Download Assistive Listening Devices

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Assistive Listening Devices
Hearing Aids
Hearing aids and assistive listening devices have been very beneficial to children
and adults with hearing losses. Additionally, there are many types of hearing aids and
amplification devices available to the hearing impaired. There are four standard
components of a hearing aid. The components consist of a microphone, amplifier,
receiver and a battery. The microphone detects the signal and turns this acoustic signal
to an electrical signal in order to be processed by the hearing aid. The amplifier modifies
and amplifies the signal depending on the controls set by the Audiologist or hearing aid
dispenser. The receiver converts the electrical signal back to an acoustical signal to be
interpreted or delivered to the external auditory canal. The batteries of the hearing aid
come in different sizes depending on the type of hearing aid. The batteries give off
strong signals and they are short-lived. Hearing aids also have some optional features
that can enhance the hearing aid. There is an on/off switch, a volume control switch and
a telecoil or t-coil on the hearing aid. The t-coil is used in instance when a person wants
to use the phone or an induction loop system. The t-coil converts an electromagnetic
signal to an electrical signal to then be shaped and amplified by the amplifier of the
hearing aid. The t-coil makes speech more intelligible on the phone because the phone
is giving off electromagnetic signals that the t-coil can pick up. Sound amplified by a
hearing aid without a t-coil is more distorted and cannot pick up these electromagnetic
signals very well.
There are five typical hearing aid styles in use. The styles of hearing aids are,
body, eyeglass, behind-the-ear (BTE), in-the-ear (ITE), in-the-canal (ITC), and
completely-in-the-canal (CIC). Body hearing aids consist of a box that holds the
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microphone, amplifier, receiver, and battery and is strapped to the body of the user.
There is a tube attached to the receiver in the hearing aid that runs up to attach to an
earmold in the person’s ear. The body aid is good for people with profound hearing
losses, but is bulky, visible and it is hard to localize sound with the microphone so far
from the ear. A second type of hearing aid is the eyeglass hearing aid; they have the
hearing aid in the eyeglasses. The microphone, amplifier, receiver and battery are in
temporal portions of the glasses. There is a tube connecting the receiver to an earmold.
A third type of hearing aid is the behind-the-ear aids, which are placed behind the pinna,
with all of the components of the hearing aid built into a small shell. The small shell is
connected to an earmold in the ear by a small tube. This type of aid is great for children
and people with arthritis because it is larger, making it easier to manipulate. The fourth
type is the in-the-ear hearing aid style, which has all of the components of the hearing
aid in a small shell that fits to the size and shape of the person’s external auditory canal.
ITE hearing aids fit into the person’s external auditory canal. This is the most popular
type of aid. A possible problem with this type of hearing aid is that it may be too small to
have extra features like at t-coil or volume control switch. The fifth type of hearing aid is
the in-the-canal aid. It is one of the smallest types and all of the components of the
hearing aid fit into a small shell casing and fits almost all the way in the external auditory
canal. ITC are good for mild to moderate, flat or gently sloping hearing losses. A
disadvantage of ITC aid is that they may be too small to have extra features like a t-coil
or volume control switch, plus you may only be able to obtain moderate amounts of gain
because of feedback. The last type of aid to be discussed is the completely-in-the-canal
hearing aid. However, it is not visible since it fits all the way in the ear canal. It has a
small wire that is used to help pull the hearing aid out of the ear. This type of hearing aid
is good for reducing feedback since it completely fills the canal. It is cosmetically
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appealing and less electronic gain is needed because the distance between the end of
the hearing aid and the tympanic membrane is minimal.
Some people are not able to wear air-conduction hearing aids, so they can wear
bone-conduction hearing aids. Bone-conduction hearing aids are worn if the person has
a deformed or absent pinna or external auditory canal. Bone-conduction hearing aids
have a bone-conduction oscillator, which replaces the receiver of the hearing aid. The
bone-conduction hearing aid still has a microphone and amplifier. The oscillator is held
on the mastoid process of the temporal bone by a headband, eyeglass or is permanently
affixed there by a doctor. The bone-conduction hearing aid bypasses the middle ear and
directly stimulates the temporal bone.
