Robinson, C.J. "Rehabilitation Engineering, Science, and Technology The Electrical Engineering Handbook Ed. Richard C. Dorf Boca raton crc Press llc. 2000
Robinson, C.J. “Rehabilitation Engineering, Science, and Technology” The Electrical Engineering Handbook Ed. Richard C. Dorf Boca Raton: CRC Press LLC, 2000
Rehabilitation Engineering, Science and Technology 119.1 Rehabilitation Concepts 119.2 Engineering Concepts in Sensory Rehabilitation 119.3 Engineering Concepts in Motor Rehabilitation Charles J. Robinson 119.4 Engineering Concepts in Communications Disorders Louisiana tech university 119.5 Appropriate Technology Overton Brooks VA Medical Center 119.6 The Future of Engineering in Rehabilitation Rehabilitation engineering requires a multidisciplinary effort. To put rehabilitation engineering into its proper context, we need to review some of the other disciplines with which rehabilitation engineers must be familiar. Robinson [1993] has reviewed or put forth the following working definitions and discussions ehabilitation: The(Re)integration of an individual with a disability into society. This can be done either by enhancing existing capabilities or by providing alternative means to perform various functions or Rehabilitation engineering: The application of science and technology to ameliorate the handicaps of indi- als with disabilities [Reswick, 1982]. In actual practice, many individuals who say that they practice rehabilitation engineering are not engineers by training. While this leads to controversies from practi- tioners with traditional engineering degrees, it also has the de facto benefit of greatly widening the scope of what is encompassed by the term"rehabilitation engineering Rehabilitation medicine: A clinical practice that focuses on the physical aspects of functional recovery, but that also considers medical, neurological and psychological factors. Physical therapy, occupational ther apy, and rehabilitation counseling are professions in their own right On the sensory-motor side, other medical and therapeutical specialties practice rehabilitation in vision, audition, and speech Rehabilitation technology (or Assistive technology): Narrowly defined, the selection, design, or manufactur of augmentative or assistive devices that are appropriate for the individual with a disability. Such devices are selected based on the specific disability, the function to be augmented or restored, the user's wishes the clinicians preferences, cost, and the environment in which the device will be used. Rehabilitation science: The development of a body of knowledge, gleaned from rigorous basic and clinical research, that describes how a disability alters specific physiological functions or anatomical structures, and that details the underlying principles by which residual function or capacity can be measured and used to restore function of individuals with disabilities c 2000 by CRC Press LLC
© 2000 by CRC Press LLC 119 Rehabilitation Engineering, Science, and Technology 119.1 Rehabilitation Concepts 119.2 Engineering Concepts in Sensory Rehabilitation 119.3 Engineering Concepts in Motor Rehabilitation 119.4 Engineering Concepts in Communications Disorders 119.5 Appropriate Technology 119.6 The Future of Engineering in Rehabilitation Rehabilitation engineering requires a multidisciplinary effort. To put rehabilitation engineering into its proper context, we need to review some of the other disciplines with which rehabilitation engineers must be familiar. Robinson [1993] has reviewed or put forth the following working definitions and discussions. Rehabilitation: The (Re)integration of an individual with a disability into society. This can be done either by enhancing existing capabilities or by providing alternative means to perform various functions or to substitute for specific sensations. Rehabilitation engineering: The application of science and technology to ameliorate the handicaps of individuals with disabilities [Reswick, 1982]. In actual practice, many individuals who say that they practice rehabilitation engineering are not engineers by training. While this leads to controversies from practitioners with traditional engineering degrees, it also has the de facto benefit of greatly widening the scope of what is encompassed by the term “rehabilitation engineering.” Rehabilitation medicine: A clinical practice that focuses on the physical aspects of functional recovery, but that also considers medical, neurological and psychological factors. Physical therapy, occupational therapy, and rehabilitation counseling are professions in their own right. On the sensory-motor side, other medical and therapeutical specialties practice rehabilitation in vision, audition, and speech. Rehabilitation technology (or Assistive technology): Narrowly defined, the selection, design, or manufacture of augmentative or assistive devices that are appropriate for the individual with a disability. Such devices are selected based on the specific disability, the function to be augmented or restored, the user’s wishes, the clinician’s preferences, cost, and the environment in which the device will be used. Rehabilitation science: The development of a body of knowledge, gleaned from rigorous basic and clinical research, that describes how a disability alters specific physiological functions or anatomical structures, and that details the underlying principles by which residual function or capacity can be measured and used to restore function of individuals with disabilities. Charles J. Robinson Louisiana Tech University Overton Brooks VA Medical Center
119.1 Rehabilitation Concepts Effective rehabilitation engineers must be well versed in all of the areas described above because they generally work in a team setting, in collaboration with physical and occupational therapists, orthopedic surgeons, physical medicine ecialists, and/or neurologists. Some rehabilitation engineers are interested in certain activities that we do in the course of a normal day that could be summarized as activities of daily living(ADL). These include eating, toileting, ombing hair, brushing teeth, reading, etc. Other engineers focus on mobility and the limitations to mobility. Mobility can be personal (e.g, within a home or office)or public(automobile, public transportation, accessibility questions in buildings). Mobility also includes the ability to move functionally through the environment. Thus, the question of mobility is not limited to that of getting from place to place, but also includes such questions as whether one can reach an object in a particular setting or whether a paralyzed urinary bladder can be made functional again Barriers that limit mobility are also studied. For example, an ill-fitted wheelchair cushion or support system will nost assuredly limit mobility by reducing the time that an individual can spend in a wheelchair before he or she must vacate it to avoid serious and difficult-to-heal