On Monday April 11th 30 members and guests heard Audiologist Alison King present on the topic
“From the Ear to the Brain – Understanding Speech Perception and Hearing Loss”
By way of introduction Alison described the role and activities of Australian Hearing – the practical clinical services, and the research division, National Acoustic Laboratories.
She went on to describe the structure of the ear in detail, as well as the range of hearing loss mechanisms.
She then played this YouTube clip “Toccata and Fugue in D minor for cochlea” – a depiction of the cochlea and basilar membrane responses to a piece of music (note: audio starts 11 secs in).
Alison then spoke on hearing loss – describing conductive hearing loss (ear wax, ear infection) and sensorineural hearing loss – inner ear problems with damaged hair cells, age/noise/other traumas. She also touched on recently identified hearing loss nerve issues.
Alison then described hearing tests and the resultant audiograms
She described the categorization of hearing loss into Mild, Moderate, Severe, and Profound categories and displayed a chart to show the range of loss in decibels associated with each category.
Alison then described air conduction tests and bone conduction test to differentiate between conduction hearing loss and sensorineural hearing loss, and then covered the mechanisms involved in high frequency hearing loss with age and noise-induced hearing loss, displaying audiograms of both noise-induced and age-related hearing loss.
She also described noise-induced hearing loss, and the levels associated with different activities – both work-related and leisure(eg “binge listening”).
She then described a recently discovered phenomenon – “hidden hearing loss” where nerve fibres in the ear become overloaded and are not recovering, even though the hair cells in the cochlea recover.
Then tinnitus was covered, describing the current theory of “Central Gain” – where hearing loss causes the brain to “turn up the neural amplifier” at the frequencies of the hearing loss in an attempt to compensate, and the brain focuses-in on other internal body sounds.
Therapies for tinnitus were covered – education thru to sound enrichment to de-emphasise the internal sounds and finally to hearing aids for people with hearing loss related tinnitus.
Auditory processing disorder was described – where people have normal hearing but have trouble hearing in the presence of noise, as was spatial processing disorder where people can’t use the spatial cues in sound to help them understand speech in the presence of noise
She also described how speech understanding is affected by hearing loss – loss of clarity, and inability to discriminate articulation cues.
Alison then covered the challenges in prescribing hearing aids to overcome severe hearing loss, noting that it is not a case of simply make it louder – damaged hair cells will not respond but the amplified frequency can excite adjacent cells, making it sound muffled.
Hearing aid prescription procedures have found that, when dealing with patients past a certain point in hearing loss, it’s more beneficial to start boosting lower frequencies rather than higher frequencies. – and once you reach a certain stage of hearing loss (about 80dB), a cochlear implant is considered.
Following the presentation a lively Q&A session showed the keen interest of the audience in this topic.
The AES Melbourne Section thanks Alison for taking the time and effort in presenting the most interesting talk to us.
This session proved to be a useful primer on the subject, and a good foundation for upcoming lectures on hearing aid technology and noise control subjects.
Alison has also been kind enough to to provide these useful web links and related resources:
https://www.hearing.com.au/ – Australian Hearing website
http://www.nal.gov.au/ – The National Acoustic Laboratories website
http://knowyournoise.nal.gov.au/ – NAL’s “Know Your Noise” website landing page
http://knowyournoise.nal.gov.au/hearing-resources – for simulations of hearing loss and tinnitus
http://knowyournoise.nal.gov.au/noise-risk-calculator – work out the noise risk based upon work and leisure noise
http://www.nal.gov.au/current-projects_tab_hearing-loss-prevention.shtml – research projects.
There is also a section of the NAL website that lists all publications. If you use the ‘search’ function, there are a number of papers about orchestras and hearing loss.
Finally, our NAL scientists are undertaking a project in Melbourne that could be of interest to members:
As part of the HEARing CRC’s ‘HEARsmart’ project NAL are working with two live music venues to conduct a trial of ‘decibel banking’ software called 10EaZy – it’s a tool to help sound engineers keep track of sound levels during an event – it encourages increased use of dynamic range and helps the user to meet a pre-determined dB limit that’s been agreed with management/musicians beforehand. So far it’s mostly been used in outdoor festivals in Europe (see below) but here they’re trying to see if/how it would work in smaller indoor venues.
AN INVESTIGATION OF THE SOUND PRESSURE LEVEL AT THE ROSKILDE FESTIVAL
Oticon A/S, Kongebakken 9, Smørum, Denmark
This paper describes the development of a small and convenient measurement system used for measuring the sound pressure level (SPL) at rock festivals. Over the years more than 500 test persons have worn the measurement system and thus contributed significantly to the data collection. Via a dedicated software tool suite, statistical analysis can be performed on the measurement data. Examples of measurement data are shown and discussed
AES 58th International Conference, Aalborg, Denmark, 2015 June 28–30