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Our outer ear functions rather like a funnel. It picks up every possible tone and sound: the gentle swooshing of the sea and the ear-splitting din made by aircraft engines, voices chatting and the sound of an orchestra. It is only in the inner ear, in the cochlea, that the soundwaves are converted into electrical impulses and transmitted via nerves to the brain. This is where the actual auditory impression is generated. Whether we perceive noises, tones and sounds as pleasant or unpleasant, as loud or quiet, can depend on various different factors: on the quality of our hearing, on our auditory experiences, and also on the way our sense of hearing interacts with our other sensory perceptions.
How deaf children learn to hear
A person who is hearing-impaired or deaf finds it difficult or impossible to process acoustic signals. According to the World Health Organization, 360 million people worldwide are impaired in this way, and nearly ten percent of them are children. These days, implants are helping many people. Each year, the Medical Center – University of Freiburg fits a cochlear implant in as many as 250 patients; it replaces the function of the cochlea in the inner ear. Despite being born deaf, there are children who are not only able to understand language but even learn to speak themselves after being fitted with a cochlear implant.
The latest generation of cochlear implants, a technology developed in the 1980s by Professor Roland Laszig, who heads the Department of Oto-Rhino-Laryngology in Freiburg, is equipped with an electronic processor that adapts well to the environment. Consequently, a person with this kind of implant can understand speech well despite background noise.
Acoustics research to combat noise
When an aircraft takes off, even people with healthy hearing can hardly understand a thing – even if the plane is already several hundred metres high. At such altitudes an aeroplane generates a sound level of 80 decibels. Anyone who is regularly exposed to such noise levels can expect to suffer damage to their health. This is why people who live close to airports are prone more frequently to cardiovascular diseases. Part of the German Aerospace Center (DLR), the Institute of Propulsion Technology is therefore working to make aircraft engines – which generate the most noise when a plane takes off – quieter. Engineers and physicists at the institute have analysed precisely where and how noise is created by the rotating components and air turbulence. They have entered their results into a mathematical model that should help designers to make engines quieter in the future.
Are our eyes involved in hearing?
Dr Hans-Joachim Maempel, a musicologist from the Staatliches Institut für Musikforschung in Berlin, studies fundamental questions related to hearing. For him it is not enough simply to measure sounds using technical apparatus. He wants to know how we hear – and how our hearing experience is influenced by what we see. To this end, he teamed up with colleagues from Technische Universität Berlin to measure the optical and acoustic properties of six concert halls – among them the Romanesque Eberbach Abbey and the Gewandhaus in Leipzig – and reproduce them in a 3D simulation. His test subjects experience this virtual concert hall on a panoramic screen measuring more than 20 square metres; they listen to the music through special headphones which, unlike conventional headphones, ensure that the acoustic environment does not rotate when test subjects move their head.
“The most important finding of the experiments is that hearing and seeing influence one another hardly at all”, says Maempel. We appear to be able to make a clear distinction between acoustic stimuli that influence our auditory perception and optical stimuli that affect our visual perception. There is just one exception to this: if our visual perception is impaired, for example because our sight is poor, people rely more on their ears for orientation. And this is equally true the other way around.
Depending on the particular situation, having a good sense of hearing can be an advantage – when it comes to understanding others, for example – or a disadvantage, like when we find noise intrusive or disturbing. In any case, research currently being carried out gives us good reason to hope that auditory perception can be adapted to the wishes of the listener in future.