PAGE 4 BRAINHEARING TECHNOLOGY RESEARCH HOW DETAILS ARE LOST Before permanent noise damage We have known for years that the brain has a unique ability to process, separate and interpret sound if it receives a robust signal that is full of detail. As you know, hearing technology modifies sound so that it is more audible, but it can also modify sound in ways that further diminish or lose these critical details. Oticon’s technology is designed to provide the clearest, purest sound details to decode. Secondly, its sound processing is designed to maintain and enhance the fine details necessary for the brain to understand and interpret sound with less effort. Cochlear Haircells After permanent noise damage Oticon hearing technology is designed to provide the clearest, purest sound details necessary for the brain to interpret speech with less effort. You may wonder, “If speech is highly redundant and understood even with distortion, why would the details in speech need to be preserved?” Remember, we are not dealing with a perfect auditory system in an optimal hearing environment. We work with a pathway from the ear to the brain introducing transmission loss and distortion. Oticon applies research in order to help make lost speech details available to the brain. In order to more fully understand how thinking “brain first” in hearing technology can improve understanding, let’s take a quick look at recent research illustrating how details in speech are distorted or lost. You might find it surprising Noise Exposure: The most preventable change to hearing acuity is noise exposure. As clinicians, we tend to think of noise exposure causing two types of hearing changes, permanent and temporary. We see the permanent changes from noise exposure as decreased sensitivity on audiograms and otoacoustic emissions testing, which never recovers. This indicates the cochlea’s hair cells are damaged or destroyed (Liberman & Dodds, 1984). Interestingly, hair cells continue to suffer damage or destruction for days after loud sound exposure (Wang et al, 2002). With permanent hearing changes from noise exposure, the damage affects much more than hair cells. The damage continues up the hearing pathway to the auditory nerve. From the spiral ganglion cells of the cochlea, on up to the brainstem cochlear nuclei, noise exposure causes damage to the outer sheath of the nerve. This slows the speed at which nerves send signals from the ear to the brain. Noise induced changes don’t stop at the hair cells. It also causes a change in the timing information received from the ear. The disruption to timing information plays a part in decreasing the ability to locate where a sound is coming from. (Tagoe et al, 2014; Kim et al, 2013; Zeng et al, 2005). So now there are less hair cells to carry the speech signal to the auditory nerve, as well as timing distortion added to what it receives. Sometimes, noise exposure can cause a Temporary Threshold Shift (TTS) and hair cells recover quickly over the course of weeks (Miller et al, 1963). Most of us have attended a great concert, only to walk out afterwards with our ears feeling clogged and ringing. A few hours or days later everything seemed to have returned to normal, so we think “no harm, no foul”. Unfortunately, those temporary symptoms are the outcries of thousands of auditory nerve cells trying to tell us “Help, save me, we’re dying”. The hair cells may return to normal, giving audiogram and otoacoustic emissions test results in the normal range. However, we now know permanent damage has occurred.
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