pressure sores. Other groups of rehabilitation engineers deal with sensory disabilities, such as sight or hearing, or with communications disorders, both on the production side g, the nonvocal)or on the comprehension side. For any given client, a rehabilitation engineer might have all of these concerns to consider (ie, ADLs, mobility, sensory, and communication dysfunctions A key concept in physical or sensory rehabilitation is that of residual function or residual capacity. Such a concept implies that the function or sense can be quantified, that the performance range of that function or sense is known in a nonimpaired population, and that the use of residual capacity by a disabled individual should be encouraged. These measures of human performance can be made subjectively by clinicians or objectively by some rather clever computerized test devices. A rehabilitation engineer asks three key questions: Can a diminished function or sense be successfully augmented? Is there a substitute way to return the function or to restore a sense? And is the solution appropriate and cost-effective? These questions give rise to two important rehabilitation concepts: orthotics and prosthetics. An orthosisis an appliance that aids an existing function. a prosthesisprovides a substitute. An artificial limb is a prosthesis, as is a wheelchair. An ankle brace is an orthosis so are eyeglasses. In fact, eyeglasses might well be the penultimate rehabilitation device. They are inexpensive, have little social stigma, and are almost completely unobtrusive to the user. They have let many millions of individuals with correctable vision problems lead productive lives. But in essence, a pair of eyeglasses is an optical device, governed by traditional equations of physical optics. Eyeglasses can be made out of simple glass(from a raw material as bundant as the sands of the earth) or complex plastics such as those that are ultraviolet sensitive. They can be ground by hand or by sophisticated computer-controlled optical grinders. Thus, crude technology can restore functional vision. Increasing the technical content of the eyeglasses(either by material or manufacturing method) in most cases will not increase the amount of function restored, but it might make the glasses cheaper, lighter, and more prone to be used 119.2 Engineering Concepts in Sensory Rehabilitation Of the five traditional senses, vision and hearing best define the interactions that permit us to be human. These two senses are the main input channels through which data with high information content can flow. We read we listen to speech or music; we view art. A loss of one or the other of these senses (or both) can have a devastating impact on the individual affected Rehabilitation engineers attempt to restore the functions of these senses,either through augmentation or via sensory substitution systems. Eyeglasses and hearing aids are examples of augmentative devices that can be used if some residual capacity remains. A major area of rehabil itation engineering research deals with sensory substitution systems [ Kaczmarek et al, 1991] The visual system has the capability to detect a single photon of light, yet also has a dynamic range that can respond to intensities many orders of magnitude greater. It can work with high contrast items and with those of almost no contrast, and across the visible spectrum of colors. Millions of parallel data channels form the optic nerve that comes from an eye; each channel transmits an asynchronous and quasi-random(in time stream of binary pulses. While the temporal coding on any one of these channels is not fast(on the order c 2000 by CRC Press LLC
© 2000 by CRC Press LLC 119.1 Rehabilitation Concepts Effective rehabilitation engineers must be well versed in all of the areas described above because they generally work in a team setting, in collaboration with physical and occupational therapists, orthopedic surgeons, physical medicine specialists, and/or neurologists. Some rehabilitation engineers are interested in certain activities that we do in the course of a normal day that could be summarized as activities of daily living (ADL). These include eating, toileting, combing hair, brushing teeth, reading, etc. Other engineers focus on mobility and the limitations to mobility. Mobility can be personal (e.g., within a home or office) or public (automobile, public transportation, accessibility questions in buildings). Mobility also includes the ability to move functionally through the environment. Thus, the question of mobility is not limited to that of getting from place to place, but also includes such questions as whether one can reach an object in a particular setting or whether a paralyzed urinary bladder can be made functional again. Barriers that limit mobility are also studied. For example, an ill-fitted wheelchair cushion or support system will most assuredly limit mobility by reducing the time that an individual can spend in a wheelchair before he or she must vacate it to avoid serious and difficult-to-heal pressure sores. Other groups of rehabilitation engineers deal with sensory disabilities, such as sight or hearing, or with communications disorders, both on the production side (e.g., the nonvocal) or on the comprehension side. For any given client, a rehabilitation engineer might have all of these concerns to consider (i.e., ADLs, mobility, sensory, and communication dysfunctions). A key concept in physical or sensory rehabilitation is that of residual function or residual capacity. Such a concept implies that the function or sense can be quantified, that the performance range of that function or sense is known in a nonimpaired population, and that the use of residual capacity by a disabled individual should be encouraged. These measures of human performance can be made subjectively by clinicians or objectively by some rather clever computerized test devices. A rehabilitation engineer asks three key questions: Can a diminished function or sense be successfully augmented? Is there a substitute way to return the function or to restore a sense? And is the solution appropriate and cost-effective? These questions give rise to two important rehabilitation concepts: orthotics and prosthetics. An orthosis is an appliance that aids an existing function. A prosthesis provides a substitute. An artificial limb is a prosthesis, as is a wheelchair. An ankle brace is an orthosis; so are eyeglasses. In fact, eyeglasses might well be the penultimate rehabilitation device. They are inexpensive, have little social stigma, and are almost completely unobtrusive to the user. They have let many millions of individuals with correctable vision problems lead productive lives. But in essence, a pair of eyeglasses is an optical device, governed by traditional equations of physical optics. Eyeglasses can be made out of simple glass (from a raw material as abundant as the sands of the earth) or complex