2Beyond the audiogram
The audiogram is the most useful single test in audiology and the worst single guide to whether a hearing aid will satisfy. It does exactly one thing: it finds the quietest tone a person can detect at each frequency. That is audibility — and audibility is real and important — but it is only the surface. Beneath it lie the suprathreshold properties of the cochlea: how loudness grows, how finely the ear resolves frequency and time, whether parts of it are functionally dead. Two people with superimposable audiograms can hear speech entirely differently because these hidden correlates differ. This module draws the distinction the rest of the chapter depends on: making sound audible is not the same as making it intelligible.
FWhat the audiogram measures
The pure-tone audiogram plots detection thresholds — the softest tone audible at each frequency — and grades loss from mild to profound. It is quick, reliable, and indispensable for describing how much sensitivity has been lost and where. What it cannot describe is what happens to sounds that are well abovethreshold — which is most of speech.
FTWhat it hides
Below the waterline sit the suprathreshold correlates of sensorineural loss: loudness recruitment (abnormally rapid loudness growth), reduced frequency resolution (broadened cochlear filters), reduced temporal resolution, cochlear dead regions, and the general distortion these produce. None of them shows on the audiogram, yet together they decide whether amplified speech is clear or merely loud.[1991]
TAudible is not intelligible
The single most important idea in this chapter is the gap between audible and intelligible. Audibility can be restored by amplification; intelligibility depends on the cochlea's ability to process the now-audible sound — and that ability is damaged. Audibility is a strong predictor of aided speech recognition, but only up to a point; beyond it, distortion and noise break the link.[2007]
CWhy this matters for the aid
This is why a patient can have a hearing aid perfectly fitted to their audiogram — every frequency made audible — and still complain that speech is loud but unclear, especially in noise. The aid did its measurable job; the audiogram simply did not capture the deficits that mattered. Recognising this turns the rest of the chapter into a tour below the waterline: the distortions, one by one, that amplification cannot reach.
What is the explanation?
What does the pure-tone audiogram actually measure?
Which suprathreshold correlates does the audiogram fail to capture?