Feasibility study for otoacoustic emission hearing assessment of classical music students

S. Dance, E. Ballestero

School of the Built Environment and Architecture London South Bank University Borough Road, London, UK

ABSTRACT Since the introduction and enforcement of the Control of Noise at Work Regulations in 2008 continuing research has been undertaken on more than five thousand students of the Royal Academy of Music to understand their hearing acuity. Standard pure tone audiometric screening methods were employed for both entry and exit testing for the undergraduate and postgraduate students. Due to COVID-19 standard audiometry was not possible, however it presented an opportunity to trial an otoacoustic emission based hearing assessment. A feasibility study was undertaken in July 2021 involving 119 classical music students. The results showed very similar trends in hearing and thus provide reassurance that OAE can be used to assess the hearing of music students .

1. INTRODUCTION

The Control of Noise at Work Regulations 2005 [1] introduced the requirement to assess the sound exposure of employees and if deemed high to undertake a regular programme of health surveillance. Since 2007, through a long term collaboration with the Royal Academy of Music approximately 330 students each year have been assessed using the standard Bekesy audiometric test procedure to determine hearing acuity [3]. There were many findings from the first 1300 student it was found that musicians consistently had reduced hearing acuity at 6 kHz [4] and that by Hearing Category [2] students had 94% “Good” hearing, 4.5% “Warning” and 1.5% “Referral” levels of hearing [5]. After 2500 students had been tested it was found that 50% of the students had on average negative hearing loss [6], as compared to the general population allowing for age and gender where the assumption was that 75% would have “normal” hearing in accordance with ISO 1999:2017 [7]. Hence, it was necessary to find and trial another solution to assess hearing acuity of classical music students as the final study found that 229 musicians on average improved their hearing on exit testing, 3.5 years later, but the improvement lessened with the level of sound exposure [8].

2. OTOACOUSTIC EMISSIONS Previously otoacoustic emission (OAE) testing has been used on new-born babies as a passive assessment method. However, in November 2019 OAE based hearing screening was

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trailed by audiologists for the Royal College of Music. In total 80 classical music students were assessed over a two week period. This methodology was then included in the newly published British Association of Performance Arts Medicine (BAPAM) Best Practice Guidance as an alternative assessment method [9]. The same instrumentation and analysis software that was used for the Royal College of Music OAE testing was used for the Royal Academy of Music assessment. This provides the dual advantage of consistency and provides the opportunity for comparison of results. The hardware used was the Path Medical OAE Senti instrument using dual ear probes with eight sizes of ear tips to ensure a good seal of the ear canal [10]. The instrument was used in simultaneous mode to speed up the testing procedure, so that an assessment could be undertaken in under three minutes. Hearing Coach software, OAE Expert package was used to provide the cochlear hear damage estimation [13]. 3. HEARING ASSESSMENT A feasibility study involving 119 classical music students was undertaken over a one week period in July 2021. The assessment consisted of a short questionnaire, pre-completed by each student to establish aural history, instrument studied and years of music exposure plus additional information on leisure activities and music listening habits.

Each student was allocated a 10 minute slot for the assessment. The assessment took place in a large well ventilated room at the Royal Academy of Music with an ambient sound level of 41 dBA (LAeq, 30 minutes), as measured with a NTi Class 1 sound level meter. This was a similar ambient noise condition as the Royal College of Music trial.

Due to the prevailing COVID condition facemasks were worn by all present and the normal otoscope examination could not be undertaken. The test procedure was explained to each student on their arrival. As touching was not possible visual inspection was limited which did lead to some difficulty in establishing the correct size of ear tip. However, the instrument automatically calibrated, or failed to calibrate which allowed the ear tip to be swapped to the next size to ensure the quality of seal and hence the assessment. Assessment categorisation of overall outer haircell (OHC) damage was based on the Hearing Coach recommendations using the following criteria, see Table 1.

Table 1: Criteria for Estimated Outer Haircell Damage

Estimated Hearing Damage Normal Hearing <21% Mild Hearing Loss <41% Moderate Hearing Loss <61% Severe Hearing Loss <81% Profound Hearing Loss >=81%

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Essentially, if the student received an estimated overall OHC damage of less than their age then they were considered to have good hearing. This was based on an arithmetic average of both ears. 4. RESULTS The 119 students were assessed, and the overall results have been presented in this feasibility study. There were 67 female and 52 males with an average age of 23.2 years. The results are presented by Royal Academy of Music department, see Table 2, where there were a significant number of data points (n>10).

Table 2. Number of Students by Music Department

Music Department Number of Students Violins 14 Woodwind 10 Voice 15 Brass 11 Piano 24 An analysis was undertaken based on the values given in Table 1 but considering the average estimated OHC damage of both ears, see Table 3.

Table 3: Number of students in each Hearing Category

Number of Students based

Percentage of

on Estimated OHC

Students

Hearing Damage

Normal Hearing 92 77.3 Mild Hearing Loss 19 16.0 Moderate Hearing Loss 5 4.2 Severe Hearing Loss 2 1.7 Profound Hearing Loss 1 0.8 Table 3 shows that 77.3% of the students had “Normal” hearing, similar to the 75% HSE screening audiometry hearing category “Good” [2]. For the HSE “Warning” hearing category, 20% of the population, by adding “Mild” to “Moderate” level of OHC hearing damage resulted in 20.2% for the music students. For the HSE “Referral” category for hearing loss, 5% of the general population, by adding “Severe” and “Profound” results 2.5% was found for the musicians.