plastics such as those that are ultraviolet sensitive. They can be ground by hand or by sophisticated computer-controlled optical grinders. Thus, crude technology can restore functional vision. Increasing the technical content of the eyeglasses (either by material or manufacturing method) in most cases will not increase the amount of function restored, but it might make the glasses cheaper, lighter, and more prone to be used. 119.2 Engineering Concepts in Sensory Rehabilitation Of the five traditional senses, vision and hearing best define the interactions that permit us to be human. These two senses are the main input channels through which data with high information content can flow. We read; we listen to speech or music; we view art. A loss of one or the other of these senses (or both) can have a devastating impact on the individual affected. Rehabilitation engineers attempt to restore the functions of these senses, either through augmentation or via sensory substitution systems. Eyeglasses and hearing aids are examples of augmentative devices that can be used if some residual capacity remains. A major area of rehabilitation engineering research deals with sensory substitution systems [Kaczmarek et al., 1991]. The visual system has the capability to detect a single photon of light, yet also has a dynamic range that can respond to intensities many orders of magnitude greater. It can work with high contrast items and with those of almost no contrast, and across the visible spectrum of colors. Millions of parallel data channels form the optic nerve that comes from an eye; each channel transmits an asynchronous and quasi-random (in time) stream of binary pulses. While the temporal coding on any one of these channels is not fast (on the order of
200 bits per second or less), the capacity of the human brain to parallel process the entire image is faster than any supercomputer yet built. If sight is lost, how can it be replaced? A simple pair of eyeglasses will not work, because either the sensor he retina), the communication channel(the optic nerve and all of its relays to the brain), or one or more essential central processors(the occipital part of the cerebral cortex for initial processing: the parietal and other cortical areas for information extraction) has been damaged. For replacement within the system, one must determine where the visual system has failed and whether a stage of the system can be artificially bypassed. If one uses another sensory modality(e.g, touch or hearing) as an alternate input channel, one must determine whether there is sufficient bandwidth in that channel and whether the higher-order processing hierarchy is plastic enough to process information coming via a different route. While the above discussion might seem just philosophical, it is more than that. We normally read printed text with our eyes. We recognize words from their(visual) letter combinations We comprehend what we read via a mysterious processing in the parietal and temporal parts of the cerebral cortex. Could we perhaps read and comprehend this text or other forms of writing through our fingertips with an appropriate interface? The nswer,surprisingly, is yes! And, the adaptation actually goes back to one of the earliest applications of coding hat of the development of Braille. braille condenses all 3 dots(26 combinations), with certain combinations reserved as indicators for the next character(such as a lumber indicator) or for special contractions. Trained readers of Braille can read over 250 words per minute of grade 2 Braille(as fast as most sighted readers can read printed text). Thus, the Braille code is in essence a rehabilitation engineering concept where an alternate sensory channel is used as a substitute and where a ng scheme has been employed. Rehabilitation engineers and their colleagues have designed other ways to read text. To replace the retina as a sensor element, a modern high-resolution, high-sensitivity, fast-imaging sensor(CCD, etc. )is employed to capture a visual image of the text. One method, used by various page scanning devices, converts the scanned image to text by using optical character recognition schemes, and then outputs the text as speech via text-to- speech algorithms. This machine essentially recites the text, much as a sighted helper might do when reading aloud to the blind individual. The user of the device is thus freed of the absolute need for a helper. Such independence is often the goal of rehabilitation Perhaps the most interesting method presents an image of the scanned data directly to the visual cortex or retina via an array of implantable electrodes that are used to electrically activate nearby cortical or retin structures. The visual cortex and retina are laid out in topographic fashion such that there is an orderly mapping of the signal from different parts of the visual field to the retina, and from the retina to corresponding parts of the occipital cortex. The goal of stimulation is to mimic the neural activity that would have been evoked had the signal come through normal channels. And, such stimulation does produce the sensation of light. Since the"image"stays within the visual system, the rehabilitation solution is said to be modality specificHowever, substantial problems dealing with biocompatibility and image processing and reduction remain in the design of the electrode arrays and processors that serve to interface the electronics and neurological tissue. Deafness is another manifestation of a loss of a communication channel, this time for the sense of hearing Totally deaf individuals use vision as a substitute input channel when communicating via sign language(also a substitute code), and can sign at information rates that match or exceed that of verbal communication. Hearing aids are now commercially available that can adaptively filter out background noise(a predictable signal)while amplifying speech(unpredictable)using autoregressive, moving average(ARMA) signal process 8. With the recent advent of powerful digital signal processing chips, true digital hearing aids are now available Previous analog aids, or digitally programmable analog aids, provided a set of tunable filters and amplifiers to cover the low-, mid-, and high-frequency ranges of the hearing spectrum. But the digital aids can be specifically and easily tailored (i. e, programmed) to compensate for the specific losses of each individual client across the frequency continuum of hearing, and still provide automatic gain control and one or more user-selectable settings that have been adjusted to perform optimally in differing noise environments An exciting development is occurring outside the field of rehabilitation that will have a profound impact on the ability of the deaf to comprehend speech. Electronics companies are now beginning to market universal translation aids for travelers, where a phrase spoken in one language is captured, parsed, translated, and restated c 2000 by CRC Press LLC
