clinical forum: measuring tinnitus parameters: loudness, pitch… · j am acad audiol 4: 139-151...

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 deter-mine the test-retest variability of each measure. The test-retest standard error of measure-ment, 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

C omparing tinnitus with external sounds has been the subject of a number of stud-ies (Wegel, 1931 ; Mortimer et al, 1940;

Reed, 1960 ; Graham and Newby, 1962 ; Feld-mann, 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 at-tempts 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 re-ported 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).

*Oregon Hearing Research Center, Department of Otolaryngology, Oregon Health Sciences University, Port-land, Oregon

Reprint requests : Curtin R . Mitchell, Oregon Hear-ing 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 pre-sented 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 labo-ratory methods. Clinical methods may be criti-cized as lacking warm-up procedures and hav-ing uncontrolled training effects as well as us-ing response criteria that are not standardized . In some cases, large frequency or intensity in-crements have also been used . Although labora-tory 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 thresh-olds, 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 deter-mine the test-retest reliability . The within- and across-session test-retest reliability was asses-sed 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 reli-ability 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 thresh-olds 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 low-level 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. A three-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 sub-jects were used for the different tasks.

Pure-tone stimuli were generated by a Hewlett Packard synthesizer/function genera-tor (#3325A) and were controlled with modular Coulbourn attenuators and a rise/fall gate to produce periodically interrupted tones. The low-level 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 pre-cision dB attenuator (350D) . Stimuli were deliv-ered 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 mini-mum masking levels . These measures were obtained using 1-dB steps for intensity and '/3-octave 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 loud-est.

The commonly used procedure for matching tinnitus involves presenting stimuli to the ear contralateral to the tinnitus sensation. The pro-cedure 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 re-sidual inhibition and temporarily altering the tinnitus sensation. We expected to encounter this problem (as mentioned previously), so short duration stimuli and ascending sequences in 1-dB 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 pretest-ing 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 inhibi-tion 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 instruc-tions to be read and discussed. This resulted in 15 to 30 minutes of each session spent on in-structing 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' suit-ability 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

Measuring Tinnitus Parameters/Mitchell et al

small amount of contralateral stimulation-in-duced tone decay was observed in some subjects (Scharf, 1991).

Contralateral matching was used in non-tinnitus subjects to avoid beats or other interac-tions between the continuous tone, used to simu-late tinnitus, and the periodically interrupted matching tone, as these interactions invalidate the matching procedures . Masking of the simu-lated 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 determi-nation were periodically interrupted pure tones, 500 msec on and 233 msec off, with 25 msec rise-decay 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, al-lowing 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 posi-tion 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 re-sponse or alter the stimulus sequence .

At each frequency, the tones were initially increased in 3-dB steps until the subject re-sponded (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 fre-quency . 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 of each test session


nine tones were presented, of which three fre-quencies 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.

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 inter-rupted 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 sub-ject'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 ran-dom order of frequency from a computer gener-ated 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 presen-tations of the first frequency on the list . A much

smaller loudness difference was seen between the second frequency on the list and its repeat presentation . By the third frequency, the loud-ness 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 differ-ence 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-inten-sity tone, was matched in the contralateral ear using the same procedure.

Pitch Matches

Pitch matches were obtained using a two-alternative forced-choice procedure. Two tones were presented at the intensity levels previ-ously matched to tinnitus or to the simulated tinnitus . The duration of each tone was 2 sec-onds (25 msec rise-decay) with zero delay be-tween 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 ex-pected in pitch matching. In the current study, these effects were embedded in the procedure. The procedure began with wide frequency spac-ing (2/3 octave) and no subject reported difficulty hearing this pitch difference . The smaller spac-ing (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

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by 1/3-octave, such that each frequency was paired with every other frequency and pre-sented in forward as well as reverse order. The tone selected the greatest percentage of time was reported as the pitch match. Tones at oc-tave 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 deter-mined 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 negligi-ble 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 be-tween the masking level obtained upon repeated presentation of the third tone was used as a measure of within-session reliability . As previ-ously mentioned, no masking levels were deter-mined 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 psycho-physical measures of tinnitus, the test-retest variability was of particular interest . The test-retest 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 sub-jects (Anastasi,1982) . For this reason the across-session SEMs were calculated for hearing thresh-olds, loudness and pitch matches, and for mask-ing levels . Comparisons between the SEM and the reliability of tinnitus and nontinnitus sub-jects were also made.

The relationship between the loudness and masking levels of tinnitus varies from one sub-ject 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 mid-way 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) demon-strated this type . The fourth type, depicted in Figure 1D, demonstrates a resistance to mask-ing 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 dif-ferent 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


Figure l. Four types of subjects with respect to hearing thresh-olds, loudness and masking lev-els 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 match-

Frequency (Hz) es are indicated by arrows on the abscissa .

not show significant changes in threshold, within or between tests.