Classroom amplification
There are many types of classroom amplification devices. The goal of classroom
devices is that they provide a good signal to noise ratio. A signal to noise ratio is simply
the ratio that represents the signal present to background noise. A good signal to noise
ratio is when the signal is louder than the background noise. Classroom amplification
includes but is not limited to, hardwire system, induction loop system and a FM
amplification system. The hardwire system provides a direct connection between the
source (teacher) and the listener (student) by means of wire. In a hardware system there
is a microphone close to the teachers voice, the electrical signal is sent to the listener
through a wire, the signal is then amplified and changed to an acoustic signal. The
listener picks up the signal by wearing a headset or by wearing a hearing aid. This
system is used in schools, churches and auditorium. The problem with a hardwire
system is that movement is limited because of the wire between the teacher and the
student. This type of system is not very common anymore. Another type of system is the
induction loop system. This was the first improvement made in classroom amplification.
The teacher wears a wireless mike; the microphone is placed near the teacher’s voice.
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The microphone transmits FM frequency or an electromagnetic field to an amplifier. The
amplifier is connected to a wire; the wire surrounds the listening area and creates an
electromagnetic field around the listeners. The t-coil in the hearing aids pick up the
electromagnetic signals and converts it to an electrical signal to be processed by the
hearing aid. This system is not very expensive and is easy to maintain. A possible
problem with this is that there could be signal spillover to adjacent rooms. The child also
must have access to a telecoil in order for them to benefit from an induction loop. The
third type of classroom amplification device is the FM amplification system. This type of
device is the most versatile wireless system. With this type of system, the teacher wears
a wireless mike that transmits FM frequency to a receiver worn by the child. It uses radio
waves to transmit sound from the source to the user. The microphone is placed near the
speaker. The signal is sent to a FM transmitter and carried on radio frequency waves to
the receivers worn by the child. The receivers have the ability to decode the FM
frequency waves. The receivers can be built into the child’s hearing aid or clipped on to
the hearing aid. There are many advantages to this system. There are no spillover
problems, it is portable and it improves the signal to noise ratio. One problem with this
type of device is that sometimes there is FM interference.
Cochlear Implant
A cochlear implant is an electronic device designed to provide sound information
by directly stimulating the auditory nerve fibers in the cochlea for people who have a
profound hearing loss, either congenital or acquired in both ears, and can obtain no
benefit from hearing aids. The cochlear implant by passes damaged hair cells and helps
establish some degree of hearing by stimulating the auditory nerve directly. It does not
eliminate the disease that resulted in deafness, nor does it restore the normal function,
and each outcome varies.
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The first research done on cochlear implants was conducted in France more than
thirty years ago. However, in 1790, a French surgeon by the name of Volta conducted
an experiment by sticking two metal rods in each of his ears and changed it with
electricity to stimulate the auditory nerve. The results were serious blows to the head,
and the experiment was not performed again. In 1961 several patients under went
cochlear implantation performed by the House Ear Institution. While work proceeded
through the 1960s and 1970s on improvements in basic design, cochlear implants were
controversial in the auditory community. This was because many people were
concerned about the long-term affect of the auditory nerve being directly stimulated by
electronic impulses. By the 1980s views were changing for the better. The Food and
Drug Administration approved the 3M / House Single – channel implant in 1984. The
Nucleus multichannel implant was approved in 1990. Both of these devices are
approved to be used by adults and children.
Cochlear implants are still controversial, expensive and have uncertain results.
The U.S. Food and Drug Administration has limited the implants to people who qualify
for the following: those who get no significant benefit from hearing aids, those who are at
least two years in age and those with severe to profound hearing loss.
Hearing loss is caused by a number of different problems that occur either in the
hearing nerve or parts of the middle or inner ear. The most common type of deafness is
caused by damaged hair cells in the cochlea, the hearing part of the inner ear. In a
healthy or normal ear hair cells stimulate the hearing nerve, which transmits sound
signals to the brain. When the hair cells stop functioning the auditory nerve remains
unstimulated, and the person cannot hear. Many things can destroy hair cells including
infection, trauma, loud noise, aging, or birth defects.
