Download Measuring Tinnitus Parameters: Loudness, Pitch, and Maskability

J Am Acad Audiol 4 : 139-151 (1993)
Measuring Tinnitus Parameters :
Loudness, Pitch, and Maskability
Curtin R. Mitchell*
Jack A. Vernon*
Thomas A. Creedon*
Abstract
Improved procedures have been developed for obtaining hearing thresholds, loudness
matches, pitch matches, and masking curves of tinnitus . Computer programs enable all of
these measures to be obtained in a single session . These measures have been obtained in
tinnitus and nontinnitus subjects, with an external stimulus used to simulate tinnitus in
nontinnitus subjects . These measures, obtained in repeated sessions, were used to determine the test-retest variability of each measure. The test-retest standard error of measurement, across-subjects, is reported, which enables changes in tinnitus to be determined . In
nontinnitus subjects, the accuracy, as well as the reliability, is described.
Key Words :
Loudness, masking level, pitch, test-retest, tinnitus
omparing tinnitus with external sounds
has been the subject of a number of studies (Wegel, 1931 ; Mortimer et al, 1940 ;
Reed, 1960 ; Graham and Newby, 1962 ; Feldmann, 1971 ; Bailey, 1979 ; Vernon et al, 1980 ;
Hazell,1981; MRC,1981 ; Tyler, 1982 ; Mitchell,
1983 ; Penner, 1983, 1986, 1988 ; Tyler and
Conrad-Armes, 1983b; Burns, 1984 ; Lindberg
et a1,1987) . Beyond obtaining basic information
about tinnitus, these efforts have included attempts to obtain differential diagnosis, monitor
changes from therapy or improve the efficiency
of masking therapy (Reed, 1960 ; Graham and
Newby, 1962 ; Musiek et al, 1975 ; Vernon, 1977 ;
Feldmann, 1984a) . Reliable matches between
tinnitus and external stimuli have been reported by some investigators (Atherley et al,
1968 ; Bailey, 1979 ; Vernon et al, 1980 ; Tyler
and Conrad-Armes, 1983b), while others have
reported poor reliability (Penner, 1983, 1986 ;
Burns, 1984).
C
*Oregon Hearing Research Center, Department of
Otolaryngology, Oregon Health Sciences University, Portland, Oregon
Reprint requests : Curtin R . Mitchell, Oregon Hearing Research Center, 3515 SW Veterans Hospital Rd .,
Portland, OR 97201-2997
Since tinnitus is a sensation associated with
damage to the auditory system, it includes a
variety of sensations that may or may not be
similar to any external sound and may vary
from time to time (Vernon, 1977 ; Hazell, 1981 ;
Feldmann, 1984b) . Thus, it is not surprising
that comparisons of tinnitus with external
stimuli have been reported as highly variable in
some cases (Penner, 1983). Another potential
complication is that when test stimuli are presented for comparison, they may change the
tinnitus sensation through residual inhibition
(Vernon and Meikle, 1988).
Tinnitus matching to external stimuli has
been accomplished using both clinical and laboratory methods. Clinical methods may be criticized as lacking warm-up procedures and having uncontrolled training effects as well as using response criteria that are not standardized .
In some cases, large frequency or intensity increments have also been used . Although laboratory methods avoid some of these problems,
they involve considerable training and testing
time and yield data from very few subjects
(Formby and Gjerdingen, 1980 ; Penner, 1987).
The purpose of this study is to investigate
loudness and pitch matching, as well as the
masking of tinnitus, in patients who describe
their tinnitus as tonal and nonfluctuating . A
compromise procedure, more precise than the
usual clinical method and less time consuming
Journal of the American Academy of Audiology/Volume 4 Number 3, May 1993
than a typical laboratory method, was used . An
attempt was made to use a sufficient number of
subjects for the results to be generalized.
Two groups of subjects were used in this
study, one group with tinnitus and one without.
In the tinnitus group, behavioral hearing thresholds, as well as the loudness, pitch, and masking
levels of tinnitus were determined . In the group
without tinnitus, a continuous external tone
was introduced to simulate tinnitus . The same
measures were obtained in this group except for
the masking levels . Both groups were tested in
two different sessions, where possible, to determine the test-retest reliability . The within- and
across-session test-retest reliability was assessed in both groups . Since an external tone of
known frequency and level was used to simulate
tinnitus in the nontinnitus group, this group
provided an opportunity to determine both reliability and accuracy of loudness and pitch
matches.
To avoid some of the criticisms of previous
studies, the following precautions were taken.
First, in the tinnitus group, only subjects with
nonfluctuating tinnitus that was matched to a
pure tone in the clinic were included to avoid
subjects with poorly defined pitch or complex
tinnitus . Second, short duration stimuli were
presented in ascending sequences whenever
possible and small intensity steps were used to
avoid residual inhibition .
METHOD
Two groups of subjects were tested, one
group with tinnitus and one without tinnitus .
The first group consisted of 25 subjects selected
from the Tinnitus Data Registry (Meikle and
Griest,1989) according to the following criteria :
(1) their tinnitus was matched to a pure tone in
the tinnitus clinic, (2) their tinnitus did not
fluctuate from day to day, and (3) hearing thresholds were less than 60 dB HL at the frequency
matched to their tinnitus in the clinic . Tinnitus
was described as unilateral or predominately on
one side by 1.9 subjects and as bilateral by 6
subjects . There were 17 men and 8 women in
this group. Eighteen of these subjects were
tested in two sessions, and 7 were tested only
once .
The second group consisted of 18 subjects, 6
men and 12 women, who did not have tinnitus
and who were tested using a continuous lowlevel tone to simulate tinnitus . These subjects
had normal hearing or moderate sensorineural
hearing loss . Fourteen subjects in this group
were tested twice and four tested only once .
