American Medical Association Family Medical Guide - American Medical Association [717]
The devices are usually implanted in only one ear, but implanting them in both ears may be an option in the future. About 4 to 6 weeks after surgery to implant the receiver-stimulator (see illustration), the person is fitted with the externally worn parts of the device. Using a computer, technicians program the speech processor to make sure the frequency and pitch of the transmitted sounds are tailored to the person’s needs.
Assistive devices
There are many different kinds of assistive devices. Assistive devices can improve a person’s hearing, alert a person when a sound occurs, or help a person communicate.
How a cochlear implant works
A cochlear implant has both internal and external parts. A microphone, which is worn like a behind-the-ear hearing aid, receives incoming sound from the environment and sends it through a thin cord to a speech processor, which fits into a pocket or can be worn on a belt or under or over clothing. (Newer, smaller speech processors can be worn behind the ear.) The speech processor converts the sounds into electrical signals that it sends to the transmitting coil, which is held in place against the skin by magnetic attraction to the receiver-stimulator implanted under the skin. The transmitting coil sends the electrical signals through the skin to the receiver-stimulator, which activates electrodes in the electrode array that stimulate specific groups of nerve fibers in the ear. The vestibulocochlear nerve transmits the signals to the brain, which interprets them as sound.
Assistive listening devices
Assistive listening devices are cordless devices that can be used with or without hearing aids to amplify sound, limit background noise, or overcome the effects of poor room acoustics. Headsets, earphones, or neckloops are used to send the sounds into the ears. Most assistive listening devices use one of three different technologies—FM, infrared, or inductive loop. An audiologist can help you decide what type of assistive device best suits your needs.
FM systems
FM systems transmit radio waves from a microphone used by a person who is speaking, to a receiver connected directly to a person’s hearing aid or to a looped cord (worn around the person’s neck). The looped cord picks up the signals and transmits them to the T-coil in the person’s hearing aid. FM systems are portable and are used in classrooms, for meetings, and on tours. The microphone and transmitter are often built into the sound system at theaters, museums, or other public places. In such settings a person is given a receiver that connects to his or her hearing aid, or a special set of headphones to wear.
Infrared systems
Infrared systems use light waves to transmit sound from the transmitter to the receiver, which is worn by the user. Infrared systems are often used in homes (with TVs), theaters, and courtrooms. Bright sunlight can interfere with infrared systems.
Induction loop systems
Induction loop systems use electromagnetic fields to transmit sounds to a person’s hearing aid. In induction loop systems, a loop of wire is installed around an area such as a classroom, theater, or home. Sound from a transmitting device (such as a microphone, sound system, or telephone) is turned into an electric current that is picked up by the loop of wire around the room. The loop transforms the electric current into electromagnetic energy, which stimulates a corresponding response in the T-coil of a person’s hearing aid. The current then travels to the speaker in the hearing aid, where it is converted back into sound that can be heard.
Induction loop systems are used in places such as public buildings, conference halls, and theaters. Electromagnetic