© 2000 by CRC Press LLC 200 bits per second or less), the capacity of the human brain to parallel process the entire image is faster than any supercomputer yet built. If sight is lost, how can it be replaced? A simple pair of eyeglasses will not work, because either the sensor (the retina), the communication channel (the optic nerve and all of its relays to the brain), or one or more essential central processors (the occipital part of the cerebral cortex for initial processing; the parietal and other cortical areas for information extraction) has been damaged. For replacement within the system, one must determine where the visual system has failed and whether a stage of the system can be artificially bypassed. If one uses another sensory modality (e.g., touch or hearing) as an alternate input channel, one must determine whether there is sufficient bandwidth in that channel and whether the higher-order processing hierarchy is plastic enough to process information coming via a different route. While the above discussion might seem just philosophical, it is more than that. We normally read printed text with our eyes. We recognize words from their (visual) letter combinations. We comprehend what we read via a mysterious processing in the parietal and temporal parts of the cerebral cortex. Could we perhaps read and comprehend this text or other forms of writing through our fingertips with an appropriate interface? The answer, surprisingly, is yes! And, the adaptation actually goes back to one of the earliest applications of coding theory — that of the development of Braille. Braille condenses all text characters to a raised matrix of 2 by 3 dots (26 combinations), with certain combinations reserved as indicators for the next character (such as a number indicator) or for special contractions. Trained readers of Braille can read over 250 words per minute of grade 2 Braille (as fast as most sighted readers can read printed text). Thus, the Braille code is in essence a rehabilitation engineering concept where an alternate sensory channel is used as a substitute and where a recoding scheme has been employed. Rehabilitation engineers and their colleagues have designed other ways to read text. To replace the retina as a sensor element, a modern high-resolution, high-sensitivity, fast-imaging sensor (CCD, etc.) is employed to capture a visual image of the text. One method, used by various page scanning devices, converts the scanned image to text by using optical character recognition schemes, and then outputs the text as speech via text-tospeech algorithms. This machine essentially recites the text, much as a sighted helper might do when reading aloud to the blind individual. The user of the device is thus freed of the absolute need for a helper. Such independence is often the goal of rehabilitation. Perhaps the most interesting method presents an image of the scanned data directly to the visual cortex or retina via an array of implantable electrodes that are used to electrically activate nearby cortical or retinal structures. The visual cortex and retina are laid out in topographic fashion such that there is an orderly mapping of the signal from different parts of the visual field to the retina, and from the retina to corresponding parts of the occipital cortex. The goal of stimulation is to mimic the neural activity that would have been evoked had the signal come through normal channels. And, such stimulation does produce the sensation of light. Since the “image” stays within the visual system, the rehabilitation solution is said to be modality specific. However, substantial problems dealing with biocompatibility and image processing and reduction remain in the design of the electrode arrays and processors that serve to interface the electronics and neurological tissue. Deafness is another manifestation of a loss of a communication channel, this time for the sense of hearing. Totally deaf individuals use vision as a substitute input channel when communicating via sign language (also a substitute code), and can sign at information rates that match or exceed that of verbal communication. Hearing aids are now commercially available that can adaptively filter out background noise (a predictable signal) while amplifying speech (unpredictable) using autoregressive, moving average (ARMA) signal processing. With the recent advent of powerful digital signal processing chips, true digital hearing aids are now available. Previous analog aids, or digitally programmable analog aids, provided a set of tunable filters and amplifiers to cover the low-, mid-, and high-frequency ranges of the hearing spectrum. But the digital aids can be specifically and easily tailored (i.e., programmed) to compensate for the specific losses of each individual client across the frequency continuum of hearing, and still provide automatic gain control and one or more user-selectable settings that have been adjusted to perform optimally in differing noise environments. An exciting development is occurring outside the field of rehabilitation that will have a profound impact on the ability of the deaf to comprehend speech. Electronics companies are now beginning to market universal translation aids for travelers, where a phrase spoken in one language is captured, parsed, translated, and restated
(either spoken or displayed) in another language. The deaf would simply require that the visual display be in the language that they use for writing Deafness is often brought on (or occurs congenitally) by damage to the cochlea. The cochlea normally transduces variations in sound pressure intensity at a given frequency into patterns of neural discharge. TI neural code is then carried by the auditory (eighth cranial)nerve to the brainstem, where it is preprocessed and relayed to the auditory cortex for initial processing and on to the parietal and other cortical areas information extraction. Similar to the case for the visual system, the cochlea, auditory nerve, auditory cortex, and all relays in between maintain a topological map, this time based on tone frequency( tonotopic). If deafness is solely due to cochlear damage(as is often the case)and if the auditory nerve is still intact, a cochlear implant an often be substituted for the regular transducer array(the cochlea) while still sending the signal through he normal auditory channel ( to maintain modality specificity) At first glance, the design of a cochlear prosthesis to restore hearing appears daunting. The hearing range of a healthy young individual is 20 to 16,000 Hz. The transducing structure, the cochlea, has 3500 inner and 12,000 outer hair cells, each best activated by a specific frequency that causes a localized mechanical resonance in the basilar membrane of the cochlea. deflection of a hair cell causes the cell to fire an all-or pulsatile) neuronal discharge, whose rate of repetition depends to