Equipment
A Macintosh II computer with LabVIEW°
software controlled the stimuli and recorded
subject responses. Athree-way switch mounted
on the arm of a comfortable chair was used to
obtain responses from the subjects . The same
response switch was used for all threshold,
loudness, pitch, and masking measures obtained .
Different programs and instructions to the subjects were used for the different tasks.
Pure-tone stimuli were generated by a
Hewlett Packard synthesizer/function generator (#3325A) and were controlled with modular
Coulbourn attenuators and a rise/fall gate to
produce periodically interrupted tones . The lowlevel continuous tone used to simulate tinnitus
was generated by a General Radio oscillator
(1309-A) . The frequency was verified with a
Monsanto frequency counter (100A) and the
intensity controlled by a Hewlett Packard precision dB attenuator (350D) . Stimuli were delivered through a Koss Pro/4X plus headset with a
modified foam cushion (Fausti et al, 1990).
The system was calibrated using KEMAR
with a Zwislocki coupler and a '/2-inch B&K
microphone . The headset was placed on KEMAR
with the foam cushions forming a tight fit. The
sound pressure level was measured over a range
of frequencies and intensities on a Hewlett
Packard Dynamic Signal Analyzer (35660A) .
The system was calibrated before, during, and
after the study.
General Procedures
In subjects with tinnitus, four measures
were obtained in each session: thresholds of
hearing, loudness and pitch matches, and minimum masking levels . These measures were
obtained using 1-dB steps for intensity and '/3octave steps for frequency. The frequency range
was 1 kHz to 12 .7 kHz, with the frequency order
randomized by computer algorithm during each
session. These measures were obtained in the
tinnitus ear, or in case of bilateral tinnitus, on
the side where tinnitus was perceived as loudest.
The commonly used procedure for matching
tinnitus involves presenting stimuli to the ear
contralateral to the tinnitus sensation. The procedure in the current study was unusual in that
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both matching masking stimuli were presented
to the ipsilateral ear relative to the tinnitus .
This procedure has the risk of producing residual inhibition and temporarily altering the
tinnitus sensation. We expected to encounter
this problem (as mentioned previously), so short
duration stimuli and ascending sequences in 1dB steps were used whenever possible . Subjects
were repeatedly questioned during and after
sessions as to whether their tinnitus was changed
by the testing procedure. In the rare case where
a decrease in tinnitus was noticed, time was
allowed for the tinnitus to recover to the pretesting loudness before testing was continued. One
subject experienced so much residual inhibition
during hearing threshold determination that
the loudness or pitch of their tinnitus could not
be matched and testing had to be terminated . In
general, these efforts to avoid residual inhibition were successful and it did not interfere with
data acquisition .
Total session times varied from about 45 to
70 minutes. Time for data collection ranged
from 27 to 40 minutes, with an average of 36
minutes. This required 150 to 280 responses
from each subject. Written instructions were
given for each procedure and discussed with the
subject to ensure that they understood the task .
It required 3 to 7 minutes for each set of instructions to be read and discussed . This resulted in
15 to 30 minutes of each session spent on instructing the subject.
After the first test session, the subjects
were retested 5 or more days later, with 15 days
being the mean and 11 the median number of
days between tests. In subjects with tinnitus,
both the first test and the retest were done as
nearly "blind" as possible . Once the clinic files
were inspected to determine the patients' suitability for the study, the files were not referred
to again until all testing was completed. Results
obtained in the first test were purposely not
referred to before retest to reduce the potential
for bias in data collection .
In nontinnitus subjects, pure-tone hearing
thresholds were obtained in one ear. Then a
continuous low-level tone (10 to 25 dB SL at
2150 Hz) was introduced in one ear to simulate
tinnitus . The frequency was chosen to be where
the majority of subjects could hear a continuous
tone at a low level, in SPL. The level was
adjusted to where no decay in loudness could be
observed for at least 1 minute . The loudness and
pitch matches of the simulated tinnitus were
then obtained in the contralateral ear with the
same methods as used in tinnitus subjects . A
small amount of contralateral stimulation-induced tone decay was observed in some subjects
(Scharf, 1991).
Contralateral matching was used in nontinnitus subjects to avoid beats or other interactions between the continuous tone, used to simulate tinnitus, and the periodically interrupted
matching tone, as these interactions invalidate
the matching procedures . Masking of the simulated tinnitus was not attempted because
contralateral masking was not relevant to the
purpose of this study and ipsilateral masking of
tones is known to be very different from the
masking of tinnitus (Mitchell, 1983 ; Tyler and
Conrad-Arnes, 1983a) .
Thresholds
The stimuli for hearing threshold determination were periodically interrupted pure tones,
500 msec on and 233 msec off, with 25 msec risedecay times . Thresholds were obtained in
'/s-octave steps, from 1 kHz to 12 .7 kHz, in
random frequency order. A fixed-frequency
tracking-procedure (Levitt, 1971) was used, allowing the subject to control the intensity with
a three-way switch . This switch has center,
forward, and back positions. The switch was
spring loaded so it returned to the center position when released . The subjects indicated when
they heard a sound with forward responses,
while backward responses indicated that no
sound was heard . In the tracking procedure,
each response, forward or backward, reversed
the intensity of the tone . When the switch was
in the center position it did not register a response or alter the stimulus sequence .
At each frequency, the tones were initially
increased in 3-dB steps until the subject responded (forward), then the intensity decreased
in 3-dB steps until the subject indicated they did
not hear it (backward), etc. After two ascending
and two descending sequences in 3-dB steps,
three ascending and three descending sequences
in 1-dB steps were obtained at each frequency .
