Pure-tone audiometry

Pure-tone audiometry is a subjective, behavioural measurement of a hearing threshold, as it relies on patient responses to pure tone stimuli.

Pure-tone audiometry only measures audibility thresholds, rather than other aspects of hearing such as sound localization and speech recognition.

However, there are benefits to using pure-tone audiometry over other forms of hearing test, such as click auditory brainstem response (ABR).

Although pure-tone audiometry has many clinical benefits, it is not perfect at identifying all losses, such as ‘dead regions’ of the cochlea and neuropathies such as auditory processing disorder (APD).

The BSA-recommended procedures provide a "best practice" test protocol for professionals to follow, increasing validity and allowing standardisation of results across Britain.

[8] In the United States, the American Speech–Language–Hearing Association (ASHA) published Guidelines for Manual Pure-Tone Threshold Audiometry in 2005.

Sound field audiometry may be more suitable when patients are unable to wear earphones, as the stimuli are usually presented by loudspeaker.

Therefore, high frequency audiometry is an effective method of monitoring losses that are suspected to have been caused by these factors.

[12] When sound is applied to one ear the contralateral cochlea can also be stimulated to varying degrees, via vibrations through the bone of the skull.

[17] Several studies have investigated whether self-reported hearing problems (via questionnaires and interviews) were associated with the results from pure-tone audiometry.

The results of this review indicated that there were two factors of a hearing loss, which were involved in the effect on speech intelligibility.

The increase in SRT depends on the degree of hearing loss only, so Factor A reflects the audiogram of that person.

[20] The shape of the audiogram resulting from pure-tone audiometry gives an indication of the type of hearing loss as well as possible causes.

Conductive hearing loss due to disorders of the middle ear shows as a flat increase in thresholds across the frequency range.

Presbycusis or age-related hearing loss for example is characterized by a high frequency roll-off (increase in thresholds).

Interaural attenuation with bone conduction
Figure 10: Speech recognition threshold (SRT) with noise. To aid explanation of this concept the CHL and the SNHL have the same magnitude of hearing loss (50 dBHL). The horizontal part of the curves is where the noise is inaudible. Thus, there is no masking effect on the SRT. The horizontal portion of the curve for the SNHL and CHL extends further than that for a normal hearing person, as the noise needs to become audible to become a problem. Thus, more noise has to be applied, to produce a masking effect. At the right hand side of the graph, to identify 50% of the speech correctly, the speech needs to much more intense than in the quiet. This is because at this end of the graph, the noise is very loud whether the person has a hearing loss or not. There is a transition between these two areas described. Factor A is a problem only in low noise levels, whereas Factor D is a problem when the noise level is high.