All cochlear implants consists of a microphone worn behind the ear that picks up sound
and sends it along a wire to a speech processor, which is worn in a small shoulder
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pouch, pocket, or belt. The processor boosts the sound, filters out the background noise,
and turns the sounds into digital signals before sending it to a transmitter behind the ear.
A magnet holds the transmitter in place through its attraction to the receiver-stimulator.
This part of the device is surgically attached beneath the skin into the skull. The receiver
picks up digital signals forwarded by the transmitter, and converts them into electrical
impulses. This flow through the electrodes contained in a narrow, flexible tube that has
been threaded into cochlea. This entire process takes seconds to be done. The sounds
heard through an implant are different than normal hearing sounds, and have been
described as artificial and robot like. Simply because its an electronic mechanism, the
implants’ small number of electrodes cannot possibly match the complexity of a person
who has fifteen-thousand functioning hair cells.
During the surgical procedure, the surgeon makes an incision behind the ear and
opens the mastoid bone leading into the middle ear. Then the surgeon places the
receiver-stimulator in the bone and gently threads the electrodes into the cochlea. This
surgical procedure takes from an hour and a half to five hours.
Before a person receives an implant, specialists at an implant clinic conduct a
careful evaluation, including extensive hearing tests to determine how well the candidate
can hear. Unfortunately, it’s not possible to predict who will benefit from the implant more
than someone with a damaged nerve. First, a candidate undergoes a trial with a
powerful hearing aid. If the aid cannot improve their hearing well enough, then a doctor
performs a physical exam and orders a hearing screening. If a candidate has a scarred
cochlea, then it is a possibility that they are not a good candidate. The doctor also
recommends a psychological evaluation to get a clearer understanding of the
candidate’s expectations as well as there understand what the implant can and cannot
do.
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After the surgery, the patient stays in the hospital for a day or two. After a month,
the surgical wounds will have healed and the patient returns to the implant clinic to be
fitted with external parts of the device, which are the speech processor, microphone, and
the transmitter. Then the speech processor is tuned and set to the levels for each
electrode, from soft to loud. The patient is then trained in how to interpret the sound
head through the device. The length of the training varies from days to years; it all
depends on how well one can interpret the sounds heard through the device.
Some risks after the surgery are dizziness; due to the acoustical nerve which has
to do with balance and facial paralysis infection at the incision sight. Great care must be
taken with many children and precautions must be made during the surgery because the
child’s skull bones are thinner and more fragile than adults. So care must be taken to
avoid puncturing during drilling of the mastoid cavity. Scientists are not sure about the
long-term effects of electrical stimulation of the nervous system.
Most profoundly deaf patients who receive implants are able to discern medium
and loud sounds, including speech at comfortable listening levels. Many use sound clues
from the implant together with speech reading and other facial cues. Almost all adults
improve their communication skills when combining the implant with speech reading.
Some adults can even understand spoken words without speech reading. More than half
of adults who lose their hearing after they learned to speak can understand most speech
without speech reading. However, about 30% can understand spoken sounds well
enough to use a telephone. Unfortunately, some people have reported that after
receiving the implant that they feel alienated from the deaf community however, at the
same time they do not feel as a part of the hearing world or mainstream.
Children who were born deaf, or who lost their hearing before they could speak have the
most difficulty in learning to use the implant. This is due to the fact that before they had a
chance to acquire language proficiency, they became deaf. Further research suggests
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that most of these children are able to learn spoken language and understand speech
using the implant.
Assistive listening devices for the deaf and hard-of hearing
The Carter Decision was an important turning point for the hearing impaired
community. In 1968 the Carter phone decision changed the face of telecommunications
when it allowed products not manufactured by AT&T to be used on AT&T lines, provided
proper precautions were taken to protect the integrity of the system. Now private industry
and special interest groups, such as the hearing-disabled, could pursue the development
of products designed for their specific needs, and more importantly, they could market
them independently of the telephone company. This in turn allows the market for
telephones to be unbelievably diverse in style and price.
For the hearing impaired, assistive products or devices include not only products
for carrying on a conversation, but also alerting products such as louder ringers, light
flashers, or strobes. Before things can be attached to the phone line, a basic
understanding and respect of the phone transmission system is required. Every
telephone consists of three subassemblies: the dialing mechanism, the speech network,
and the ringer. The speech network performs the tasks of taking in the incoming
electrical signal from the remote party and convert it to an acoustic signal in the
earpiece: and, in turn, to translates the talker’s acoustic signal from the microphone into
an electrical signal to be transmitted back down the line. The dialing mechanism and the
ringer are pretty self-explanatory.
