When I was in graduate school, we would see older dentists who used drills that were positioned on one side of the head, and they developed a hearing loss. ![]() Sometimes an asymmetry is based on asymmetrical exposure to noise. Asymmetrical Hearing LossĪny audiologist knows the classic etiologies that can cause asymmetrical hearing loss. While unified sound is not the only thing you are trying to accomplish when fitting asymmetrical hearing losses, it is it is one of the most important. As you go through the process of fitting hearing aids, you are trying to achieve some sort of unified percept, which is sometimes easier to achieve in some patients compared to others. This becomes more complicated in cases of asymmetrical hearing loss because there is not balanced hearing from both sides. Normally, it should be a relatively seamless experience for the patients so that they have a unified percept. One of the almost unstated assumptions is that we are trying to create a single unified sound for the patient, and it is only when something odd happens that the patient might report that they hear two different sounds from one side of the head versus the other. We also expect this to happen when we fit hearing aids binaurally to a patient with bilateral hearing loss. Although sound comes from two sides, the individual with normal hearing will experience a single unified sound. The brain uses differential information between the ears, such as amplitude, frequency and timing cues of sound sources at the ears to make distinctions between sounds. The crossover and mixing of information happens at a relatively low level in the auditory system. Binaural HearingĪs you know, sound comes in on two sides of the head and travels distinct parallel pathways to the brain. I will provide some background information, but then will move into a discussion on recommendations, strategies and examination of some cases. I am going to talk briefly about binaural hearing. I will use case examples from patients with whom I have been involved either directly or indirectly. Hopefully I can present some viable strategies that are based on published literature as well as lessons that I have learned over the years in dealing with these complex hearing losses. In his most recent Hearing Aids book, Harvey Dillon (2012), spends three or four pages addressing asymmetrical hearing loss. ![]() In preparation for this course, I reviewed a book chapter by the late Bob Sandlin and Rose Giovanni in one of Michael Valente’s (1994) books, to which I will refer in the course of this presentation. There is a good amount of dated literature on fitting asymmetrical hearing losses, but not so much that I can recall recently. However, when you approach a case of asymmetrical hearing loss, the fitting path is a bit less clear. Many hearing aid fitting techniques that have been developed over the years have been built on the assumption that hearing loss is similar between the two ears. These findings are thought to have important implications for the fitting of hearing aids.Editor’s Note: This text course is an edited transcript of a live seminar. A binaural fitting of a subjectively preferred monaural hearing aid produced speech discrimination scores which were at least as good as, if not better than, those obtained from the optimum monoaural fitting. A much more pronounced improvement, was however found for a binaural fitting of the preferred aid, resulting in increased discrimination score and subjective ratings of sound quality, speech clarity and overall impression. Slight variations in speech discrimination score resulted from changing the frequency response of a monaurally fitted aid while subjective preferences favoured an aid with adaptive low-frequency gain regulation for more severe high-frequency losses. A recent study has examined the differences between certain monaural and binaural frequency responses as used in hearing aids for persons with high-frequency (often noise induced) hearing loss, in terms of both speech discrimination score and subjective rating methods.
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