Category: Audiology in nutshell

As audiologists we all learn masking as part of our training. But the truth is, the real learning is in the experience of the various hearing losses we come across. Unfortunately for some, we’re not always in the position to reflect with another practitioner about some of the more complex hearing losses – so how can we really learn?

Masking is carried out as a result of the minimal interaural attenuation of 40dB when using headphones, 55dB when using inserts and 0dB when using a bone conductor. As a result, we follow certain rules to decide when masking should be carried out (BSA recommended procedure 2011) to ensure an accurate hearing test is obtained.

We probably know the rules by heart. But…

Why do we need to do Rule 3 and what is it’s relationship to Rule 1? What about central masking and the effect of conductive losses on masking? When are inserts more appropriate than headphones? When do we choose to mask bone conduction on both ears? What is effective masking? Even the most experienced of audiologists have to reflect on such questions when considering best practice.

A training course in masking in audiometry will enable audiologists to consider and understand why we need to mask, rather than just learning the rules. TJ Audiology Services uses audiometry simulation software to practice different scenarios, alongside interpretation of working audiograms. Audiology Courses are available in 2016 at Audiology House, London. Bring yourself up to speed, or start from scratch and benefit from having the time to ask all those questions and more in a safe learning environment and discussion with other colleagues.

 

BSA Recommended Procedure (2011): Pure-tone air-conduction and bone-conduction threshold audiometry with and without masking.

 

A hearing test (audiometry) measures the quietest sound and individual can hear, at least 50% of the time – known as hearing threshold level (HTL). An individual’s HTL at different frequencies is recorded in an audiogram for each ear, and this information can be used to categorise hearing as within normal range, or a hearing loss that can range from mild to profound. Otoscopy and tympanometry is used alongside audiometry to identify any abnormalities of the middle ear that may be affecting the hearing, e.g. perforation or glue ear.

In hospitals and hearing aid dispensing practices, audiometry and tympanometry is typically carried out by audiologists who are trained to undertake these procedures during their university course. In the UK, audiometry is carried out according the British Society of Audiology Recommended Procedure.

However, basic hearing tests and tympanometry can also be performed by GPs, occupational health nurses, audiometricians, assistant technical officers, teachers of the deaf and hearing aid assistants. The British Society of Audiology has a Practice Guidance Document for “Hearing assessment in general practice, schools and health clinics: guidelines for professionals who are not qualified audiologists”.

A British Society of Audiology accredited course in basic audiometry and tympanometry trains non-audiologists to undertake hearing tests in the field and interpret the results, according to minimum training criteria.

Good fitting custom earmoulds and hearing protection, ITE and CIC hearing aids can only be created from accurate impressions. The key is having the confidence to know when you’ve inserted your otostop deep enough down the canal, and to point the otostop in the direction of the eardrum. A good, deep impression means getting to the 2^nd bend of the ear canal. Some tell-tale signs that you’ve reached the 2^nd bend include a characteristic slip of the otostop into position which often coincides with slight resistance as it enters the bony portion of the canal. When you look on otoscopy, you will see that the otostop is framed by the cartilaginous portion of the canal.

 

All ear canals are very different from one another and taking good impressions takes practice. Patient/client safety is paramount and the British Society of Audiology has a recommended procedure for impression-taking in adults/children over 5 years of age and for children under 5 years of age.