Читать книгу Engineering Acoustics - Malcolm J. Crocker - Страница 173

Another form of sensory‐neural hearing loss is presbycusis. This loss in hearing sensitivity occurs in all societies. Figure 4.24 shows the shift in hearing threshold at different frequencies against age [52]. As can be seen, presbycusis mainly affects the high frequencies, above 2000 or 3000 Hz. It affects men more than women. The curves shown in Figure 4.24 show the average hearing loss (with average hearing at the age of 25 assumed to be zero hearing loss). The group of people tested was subject to both presbycusis (the so‐called natural hearing loss with age), and sociocusis (a term coined by Glorig [53] to include all the effects of noise damage in our everyday lives with the exception of excessive industrial noise).

Figure 4.24 Shift in hearing threshold at different frequencies against age for men and women [52].

Presbycusis is believed to be caused by central nervous system deterioration with aging, in addition to changes in the hearing mechanism in the inner ear. Hinchcliffe [54] believes that these changes explain the features normally found in presbycusis: loss of discrimination of normal or distorted speech, increase in susceptibility to masking particularly by low‐frequency noise, and a general loss in sensitivity. Rosen [55] suggested that degenerative arterial disease is a major cause of presbycusis. Others have suggested that a diet low in saturated fat may, in addition to protecting a person against coronary heart disease, also protect him or her against sensory‐neural hearing loss (presbycusis).

The sensory‐neural hearing loss caused by intense noise is discussed in Chapter 5.