**4. User subjective assessment of hearing aids**

of the DSP is the ability to adjust the output gain in each one or one-third octave frequency band. The computer program designs the shape of a digital filter and modifies the signal passing through the filter (multichannel analysis). Because sound energy in human voice is distributed in a frequency range of 200 Hz to 4 kHz, unwanted noise can be weakened by amplifying only the desired frequency range. Audiograms of people with hearing loss differ according to individual sensitivity to each frequency band (e.g., high tone deafness, horizontal deafness, convex deafness, or concave deafness). The multichannel output can thus limit compensation to the frequency bands for which a person has difficulty in

**Figure 6.** Example of software used to adjust a hearing aid's digital signal processing.

The multichannel output is also useful for suppressing acoustic feedback. Acoustic feedback occurs when the following happens simultaneously: (1) attenuation of the speaker's voice by the time it reaches the microphone is less than the amount of sound gain and (2) the phases of the original and feedback signals are mostly overlapped. ITC and CIC hearing aids have a vent to reduce the uncomfortable feeling that can occur in the occluded ear, and the output sound transmitted through the vent can cause acoustic feedback. The solution is a feedback canceller in the hearing aid that identifies the offending frequency-repeating amplification

The other important role of DSP is to create a compression system for the output sound. If a hearing aid amplifies sound linearly, it makes already loud sounds excessively loud. Patients with sensorineural hearing loss hear sounds above a certain sound level louder than normal listeners (recruitment hearing). Thus, the sound of a closing door or a cry from a child can annoy hearing aid users. The compression system suppresses the amplification of sounds above a certain sound level and instead fits them within the restricted dynamic range of the user. This system can therefore avoid unpleasant sounds, normalizes the perceived loudness,

Another advantage of digital hearing aids is their ability to work wirelessly. In their times, the BTE hearing aid only had a short cord, and the ITC and CIC hearing aids did not

and reduces the sound gain in the corresponding band.

and improves speech intelligibility.

hearing.

156 An Excursus into Hearing Loss

Against a background of various technological advances, the hearing aid has continued to respond to user expectations. Are users today satisfied with the current hearing aid? Countries in Europe and Japan have conducted large-scale market research surveys called *EuroTrak* and *JapanTrak* since 2009 [10]. According to JapanTrak 2015, 1306 people with hearing loss filled out their marketing surveys. Along with a corresponding survey in the US (*MarkeTrak IX* in 2014), we can discuss how satisfied hearing-aid users are in countries whose citizens have access to the latest technology.

**Figure 7** shows basic demographic information. The percentage of people with hearing loss is higher for countries with aging populations (i.e., Germany, Italy, and Japan). However, the percentage of people with hearing loss who own hearing aids is lower in these countries than

**Figure 7.** (a) Percentage of people with hearing loss in several high-tech countries. (b) Percentage of people using hearing aids to the number of people with hearing loss in each country.


Switzerland (whose out-of-pocket expenses are higher) were satisfied with their hearing aids. This result seems to support the idea that the user's own expense adds value to the hearing aid. However, users in Japan who receive no public assistance feel the most dissatisfied among the surveyed countries and have one of the lowest percentages of people with hearing aids (**Figure 7b**). Aside from Japan, other countries believe that rehabilitation for hearing loss is a medical practice, and only a state-certified technician can permit a hearing aid to be sold or adjusted. In Japan, however, a private association (The Association for Technical Aids) certifies hearing aid technicians, who can then recommend people to buy hearing aids or to have their hearing aids adjusted. These data imply that a government guarantee earns the trust of hearing aid owners and is related to satisfaction. In terms of hearing aids, the role of government is not to disburse tax money but to make people with hearing loss feel secure. Thus, the current digital hearing aid has already reached the technical ceiling, and satisfaction will

Hearing Aids

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http://dx.doi.org/10.5772/intechopen.73527

Although wearable hearing aids come close to the goal desired by people with hearing loss, implanted hearing devices allow room for further improvements. Several types of implanted hearing devices exist, with one being the bone-anchored hearing aid (BAHA), shown in **Figure 9a**. People have known for centuries that we can perceive sound when our skull bones vibrate, and bone conduction hearing was first described in the sixteenth century [11]. Currently, some commercially available hearing aids utilize bone conduction, and the user fixes a vibrator over the mastoid bone using a hair band. However, vibrating the skull through skin and fat tissue effectively is difficult. Therefore, the BAHA implants a titanium anchor on the temporal bone (behind the ear) to work as a bridge for vibration transmission [12, 13]. The other end of the anchor appears on the skin, and the user attaches the vibrator and receiver to the edge. Compared with previous bone

**Figure 9.** Implanted hearing devices: (a) bone-anchored hearing aid, (b) artificial middle ear and (c) cochlear implant.

depend only on the user's feelings.

**5. Implanted hearing devices**

**Table 1.** Amount of money granted by governments for hearing aids.

in other countries. This trend is easy to understand after considering how much support people receive to mitigate the cost of hearings aids. **Table 1** shows public financial support for the purchase of hearing aids for each country listed in **Figure 7**. Not surprisingly, the countries showing the highest percentages of people with hearing aids are Denmark, Norway, and the UK, all of which prescribe hearing aids at no cost when a patient is diagnosed with hearing loss. We can thus say that government aid is needed to increase hearing aid distribution or the cost for these hearings aids is too high.

**Figure 8** shows the percentage of people in each country who are satisfied with their hearing aids. It is interesting that people in different countries have different views about the performance of their hearing aids, even though the specification criteria are almost the same in all these countries. The countries with established social security systems are ranked in the bottom half, while more than 80% of the people with hearing loss in France, the US, and

**Figure 8.** Percentage of people in each country who are satisfied with their hearing aids.

Switzerland (whose out-of-pocket expenses are higher) were satisfied with their hearing aids. This result seems to support the idea that the user's own expense adds value to the hearing aid. However, users in Japan who receive no public assistance feel the most dissatisfied among the surveyed countries and have one of the lowest percentages of people with hearing aids (**Figure 7b**). Aside from Japan, other countries believe that rehabilitation for hearing loss is a medical practice, and only a state-certified technician can permit a hearing aid to be sold or adjusted. In Japan, however, a private association (The Association for Technical Aids) certifies hearing aid technicians, who can then recommend people to buy hearing aids or to have their hearing aids adjusted. These data imply that a government guarantee earns the trust of hearing aid owners and is related to satisfaction. In terms of hearing aids, the role of government is not to disburse tax money but to make people with hearing loss feel secure. Thus, the current digital hearing aid has already reached the technical ceiling, and satisfaction will depend only on the user's feelings.
