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14.6 Sensory Aids
Our brain receives information about the outside world through sight and hearing.
The eyes and ears transmit light and sound to the brain and are often damaged.
Eyeglasses were used in the 1200s.
The first visual aids provided simple magnified images of objects.
Gradually a sophisticated technology evolved that produces eyeglasses to compensate for a wide range of visual problems.
Ear horns have been used to aid hearing for many years.
The devices collect sound from a larger area than the pinna.
Some of the devices that enhance hearing and restore hearing are the result of electrical technology.
The restoration of vision is more difficult and the final goal seems far off in the future.
The principle of hearing aids is easy to understand.
A microphone is used to amplify sound.
A speaker-type device converts the electrical signal into sound.
The amplification of sound enters the ear.
The first hearing aids were available in the 1930s.
They were large and cumbersome using a vacuum tube amplifier.
The batteries needed to be replaced daily.
Hearing aids were made easier by the transistor amplifier that became available in the 1950s.
The hearing aids were small enough to fit in the ear.
The application of digital computer technology to hearing aids allowed individual tailoring of the device to compensate for the specific hearing deficits of the user.
Modern hearing aids use feedback networks to adjust the volume of the sound so that quiet sounds can be heard and loud sounds are not overwhelming.
A hearing aid is used to amplify incoming sound.
The sound that enters the ear is converted into electrical signals by the inner ear.
The microphone picks up sounds.
The signal is turned into a pattern of electrical impulses.
The pulse is transmitted across the skin to the implant.
The implant sends electrical impulses to the cochlea.
The brain gets the electrical impulses from the auditory nerve.
The brain listens to sound.
The signal is sent to the inner ear.
The sensation of sound is created by the stimulation of the auditory nerve.
The implant mimics the functions of the ear and can restore partial hearing to the deafness.
The small part of the system can be placed behind the ear.
There is a microphone, a signal processor, and a transmitter.
The internal part consists of a receiver and an array of wires.
The sound is converted into an electrical signal by the microphone.
Neural signals produced by stimulation of the auditory nerve would not be seen as sound by the brain.
In the normal ear the fluid filled cochlea processes the sound signal according to the frequencies of the incoming sound and stimulates nerve endings in different parts of the basilar membrane.
This type of stimulation of the neural network provided by the cochlea is essential if the signal is to be interpreted as sound.
The development of signal-processing techniques that duplicated the action of a normal cochlea was one of the main challenges in the design of cochlear implants.
The work done in this area was done in the 50s and 60s.
The first experiments with human implants began in the 1960s.
In 1984 the FDA approved implanting into adults and children.
A person receiving an implant may not be able to hear sounds immediately.
Before the full benefits of the device are realized, a period of training and speech therapy is needed.
The magnitude of the average current flowing during the pulse can be calculated from the data in the text.
The following control systems have a block diagram drawn on them.
The type of control the brain can exercise on this movement is included here.
Discuss the issue of implants.
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