NMA/NCMM Approved Doctors' Meeting 2014

Kjell Grøndahl, M.Sc. Dept of Medical Engineering

Haukeland University Hospital Bergen, Norway

TESTING SEAFARERS HEARING CAPACITY WHILE USING HEARING AIDS

INTERNATIONAL LABOUR OFFICE / INTERNATIONAL MARITIME ORGANIZATION, 2013

APPENDIX B: HEARING STANDARDS

UNAIDED HEARING

PTA «Pure Tone Average» max:

30 dB in the better ear and

40 dB in the less good ear

Measured at the frequencies 500, 1000, 2000 and 3000 Hz.

AUDIOGRAM

Left

Right

Is this an acceptable hearing loss?

PURE TONE AUDIOMETRY

• Independent of language

• Standardized equipment and methods

• Not suitable for testing with hearing aids

• Does not measure speech recognition

SPEECH AUDIOMETRY

SPEECH AUDIOMETRY

• Routine test in many countries

• Calibration issues: Values for sound field (loudspeaker) may not be available.

• Difficult to compare across languages

• Speech without background noise is not representative for normal working conditions

AIDED HEARING

Appendix B: ”Alternative assessment methods using validated and standardized tests that measure impairment to speech recognition are also acceptable.”

AIDED HEARING

Testing with headphones not possible

We want to test speech recognition in realistic conditions (background noise)

Speech Noise

SPEECH-IN-NOISE (SIN) TEST

Result: The speech/noise ratio (SNR) where 50% of the words are repeated correctly

Speech Noise

SPEECH-IN-NOISE (SIN) TEST

Example:

67 dB 65 dB

SNR: + 2 dB Sound examples: people.kth.se/~e99_ehe/project.html

SPEECH-IN-NOISE (SIN) TEST

Many different methods in use. Manual, adaptive, single-speaker, multi-speaker, different types of noise. But they all measure the SNR at 50 %.

AVAILABLE TESTS

• Validated tests are available in many languages

• A few tests are standardized and available in more than one language. One of the most common is HINT (Hearing In Noise Test) from House Ear Institute.

• Some require proprietary equipment

• Often used to evaluate the fitting of hearing aids

• Main users: University hospitals, hearing aid dispensers

WHAT SHOULD BE AN ACCEPTABLE RESULT?

According to the guidelines:

“Hearing aids are only acceptable in serving seafarers where it has been confirmed that the individual will be capable of safely and effectively performing the specific routine and emergency duties required of them”

WHAT SHOULD BE AN ACCEPTABLE RESULT?

SIN tests are validated using young, normal-hearing subjects. We can compare the results to this reference (similar to the audiogram) We assume that the validation measurements follow a normal distribution. A reasonable «rule of thumb» may be using the 5 % percentile or 2 standard deviations (= 2.3 % percentile). The requirements of the actual workplace must be taken into consideration.

WHAT SHOULD BE AN ACCEPTABLE RESULT?

REFERENCES

Audiogram figure: Public Domain (Wikipedia / User:Carnildo). Hearing loss example by Kjell Grøndahl

Hearing aid image: Oticon

Speaker setup illustration: HINT test, House Ear Institute

Sound examples: people.kth.se/~e99_ehe/project.html

(Dept. of Speech, Music and Hearing, KTH, Sweden)