Only the last six reversal points, with 1-dB
steps, were used to calculate a mean, defined as
threshold. The standard deviation and range of
these six points were calculated at each frequency . Data were considered acceptable when
the standard deviation was less than 4 dB and
the total range was less than 12 dB . Data points
that did not meet these criteria were repeated or
omitted from data analysis .
The effects of warm-up and practice on the
thresholds were evaluated by obtaining repeated
thresholds . At the beginning ofeach test session
Journal of the American Academy of Audiology/Volume 4 Number 3, May 1993
nine tones were presented, of which three frequencies were presented three times each . This
within-session control procedure indicated that
about 20 percent of the subjects had differences,
5 dB or greater, in the first or second frequency
presented. This effect was negligible by the
third frequency tested . Data from the practice
sessions were excluded from the data analysis
and in this way the effects of warm-up and
practice were controlled .
The stimulus on and off times described
above were chosen from a pilot study using six
subjects. Thresholds were obtained using the
following on/off times (in seconds), 0.2/0 .1, 0.2/
0.2,0 .2/0 .4,0 .2/0.8,0 .5/0 .23,0 .8/0 .2,0 .8/0 .4,0 .8/
0.8, 1 .0/0 .3, 1 .6/0 .4, and 1 .6/0 .8 as well as step
sizes of 1, 2, 3, and 5 dB . The threshold level,
standard deviation, and range were used as
criteria to evaluate the on/off times and step
sizes while minimizing the testing time . The
parameters chosen for the current study (0 .5
second on and 0.23 second off with a 1-dB step
size) were found to have the most sensitive
threshold, the smallest range, and a moderate
standard deviation.
smaller loudness difference was seen between
the second frequency on the list and its repeat
presentation . By the third frequency, the loudness match difference was rarely greater than 2
dB . Thus we observed, in about half the subjects
tested, a warm-up effect for this task on the first
or second tone presented . The loudness difference between the two presentations of the third
tone was used as a measure of within-session
reliability .
In subjects with no tinnitus, the loudness of
the simulated tinnitus, a continuous, low-intensity tone, was matched in the contralateral ear
using the same procedure.
Pitch Matches
Pitch matches were obtained using a twoalternative forced-choice procedure. Two tones
were presented at the intensity levels previously matched to tinnitus or to the simulated
tinnitus . The duration of each tone was 2 seconds (25 msec rise-decay) with zero delay between them . Longer stimuli were used for this
task than were used for threshold and loudness
measures to enable the subject to judge pitch at
low sensation levels . The subject indicated which
tone, the first or the second, sounded the closest
in pitch by manipulating the response switch
forward or backward . To avoid a frequency bias
in sampling, tone pairs were presented to all
subjects at frequencies over the entire range of
1 kHz to 12 .7 kHz.
Warm-up and practice effects could be expected in pitch matching. In the current study,
these effects were embedded in the procedure .
The procedure began with wide frequency spacing (2/3 octave) and no subject reported difficulty
hearing this pitch difference . The smaller spacing (1/a octave) was only given after tone pairs
with wide frequency spacing were presented
over the entire range, 1 kHz to 12 .7 kHz. Thus
the procedure provided ample time for warm-up
and practice to occur without affecting the final
pitch match.
The tone pairs, initially separated by 2/3_
octave, were presented in ascending and then
descending frequency steps. Both ascending and
descending frequency steps were used to avoid
order preferences, that is, the tendency to choose
the first tone of the two. These sequences were
repeated so that each frequency was presented
four times. Results of this procedure identified
the general area, or areas, of pitch. Within each
area identified, three tones were selected . These
three tones were presented in pairs, separated
Loudness Matches
Loudness matches oftinnitus were obtained
using tones at the same frequencies and with
the same on/off times (0 .5/0 .23 sec) as those
used for thresholds . Using periodically interrupted tones avoided confusion between the
stimulus and the subject's tinnitus . The subject
was instructed to adjust the loudness of the
comparison tones to match that of their tinnitus .
The tones were initially presented at 6 dB above
threshold and the subject adjusted the intensity
of the stimuli up or down, in 1-dB steps, until a
satisfactory loudness match was obtained . A
loudness match at a single frequency required
from 14 to 60 seconds, depending on the subject's responses, as no time limit for obtaining a
satisfactory match was imposed. The criterion
for a loudness match was 7 seconds at one
intensity without a loudness adjustment.
Loudness matches were obtained in random order of frequency from a computer generated list . The first three frequencies of the
randomized list were repeated at the end of the
list . These duplicate loudness matches were
included as a control for warm-up or practice
effects and to measure reliability . In about half
the subjects, a difference of greater than 4 dB
was found between the first and second presentations of the first frequency on the list . A much
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Measuring Tinnitus Parameters/Mitchell et al
by 1/3-octave, such that each frequency was
paired with every other frequency and presented in forward as well as reverse order. The
tone selected the greatest percentage of time
was reported as the pitch match. Tones at octave intervals relative to the pitch match were
also presented to check for octave errors .
Minimum Masking Levels
The minimum masking levels, referred to
hereafter as the masking levels, were determined using tones with the same on/off times
(0 .5/0 .23 sec) as the tones used for threshold and
the loudness match. Instructions emphasized
the task of adjusting the intensity level until it
just masked or "covered up" the tinnitus, i.e ., so
subjects could not hear their tinnitus when the
masking sound was present. The criterion for
masking was 7 seconds at one intensity without
an adjustment . The control for warm-up and
practice on masking levels was similar to that
used for the loudness measures . That is, the
first three frequencies tested were repeated at
the end of the test . The differences between the
first frequency and its repeat were greater than
for the second or third frequency presented.
These differences were rarely greater than 4 dB
for the first frequency and decreased to negligible levels by the third frequency presented.
