Meeting Topic: From the Ear to the Brain: Understanding Speech Perception and Hearing Loss
Moderator Name: Graeme Huon
Speaker Name: Alison King - Australian Hearing
Meeting Location: SAE Institute, South Melbourne
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 a YouTube clip "Toccata and Fugue in D minor for cochlea" - a depiction of the cochlea and basilar membrane responses to a piece of music.
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.
Written By: Peter Smerdon