a first approximation on the amplitude of the stimulus. The outputs of these hair cells have an orderly convergence on the 30,000 to 40,000 fibers that make up the auditory portion of the eighth cranial nerve. These afferent fibers, in turn, go to brainstem neurons that process and relay the signals on to higher brain centers Klinke, 1983]. For many causes of deafness, the hair cells are destroyed, but the eighth nerve remains intact. Thus, if one could elicit activity in a specific output fiber by means other than the hair cell motion, perhaps some sense of hearing could be restored. The geometry of the cochlea helps in this regard as different portions of the nerve are closer to different parts of the cochlea Electrical stimulation is now used in the cochlear implant to bypass hair cell transduction mechanisms[ Loeb, 1985; Clark et al., 1990]. These sophisticated devices have required that complex signal processing, electronic, and packaging problems be solved One current cochlear implant has 22 stimulus sites along the scala tympani of the cochlea. Those sites provide excitation to the peripheral processes of the cells of the eighth cranial nerve, which are splayed out along the length of the scala. The electrode assembly itself has 22 ring electrodes spaced along its length and some additional guard rings between the active electrodes and the receiver to aid in securing the very flexible electrode assembly after it is snaked into the cochleas very small(a few millimeters)round window(a surgeon related to me that positioning the electrode was akin to pushing a piece of cooked spaghetti hrough a small hole at the end of a long tunnel). The electrode is attached to a receiver that is inlaid into a slot milled out of the temporal bone. The receiver contains circuitry that can select any electrode ring to be a source and any other electrode to be a sink for the stimulating current, and that can rapidly sequence between various pairs of electrodes. The receiver is powered and controlled by a radiofrequency link with an external transmitter, whose alignment is maintained by means of a permanent magnet imbedded in the receiver. igital signal processor stores information about a specific user and his or her optimal electrode locations for specific frequency bands. The object is to determine what pair of electrodes best produces the subjective perception of a certain pitch in the implanted individual himself or herself, and then to associate a particular lter with that pair via the controller. An enormous amount of compression occurs in taking the frequency range necessary for speech comprehension and reducing it to a few discrete channels. At present, the optimum ompression algorithm is unknown, and much fundamental research is being carried out in speech processing, compression, and recognition. But, what is amazing is that a number of totally deaf individuals can relearn to omprehend speech exceptionally well without speech-reading through the use of these implants. Other indi- viduals find that the implant aids in speech-reading. For some, only an awareness of environmental sounds is apparent; and for another group, the implant appears to have little effect. But, if you could(as I have been able to)finally converse in unaided speech with an individual who had been rendered totally blind and deaf by a traumatic brain injury, you would certainly begin to appreciate the power of rehabilitation engineering 119. 3 Engineering Concepts in Motor Rehabilitation Limitations in mobility can severely restrict the quality of life of an individual so affected. a wheelchair is a prime example of a prosthesis that can restore personal mobility to those who cannot walk. Given the proper c 2000 by CRC Press LLC
© 2000 by CRC Press LLC (either spoken or displayed) in another language. The deaf would simply require that the visual display be in the language that they use for writing. Deafness is often brought on (or occurs congenitally) by damage to the cochlea. The cochlea normally transduces variations in sound pressure intensity at a given frequency into patterns of neural discharge. This neural code is then carried by the auditory (eighth cranial) nerve to the brainstem, where it is preprocessed and relayed to the auditory cortex for initial processing and on to the parietal and other cortical areas for information extraction. Similar to the case for the visual system, the cochlea, auditory nerve, auditory cortex, and all relays in between maintain a topological map, this time based on tone frequency (tonotopic). If deafness is solely due to cochlear damage (as is often the case) and if the auditory nerve is still intact, a cochlear implant can often be substituted for the regular transducer array (the cochlea) while still sending the signal through the normal auditory channel (to maintain modality specificity). At first glance, the design of a cochlear prosthesis to restore hearing appears daunting. The hearing range of a healthy young individual is 20 to 16,000 Hz. The transducing structure, the cochlea, has 3500 inner and 12,000 outer hair cells, each best activated by a specific frequency that causes a localized mechanical resonance in the basilar membrane of the cochlea. Deflection of a hair cell causes the cell to fire an all-or-none (i.e., pulsatile) neuronal discharge, whose rate of repetition depends to a first approximation on the amplitude of the stimulus. The outputs of these hair cells have an orderly convergence on the 30,000 to 40,000 fibers that make up the auditory portion of the eighth cranial nerve. These afferent fibers, in turn, go to brainstem neurons that process and relay the signals on to higher brain centers [Klinke, 1983]. For many causes of deafness, the hair cells are destroyed, but the eighth nerve remains intact. Thus, if one could elicit activity in a specific output fiber by means other than the hair cell motion, perhaps some sense of hearing could be restored. The geometry of the cochlea helps in this regard as different portions of the nerve are closer to different parts of the cochlea. Electrical stimulation is now used in the cochlear implant to bypass hair cell transduction mechanisms [Loeb, 1985; Clark et al., 1990]. These sophisticated devices have required that complex signal processing, electronic, and packaging problems be solved. One current cochlear implant has 22 stimulus sites along the scala tympani of the cochlea. Those sites provide excitation to the peripheral processes of the cells of the eighth cranial nerve, which are splayed out along the length of the scala. The electrode assembly itself has 22 ring electrodes spaced along its length and some additional guard rings between the active electrodes and the receiver to aid in securing the very flexible electrode assembly after it is snaked into the cochlea’s very small (a few millimeters) round window (a surgeon related to me that positioning the electrode was akin