two ears will often not fuse,
but will remain localized at the two ears (Vernon, 1978a).
. . . · · . .
SUMMARY OF MEASUREMENT PROCEDU~ S
This section has been concerned with psychophysical pro-
cedures and techniques for measuring and describing tin-
nitus. For the foreseeable future, such procedures will
continue to be the primary source of clinical and experi-
mental information about tinnitus, but it is believable
that the long-term future will see the development and
wide application of new and modified objective measures
of tinnitus (or its correlates) useful in diagnosis and
in choice of treatment. m e recording of spontaneous oto-
acoustic emissions (OAEs) from the canal of the outer ear
(Kemp, 1979b; Wilson and Sutton, 1981; Zurek, 1981) has
already been discussed (see " m e Objective/Subjective
Issue" in Chapter 2), but other possibilities exist. For
example, Shulman and Seitz (1981) have claimed that the
brain-stem-evoked response (BSER) in patients having tin-
nitus of central origin is different in specifiable ways
from that of people with normal hearing. Some other pos-
sibilities are that the response of tinnitus to manipula-
tions of air pressure in the middle ear (see "Alteration
in Air Pressure" in Chapter 4) may prove to have diag-
nostic value, as may its response to electrical stimula-
tion (see" Electrical Stimulation" in Chapter 4) or to
certain drugs (see "Drug m erapy for Tinnitus" in Chapter
4). m e development and use of such diagnostic aids is
clearly to be encouraged.
Representative terms from entire chapter:
pitch matching