Thus, this procedure controlled for warm-up
and practice, as well as the effect of the masker
on the tinnitus sensation. The difference between the masking level obtained upon repeated
presentation of the third tone was used as a
measure of within-session reliability . As previously mentioned, no masking levels were determined in the nontinnitus group, that is, for the
simulated tinnitus .
RESULTS
n this study, subjects both with and without
tinnitus were tested . As the monitoring of
tinnitus is an important application of psychophysical measures of tinnitus, the test-retest
variability was of particular interest . The testretest standard error of measurement (SEM) is
useful for detecting changes when a test is
repeated, i.e ., the across-session SEM can be
used to detect significant changes among subjects (Anastasi,1982) . For this reason the acrosssession SEMs were calculated for hearing thresholds, loudness and pitch matches, and for masking levels . Comparisons between the SEM and
the reliability of tinnitus and nontinnitus subjects were also made .
The relationship between the loudness and
masking levels of tinnitus varies from one subject to the next . Subjects were categorized into
different types according to the relationship
between the loudness and masking levels of
their tinnitus . Subjects representing the four
types are shown in Figure 1. In the first type,
shown in Figure 1A, the loudness and minimum
masking levels were parallel and both within
about 10 dB of the threshold of hearing. This
type was found in 40 percent of the subjects with
tinnitus (10 of 25). In the second type, shown in
Figure 113, the masking level was about 20 dB
above threshold with the loudness levels midway between the threshold and masking level.
This type was found in 32 percent of the subjects
(8 of 25) . In the third type, shown in Figure 1C,
both the masking level and the loudness level
were elevated about 20 dB above threshold.
Twenty percent of the subjects (5 of 25) demonstrated this type . The fourth type, depicted in
Figure 1D, demonstrates a resistance to masking with the masking level more than 20 dB
above threshold and the loudness match less
than 10 dB . Only 8 percent of the subjects (2 of
25) showed this type . The classification was not
related to the pitch or etiology of the tinnitus .
Thresholds
Hearing thresholds were obtained over the
frequency range from 1 kHz to 12 .7 kHz in two
different sessions separated by 5 days or more .
The test-retest standard errors ofmeasurement
(SEMs) of thresholds for the nontinnitus and
tinnitus groups are shown in Table 1 and were
calculated in the usual manner (Anastasi,1982).
For large samples (N > 100), the 95 percent
confidence interval is ± 1.96 x SEM, while the 99
percent confidence interval is ± 2.58 x SEM. For
smaller samples (e .g ., N = 10 to 30), values from
the t distribution can be employed .
In Table 1, the across-session SEMs reach
minimum values in the middle frequencies, 2
kHz to 4 kHz, in both groups . Nontinnitus
subjects have slightly smaller SEMs than the
subjects with tinnitus although there were no
significant differences between the two groups .
Across-session test-retest correlations, at different frequencies, were 0.78 to 0 .97 in
nontinnitus subjects and 0.62 to 0.98 in tinnitus
subjects . Within-session test-retest correlations
were 0.93 for nontinnitus subjects and 0.98 for
tinnitus subjects (the SEMs were 2.6 dB and 1 .9
dB, respectively). An analysis of repeated tests
in individual subjects, using these SEMs, did
Journal of the American Academy of Audiology/Volume 4 Number 3, May 1993
Figure l. Four types of subjects
with respect to hearing thresholds, loudness and masking levels of tinnitus are shown. The
results are from testing on two
different days. The individual
data points from each test day are
plotted for the loudness matches
(o) and the minimum masking
levels ( " ) along with the mean of
each (Mean LM and MML) . Only
the mean values for the hearing
thresholds (Mean TH) are shown.
The frequency of the pitch matches are indicated by arrows on the
abscissa .
Frequency (Hz)
not show significant changes in threshold, within
or between tests.
Loudness matches were obtained over the
same frequency range (1 kHz to 12 .7 kHz) with
the same procedure in both groups of subjects .
Nontinnitus subjects matched the loudness in
the ear contralateral to the simulated tinnitus .
Tinnitus subjects matched the loudness of their
tinnitus ipsilaterally. Differences between
ipsilateral and contralateral matches would be
expected to be minimal (Tyler and ConradArmes, 1983a) .
The SEMs of the sensation level of loudness
matches across-sessions are shown in Table 2 .
Across-session test-retest correlations were 0.40
to 0.94 in nontinnitus subjects, and 0.42 to 0.83
in tinnitus subjects . Within-session test-retest
Table 1 Hearing Threshold Test-Retest Results
for Nontinnitus and Tinnitus Subjects
Table 2 Loudness Match Test-Retest Results
for Nontinnitus and Tinnitus Subjects
Loudness and Pitch
Frequency
(Hz)
Nontinnitus Subjects Tinnitus Subjects
(n = 15)
(n = 19)
4.1
5.5
1000
1260
1590
2000
2520
3175
4000
5040
6350
8000
10080
12700
Mean SEM
Data is given in dB .
4 .0
2 .1
1 .7
2 .1
2 .6
2 .3
2 .7
4 .4
3 .5
3 .4
4 .7
3 .13
3 .5
6 .6
3 .3
3 .2
2 .8
2 .4
3 .5
2 .5
6 .2
2 .4
3 .0
3 .74
Frequency
(Hz)
Nontinnitus Subjects Tinnitus Subjects
(n = 14)
(n = 19)
1000
1260
1590
2000
2520
2 .8
2 .5
3 .0
2 .8
2 .7
5 .0
4 .5
6 .6
6 .5
5 .1
4000
5040
6350
8000
10080
12700
2 .9
2 .2
3 .9
4 .6
5 .1
2 .7
4 .2
5 .9
5 .0
5 .8
3 .6
5 .0
3175
3.0
Mean SEM
3 .18
3.9
5 .09
Data is given in dB SL .
