The Handbook of Language and Speech Disorders. Группа авторов. Читать онлайн. Newlib. NEWLIB.NET

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Издательство: John Wiley & Sons Limited
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isbn: 9781119606994
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changes in high‐frequency hearing sensitivity that occur between the 60‐ and the 80‐year data from ISO 7029, median audiometric thresholds appear to be relatively stable between 40 and 60 years (see Figure 3.1). This may reflect that members of this age group are not yet suffering the hearing consequences of aging. However, there is an alternative interpretation of this relative stability. It involves subclinical hearing impairment that is not adequately captured in pure tone audiometric results, but that can cause functional communication difficulties in day‐to‐day life. The term coined to describe this is “hidden hearing loss”: hidden, as it is not evident in pure tone thresholds (Schaette & McAlpine, 2011).

      While audiometric quantification of hearing loss is useful in many contexts including medical, rehabilitation, and workplace health and safety settings, current research suggests that there are subclinical hearing impairments that are not adequately captured in pure tone audiometric results but that, despite this, still cause functional communication difficulties in day‐to‐day life. For instance, the prevalence rate of hearing difficulties in the absence of recordable audiometric loss has been reported as being around 10% (Tremblay et al., 2015). We have only a nascent understanding of the underlying pathophysiology and perceptual consequences involved in this type of hearing loss, but it is thought to be in some way linked to noise exposure.

       3.2.2 Physiological Correlates of Noise‐Induced Hearing Loss

      Our understanding of the physiological changes that contribute to noise‐induced hearing loss have recently undergone substantial revision. Previously, exposure to high‐intensity sounds were thought to lead to the mechanical damage of structures in the cochlea, including the sensory stereocilia of the inner hair cells and also to secondary effects that included the mixing of fluid from the normally separate cochlear compartments and alteration of the supporting cells (Slepecky, 1986). Noise‐induced damages to the cochlea have now been attributed not only to direct mechanical stress, but also to secondary metabolic disruption. Direct mechanical stress occurs during noise exposure when acoustic stimuli apply a physical force to the cochlea causing immediate trauma. Metabolic disruption is likewise initiated during noise exposure, but the effects continue to develop for a number of weeks after the cessation of noise exposure.

      One of the most consequential revisions to our understanding of the causes of noise‐induced hearing loss is that the connection between afferent nerve terminals and sensory hair cells is likely to be compromised at a stage that pre‐dates morphological damage to the hair cell (Kujawa & Liberman, 2009). This disconnection between sensory cell and neural relay system selectively affects auditory nerve fibers that transmit supra‐threshold stimuli, that is, those with a low spontaneous firing rate and a high activation threshold. The perceptual consequence of this disconnection is that challenging tasks, like listening in noise, become harder, while auditory thresholds remain unchanged. This, in turn, has prompted a fundamental re‐evaluation of the previously widely held view that only noise exposure resulting in permanent threshold shifts is damaging to hearing (Liberman, 2017).

       3.2.3 Hearing Loss and the Individual

      In considering hearing loss and the individual, let us turn to one of the greatest individuals, who is arguably also the greatest Romantic composer of all time. Ludwig van Beethoven (1770–1827) was such an individualist that he broke with the tradition of indenture, which was servitude to the aristocracy. In doing so he became the first composer of Western music who was able to make a living essentially as a freelance artist. He was also plagued by hearing loss, with onset at the age of approximately 26, a perilous condition for one whose livelihood revolved around creating music. His 1802 unsent letter to his brother, what has come to be called the Heiligenstadt Testament, offers a unique view into the inner world of one who suffered due to their hearing loss:

      Oh I cannot do it; therefore forgive me when you see me draw back when I would have gladly mingled with you. My misfortune is doubly painful to me because I am bound to be misunderstood; for me there can be no relaxation with my fellow men, no refined conversations, no mutual exchange of ideas.

      It is evident that at this stage Beethoven has given up on coping strategies and withdrawn into himself. He also admits that his hearing loss encroaches on his ability to participate in community and also to articulate and respond to abstract thought. Or in the terminology of the International Classification of Functioning, Disability and Health Core Sets (World Health Organization [WHO], 2019), Beethoven articulates a disability which is both an activity limitation and a participation restriction. He goes on:

      I must live almost alone, like one who has been banished; I can mix with society only as much as true necessity demands. If I approach near to people a hot terror seizes upon me, and I fear being exposed to the danger that my condition might be noticed.

      Had Beethoven been alive today, and, of course, depending on the diagnosis and type of his hearing loss, he may have been a candidate for cochlear implantation. CIs may have been helpful for his communication needs, but it is unlikely that he would have been wholly satisfied with his implants due to the poor cuing of pitch that many CI recipients experience.

       3.2.4 Hearing Loss and Cochlear Implants