14.6 Sensory Aids

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.