- Assistive Listening Devices
- Cochlear Implants
- Implantable Middle Ear Hearing Devices
- Bone-anchored Hearing Aids
- Personal Sound Amplification Products
Assistive listening devices (ALDs) or assistive listening systems include a large variety of devices designed to help you hear sounds in everyday activities. ALDs are available in some public places such as auditoriums, movie theaters, houses of worship, and meeting rooms. They may be used by both normal hearing and hearing impaired people to improve listening in these settings.
ALDs can be used to overcome the negative effects of distance, poor room acoustics, and background noise. To achieve this purpose, many ALDs consist of a microphone near the source of the sound and a receiver near the listener. The listener can usually adjust the volume of the receiver as needed. Careful microphone placement allows the level of the speaker's voice to stay constant regardless of the distance between the speaker and the audience. The speaker's voice is also heard clearly over room noises such as chairs moving, fan motors running, and people talking.
ALDs can be used with or without hearing aids.
A cochlear implant is an implanted electronic device that can produce useful hearing sensation by electrically stimulating nerves inside the inner ear. Cochlear implants currently consist of 2 main components:
- external component, comprised of an externally worn microphone, sound processor and transmitter system,
- internal component, comprised of an implanted receiver and electrode system, which contains the electronic circuits that receive signals from the external system and send electrical signals to the inner ear.
Cochlear implants are different from hearing aids in some aspects:
|Hearing Aids||Cochlear Implants|
|Hearing aids are indicated for individuals with all degrees of hearing loss (from mild to profound).||Cochlear implants are indicated only for individuals with severe-profound hearing loss.|
|Most hearing aids are not implanted (although some bone-conduction hearing aids have an implanted component).||Cochlear implants are composed of both internal (implanted) and external components. A surgical procedure is needed to place the internal components.|
|In hearing aids, sound is amplified and conveyed through both the outer and middle ear and finally to the sensory receptor cells (hair cells) in the inner ear. The hair cells convert the sound energy into neural signals that are picked up by the auditory nerve.||Cochlear implants bypass the outer and middle ears, and the damaged hair cells and replace their functions by converting sound energy into electrical energy that directly stimulates the auditory nerve.|
Implantable Middle Ear Hearing Devices (IMEHD) help increase the transmission of sound to the inner ear. IMEHDs are small implantable devices that are typically attached to one of the tiny bones in the middle ear. When they receive sound waves, IMEHDs vibrate and directly move the middle ear bones. This creates sound vibrations in the inner ear, which helps you to detect the sound. This device is generally used for people with sensorineural hearing loss.
A bone-anchored hearing aid (BAHA), like a cochlear implant, has both implanted and external components. The implanted component is a small post that is surgically attached to the skull bone behind your ear. The external component is a speech processor which converts sound into vibrations; it connects to the implanted post and transmits sound vibrations directly to the inner ear through the skull, bypassing the middle ear. BAHAs are for people with middle ear problems (usually a mixed hearing loss) or who have no hearing in one ear.
Personal Sound Amplification Products (PSAPs), or sound amplifiers, increase environmental sounds for non-hearing impaired consumers. Examples of situations when these products would be used include hunting (listening for prey), bird watching, listening to a lecture with a distant speaker, and listening to soft sounds that would be difficult for normal hearing individuals to hear (e.g., distant conversations, performances). PSAPs are not intended to be used as hearing aids to compensate for hearing impairment.
For more information about PSAPs, please see "Guidance for Industry and FDA Staff: Regulatory Requirements for Hearing Aid Devices and Personal Sound Amplification Products" and "FDA Consumer Update: Hearing Aids and Personal Sounds Amplifiers: Know the Difference".