Section 14.6
Section 14.6 Sensory Aids
14.6
Sensory Aids
Sight and hearing are the two principal pathways through which our brain receives information about the external world. The two organs, eyes and ears, that transmit light and sound information into the brain are often damaged and their function needs to be supplemented. Eyeglasses came into use in the 1200s. At first these visual aids provided only simple magnified images of objects. Gradually a sophisticated technology evolved that produces eyeglasses to compensate for a wide range of visual problems (see Chapter 15).
Ear horns, in one form or another, have been used to aid hearing for thou sands of years. These devices improve hearing by collecting sound from an area significantly larger than the pinna (see Chapter 12).
Electrical technology has led to the development of devices that greatly enhance hearing and in some cases even restore hearing. The restoration of vision is far more challenging and while several avenues of research are being pursued the final goal seems far in the future.
14.6.1 Hearing Aids
The basic principle of hearing aids is simple. A microphone converts sound to an electrical signal. The electrical signal is amplified and converted back into sound using a speaker-type device. The net result is an amplification of the sound that enters the ear.
The first hearing aids became commercially available in the 1930s. They were relatively large cumbersome devices using battery-powered vacuum tube amplifiers. The batteries had to be replaced daily.
The much smaller transistor amplifiers that became available in the 1950s made hearing aids truly practicable. Transistorized hearing aids were now small enough to be placed in the ear. The application of digital computer technology to hearing aids was another major improvement that allowed individual tailoring of the device to compensate for the specific hearing deficits of the user. Using various feedback networks, modern hearing aids automatically adjust the volume of the sound so that quiet sounds can be heard and loud sounds not be painfully overwhelming.
14.6.2 Cochlear Implant
A cochlear implant functions differently from a hearing aid. A hearing aid simply amplifies incoming sound compensating for the diminished functioning of the ear. A cochlear implant converts sound to electrical signals of the type produced by the inner ear in response to sound that enters the ear.
Chapter 14 Electrical Technology 3
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FIGURE 14.10 Cochlear implant. 1. Sounds are picked up by the microphone.
2. The signal is then “coded” (turned into a special pattern of electrical pulses). 3. These pulses are sent to the coil and are then transmitted across the skin to the implant. 4. The implant sends a pattern of electrical pulses to the electrodes in the cochlea. 5. The auditory nerve picks up these electrical pulses and sends them to the brain. The brain recognizes these signals as sound.
The electrical signal is wirelessly transmitted to electrodes surgically implanted in the inner ear. The signals applied to the electrodes stimulate the auditory nerve to produce the sensation of sound. Thus the cochlear implant actually mimics the functions of the ear and can restore partial hearing to the deaf.
A sketch of a cochlear implant system is shown in Fig. 14.10. The exter nal part of the system is small enough to be placed behind the ear. It consists of a microphone, a signal processor, and a transmitter. The internal part consists of the receiver and an array of electrodes implanted and wound through the cochlea.
The microphone converts the sound to an electrical signal. Such electri cal signals as are produced by the microphone could themselves stimulate the auditory nerve, but the neural signals produced by such stimulation would not be interpreted by the brain as sound. In the normal ear the fluid filled cochlea processes the sound signal according to frequency such that the various frequency components of the incoming sound stimulate nerve endings along different parts of the basilar membrane (see Chapter 12). This type of a frequency-selective stimulation of the neural network provided by the cochlea is essential if the signal is to be interpreted by the brain as sound.
One of the main challenges in the design of cochlear implants was the development of signal-processing techniques that duplicated the action of a normal cochlea. Much of the work in this area was done in the 1950s and 60s.
First experiments with human implants began in the mid-1960s and continued through the 1970s. In 1984, FDA approved implantation into adults and shortly after, into children.
Usually a person receiving an implant is not immediately able to hear sounds properly. A period of training and speech therapy are needed before the full benefits of the device are realized.
EXERCISES
14-1. From the data in the text, compute the capacitance of the capacitor in the defibrillator and calculate the magnitude of the average current flowing during the pulse.
14-2. Verify Eq. 14.5.
14-3. Draw a block diagram for the following control systems. (a) Control of the body temperature in a person. (b) Control of the hand in drawing a line. (c) Control of the reflex action when the hand draws away from a painful stimulus. Include here the type of control that the brain may exercise on this movement. (d) Control of bone growth in response to pressure.
14-4. For each of the control systems in Exercise 14-3, discuss how the sys tem could be studied experimentally.
14-5. Discuss the controversy surrounding cochlear implants.
Chapter 15 Optics
Light is the electromagnetic radiation in the wavelength region between about 400 and 700 nm (1 nm 10−9 m). Although light is only a tiny part of the electromagnetic spectrum, it has been the subject of much research in both physics and biology. The importance of light is due to its fundamental role in living systems. Most of the electromagnetic radiation from the sun that reaches the Earth’s surface is in this region of the spectrum, and life has evolved to utilize it. In photosynthesis, plants use light to convert carbon dioxide and water into organic materials, which are the building blocks of living organisms. Animals have evolved light-sensitive organs which are their main source of information about the surroundings. Some bacteria and insects can even produce light through chemical reactions.
Optics, which is the study of light, is one of the oldest branches of physics.
It includes topics such as microscopes, telescopes, vision, color, pigments, illumination, spectroscopy, and lasers, all of which have applications in the life sciences. In this chapter, we will discuss four of these topics: vision, telescopes, microscopes, and optical fibers. Background information needed to understand this chapter is reviewed in Appendix C.
15.1
Vision
Vision is our most important source of information about the external world.