Loudness and Pitch

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 Conrad-Armes, 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 Table 2 Loudness Match Test-Retest Results for Nontinnitus and Tinnitus Subjects for Nontinnitus and Tinnitus Subjects

Frequency Nontinnitus Subjects Tinnitus Subjects Frequency Nontinnitus Subjects Tinnitus Subjects (Hz) (n = 15) (n = 19) (Hz) (n = 14) (n = 19) 1000 4.1 5.5 1000 2 .8 5 .0 1260 4 .0 3 .5 1260 2 .5 4 .5 1590 2 .1 6 .6 1590 3 .0 6 .6 2000 1 .7 3 .3 2000 2 .8 6 .5 2520 2 .1 3 .2 2520 2 .7 5 .1 3175 2 .6 2 .8 3175 3.0 3.9 4000 2 .3 2 .4 4000 2 .9 4 .2 5040 2 .7 3 .5 5040 2 .2 5 .9 6350 4.4 2 .5 6350 3 .9 5 .0 8000 3.5 6 .2 8000 4 .6 5 .8 10080 3.4 2 .4 10080 5 .1 3 .6 12700 4.7 3 .0 12700 2 .7 5 .0

Mean SEM 3.13 3.74 Mean SEM 3.18 5 .09 Data is given in dB . Data is given in dB SL .

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Table 3 Loudness and Pitch Matches for Nontinnitus Subjects Loudness Match (dB SL) Pitch Match (Hz)

Presentat ion First Second LM Diff Absolute First Second PM Diff PM Diff Subject Level (dB SL) (dB) LM Diff (dB) (Hz) (Octaves) NT1 25 18 17 1 1 2520 2520 0 0 NT2 15 19 24 -5 5 3175 2000 1175 0.67 NT3 15 1 4 -3 3 2000 2000 0 0 NT4 24 15 21 -6 6 2000 3175 1175 0 67 NT5 13 -5 1 -6 6 2520 1590 930

. 0 67 NT6 22 18 8 10 10 6350 2000 4350

. 1 67 NT7 19 6 7 -1 1 4000 1260 2740

. 1 67 NTS 20 11 12 -1 1 2520 2000 520

. 0 33 NT9 15 20 16 4 4 1260 1260 0

. 0 NT10 10 6 8 -2 2 2000 2000 0 0

NT11 15 11 10 1 1 2000 1590 410 0 33 NT12 10 0 2 -2 2 2520 4000 1480 .

0 67 NT13 20 21 14 7 7 2520 2000 520 .

0 33 NT14 20 6 15 -9 9 2200 3175 975 .

0 .54

Mean -0 .9 4 .1 1020 0 54 SD 5.22 3 .08 1220 .

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-ses-sions, were slightly smaller for nontinnitus sub-jects matching to simulated tinnitus than sub-

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 sub-jects are shown in Table 3. The mean of the

Table 4 Loudness and Pitch Matches for Tinnitus Subjects

Subject Loudness First

Match (dB SL ) Second LM Diff (dB) Absolute

LM Diff (dB)

Pitch First

Match (Hz) Second PM Diff

(Hz) PM Diff

(Octaves) T1 4 2 2 2 6700 6500 200 0 03 T2 -6 -3 -3 3 2000 3175 1175

. 0 67 T3 7 -1 8 8 4000 2520 1480

. 0 67 T4 17 10 7 7 3175 2520 655

. 0 33 T5 7 4 3 3 6350 6350 0

. 0 T6 11 14 -3 3 4000 8000 4000 1 T7 12 18 -6 6 10080 8000 2080 0 33 T8 22 28 -6 6 5040 4000 1040

. 0 33 T9 1 -2 3 3 12700 10080 2620

. 0 33 T10 4 3 1 1 8000 8000 0

. 0 T11 17 12 5 5 6350 8000 1650 0 33 T12 8 7 1 1 1590 1000 590

. 0 66 T13 -2 -4 2 2 1000 1260 260

. 0 33 T14 9 13 -4 4 10080 12700 2620

. 0 33 T15 4 8 -4 4 8000 10080 2080

. 0 33 T16 2 12 -10 10 5040 4000 1040

. 0 33 T17 16 2 14 14 12700 5040 7660

. 1 33 T18 2 5 -3 3 12700 6350 6350

. 1 T19 6 4 2 2 5040 2520 2520 1

Mean 0.5 4 .6 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 sub-jects, (NT6, NT13, NT14) the loudness differ-ence was greater than 2 SEM, indicating greater loudness match variability than would be ex-pected by chance (0.05 level) . Since the actual loudness presented remained the same in both sessions, it appears that the across-session reli-ability of these three subjects was poor, how-ever, the within-session reliability in these sub-jects was quite good .

For the tinnitus subjects, the mean abso-lute 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 loud-ness 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 be-tween tests more than would be expected by chance .