to pushing a piece of cooked spaghetti through a small hole at the end of a long tunnel). The electrode is attached to a receiver that is inlaid into a slot milled out of the temporal bone. The receiver contains circuitry that can select any electrode ring to be a source and any other electrode to be a sink for the stimulating current, and that can rapidly sequence between various pairs of electrodes. The receiver is powered and controlled by a radiofrequency link with an external transmitter, whose alignment is maintained by means of a permanent magnet imbedded in the receiver. A digital signal processor stores information about a specific user and his or her optimal electrode locations for specific frequency bands. The object is to determine what pair of electrodes best produces the subjective perception of a certain pitch in the implanted individual himself or herself, and then to associate a particular filter with that pair via the controller. An enormous amount of compression occurs in taking the frequency range necessary for speech comprehension and reducing it to a few discrete channels. At present, the optimum compression algorithm is unknown, and much fundamental research is being carried out in speech processing, compression, and recognition. But, what is amazing is that a number of totally deaf individuals can relearn to comprehend speech exceptionally well without speech-reading through the use of these implants. Other individuals find that the implant aids in speech-reading. For some, only an awareness of environmental sounds is apparent; and for another group, the implant appears to have little effect. But, if you could (as I have been able to) finally converse in unaided speech with an individual who had been rendered totally blind and deaf by a traumatic brain injury, you would certainly begin to appreciate the power of rehabilitation engineering. 119.3 Engineering Concepts in Motor Rehabilitation Limitations in mobility can severely restrict the quality of life of an individual so affected. A wheelchair is a prime example of a prosthesis that can restore personal mobility to those who cannot walk. Given the proper
environment(fairly level floors, roads, etc. ) modern wheelchairs can be highly efficient. In fact, the mes in one of mans greatest tests of endurance, the Boston Marathon, are achieved by the wheelchair r Although they do gain the advantage of being able to roll, they still must climb the same hills, and do only one fifth of the muscle power available to an able-bodied marathoner. While a wheelchair user could certainly go down a set of steps(not recommended), climbing steps in a normal manual or electric wheelchair is a virtual impossibility. Ramps or lifts are engineered to provide accessibility in these cases, or special climbing wheelchairs can be purchased. Wheelchairs also do not work well on surfaces with high rolling resistance or viscous coefficients(e.g, mud, rough terrain, etc. ) so alternate mobility aids must be found if access to these areas is to be provided to the physically disabled. Hand-controlled ars,vans,tractors,and even airplanes are now driven by wheelchair users. The design of appropriate control modifications falls to the rehabilitation engineer. oss of a limb can greatly impair functional activity. The engineering aspects of artificial limb design increase complexity as the amount of residual limb decreases, especially if one or more joints are lost. As an example, a person with a mid-calf amputation could use a simple wooden stump to extend the leg, and could ambulate reasonably well. But such a leg is not cosmetically appealing and completely ignores any substitution for ankle Immediately following World War II, the U.S. government began the first concerted effort to foster better engineering design for artificial limbs. Dynamically lockable knee joints were designed for artificial limbs for above-knee amputees. In the ensuing years, energy-storing artificial ankles have been designed, some with prosthetic feet so realistic that beach thongs could be worn with them. Artificial hands, wrists, and elbows were signed for upper-limb amputees. Careful design of the actuating cable system also provided for a sense of hand grip force, so that the user had some feedback and did not need to rely on vision alone for guidance. 6 Perhaps the most transparent(to the user)artificial arms are the ones that use electrical activity generated the muscles remaining in the stump to control the actions of the elbow, wrist, and hand Stein et al., 1988] This electrical activity is known as myoelectricity, and is produced as the muscle contraction spreads through ne muscle. Note that these muscles, if intact, would have controlled at least one of these joints(e. g, the biceps and triceps for the elbow). Thus, a high level of modality specificity is maintained because the functional element is substituted only at the last stage. All of the batteries, sensor electrodes, amplifiers, motor actuators, and controllers(generally analog) reside entirely within these myoelectric arms. An individual trained in the use of a myoelectric arm can perform some impressive tasks with this arm. Current engineering research efforts involve the control of simultaneous multi-joint movements (rather than the single joint movement now available)and the provision for sensory feedback from the end effector of the artificial arm to the skin of the stump via electrical means. 119.4 Engineering Concepts in Communications Disorders Speech is a uniquely human means of interpersonal communication. Problems that affect speech can occur at the initial transducer(the larynx) or at other areas of the vocal tract. They can be of neurological(due to cortical, brainstem, or peripheral nerve damage), structural, and/or cognitive origin. a person might only be le to make a halting attempt at talking, or might not have sufficient control of other motor skills to type or If only the larynx is involved, an externally applied artificial larynx can be used to generate a resonant column of air that can be modulated by other elements in the vocal tract. If other motor skills are intact, typing can be used to generate text, which in turn can be spoken via text-to-speech devices described above. And the rate of typing(either whole words or via coding) might be fast enough so that reasonable speech rates could be achieved The rehabilitation engineer often becomes involved in the design or specification of augmentative commu- nication aids for individuals who do not have good muscle control, either for speech or for limb movement. An entire industry has developed around the design of symbol or letter boards, where the user can point out often painstakingly) letters, words, or concepts. Some of these boards now have speech output. Linguistics and information theory have been combined in the invention of acceleration techniques intended to speed up c 2000 by CRC Press LLC