Most importantly for the hearing impaired community is the types of alerts used
to demonstrate the ringing of the phone. The most common alert is an additional bell or
tone signaler. These signals make the ring louder and are for the moderately hearing
impaired. Some of the newer electronic tone ringers are good for hearing impaired,
because in addition to being louder, the frequency or pitch can be adjusted to the loss of
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the user. However, most of these electronic ringers are in the high frequencies, so the
pitch might not be appropriate for persons with sever high-frequency hearing loss. In
addition to the pitch of the ring many phone systems come with other alerting devices.
Some of these devices include an exterior telephone bell, ring light flasher, ring signal
with flashing light and bed shake, line powered phone strobe light, lamp activation light,
and a tactile body-worn remote receiver (like a pager).
In addition to the alerting devices for the phone there are also devices to amplify
the conversation. Amplified replacement handsets are probably the easiest and most
efficient means of adding amplification to the telephone. However, replacement
handsets can only be adding to modular phones-those with detachable receivers. Also
they will not work on phones with dials in the handset, as with cordless phones. These
only help those with mild hearing loss. Many of the newer phones have built in
amplification devices. Though they are not very efficient the volume can be turned up or
down in most modern phones. Telephones are even created to comfort the hearing aid
wearer. They accomplish this by adding a pad to the earpiece of the phone.
The most commonly used telecommunication device among the deaf is the TTY
derived from the Teletypewriter. Robert Weitbrecht, a deaf physicist, first developed the
TTY. He realized that these machines, which were becoming available in large numbers
from military and telephone company surplus, could be used by deaf people to converse
over the telephone. Based on teletypewriter standard devices, modern teletexts transmit
over regular telephone lines. Each teletext has a typewriter keyboard. Typed
communications appears on either a soft light-emitting character display or on paper.
Teletexts connect to the telephone system either acoustically through a built-in or add-on
modern or directly using a standard telephone cord. In order for a teletext conversation
to take place, both parties calling must have a teletext unit and each must be compatible
with the other like common software in our terms. There is now computer-based teletext
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along with email, which has become extremely popular amongst deaf people. Along with
email, deaf people frequently visit chat rooms. In an environment such as this they are
no different than any other computer user. That is why this is such an excellent outlet for
the deaf community.
Alarm clocks not only vital for the hearing population but are as equally important
for the deaf. There are a few different types of alarm clocks that the deaf use. A flashing
alarm clock is a device that consists of an extremely bright light that will blink or flash
when the alarm goes off. Some will have a plug in so the user can plug any light that
they wish into the clock and the alarm will turn that light on or off. A vibrating alarm clock
is a device that will cause a vibration in a small pad. The vibration is usually sufficient
enough to wake most sleepers. Some are designed to vibrate a pillow and others will
vibrate either a section of a bed or even the entire bed. They may have adjustable
settings for the amount of vibration needed. A combination clock combines the vibrating
and the flashing in one clock.
Many devices have been designed to help hearing-impaired individuals become
aware of the sounds in the environment that are needed for personal safety or
convenience. These devices may have a bright light that will blink or flash when the
sensor goes off. Some will have a plug in so the user can plug any light that they wish
into the sensor and when activated, the sensor will turn the light on and off. Others have
a loud horn that is activated by the sensor. Things that are often hooked to sensors
would include doorbells, timers (for cooking or laundry), telephones, smoke detectors or
fire alarms, alarm clocks, sound monitor, personal pagers and many others.
Personal alerting pager transmitters can be attached to items such as doorbells
and then when someone uses the doorbell, a light or a vibration will be activated on
persons receiving pager. Pagers may have four or more different colored lights to
separate the incoming transmission so those doorbells, are different then smoke
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detectors etc. These pagers could also be used by wristwatches which can intern
perform the same tasks.
