Research may break the sound barrier
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Dr Catherine McMahon |
Children suffering a rare type of hearing loss, known as auditory neuropathy, will benefit from groundbreaking research being carried out by audiologist Dr Catherine McMahon from Macquarie University.
Auditory neuropathy
Auditory neuropathy is a complex congenital disorder caused by an abnormality in the transmission of nerve impulses travelling from the inner ear to the brain. Usually both ears are affected with hearing loss ranging from mild to severe.
“The term auditory neuropathy was only coined in 1996 and so research into the disorder is still in its early stages,” explains McMahon. “It is so interesting as it has confounded audiologists and speech therapists alike. Some children hear sounds at a near normal level but they can’t develop spoken language. Some children understand speech in quiet but as soon as you get them into a noisy room (such as a classroom) they can’t understand it anymore. It is a wide spectrum as to how well they perform.”
Cochlear implants
While audiologists are still unsure of the best management strategies to use, many young children receive a cochlear implant. McMahon, who has been researching auditory neuropathy since undertaking her PhD, today works with 22 children with cochlear implants.
“While most children do well with a cochlear implant what we are trying to work out is whether we can predict those who will do well with a cochlear implant and those who won’t do well before they undergo implantation,” McMahon says. “This is necessary because cochlear implantation is a very invasive procedure.”
A cochlear implant procedure involves drilling behind the ear to insert an electrode relay through the hearing organ which is what directly stimulates the nerve. Children then go through months of rehabilitation with an audiologist and speech pathologist.
Surprising results
By measuring the electrical potential of the hearing organ, McMahon found two differing patterns – one that is consistent with children doing well with a cochlear implant and one which is consistent with children not doing well.
What surprised McMahon was that the pattern looked very simple. Those with pattern A had good outcomes, and those with pattern B had poor outcomes. However, those with poor objective outcomes could be divided into two groups in terms of spoken language development. One group were not able to use the implant at all and are now within a signing program. The other group were able to use the cochlear implant to develop spoken language but they were delayed.
“The most interesting thing is that while those with pattern B who could develop spoken language but were delayed, caught up to those who did very well with the cochlear implant within three years. That suggests that we don’t have a clear idea who and who should not be implanted. Our research needs to now look at additional factors as well.”
Reaching the world
McMahon originally presented her research into auditory neuropathy at a conference in Cuba last year. She has since been the keynote speaker at a workshop in London and has been invited to present at the University of Tokyo’s auditory neuropathy program in 2007.
For further information contact Dr Catherine McMahon cath.mcmahon@mq.edu.au To find out more about the varied research being undertaken in the Audiology section of Macquarie University’s Linguistics Department visit www.ling.mq.edu.au/centres/audiology/research.htm