144
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Measuring Tinnitus Parameters/Mitchell et al
Table 3
Subject
Loudness and Pitch Matches for Nontinnitus Subjects
Loudness Match (dB SL)
Presentat ion
First
Second
LM Diff
Absolute
Level (dB SL)
(dB)
LM Diff (dB)
NT1
25
NT4
24
NT7
NTS
19
20
NT2
NT3
15
15
NT5
NT6
18
17
15
21
19
1
-5
18
15
10
20
6
10
20
20
0
21
6
NT9
NT10
13
22
NT11
15
NT12
NT13
NT14
-5
-3
1
8
-6
10
16
8
4
-2
6
11
7
12
11
10
1
5
3
6
6
10
1
1
4
2
1
2
7
9
1
24
4
-6
-1
-1
1
2
14
15
-2
7
-9
Mean
SD
-0 .9
5 .22
Pitch Match (Hz)
First
Second
2520
3175
2000
2000
2520
6350
4000
2520
1260
2000
2000
2520
2520
2200
2520
2000
2000
3175
1590
2000
1260
2000
1260
2000
1590
4000
2000
3175
4 .1
3 .08
PM Diff
(Hz)
PM Diff
(Octaves)
0
1175
0
1175
930
4350
2740
520
0
0
410
1480
520
975
0
0 .67
0
0 . 67
0 . 67
1 . 67
1 . 67
0 . 33
0
0
0 . 33
0 . 67
0 . 33
0 .54
1020
1220
0 . 54
0 .55
Matching was performed to a continuous external tone at 2150 Hz, tested in two different sessions . For
consistency in
data analysis, both the first and second loudness match values are at the frequency of the first pitch
match .
correlations were 0.97 in nontinnitus subjects
and 0 .92 in subjects with tinnitus . The SEMs of
the sensation levels of the loudness matches
within a session were 2 .8 dB in nontinnitus
subjects and 3.8 dB in subjects with tinnitus .
Thus the SEMs, both within and across-sessions, were slightly smaller for nontinnitus subjects matching to simulated tinnitus than subTable 4
Subject
T1
Loudness and Pitch Matches for Tinnitus Subjects
Loudness Match (dB SL )
First
Second
4
2
LM Diff (dB)
2
T2
T3
T4
T5
T6
T7
T8
T9
T10
-6
7
17
7
11
12
22
1
4
-3
-1
10
4
14
18
28
-2
3
-3
8
7
3
-3
-6
-6
3
1
T12
T13
T14
T15
T16
T17
T18
T19
8
-2
9
4
2
16
2
6
7
-4
13
8
12
2
5
4
1
2
-4
-4
-10
14
-3
2
T11
Mean
17
12
jects with tinnitus matching to their actual
tinnitus sensation.
,Loudness and pitch matches for both groups
of subjects are shown in Tables 3 and 4. Table 3
contains the data for nontinnitus subjects while
Table 4 shows the data for subjects with tinnitus .
The test-retest differences for nontinnitus subjects are shown in Table 3. The mean of the
5
0 .5
Absolute
LM Diff (dB)
2
3
8
7
3
3
6
6
3
1
5
1
2
4
4
10
14
3
2
4 .6
Pitch Match (Hz)
First
Second
6700
2000
4000
3175
6350
4000
10080
5040
12700
8000
6350
1590
1000
10080
8000
5040
12700
12700
5040
6500
3175
2520
2520
6350
8000
8000
4000
10080
8000
8000
1000
1260
12700
10080
4000
5040
6350
2520
PM Diff
(Hz)
200
1175
1480
655
0
4000
2080
1040
2620
0
1650
590
260
2620
2080
1040
7660
6350
2520
PM Diff
(Octaves)
0 . 03
0 . 67
0 . 67
0 . 33
0
1
0 . 33
0 . 33
0 . 33
0
0 . 33
0 . 66
0 . 33
0 . 33
0 . 33
0 . 33
1 . 33
1
1
2001
0 .49
The results obtained in two different sessions are shown . For consistency in data analysis, both the first
and second
loudness match values are at the frequency of the first pitch match .
Journal of the American Academy of Audiology/Votume 4 Number 3, May 1993
absolute difference is 4.1 dB, comparable to the
mean SEM of 3 .18 (see Table 2) . In three subjects, (NT6, NT13, NT14) the loudness difference was greater than 2 SEM, indicating greater
loudness match variability than would be expected by chance (0 .05 level) . Since the actual
loudness presented remained the same in both
sessions, it appears that the across-session reliability of these three subjects was poor, however, the within-session reliability in these subjects was quite good .
For the tinnitus subjects, the mean absolute difference in loudness of 4.6 dB (see Table
4) is comparable with the mean SEM of 5.09 (see
Table 2) . In two subjects (T16, T17), the loudness difference was greater than 2 SEM. This
could be due to poor loudness match reliability,
the tinnitus actually changing, or both . It should
be noted that for 17 of the 19 subjects, the
tinnitus loudness measured did not change between tests more than would be expected by
chance .
Two subjects in the tinnitus group and two
subjects in the nontinnitus group showed loudness differences greater than 8 dB . This suggests similar test-retest variability in the two
groups of subjects . It also suggests that the
tinnitus loudness was reasonably constant over
time .
Pitch matches were determined using the
two-alternative, forced-choice procedure described. Because the conversions from Hertz to
octaves are not linear transformations, as they
depend upon the base frequency, it is useful to
view the results in both metrics. Across-session
SEMs were 1.09 kHz or 0.52 octave in non-
tinnitus subjects . The SEMs in subjects with
tinnitus were 1.97 kHz or 0.43 octave . Pitch
matches obtained in the tinnitus and nontinnitus
subjects in two different sessions are shown in
Tables 3 and 4. Test-retest differences are shown
in both frequency and in octaves. In nontinnitus
subjects, the mean difference was 0.54 octave
(see Table 3), comparable with the SEM of 0.52.