These results were in-line with previous audiometric screening research where 94% of classical musicians had “Good” hearing 4.5% with “Warning” levels and 1.5% with “Referral” levels of hearing loss [5]. Hence, it appears that the OAE testing did show up

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potential damage earlier than audiometric testing, 2.5% vs 1.5% of the population with identified hearing issues

Figure 1 shows the overall cochlear damage, as well as by music department, see Table 2.

25OverallViolinsVoicePianoBrassWoodwind

Estimated Outder Hair Cell

20

Damage (%)

15

Left

10

Right

5

0

Figure 1. Estimated cochlear damage overall musicians and by music department The overall estimated cochlear damage was 16% for either ear for the 119 music students, see figure 1. This provides support that musicians have good hearing, as the damage is less than the average age, 23.4 years. Studying the results for each department only the students of the Voice department had less damage for the right ear than the left ear. For audiometry based assessment it is known that the right ear tends to give better results [12].

By analysing the 12 frequencies measured, 1000 to 6500 Hz with 500 Hz intervals, a more in-depth investigation was possible. The results shown in figure 2 were found by averaging the 119 OHC estimated hearing damage results for each music student’s ear to establish a trend and to use that trend to compare with traditional audiometric screening results for classical musicians.

35100015002000250030003500400045005000550060006500

Estimated Outer Haircell

30

25

Damage (%)

20

Left

15

Right

10

5

0

Figure 2. Averaged Estimated Outer Haircell Damage (%) for Classical Musicians, n=119

The averaged outer haircell damage for all students, n=119, is shown in figure 2. This shape of the damage closely matches that found using the Bekesy audiometric test [4] ie. Music

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exposure creates hearing loss at 6 kHz for students of all instrument types [5,6]. Here it is clear that 5 kHz was found to be the principal frequency, see figure 2. However, OAE were measured at a finer frequency resolution than automated audiometric screening, 500, 1000, 1500, 2000, 3000, 4000, 6000, 8000 Hz, and hence the results could be considered in-line with previous work. Mild OHC hearing damage was consistently found at three frequencies, 4000, 4500, 5000 Hz in the classical music students. Typical noise induce hearing loss is known to occur at 4 kHz and hence further OAE studies of exposed populations is strongly recommended. 5. DISCUSSION In terms of overall results, the population breakdown based on hearing categories was extremely well aligned with the OAE data, see Table 4. It should be noted that as the music students were all young, average age 23.4 years (standard deviation 4.79 years) and were a mix of gender (Female=67, Male=52), the allowances used in the HSE hearing health categories were nullified. In addition, when compared to the Bekesy PTA test results, the classical music students can game the subjective test procedure, as the students results [3-6,8] greatly exceed the Health and Safety guidance categories [2] whilst the OAE results were found to be well aligned, see Table 4. Table 4. Comparison of Hearing Population Categories using Pure Tone Audiometry and Otoacoustic Emissions

Measured OAE Categorization

Measured Audiometry Categorization

Health and Safety Hearing Categories Normal Hearing 77.3% 94% 75% Warning Levels of Hearing Loss

20.2% 4.5% 20%

Referral Levels of Hearing Loss

2.5% 1.5% 5%

6. CONCLUSIONS This preliminary research has shown the value of otoacoustic emission testing. The assessment method has multiple advantages: portability, speed, simplicity, and an objective based procedure. The results have demonstrated that OAEs can be used to indicate at the earliest possible time risk of hearing damage with 2.5% of student identified of being at risk compared to the normal 1.5% of the population. The situation, a COVID pandemic, forced the adoption of OAE testing as they do not require soundproof rooms. The feasibility study found results which showed good agreement with previous studies which were based on pure tone audiometry for classical music students with alignment found with hearing categories, although a slight frequency shift down for peak hearing damage to 5 kHz was seen, but this could be explained by the lack of 5 kHz pure tone in audiometry testing. There is now enough

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confidence in the OAE tests for a more complete twin study to be commissioned involving hundreds of classical music students to directly compare objective based OAEs with the response based pure tone audiometry. It is also strongly recommended that 5 kHz be introduced in the procedure for pure tone audiometry. 7. REFERENCES

1. The Control of Noise at Work Regulations, Health and Safety Executive, (2005). 2. Controlling noise at work. The control of noise at work Regulations 2005, Guidance

on Regulations L108, 3 rd Edition, Health and Safety Executive. (2021) 3. Dance S., Morant S., Zepidou G. Hearing loss amongst classical music students, Proc.

Institute of Acoustics , Reading, (2008). 4. Zepidou G., Dance S., Hearing loss amongst classical music students, Proceedings of

the 10 th International Congress on Noise as a Public Health Problem (ICBEN), 68- 73 (2011) 5. Dance S., Zepidou G., Shearer D. Face the Music: A 12 year study of the sound of

performance and hearing of classical music students, Proc International Congress on Acoustics , Aachen, (2019) 6. Dance S., Dymock B. Sound exposure and the hearing of musicians, Proc. Euronoise

2015 , Maastricht, (2015) 7. ISO 1999: 2013 Acoustics — Estimation of noise-induced hearing loss, Geneva, Switzerland

(2013) 8. Dance S., Shearer D. Facing the Music: A Before and after study of the hearing acuity

of classical music students, P roc. International congress on Sound and Vibration , 24, London (2017) 9. Hearing Conservation for Performers: Best Practice Guidance, British Association for

Performance Arts Medicine, (2020) 10. www.pathme.de 11. www.hearingcoachsoftware.com 12. Backus B., Williamon A. Evidence of noise-induced hearing loss among orchestral

musicians, Proc. International Symposium on Performance Science , (2009) ISBN 978-94-90306-01-4

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