Name: Stefan Stenfelt
Position: Professor of Technical Audiology, manages Linnaeus Centre HEAD’s core group for researchers with project management responsibilities.
Lives: In Berg, outside Linköping.
Likes: The outdoors. Oceans and mountains are my passion – I go diving, kayaking, on mountain tours and skiing. I was a boy scout for years. As a home owner maintenance work also occupies my time.
Stefan Stenfelt is an expert on how sound signals reach the brain from different routes and has, among other things, participated in developing a headset which builds upon so-called bone transmission technology. But that he became a hearing scientist was mainly due to circumstance.
“I studied to become an electro technology engineer at Chalmers in Gothenburg at the late 80s and early 90s. What I really was interested in were lasers and other optical technologies. I really wanted to write a thesis with that emphasis in industry, but times were bad and I was unsuccessful.”
“Instead I chose to write my thesis at the institution for applied and medical electronics and was placed in a project about bone anchored hearing aids. When they offered me a doctoral post at the same time as the labour market was still harsh, I remained”, says Stefan Stenfelt.
By then his interest for the field of hearing had awakened in a big way.
“My assignment was to develop the next generation of bone anchored hearing aids. But after a while I realized that the hearing in itself, how is it we hear, was more exciting to work with than the actual hearing aid.”
His thesis was given an emphasis on bone transmission physiology and since then it has been a special interest of his. It is about an alternative way for sound signals to reach the inner ear.
“Normally sounds are received by sound waves in the air entering the auditory meatus. But sounds can also be transmitted via bone. Vibrations in the skull travel directly to the cochlea where they, just as the air transmitted sounds, are converted into nerve signals which are sent on to the brain”, explains Stefan Stenfelt.
A bone anchored hearing aid builds upon a titanium screw being operated into the skull behind the ear. The skull is integrated with the titanium screw and when a hearing aid is connected to the screw it creates vibrations in the skull which are then captured by the cochlea. The method is used when illnesses or defects of the auditory meatus, the ear drum, the middle ear (the hammer, anvil and the stirrup bone) or when other reasons prevent putting a hearing aid into the ear.
But Stefan Stenfelt has also used knowledge of bone transmitted sound in a completely different context.
“In the reverberations of the attack on the World Trade Center in New York, it was concluded that there was a need for emergency staff to have access to secure communication and be able to hear surrounding sounds. For a few years there were a few of us in Gothenburg who worked on creating a headset which uses bone transmission technology.”
Since January 2006 Stefan Stenfelt is professor of technical audiology at the University of Linköping. He conducts research within hearing technology and hearing physiology, mainly aimed at the use of hearing aids, hearing diagnosis and noise protection.
Within the framework of HEAD he contributes with and builds upon his knowledge of bone transmitted- as well as air transmitted sounds.
“You could say that my main role is to study what happens to the sound signal until it reaches the cognitive system of the brain. There other scientists take over. At the same time, there is an exciting borderland where we meet. Together we examine the interface between the incoming signal and its interpretation in the brain.”
When it comes to the sound signal's path to the brain we are trying to get a more detailed image of what relative importance deficiencies in different parts of the peripheral auditory organ has for a person's hearing and understanding of speech.
“We are developing a whole battery of testing methods. We are going to use these on people with hearing impairment resulting from exposure to high noise levels, elderly people with impaired hearing, people with congenital hearing problems and people with normal hearing.”
A second track is to test how good people with hearing disabilities are at hearing and understanding speech in a disturbed sound environment, so-called "speech in noise".
“Here it is about studying both how the signal is perceived and how it is interpreted and understood. We get a hearing profile and a cognitive profile and look at how these co-operate”, explains Stefan Stenfelt.
We will also be carrying out brain reproduction studies in co-operation with professor Ingrid Johnsrude. The most difficult thing is to get the camera to see exactly what you want to get at.
“A problem with the MRI camera is that the entire packet vibrates and creates a racket. It sounds like an entire rock concert, but a lot worse! We are currently trying to create short, silent intervals in which the hearing is stimulated and then we start the camera.”
“Another difficulty we have to handle is that you cannot wear a hearing aid in the MRI. It does not work with magnetic materials. Instead we have to simulate this by everybody having the sound stimulation pre-processed as if they had their own hearing aids.”
With increased knowledge about the importance of the different parts of the auditory system and how these interact, the scientists hope to contribute to hearing aids which more and more are individually customised.
“Currently hearing aids are still manufactured in a relatively general manner and their foremost aim is to recreate sound volume. We see a future where you, with greater precision, can diagnose what the hearing deficiencies are due to. From this the hearing aids can be customised in accordance with each person's specific requirements”, says Stefan Stenfelt.
Last updated: 2013-01-16