14Psychoacoustic Measures and Severity Grading

FThe visual analogue scale — fast, flexible, dimensional

The visual analogue scale (VAS) is the simplest measure in the tinnitus clinic: a line, usually 10 cm or rated 0–10, anchored at “none” and “worst imaginable”, on which the patient marks their experience. Its power is that it can be aimed at any single dimension — loudness, annoyance, distress, or sleep interference — and repeated daily, which makes it ideal for tracking short-term fluctuation and immediate treatment effects [2012].

The crucial teaching point is that loudness and annoyance are separate dimensions. A patient may rate loudness 8 and annoyance 3, or the reverse. Because distress — not loudness — drives help-seeking, the annoyance and distress VAS often matter more clinically than the loudness VAS. Psychometric work has shown the tinnitus VAS to be reliable and valid when used for the dimension it is anchored to [2012].

TPitch matching and loudness matching

Pitch matching asks the patient to compare an externally presented tone with their tinnitus and choose the frequency that sounds closest. The matched pitch usually falls in the region of hearing loss, often near the edge of the audiometric notch, consistent with the central-gain account of tinnitus generation [2014]. Pitch matching is notoriously unstable — patients fall into octave-confusion errors — so it is recorded as an approximation, not a fixed value.

Loudness matching presents a tone at the matched (or a reference) frequency and raises its level until it equals the tinnitus. Strikingly, the matched loudness is usually only a few decibels above threshold — commonly in the order of 5–15 dB sensation level — even in patients who describe their tinnitus as overwhelming. This dissociation between a quiet matched loudness and severe reported distress is one of the most important facts in the field and the strongest argument for measuring handicap separately [2013].

TMinimum masking level and residual inhibition

The minimum masking level (MML) is the lowest level of a broadband (or specified) noise that just renders the tinnitus inaudible. It indexes how readily the tinnitus can be covered and historically helped predict who might benefit from masking-based sound therapy. A low MML means the tinnitus is easily masked; a high MML signals a percept that is hard to cover.

Residual inhibition (RI) is the temporary suppression of tinnitus that some patients experience for seconds to minutes after a masking sound is switched off. It is measured by masking for about a minute and then timing how long the tinnitus stays reduced or absent. RI is fascinating because it is a transient, reproducible reduction of the percept and offers a window onto the plastic neural processes that sustain tinnitus [2013]. Both MML and RI are research-grade measures whose clinical predictive value remains modest, but they remain valuable for characterising the percept.

CWhy the psychoacoustics and the questionnaire disagree

Time and again, matched loudness, MML and pitch correlate weakly with THI or TFI handicap. The percept and the suffering travel on different tracks: the auditory system generates the signal, but limbic and attentional networks set how threatening and intrusive it feels [2013]. A faint tinnitus filtered through a frightened, hypervigilant nervous system can be disabling; a loud one in a calm, well-counselled patient may be a background nuisance.

For the clinician this has a direct consequence: never grade severity from psychoacoustics alone. A patient with 8 dB SL matched loudness who is suicidal is severe, full stop. The psychoacoustic measures characterise and validate the percept; the questionnaire and the patient’s function tell you how bad it is.

CCombining it all into a severity grade

A defensible severity grade triangulates three streams: the self-report handicap (THI/TFI band), the VAS for annoyance and distress, and the functional impact on sleep, mood, work and concentration — with psychoacoustic measures used to characterise rather than to score the percept. Guidelines emphasise that the grade should drive management: mild/non-bothersome tinnitus needs education and reassurance, whereas moderate-to-severe bothersome tinnitus warrants structured intervention [2014].

Document the grade with the numbers behind it — for example, “moderate: TFI 54, annoyance VAS 7/10, sleep-onset insomnia, working but reduced productivity” — so that the next clinician can read both the level and the reasoning, and so that change can be judged against a transparent baseline.