Pure tone audiometry (PTA) is not the only means by which audiometric thresholds are measured. Audiometric thresholds can also be measured with a Békésy audiometer and through computerized audiometry.
‘The basic idea behind the Békésy audiometer is that the patient records his own threshold automatically on an audiogram blank. When the audiometer is turned on, a pure tone of very low frequency comes into the earphone, and a motor causes the frequency to move slowly upward. At the same time another motor causes the tone to become gradually louder. As soon as the patient hears the tone he pushes a button. This reverses the loudness motor and the tone becomes gradually fainter. As soon as the patient doesn’t hear the tone any more he releases the button. This reverses the loudness motor again and the tone gets gradually louder. The patient keeps doing this over and over; pushing the button when he hears the tone, and releasing the button when he doesn’t hear it. All this time the frequency is moving slowly upward [a ‘glide tone’[i]]’.[ii]
Thus, the key difference between PTA and Békésy-generated audiometry is the fact that the former is generated with the input of a qualified specialist audiometrician (who selects the frequency and hearing level of the test subject, as well as noting down responses), i.e. manually generated, whereas the latter is self-reported, i.e. automatically generated.
In some cases, it may be that claimants have undergone conventional PTA testing, but disclosed occupational health (OH) records also contain Békésy audiograms.
Given that both types of audiometry are directly incomparable (in PTA, the intensity of noise stimuli increases by distinct 5 dB increments), what action can be taken for Békésy to be equated with PTA?
For a succinct answer to this question, we need look no further than the analysis of Parklane Plowden barrister, Jim Hester, who addressed this issue in one of his recent blog posts.[iii]
He derives the formula for adjusting hearing threshold level readings from Békésy audiometry to PTA by quoting the ‘Black Book’ [Assessment of Hearing Disability: Guidelines for Medicolegal Practice, by King, Coles, Lutman and Robinson[iv]], in accordance with British Standard (BS) 6655:1986:[v]
‘Add 3 dB to the self-recorded measurement, then round to the nearest 5 dB’.
The ‘Black Book’ includes example adjustments for 2 Békésy tests – see our table, below:
Of course, whether or not it is necessary to make these adjustments is primarily conditional upon the perceived reliability and accuracy of Békésy audiograms.
In the case of Aldred v Cortaulds Northern Textiles Limited (2012),[vi] HHJ Wood QC summarised the medical experts’ opinion on Békésy audiometry, as follows:
‘It was an intermittent test that sometimes produced better thresholds than the pure tone audiograms which required a technician to measure. He [Mr. Zeitoun] felt that it was a reliable test if carried out in good conditions. Mr Parker did not demur from this general observation’.
However, this is not to say that Békésy audiometry is without controversy, nor that it cannot be disregarded.
For instance, in Ransome v Secretary of State for Energy & Climate Change (2018),[vii] HHJ Saffman established that a Békésy audiogram (dated 1989), was unreliable.[viii] He did so, having accepted deficiencies identified by ENT Consultant, Mr Ahmad, namely that the person operating the audiometric equipment was not as skilled as expected.
Thus, the ‘Black Book’ method of modifying Békésy audiometry should only be completed on a case-by-case basis, as the merit of each audiogram can vary.
[i] Lawton BW, ‘ISVR Technical Report (No 336): Variability of the threshold of hearing: Its importance in cases of noise induced hearing loss’ (April 2015 University of Southampton) <https://eprints.soton.ac.uk/383189/1/__userfiles.soton.ac.uk_Users_slb1_mydocuments_Intreppdf_TR336.pdf> accessed 15 January 2021.
[ii] Jerger J, Bekesy Audiometry. International Audiology. (1962) 1:2, 160-164, <https://www.tandfonline.com/doi/abs/10.3109/05384916209074031> accessed 15 January 2021.
[iii] Jim Hester, Adjusting Self-Recording Audiometry to compare to Pure Tone Audiometry’ (15 July 2020) <https://jimhester.me/2020/07/adjusting-self-recording-audiometry-to-compare-to-pure-tone-audiometry/> accessed 15 January 2021.
[iv] Whurr Publishers Ltd (1992).
[v] BS 6655:1986, EN 26189:1991, ISO 6189:1983. Specification for pure tone air conduction audiometry for hearing conservation purposes. British Standards Institution, London. <https://shop.bsigroup.com/ProductDetail/?pid=000000000000152460> accessed 15 January 2021.
[vi] Liverpool County Court, November 2012.
[vii] Leeds County Court, July 2018.
[viii] Taymour Akhtar, ‘Békésy Audiometry – Reliability Tested’ (25 October 2018 Curtis Law) <https://curtislaw.co.uk/latest-news/b%C3%A9k%C3%A9sy-audiometry-reliability-tested/> accessed 15 January 2021.