In tinnitus subjects, mean difference was 0.49
octave (see Table 4), comparable with the SEM
of 0.43.
Minimum Masking Level
The minimum masking level was obtained
over the frequency range of 1 kHz to 12 .7 kHz in
two different sessions in the tinnitus group .
(The masking level was not obtained in
nontinnitus subjects for the reasons described
previously .) SEMs for the masking levels are
shown in Table 5 for each frequency. The acrosssession test-retest correlations varied from 0.58
to 0.96 at different frequencies . The withinsession SEM was 4.4 dB and the correlation was
0.94. Thus, the within-session SEM is similar to
the mean across-session SEM (see Table 5) .
The masking level, at the frequency of the
pitch match of the tinnitus, is shown in Table 6 .
The average difference between the two sessions was 4.8 dB while the average SEM was
4.32 (see Table 5) . In two subjects (see Table 6)
the absolute masking level difference (MML
Diff) was greater than 2 SEMs (8 .6 dB, see Table
5) . These changes could be due to poor masking
level reliability or actual changes in maskability.
A comparison between the SEMs of the loudness matches (see Table 2) and the masking
Table 6 Minimum Masking Levels
at the Pitch Match of Tinnitus
Table 5 Minimum Masking Level Test-Retest
Results for Tinnitus Subjects
Frequency (Hz)
Tinnitus Subjects
(n = 13)
1000
1260
1590
2000
2520
3175
4000
5040
6350
8000
10080
12700
8 .7
3 .3
4 .9
5 .4
3 .5
3 .1
3 .1
4 .7
4 .3
5 .9
2 .1
2 .8
Mean SEM
4 .32
Data is given in dB .
MML 1
MML 2
Relative
MML Diff
Absolute
MML Diff
T5
T7
T6
T8
T9
11
17
26
20
5
18
26
18
15
5
7
9
-8
-5
0
7
9
8
5
0
T12
T14
T15
T16
T18
T19
10
10
5
11
2
8
17
10
14
16
6
5
7
0
9
5
4
-3
7
0
9
5
4
3
ubject
T11
21
20
-1
2 .0
5 .7
Mean
SD
1
4 .8
3 .3
Data is given in dB SL .
146
1-~ 11W*V
> itFG" U
hy, . « t, ~, ~=. Mill' :~ '
11''
Measuring Tinnitus Parameters/Mitchell et al
levels (see Table 5) in tinnitus subjects suggests
that the masking level has slightly smaller testretest variability .
Across-Session Test-Retest Variability
Test-retest correlation coefficients in subjects with tinnitus were calculated for loudness
matches and minimum masking levels at the
frequency matched to the pitch of the tinnitus .
The test-retest correlation for the loudness match
was 0.56 (p < .01), for the minimum masking
level it was 0.75 (p < .01), and for pitch it was
0.69 (p < .01) . It should be remembered that
correlation coefficients are sensitive to scaling
and a restricted range reduces the correlation .
The loudness match range is quite small, especially in relation to the SEM, while the range for
the pitch of tinnitus is very large (see Table 4) .
Thus, differences between the correlation coefficients must be interpreted with caution. What
is important is that the test-retest correlations
are significant for each measure .
In subjects with tinnitus, the test-retest
reliability may be determined, but the accuracy
of these matches cannot be known. With external tones, which stimulate or mimic tinnitus,
both the test-retest reliability and the accuracy
of matches can be determined. Loudness and
pitch matches of a continuous 2.15 kHz external
tone, used to simulate tinnitus, were obtained .
The across-session test-retest correlation for
loudness was 0.83 (p < .01) at the frequency
20
matched to the external tone . (The correlation
for the pitch would not be meaningful due to the
restricted range.) The accuracy of the pitch and
loudness matches are shown in Figure 2. This
figure shows that the loudness of the simulated
tinnitus was consistently underestimated,
whereas the pitch matches showed only a slight
trend toward overestimating the frequency.
From the data presented in Figure 1, the
loudness and masking levels appear to be independent and no relationship between loudness
matches and minimum masking levels would be
expected. However, when the data are limited to
the pitch region of the tinnitus and all subjects
are considered, a relationship is suggested. The
loudness and masking levels, at the frequency
matched to the tinnitus, are shown in Figure 3.
The correlation between loudness matches and
masking levels is 0.78 (N = 22), which is significant at the .001 level. Thus these data suggest
that the louder the tinnitus, the greater the
masking necessary. While this relationship may
hold for the majority of subjects with tinnitus,
there may be striking exceptions, such as subject T10 shown in Figure 1D .
DISCUSSION
n a group of subjects with tonal tinnitus,
the loudness, pitch, and masking levels of
tinnitus were measured, as well as the threshold of hearing (see Fig. 1) . While each of these
separate measures has been previously reported
in subjects with tinnitus, there are no reports
30
25
10
20
5
15
0
0
-s
8
10
0
15
O
20
-5
1
-3
-9
-1
00b
1
0
O
O
1
0
7_1
00
10
Frequency Merence, kHz
Figure 2 The accuracy of the pitch and loudness
matches to external tones simulating artificial tinnitus
are shown. The intensity and frequency differences between the match and the actual external tone presented,
with two matches for each subject (n = 15), are plotted
(see Table 3) . The loudness matches were typically below
the actual intensity levels presented (25 of 30 matches) .
The pitch matches were usually within 1/3-octave of the
frequency presented (17 of 30 matches) .