© 2000 by CRC Press LLC environment (fairly level floors, roads, etc.), modern wheelchairs can be highly efficient. In fact, the fastest times in one of man’s greatest tests of endurance, the Boston Marathon, are achieved by the wheelchair racers. Although they do gain the advantage of being able to roll, they still must climb the same hills, and do so with only one fifth of the muscle power available to an able-bodied marathoner. While a wheelchair user could certainly go down a set of steps (not recommended), climbing steps in a normal manual or electric wheelchair is a virtual impossibility. Ramps or lifts are engineered to provide accessibility in these cases, or special climbing wheelchairs can be purchased. Wheelchairs also do not work well on surfaces with high rolling resistance or viscous coefficients (e.g., mud, rough terrain, etc.), so alternate mobility aids must be found if access to these areas is to be provided to the physically disabled. Hand-controlled cars, vans, tractors, and even airplanes are now driven by wheelchair users. The design of appropriate control modifications falls to the rehabilitation engineer. Loss of a limb can greatly impair functional activity. The engineering aspects of artificial limb design increase in complexity as the amount of residual limb decreases, especially if one or more joints are lost. As an example, a person with a mid-calf amputation could use a simple wooden stump to extend the leg, and could ambulate reasonably well. But such a leg is not cosmetically appealing and completely ignores any substitution for ankle function. Immediately following World War II, the U.S. government began the first concerted effort to foster better engineering design for artificial limbs. Dynamically lockable knee joints were designed for artificial limbs for above-knee amputees. In the ensuing years, energy-storing artificial ankles have been designed, some with prosthetic feet so realistic that beach thongs could be worn with them. Artificial hands, wrists, and elbows were designed for upper-limb amputees. Careful design of the actuating cable system also provided for a sense of hand grip force, so that the user had some feedback and did not need to rely on vision alone for guidance. Perhaps the most transparent (to the user) artificial arms are the ones that use electrical activity generated by the muscles remaining in the stump to control the actions of the elbow, wrist, and hand [Stein et al., 1988]. This electrical activity is known as myoelectricity, and is produced as the muscle contraction spreads through the muscle. Note that these muscles, if intact, would have controlled at least one of these joints (e.g., the biceps and triceps for the elbow). Thus, a high level of modality specificity is maintained because the functional element is substituted only at the last stage. All of the batteries, sensor electrodes, amplifiers, motor actuators, and controllers (generally analog) reside entirely within these myoelectric arms. An individual trained in the use of a myoelectric arm can perform some impressive tasks with this arm. Current engineering research efforts involve the control of simultaneous multi-joint movements (rather than the single joint movement now available) and the provision for sensory feedback from the end effector of the artificial arm to the skin of the stump via electrical means. 119.4 Engineering Concepts in Communications Disorders Speech is a uniquely human means of interpersonal communication. Problems that affect speech can occur at the initial transducer (the larynx) or at other areas of the vocal tract. They can be of neurological (due to cortical, brainstem, or peripheral nerve damage), structural, and/or cognitive origin. A person might only be able to make a halting attempt at talking, or might not have sufficient control of other motor skills to type or write. If only the larynx is involved, an externally applied artificial larynx can be used to generate a resonant column of air that can be modulated by other elements in the vocal tract. If other motor skills are intact, typing can be used to generate text, which in turn can be spoken via text-to-speech devices described above. And the rate of typing (either whole words or via coding) might be fast enough so that reasonable speech rates could be achieved. The rehabilitation engineer often becomes involved in the design or specification of augmentative communication aids for individuals who do not have good muscle control, either for speech or for limb movement. An entire industry has developed around the design of symbol or letter boards, where the user can point out (often painstakingly) letters, words, or concepts. Some of these boards now have speech output. Linguistics and information theory have been combined in the invention of acceleration techniques intended to speed up
he communication process. These include alternative language representation systems based on semantic (iconic), alphanumeric, or other codes; and prediction systems, which provide choices based on previously selected letters or words Some individuals can produce speech, but it is dysarthric and very difficult to understand. Yet the utterance does contain information. Can this limited information be used to figure out what the individual wanted to say, and then voice it by artificial means? Research labs are now employing neural network theory to determine which pauses in an utterance are due to content (ie, between a word or sentence)and which are due to unwanted halts in speech production 119.5 Appropriate Technology Rehabilitation engineering lies at the interface of a wide variety of technical, biological, and other concerns. a user might(and often does) put aside a technically sophisticated rehabilitation device in favor of a simpler device that is cheaper and easier to use and maintain. The cosmetic appearance of the device(or cosmesis)sometimes ecomes the overriding factor in acceptance or rejection of a device. A key design factor often the appropriate technology accomplish the task adequately, given the extent of the resources available to solve the problem and the residual capacity of the client Adequacy can be verified by determining that increasing the technical content of the solution results in disproportionately diminishing gains or escalating costs. Thus, a rehabilitation engineer must be able to distinguish applications where high technology is required from those where such technology results in an incremental gain in cost, durability, acceptance, and other factors. Further, appropriateness very much depends on location. What is appropriate to a client near a major medical center in a highly developed country might not be appropriate to one in a rural setting or in a developing country. This is not to say that rehabilitation engineers should shun advances in technology. In fact, a fair proportion of rehabilitation engineers work in a research