Two subjects in the tinnitus group and two subjects in the nontinnitus group showed loud-ness differences greater than 8 dB. This sug-gests 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 de-scribed. 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 across-session test-retest correlations varied from 0.58 to 0.96 at different frequencies . The within-session 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 ses-sions 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 loud-ness matches (see Table 2) and the masking

Table 6 Minimum Masking Levels Table 5 Minimum Masking

Results for Tinnitus

Frequency (Hz)

Level Test-Retest Subjects

Tinnitus Subjects ubject

at the

MML 1

Pitch Match

MML 2

of Tinnitus

Relative MML Diff

Absolute MML Diff

(n = 13) T5 11 18 7 7

1000 8.7 T7 17 26 9 9 1260 3.3 T6 26 18 -8 8 1590 4.9 T8 20 15 -5 5 2000 5 .4 T9 5 5 0 0 2520 3 .5 T11 21 20 -1 1 3175 3 .1 T12 10 17 7 7 4000 3 .1 T14 10 10 0 0 5040 4 .7 T15 5 14 9 9 6350 4.3 T16 11 16 5 5 8000 5.9 T18 2 6 4 4 10080 2 .1 T19 8 5 -3 3 12700 2 .8

Mean 2.0 4 .8 Mean SEM 4.32 SD 5.7 3 .3

Data is given in dB . Data is given in dB SL .

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levels (see Table 5) in tinnitus subjects suggests that the masking level has slightly smaller test-retest variability .

Across-Session Test-Retest Variability

Test-retest correlation coefficients in sub-jects 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, espe-cially in relation to the SEM, while the range for the pitch of tinnitus is very large (see Table 4) . Thus, differences between the correlation coef-ficients 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 exter-nal 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

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 inde-pendent 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 signifi-cant 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 sub-ject 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 thresh-old of hearing (see Fig. 1) . While each of these separate measures has been previously reported in subjects with tinnitus, there are no reports

20

10

5

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20 - 5 1 - 3 - 9 - 1 1 1 e

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 be-tween 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) .

30

25

20

15 00

10 0

5 O

88 e

0

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10 -5 0 5 10 15 20 25

Loudness Match, dB SL

Figure 3 Loudness levels and minimum masking lev-els at the frequency matched to the tinnitus . This rela-tionship 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 .


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 meas-ure of the test-retest variability across sessions and subjects . The SEM is considered useful when repeated testing is used, because a confi-dence 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, loud-ness 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 thresh-olds 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 rec-ognized that a two-interval, forced-choice proce-dure 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 investi-gators (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 evi-dence that tinnitus masked or otherwise inter-fered 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 loud-ness matches of tinnitus and that of an external tone (simulated tinnitus) are shown in Table 2. These test-retest SEMs of matches to an exter-nal 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 us-ing interrupted tones and is in general agree-ment 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 stud-ies, 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 loud-ness of external tones and the loudness of tinnitus are somewhat tenuous. However, it

148

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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 psycho-physical studies, when comparisons are made between two low level sounds, there is a consist-ent 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 underes-timate the loudness of their tinnitus ; however, the effects of long-term adaptation of the exter-nal 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 loud-ness 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 hear-ing is normal . When hearing loss is present, especially in high frequencies, loudness match-ing curves usually converge with the hearing thresholds and parallel loudness curves in sub-jects with hearing loss are not commonly re-ported (Reger, 1936).

Similarities between the loudness of exter-nal tones and the loudness of tinnitus are sug-gested 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 test-retest differences and SEMs were similar be-tween 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 be-tween 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 find-ings (Feldmann, 1971 ; Penner, 1980 ; Shailer et


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 differ-ent, it is possible that the "masking" of tinnitus may involve both masking and neural interac-tions. This poses the dilemma of how to study tinnitus with these techniques when the input stimulus (tinnitus) is unknown and its "mask-ing" could involve mechanical as well as neural processes.

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 audio-meter as compared to a documented laboratory system . J Am Acad Audiol 1:162-170 .

Feldmann H. (1971) . Homolateral and contralateral mask-ing of tinnitus by noise-bands and by pure tones. Audiol-ogy 10:138-144 .

Feldmann H. (1981) . Homolateral and contralateral mask-ing of tinnitus . Proceedings of the First International Tinnitus Seminar, New York, 1979 . J Laryngol Otol 4(Suppl) :60-70 .

Feldmann H. (1984a). Masking-mechanisms JPSI, contralateral masking) . J Laryngol Otol Suppl 9:54-58 .

Monitoring Tinnitus

One of the reasons for obtaining psycho-physical measures of tinnitus is to monitor changes in tinnitus . Reliable measures of tinni-tus are needed to allow treatment-related changes in tinnitus to be studied. The determi-nation of test-retest variability is a prerequisite to the detection of significant changes. The SEM data in Tables 2 and 5 describe the across-session, test-retest variability of tinnitus loud-ness 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 .

Acknowledgment . This work was supported by Dept . of Education Project #610860006 .

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n ki ft ' 11mH An I 11110 iptlkl 141 e r 1111 Oil I I I I I fll 41 l ~illllg~ r11R~1

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