88
e
0
O
-5
e
0
O
5
10
-5
0
5
10
15
Loudness Match, dB SL
20
25
Figure 3 Loudness levels and minimum masking levels at the frequency matched to the tinnitus . This relationship was unexpected in that it is commonly thought
that the loudness of tinnitus is not related to its
maskability. This may be the case in some patients,
especially at frequencies outside the tinnitus region;
however, loudness and masking, at the frequency matched
to the tinnitus, appear to be related in this group of
subjects .
Journal of the American Academy of Audiology/Volume 4 Number 3, May 1993
that we know of where all of these measures
have been obtained in the same subjects . In
another group of subjects without tinnitus, an
external sound was introduced to simulate
tinnitus, and loudness as well as pitch matches
were obtained in order to compare pitch and
loudness matching capabilities to those with
tinnitus .
These measures were repeated in both
groups of subjects in a second session. The
standard error ofmeasurement (SEM) is a measure of the test-retest variability across sessions
and subjects . The SEM is considered useful
when repeated testing is used, because a confidence interval can be calculated from the SEM.
Thus, when monitoring tinnitus the SEM can be
used to determine when significant changes
occur, beyond the test-retest variability. The
test-retest SEMs for hearing thresholds, loudness matches, and masking levels are shown in
Tables 1, 2, and 5. The SEMs for loudness and
masking have not been previously reported .
Threshold
The across-session SEMs of hearing thresholds are shown in Table 1 for both groups of
subjects. These data indicate that the test-retest
variability are as good or better than those
reported by other investigators (Fausti et al,
1979 ; Brummett and Morrison, 1990). It is recognized that a two-interval, forced-choice procedure may give thresholds as much as 6 dB lower
than those obtained by the tracking method
used in the current study (Fausti et al, 1979 ;
Marshall and Jesteadt, 1986).
Patients in the tinnitus clinic often report
that tinnitus interferes with their hearing. This
apparent masking of hearing threshold by
tinnitus has been mentioned by various investigators (Minton, 1923 ; Mortimer et al, 1940 ;
Langenbeck, 1953 ; Katz, 1978) and Feldmann
(1984a) considers this an unanswered question .
If tinnitus did mask hearing threshold, it could
increase the tracking pattern excursions near
the pitch of the tinnitus and, indeed, this has
been reported elsewhere (Katz, 1978). For this
reason, the threshold tracking pattern in the
frequency region matched to tinnitus was
analyzed . The range and standard deviation of
the tracking pattern in the tinnitus region were
compared to regions outside the tinnitus region .
No difference between tracking patterns in these
regions was found. Thus, we did not see evidence that tinnitus masked or otherwise interfered with hearing thresholds .
Loudness
In the current study, loudness matches to
pure tones were obtained over a wide frequency
range. The across-session variability in loudness matches of tinnitus and that of an external
tone (simulated tinnitus) are shown in Table 2.
These test-retest SEMs of matches to an external tone have slightly smaller SEMs than the
tinnitus matches. These differences would not
be expected to be simply a result of ipsilateral
versus contralateral loudness matching (Tyler
and Conrad-Armes, 1983a) .
The current study quantitatively describes
test-retest variability of loudness matches using interrupted tones and is in general agreement with others reporting small variations in
loudness (Bailey, 1979 ; Vernon et al, 1980 ;
Tyler and Conrad-Armes, 1982). The current
study is not in agreement with other findings of
large variations in loudness matches (Penner,
1983) and we do not have an explanation for
this . Several different methods of measuring
the loudness of tinnitus have been reported and
large differences have been reported between
loudness matches in the tinnitus region and
those at frequencies very different from the
tinnitus pitch (Goodwin and Johnson, 1980 ;
Tyler and Conrad-Armes, 1983a) . The loudness
matches in the present study are consistent
with these findings .
There are some differences between the
method used in the current study and other
studies. These differences make quantitative
comparisons with the other studies difficult.
The thresholds and loudness matches in the
current study were collected a few minutes
apart, whereas, in other studies they have been
collected sequentially, that is, the threshold and
loudness are determined at one frequency and
then the next, etc. This procedural difference
may have increased the SEM of the loudness
match in the current study. Also, in other studies, continuous tones have been used to match
and to mask tinnitus, whereas, in the current
study periodically interrupted tones have been
used . Hearing thresholds may be different when
periodically interrupted stimuli are compared
with continuous stimuli (Jerger and Herer,
1961), especially when retrocochlear deficits
have not been ruled out. Similarly, one could
expect differences between loudness matches of
tinnitus obtained with continuous or interrupted
stimuli.
Comparisons between studies of the loudness of external tones and the loudness of
tinnitus are somewhat tenuous. However, it
148
!,1a
ii
. .,
~wu~L11 :
I
Measuring Tinnitus Parameters/Mitchell et al
should be noted that near threshold, at levels
similar to tinnitus, the intensity difference limen
and the just noticeable difference in loudness
are larger than those obtained at higher levels,
such as at 40 dB SL (Stevens, 1955 ; Houtsma et
al, 1980 ; Schlauch and Wier, 1987). In psychophysical studies, when comparisons are made
between two low level sounds, there is a consistent tendency to underestimate intensity (Stevens
and Tulving, 1957). Data in the current study
suggest that the sensation level of an external
tone, 10 to 25 dB SL, designed to simulate
tinnitus was also underestimated (see Table 3
and Fig. 2) . This suggests that subjects with
tinnitus, tested with this method, may underestimate the loudness of their tinnitus ; however,
the effects of long-term adaptation of the external stimulus cannot be ruled out.
In the current study, two types of loudness
matching curves of tinnitus were found. In the
first type, the loudness curve is parallel with the
hearing threshold and is also called congruent
(Feldmann, 1971). In the second type, the loudness curve converges upon the threshold in the
high frequencies. The presence of both types
have been reported previously (Feldmann,1981 ;
Mitchell, 1983) and parallel curves, as shown in
Figure 1, are commonly found (Feldmann,1971 ;
Mitchell, 1983 ; Tyler and Conrad-Armes,1983a) .