It has been estimated that about 70% of a person’s sensory input is obtained through the eye. The three components of vision are the stimulus, which
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14.6
Sensory Aids
Sight and hearing are the two principal pathways through which our brain receives information about the external world. The two organs, eyes and ears, that transmit light and sound information into the brain are often damaged and their function needs to be supplemented. Eyeglasses came into use in the 1200s. At first these visual aids provided only simple magnified images of objects. Gradually a sophisticated technology evolved that produces eyeglasses to compensate for a wide range of visual problems (see Chapter 15).
Ear horns, in one form or another, have been used to aid hearing for thou sands of years. These devices improve hearing by collecting sound from an area significantly larger than the pinna (see Chapter 12).
Electrical technology has led to the development of devices that greatly enhance hearing and in some cases even restore hearing. The restoration of vision is far more challenging and while several avenues of research are being pursued the final goal seems far in the future.
14.6.1 Hearing Aids
The basic principle of hearing aids is simple. A microphone converts sound to an electrical signal. The electrical signal is amplified and converted back into sound using a speaker-type device. The net result is an amplification of the sound that enters the ear.
The first hearing aids became commercially available in the 1930s. They were relatively large cumbersome devices using battery-powered vacuum tube amplifiers. The batteries had to be replaced daily.
The much smaller transistor amplifiers that became available in the 1950s made hearing aids truly practicable. Transistorized hearing aids were now small enough to be placed in the ear. The application of digital computer technology to hearing aids was another major improvement that allowed individual tailoring of the device to compensate for the specific hearing deficits of the user. Using various feedback networks, modern hearing aids automatically adjust the volume of the sound so that quiet sounds can be heard and loud sounds not be painfully overwhelming.
14.6.2 Cochlear Implant
A cochlear implant functions differently from a hearing aid. A hearing aid simply amplifies incoming sound compensating for the diminished functioning of the ear. A cochlear implant converts sound to electrical signals of the type produced by the inner ear in response to sound that enters the ear.
Chapter 14 Electrical Technology 3
2
1
5
4
FIGURE 14.10 Cochlear implant. 1. Sounds are picked up by the microphone.
2. The signal is then “coded” (turned into a special pattern of electrical pulses). 3. These pulses are sent to the coil and are then transmitted across the skin to the implant. 4. The implant sends a pattern of electrical pulses to the electrodes in the cochlea. 5. The auditory nerve picks up these electrical pulses and sends them to the brain. The brain recognizes these signals as sound.
The electrical signal is wirelessly transmitted to electrodes surgically implanted in the inner ear. The signals applied to the electrodes stimulate the auditory nerve to produce the sensation of sound. Thus the cochlear implant actually mimics the functions of the ear and can restore partial hearing to the deaf.
A sketch of a cochlear implant system is shown in Fig. 14.10. The exter nal part of the system is small enough to be placed behind the ear. It consists of a microphone, a signal processor, and a transmitter. The internal part consists of the receiver and an array of electrodes implanted and wound through the cochlea.
The microphone converts the sound to an electrical signal. Such electri cal signals as are produced by the microphone could themselves stimulate the auditory nerve, but the neural signals produced by such stimulation would not be interpreted by the brain as sound. In the normal ear the fluid filled cochlea processes the sound signal according to frequency such that the various frequency components of the incoming sound stimulate nerve endings along different parts of the basilar membrane (see Chapter 12). This type of a frequency-selective stimulation of the neural network provided by the cochlea is essential if the signal is to be interpreted by the brain as sound.
One of the main challenges in the design of cochlear implants was the development of signal-processing techniques that duplicated the action of a normal cochlea. Much of the work in this area was done in the 1950s and 60s.
First experiments with human implants began in the mid-1960s and continued through the 1970s. In 1984, FDA approved implantation into adults and shortly after, into children.
Usually a person receiving an implant is not immediately able to hear sounds properly. A period of training and speech therapy are needed before the full benefits of the device are realized.
EXERCISES
14-1. From the data in the text, compute the capacitance of the capacitor in the defibrillator and calculate the magnitude of the average current flowing during the pulse.
14-2. Verify Eq. 14.5.
14-3. Draw a block diagram for the following control systems. (a) Control of the body temperature in a person. (b) Control of the hand in drawing a line. (c) Control of the reflex action when the hand draws away from a painful stimulus. Include here the type of control that the brain may exercise on this movement. (d) Control of bone growth in response to pressure.
14-4. For each of the control systems in Exercise 14-3, discuss how the sys tem could be studied experimentally.
14-5. Discuss the controversy surrounding cochlear implants.
Chapter 15 Optics
Light is the electromagnetic radiation in the wavelength region between about 400 and 700 nm (1 nm 10−9 m). Although light is only a tiny part of the electromagnetic spectrum, it has been the subject of much research in both physics and biology. The importance of light is due to its fundamental role in living systems. Most of the electromagnetic radiation from the sun that reaches the Earth’s surface is in this region of the spectrum, and life has evolved to utilize it. In photosynthesis, plants use light to convert carbon dioxide and water into organic materials, which are the building blocks of living organisms. Animals have evolved light-sensitive organs which are their main source of information about the surroundings. Some bacteria and insects can even produce light through chemical reactions.
Optics, which is the study of light, is one of the oldest branches of physics.
It includes topics such as microscopes, telescopes, vision, color, pigments, illumination, spectroscopy, and lasers, all of which have applications in the life sciences. In this chapter, we will discuss four of these topics: vision, telescopes, microscopes, and optical fibers. Background information needed to understand this chapter is reviewed in Appendix C.
15.1
Vision
Vision is our most important source of information about the external world.
It has been estimated that about 70% of a person’s sensory input is obtained through the eye. The three components of vision are the stimulus, which
214