One important device for hearing impaired people consists of access to programs
such as Paws with a Cause. Paws with a Cause is a non-profit organization that was
founded in 1979, by Michael Sapp. Paws with a Cause were originally referred to as
Ears for the Deaf, because they used to only train the dogs as Hearing Dogs. Then they
decided to provide services that could help everyone with a disability.
Once Paws with a Cause was a well-established organization they would send a
Community Field Instructor out to only train the dogs as Hearing Dogs. This also allowed
the dogs to become familiar with the severity of the situation from day one. Now that
Paws has a national headquarters they train the dogs at their facility then send the dog
out with the field instructor to be placed with a client.
In addition to all the training provided by the Paws organization, people who are
in need of help can get a Paws Dog free of charge. Numerous organizations sponsor
Paws, such as the United Way. Donations from service clubs, corporate donor and
individual donors; they have made it possible to lift at least one financial burden from the
disabled. It was estimated in 1997, twelve thousand dollars were donated for the service
dogs, five thousand dollars were donated for hearing dogs and fifteen thousand were
donated for combination dogs.
Most of the Paws dogs come from animal shelters, local breeders, or company
breeding programs. The dogs that are received are placed in foster families. These
volunteer foster families take care and help socialize the dogs until they are between
fourteen to sixteen months old. Once they are old enough, the dogs are evaluated to
determine what future training will be appropriate.
The Paws hearing dogs are trained to alert people who are hard-of-hearing.
These dogs respond to sounds such as smoke alarms, telephones, doorbells, babies
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crying, and any other noises. In emergency situations such as a smoke alarm going off,
the dog is trained to lead their owner to the nearest exit and safety. Another type of
Paws dog is a service dog. A few of their jobs are to help open and close doors, help in
situations of clientele seizure and to position themselves, as a brace (if their owner falls
the dog would help them become stable again). If the owner has a seizure, the Service
dog is trained to either comfort the individual, go for help, or bring the telephone to their
master. These dogs are often able to alert their owners before a seizure happens.
Service dogs are trained to help with many of the tasks, but these are just a few
remarkable examples. Last there are the combination dogs that are trained for numerous
purposes. For example, they are trained as hearing, guide, or service dogs. These dogs
are trained to help with obstacles such as traffic, curbs, or any other restrictions that
might be in their master’s way. Additional tasks that a Combination Dog may perform are
to “find” things such as the door or any other obstacles.
Although Paws with a Cause is a wonderful organization that provides services to
help people who are disabled, there are many other services that individuals who are
disabled can rely on, such as Closed Captioning.
Closed Captioning has been around for a long time. In 1972, the first nationally
broadcasted closed captioning program was aired on PBS, eight years later major
television stations began to air programs containing closed captioning. By the nineteennineties most of the primetime television shows contained closed captioning for the
hearing impaired. Along with closed captioning came laws, one of those laws is the
American’s with disabilities act. The ADA’s only specific requirement is that all public
service announcements that are funded by the government must be closed-captioned.
The ADA does not have that great of an impact on closed captioning. However, another
law that effects captioning is the Television Decoder Circuitry Act. The TDCA requires at
that all televisions sold in the United States have a decoder chip. In addition, all
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decoders must meet the standards set by the Federal Communication Commission
(FCC). The TDCA states that, “to the fullest extent made possible by technology, deaf
and hard of hearing people should have equal access to the television medium.” The last
law for captioning is the Telecommunications Act of 1996. This law is similar to the ADA,
because it too is not very specific about its requirements. The Telecommunications Act
does state, “video programming first published or exhibited after the effective date of
such regulations is fully accessible through the provisions of closed captions.” (Journal)
Another aspect of the Telecommunications Act is in mandatory captioning for
“new” programs on television after Jan. 1, 1998 is allowed an eight-year transition
period. These new programs have standards set each year they must meet. This means
that by Jan. 1, 2006 all “new” programming must be captioned. However, there is
different rules set up for “old” programs. “Old” television programs that aired before Jan.
1, 1998 must be fully captioned by Jan.1 2008.
Even though all these laws are complicated because the generally vague, they
are helping the deaf and hard of hear population become more involved with activities
the hearing people have. Another organization that is helping the deaf and hard of
hearing is Paws with a Cause. This organization also allows people with disabilities to
function enough in today’s society. All of these services are beneficial to anyone who
may have a disability.
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