Loudness matching to external stimuli
yields parallel equal loudness curves when hearing is normal . When hearing loss is present,
especially in high frequencies, loudness matching curves usually converge with the hearing
thresholds and parallel loudness curves in subjects with hearing loss are not commonly reported (Reger, 1936).
Similarities between the loudness of external tones and the loudness of tinnitus are suggested by the above studies. When the damage
is limited to the high frequency regions, the
loudness contours in both external tones and
tinnitus converge on the hearing threshold. It is
possible to speculate that when the hearing loss
extends into the low frequencies, both tinnitus
loudness curves and conventional loudness
curves may be parallel . How differences in the
area of damage are related to the origin or
generation of tinnitus is not known. Further
studies where the loudness curves of external
stimuli are compared with the loudness curves
of tinnitus in the same subjects are needed .
Pitch Match
Test-retest differences in pitch are shown
in Tables 3 and 4 for the nontinnitus and tinnitus
subjects respectively . Similarities between the
mean difference and SEM in each group suggest
that the data are internally consistent in both
groups . A comparison of the tinnitus test-retest
values with other studies does not show major
differences (Mortimer et al, 1940 ; Graham and
Newby, 1962 ; Lindberg et al, 1987). Mean testretest differences and SEMs were similar between tinnitus and external stimuli, a finding
different from those reported by others (Penner,
1983 ; Tyler, 1992). These results indicated that
external tones were more reliably matched than
tinnitus sensations . However, in both studies
subjects reported that their tinnitus fluctuated .
Also the external stimuli, in at least one study
(Penner, 1983), were presented to the same ear
and interactions between the two stimuli being
matched could provide cues, such as beats, which
could aid the external tone matching . These
interactions were avoided in the current study
by presenting the matching tones to the ear
contralateral to the tone being matched.
In the current study, subjects with constant
tonal tinnitus were selected. This type oftinnitus
is the most common type of tinnitus, found in
about 74 percent ofthe clinic population (Meikle
and Griest, 1989). Pitch matching is far less
ambiguous and probably an easier task in cases
of tonal tinnitus . The perception of a tone is
usually associated with localized, such as
punctate or regular, activity in the auditory
system . Thus, it is surprising that one researcher
reported that of six patients with head injury,
where one would expect diffuse damage, five
patients matched their tinnitus to tones and
even reported beats with external stimuli
(Lackner, 1976).
Masking Level
Representative masking curves of tinnitus
are shown in Figure 1 and the across-session
SEMs of the masking levels for the group of
subjects with tinnitus are shown in Table 5 .
Although there are tantalizing similarities between the masking of external sounds and the
"masking" of tinnitus (Wegel, 1931 ; Formby
and Gjerdingen,1980; Shailer et a1,1981; Burns,
1984), it has been clear for many years that
these processes are not the same (Josephson,
1931 ; Langenbeck, 1953 ; Mitchell, 1983 ;
Feldmann,1984b) . One researcher (Langenbeck,
1953) concluded, "the law of masking is not
true" when masking tinnitus . Several studies
have confirmed and quantified these early findings (Feldmann, 1971 ; Penner, 1980 ; Shailer et
Journal of the American Academy of Audiology/Volume 4 Number 3, May 1993
al, 1981 ; Tyler and Conrad-Armes, 1982, 1984;
Mitchell, 1983 ; Penner,1987) . Feldmann (1984)
concluded that the masking of tinnitus was not
based on mechanical interaction but neural
inhibition . If we accept that the process is different, it is possible that the "masking" of tinnitus
may involve both masking and neural interactions. This poses the dilemma of how to study
tinnitus with these techniques when the input
stimulus (tinnitus) is unknown and its "masking" could involve mechanical as well as neural
processes.
Monitoring Tinnitus
One of the reasons for obtaining psychophysical measures of tinnitus is to monitor
changes in tinnitus . Reliable measures of tinnitus are needed to allow treatment-related
changes in tinnitus to be studied. The determination of test-retest variability is a prerequisite
to the detection of significant changes. The SEM
data in Tables 2 and 5 describe the acrosssession, test-retest variability of tinnitus loudness and masking levels . These data suggest
that the variation in masking levels is smaller
than loudness matches. The fact that loudness
has a larger SEM in relation to its range than
the masking level makes it more difficult to
show significant changes in loudness, except
when the tinnitus is completely abolished. For
these reasons, the masking might be preferred
for monitoring purposes .
Fausti SA, Frey RH, Henry JA, Knutsen JL, Olson DJ.
(1990) . Reliability and validity of high-frequency (8-20
kHz) thresholds obtained on a computer-based audiometer as compared to a documented laboratory system .
J Am Acad Audiol 1:162-170 .
Feldmann H. (1971) . Homolateral and contralateral masking oftinnitus by noise-bands and by pure tones. Audiology 10 :138-144 .
Feldmann H. (1981) . Homolateral and contralateral masking of tinnitus . Proceedings of the First International
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4(Suppl) :60-70 .
Feldmann H. (1984a). Masking-mechanisms JPSI,
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Feldmann H. (1984b). Tinnitus masking curves (updates
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Formby C, Gjerdingen DB . (1980) . Pure-tone masking of
tinnitus . Audiology 19 :519-535 .
Goodwin PE, Johnson RM . (1980) . The loudness of
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Graham JT, Newby HA . (1962) . Acoustical characteristics of tinnitus . Arch Otolaryngol 75 :162-167 .
Hazell JWP. (1981) . Measurement oftinnitus in humans .
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