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HEARING AID FEATURES: COMPATIBILITY WITH ASSISTIVE LISTENING TECHNOLOGIES

Hearing aids, especially those with features like those just discussed, can improve speech understanding in noise. The only thing more effective is combining hearing aids with assistive listening technology (this is the best way to improve speech understanding in difficult listening conditions). Although these technologies are discussed in detail in Chapter 9, the features that make them compatible with hearing aids are included here. Basically, these features allow a hearing aid to receive input directly from an external source (for example, a microphone worn by another person), without passing through the microphone on the hearing aid. In this case, the speech signal is louder and clearer than the background noise. If you’re interested in using assistive listening technology (and you probably should be), choose a hearing aid that can support it (like a BTE or ITE).

Ear-level FM

To understand speech clearly, people with sensorineural hearing loss need better listening conditions than do people with normal hearing. More specifically, they need a better signal-to-noise relationship (SNR); for them, speech must be louder than the background noise by approximately 20 dB. Because sound is measured on a logarithmic scale, this means speech must be ten times louder than the noise (see Chapter 3). In many situations, this SNR cannot be achieved with hearing aids alone. One way to improve the SNR is to move the talker closer to the listener. Ideally, the talker’s mouth would be 8 to 12 inches from the listener’s ear at all times, but, of course, that’s unrealistic. A better solution is to use remote microphone technology in which the microphone is “remote” to the user’s hearing aid. In other words, we put a microphone close the talker’s mouth and transmit the signal by FM radio waves to a receiver worn on the listener’s ear. It’s like a tiny FM radio station with a single transmitter and receiver—no wires or cables are involved. When the microphone/transmitter is worn by the talker, the effects of distance are eliminated because sound is transmitted directly from the talker’s mouth (which is close to the microphone) to the listener’s ear. It’s as if the talker is speaking into the ear of the listener. The effects of noise and reverberation are reduced because the signal from the talker’s mouth is closer to the microphone and therefore louder than the background. The SNR can also be improved, to a slightly lesser degree, by placing the microphone near the talker or holding the microphone and aiming at the talker.

The signal from the talker’s microphone bypasses the hearing aid’s microphone. It can be the only signal that the listener hears or the microphone on the hearing aid can also be active, making it possible for the listener to communicate with others nearby. Using both microphones can make the

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Figure 7.8. Examples of Ear-level FM Receivers and Adapters. Left, an FM receiver integrated into a “boot” adapter (bottom) that attaches to the end of a compatible BTE. Right, an FM receiver (bottom) that plugs into to a universal boot adapter (center) that slides onto the end of almost any BTE (top). (Courtesy of Phonak.)

SNR less favorable, so amplification of the two inputs must be properly balanced by the audiologist. The remote microphone/transmitter can also be connected to an external source such as a television, radio, telephone, CD player, or personal computer. In this case, the hearing aid’s microphone is turned off, and the listener hears only the input from the external source.

To receive an FM signal, the listener must wear an FM receiver. Traditionally, the receiver has been worn like a pager (see Chapter 9), but several ear-level options are also available. Some BTE hearing aids have an FM receiver built inside (not shown in Figure 7.8). Others are compatible with a special boot or audio shoe adapter that contains an FM receiver. The boot attaches to the bottom of a compatible BTE hearing aid (see Figure 7.8 left). In other cases, an FM receiver plugs into a universal boot adapter that connects to the bottom of almost any BTE (see Figure 7.8 right). Switching to the FM mode can be done by pushing a button on the hearing aid or using a remote control. With many digital hearing aids, the FM receiver automatically activates when it senses the presence of a signal from an FM transmitter.

Telecoils

A telecoil is an optional hearing aid feature originally intended to make listening over the telephone easier. Telecoils have been around for a long time (they’re one of the few features available on analog and programmable analog hearing aids); however, their versatility has sparked

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renewed interest. For example, in addition to their use with telephones, they can conveniently double as receivers for the assistive listening systems used in public places (see Chapter 9).

To use a telecoil with the telephone, the hearing aid is switched to the telecoil setting, and the telephone handset is placed over the hearing aid. The telecoil picks up electromagnetic energy produced by the telephone. This energy is amplified and converted back into sound by the hearing aid’s receiver. The hearing aid’s microphone is turned off, dramatically reducing the interference of room noise and eliminating the feedback that normally occurs when the handset is held over the hearing aid’s microphone.

Telecoils are tiny; ten or more could fit on the surface of a dime. They fit in BTEs, ITEs, and some ITCs. CIC hearing aids are too small to accommodate them. In hearing aids with multiple programs, the telecoil setting can be one of the programs held in the hearing aid’s memory. A telecoil can be manually activated by touching a switch or a button on the hearing aid or by using a remote control. Some digital hearing aids switch into and out of the telecoil mode automatically when a telephone is moved toward or away from the hearing aid. This is particularly helpful for listeners with poor manual dexterity.

Direct Audio Input

Direct audio input (DAI) is an optional feature that allows an external sound source (for example, a telephone, television, stereo, radio, computer, external microphone, CD player, or assistive listening device) to be plugged into a hearing aid with a patch card. The direct connection is made by a DAI jack (available on a limited number of hearing aids) or a universal DAI boot that slips over the end of almost any BTE hearing aid. Like all assistive listening devices, direct audio input bypasses the hearing aid’s microphone.

Compared with the telecoil, DAI has at least two advantages: DAI is subject to less electromagnetic interference than a telecoil (interference from computers, florescent lights, and other electronics can cause buzzing in a telecoil), and signal strength is unaffected by head position or orientation (which can cause “dead” spots with a telecoil). On the other hand, a telecoil is wireless, and DAI is not. FM technology eliminates all of these problems, but it’s more expensive.

HEARING AID FEATURES: LISTENER CONVENIENCE AND COMFORT

Delayed Start-up

Some hearing aids can be set (by the audiologist) to turn on several seconds after the battery compartment door has been closed. This gives

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the listener a few seconds to place the hearing aid in or on the ear without the annoying feedback that usually occurs when a hearing aid is being handled.

Audio Signals

Some hearing aids use beeps or tones to let the listener know the status of his hearing aid (which listening program or volume setting has been selected, when the battery is low, and so forth). For listeners who have difficulty remembering the significance of tones, voice indicators are also available (in several languages). Some aids can even be programmed to provide voice reminders about maintenance and follow-up visits.

Diagnostic Tools

Some hearing aids have internal diagnostic capabilities and can provide the user with a performance report on the hearing aid’s circuitry, receiver, and microphone.

Wind Noise Protector

Some hearing aids are equipped with a microphone hood that helps to reduce wind noise. Wind noise that does enter the microphone can be further reduced digitally by some hearing aids.

Remote Control

Some digital (and programmable analog) hearing aids have features that can be operated by remote control (such as volume, program selection, and activation of FM receivers). Using a remote control allows changes to be made without having to touch the hearing aid, and some users feel that’s more discreet. In addition, using a remote device is easier for listeners who have dexterity problems. Remote controls sometimes allow features to be incorporated into ITC or CIC hearing aids, which are too small for buttons, switches, and wheels. More sophisticated remote devices also display a hearing aid’s settings and battery status. For listeners who wear two hearing aids, one remote can be used to control both. Remote control devices come in a variety of styles that range from the traditional television-type to watches, key chains, necklaces, and belt clips.

Manual Volume Control

In the past, virtually all hearing aids had manual volume controls. As hearing aids become smaller and more models have features that are adaptive and automatic, however, fewer have them. Nonetheless, many listeners