Hearing Aids

The goal of a hearing aid is to amplify (or otherwise process) sounds so that they can be comfortably heard and understood. Most people who need hearing aids and try them end up using them. In such cases hearing aids can make an enormous difference in a person’s ability to communicate with others and to function in daily life. But some people who try hearing aids reject them.  There are many possible reasons for hearing aid rejection, including cost, cosmetics, comfort, social attitudes, and auditory/acoustic factors. This discussion and the demonstrations to follow only concern this last category, which deals with how hearing aid amplification interacts with the degree and type of hearing loss.

Loudness recruitment can be a help or a hindrance, depending on the degree of hearing loss. For lower degrees of sensory hearing loss, less than about 40 dB HL, recruitment is a beneficial feature that helps to make hearing aids less necessary than they would be without recruitment. Recall from the discussion in the Loudness Recruitment demo that, because of recruitment, sensory loss is actually a loss only for low-level sounds; sounds that exceed threshold by a fair amount (about 20 dB) are heard at their normal loudness. Because so many of the sounds that are important in our daily lives are above 50-60 dB SPL, those sounds will be heard at roughly normal loudness levels by a person whose sensory loss is 40 dB or less.

Contrast that situation of a mild/moderate sensory loss with that of a conductive loss of the same degree. To have all sounds attenuated by 40 dB leaves one constantly straining to hear very soft sounds. Such a person would likely seek either a hearing aid or surgical treatment for the conductive impairment. Hearing aids provide amplification that compensates effectively for the attenuation of the conductive impairment. This difference between sensory and conductive losses is illustrated in Hearing Aid Demo 4A.

For larger degrees of sensory loss loudness recruitment is a problem. When the loss is severe enough that everyday speech communication is difficult, then amplification is required. But amplification that is sufficient to make sub-threshold sounds audible will tend to make higher-level sounds uncomfortably loud. Amplitude compression is widely used in hearing aids to address this problem. However, even with the best methods of compression, it is inevitable that hearing-aid amplified sounds will be at least somewhat louder than they would be for a normal-hearing person. These effects with a moderate hearing loss are illustrated in Hearing Aid Demo 4B.

Click here to open the HeLPS Hearing Aid Demo in a new window.