Tinnitus Archive > Data Sets > 1 > Methods > Tinnitus Clinic Test Protocol
All patients received routine audiometric evaluation including discrete-tone threshold testing and speech audiometry. For most of the patients, HL - hearing level (in dB) were determined at 8 frequencies (0.25, 0.5, 1, 2, 3, 4, 6, and 8 kHz. ( However, a small percentage of patients with recent audiograms performed elsewhere were not retested; in some of those cases, data were not available for one or more frequencies, most commonly at 3k and/or 6k Hz). Bone-conduction thresholds were always obtained when there was reason to suspect conductive hearing impairment. (See Audiometric Tests coding form.)
Development of standardized methods for measuring the pitch, loudness, and other characteristics of tinnitus was completed prior to the initiation of the Tinnitus Data Registry (Vernon, 1977; Vernon & Meikle, 1981; Vernon & Schleuning, 1978). Briefly, all testing was done with extended-frequency earphones (e.g. Koss Pro/4x), using the Norwest SG-1 Tinnitus Synthesizer Vernon & Fenwick, 1984. The basic test protocol involved measurement of four tinnitus parameters: (1) pitch, (2) loudness match to external tones, (3) maskability, and (4) residual inhibition. (Also see Tinnitus Test Results coding form.)
In general the test ear was the ear contralateral to the predominant or louder tinnitus, if there was a difference between the two sides. If the tinnitus was equally loud on both sides or was localized in the head, the test ear was the one with the better hearing (the ear was chosen randomly if there was no difference between the acuity of the two ears). A two-alternative forced-choice (2AFC) method was used, in which pairs of tones were presented and subjects were asked to identify which one best matched the pitch of their tinnitus. Test frequencies were typically multiples of 1 kHz. Before each tone pair was presented, each tone was adjusted to a loudness level equivalent to that of the tinnitus (see details of loudness-matching). Once the dB settings for a given pair of tones were established the two tones were then presented in alternating manner until the subject indicated which one was closest to the pitch of the tinnitus. A typical test sequence might yield a pitch match of 4000 Hz as the closest to the tinnitus pitch, as follows:
| Comparison Tones (Hz) | Tone Judged Most Like Tinnitus | |
| Trial 1 | 1000 vs 2000 | 2000 |
| Trial 2 | 2000 vs 3000 | 3000 |
| Trial 3 | 3000 vs 4000 | 4000 |
| Trial 4 | 4000 vs 5000 | 4000 |
Care was taken to randomize the selection of which tone is presented first in each trial, so that the lower of the two frequencies was not always the one presented first. Using the same 2AFC procedure, a test for "octave confusion" was then performed:
| Comparison Tones (Hz) | Tone Judged Most Like Tinnitus | |
| Trial 5 | 4000 vs 8000 | 4000 |
If the patient had selected 8000 as the best match for the pitch of his tinnitus, stopping the test after Trial 4 would have yielded an erroneous pitch match that was one octave too low.
Because the majority of tinnitus patients have high-pitched tinnitus, there was seldom need for the test procedure to include tones below 1 kHz. Occasionally, however, patients indicated that 1 kHz was higher-pitched than their tinnitus. In those cases the selection of test frequencies below 1 kHz was left to the discretion of the examiner.
The test ear was normally the contralateral ear, as described in the procedure for tinnitus pitch matching. As indicated there, a loudness match for the subject's tinnitus was obtained at each of the test tones used in the pitch-matching procedure. The loudness-matching technique used in the Oregon Tinnitus Clinic involved the following steps at each test frequency of interest:
In the present document, only the loudness matches at 1 kHz and at the tinnitus pitch are provided. (However, it should be noted that the pitch-matching method described above could be used to plot loudness as a function of test frequency, i.e. a "loudness function" (Meikle, Henry, & Mitchell, 1996).
Maskability of tinnitus: Minimum Masking Levels (MMLs)
This test attempted to determine the lowest level at which a standard band of noise "covered" the tinnitus (i.e. rendered it inaudible). The test ear was typically on the side with the louder or predominant tinnitus; if there was no difference between the sides, each ear was tested separately. In many cases, binaural masking tests were also performed to determine the dichotic MML . The test stimulus consisted of a standardized band of noise generated by the Norwest Synthesizer (2k-12 kHz, rolling off at approximately 12 dB per octave) The patient's threshold for the noiseband was measured in dB SL , and the level of the noiseband was then raised in 1 dB increments until the patient reported that the tinnitus was no longer audible (up to the limits of the equipment or the patient's tolerance level, whichever was reached first). The level at which the tinnitus was just rendered inaudible was recorded in dB SL and was referred to as the Minimum Masking Level (MML) . When the masking sound was able to render the tinnitus inaudible, that result was recorded as "complete masking". In some cases, the masking stimulus was only able to make the tinnitus somewhat less audible (i.e. quieter than usual), regardless of the stimulus level, a result that was recorded as "partial masking". In a small percentage of cases, the masking stimulus had no effect on the loudness of the tinnitus (masking effect recorded as "none") and in rare cases, the tinnitus was reported as louder for a short period following the presentation of the masking stimulus (recorded as "exacerbation of tinnitus").
Following the masking tests (and assuming there was no exacerbation of the tinnitus), the level of the masking stimulus (2k-12 kHz noiseband) was adjusted to MML + 10 dB. Prior to turning the stimulus on, the patient was instructed that the masking sound would now be presented for 1 minute, but that if it was uncomfortable the patient should ask to have it terminated. The masking stimulus at +10 dB was then presented for exactly 60 seconds; as soon as it was turned off, the patient was asked "How does your tinnitus sound right now?" This test was repeated for each ear, if appropriate, and in addition may be done binaurally (diotically).
Most commonly, patients reported that their tinnitus was reduced or absent in the stimulated ear, for a brief interval ranging from a few seconds to many minutes; after that, the typical situation was that the tinnitus gradually returned to its normal loudness level. The examiner then recorded the duration of the suppression or inhibition. About 10-12% of patients do not exhibit residual inhibition following a masking trial such as that described here.
When it occurs, the tinnitus suppression may be complete (CRI) or partial (PRI) or some combination of these two effects, and the effects may occur differently for the two ears of a given patient. The most common result was to obtain complete residual inhibition followed by partial residual inhibition, typically for no more than approximately 30-60 seconds (but longer intervals were fairly common). All possible permutations of the various types of effect (none, partial, or complete suppression, as well as tinnitus exacerbation in a few cases) have been observed in the patient population of the Tinnitus Clinic.
Evaluation of ear-level equipment, and Clinic recommendations
Following the synthesizer tests described above, patients' reactions to the use of ear-level (wearable) equipment were evaluated using a variety of commercially-available devices. However, detailed procedures for evaluating such devices are not included in this summary of tinnitus testing methods, as data from such evaluations have not yet been added to the Archive.