setting where state-of-the-art technology is being applied to the needs of the disabled. However, it is often difficult to transfer complex technology from a laboratory to disabled consumers not directly associated with that laboratory. Such devices are often designed for use only in a structured environment, are difficult to repair properly in the field, and often require a high level of user interaction or sophistication Technology transfer in the rehabilitation arena is difficult, due to the limited and fragmented market. dvances in rehabilitation engineering are often piggybacked onto advances in commercial electronics. For example, the exciting developments in text-to-speech and speech-to-text devices mentioned above are being driven by the commercial marketplace, and not by the rehabilitation arena. But such developments will be welcomed by rehabilitation engineers no less. 119.6 The Future of engineering in rehabilitation The traditional engineering disciplines permeate many aspects of rehabilitation. Signal processing, control and information theory, materials design, and computers are all in widespread use from an electrical engineering perspective. Neural networks, microfabrication, fuzzy logic, virtual reality, image processing, and other emerg- ing electrical and computer engineering tools are increasingly being applied. Mechanical engineering principles are used in biomechanical studies, gait and motion analysis, prosthetic fitting, seat cushion and back support design, and the design of artificial joints. Materials and metallurgical engineers provide input on newer bio- compatible materials. Chemical engineers are developing implantable sensors. Industrial engineers are increa ingly studying rehabilitative ergonomics The challenge to rehabilitation engineers is to find advances in any field -engineering or otherwise-that will aid their clients who have a disability. c 2000 by CRC Press LLC
© 2000 by CRC Press LLC the communication process. These include alternative language representation systems based on semantic (iconic), alphanumeric, or other codes; and prediction systems, which provide choices based on previously selected letters or words. Some individuals can produce speech, but it is dysarthric and very difficult to understand. Yet the utterance does contain information. Can this limited information be used to figure out what the individual wanted to say, and then voice it by artificial means? Research labs are now employing neural network theory to determine which pauses in an utterance are due to content (i.e., between a word or sentence) and which are due to unwanted halts in speech production. 119.5 Appropriate Technology Rehabilitation engineering lies at the interface of a wide variety of technical, biological, and other concerns. A user might (and often does) put aside a technically sophisticated rehabilitation device in favor of a simpler device that is cheaper and easier to use and maintain. The cosmetic appearance of the device (or cosmesis) sometimes becomes the overriding factor in acceptance or rejection of a device. A key design factor often lies in the use of the appropriate technology to accomplish the task adequately, given the extent of the resources available to solve the problem and the residual capacity of the client. Adequacy can be verified by determining that increasing the technical content of the solution results in disproportionately diminishing gains or escalating costs. Thus, a rehabilitation engineer must be able to distinguish applications where high technology is required from those where such technology results in an incremental gain in cost, durability, acceptance, and other factors. Further, appropriateness very much depends on location. What is appropriate to a client near a major medical center in a highly developed country might not be appropriate to one in a rural setting or in a developing country. This is not to say that rehabilitation engineers should shun advances in technology. In fact, a fair proportion of rehabilitation engineers work in a research setting where state-of-the-art technology is being applied to the needs of the disabled. However, it is often difficult to transfer complex technology from a laboratory to disabled consumers not directly associated with that laboratory. Such devices are often designed for use only in a structured environment, are difficult to repair properly in the field, and often require a high level of user interaction or sophistication. Technology transfer in the rehabilitation arena is difficult, due to the limited and fragmented market. Advances in rehabilitation engineering are often piggybacked onto advances in commercial electronics. For example, the exciting developments in text-to-speech and speech-to-text devices mentioned above are being driven by the commercial marketplace, and not by the rehabilitation arena. But such developments will be welcomed by rehabilitation engineers no less. 119.6 The Future of Engineering in Rehabilitation The traditional engineering disciplines permeate many aspects of rehabilitation. Signal processing, control and information theory, materials design, and computers are all in widespread use from an electrical engineering perspective. Neural networks, microfabrication, fuzzy logic, virtual reality, image processing, and other emerging electrical and computer engineering tools are increasingly being applied. Mechanical engineering principles are used in biomechanical studies, gait and motion analysis, prosthetic fitting, seat cushion and back support design, and the design of artificial joints. Materials and metallurgical engineers provide input on newer biocompatible materials. Chemical engineers are developing implantable sensors. Industrial engineers are increasingly studying rehabilitative ergonomics. The challenge to rehabilitation engineers is to find advances in any field — engineering or otherwise — that will aid their clients who have a disability
Defining Terms [ Note: the first five terms below have been proposed by the National Center for Medical Rehabilitation and Research(NCMRR)of the U.S. National Institutes of Health(NIH). Activities of daily living (ADL): Personal activities that are done by almost everyone in the course of a normal ay, including eating, toileting, combing hair, brushing teeth, g,etc. ADLs are distinguished from hobbies and from work-related activities(e.g, typing Appropriate technology: The technology that will accomplish a task adequately, given the resources available. Adequacy can be verified by determining that increasing the technological content of the solution result in diminishing gains or increasing costs. Disability: Inability or limitation in performing tasks, activities, and roles to levels expected within physical nd social contexts Functional limitation: Restriction or lack of ability to perform an action in the manner or within the range consistent with the purpose of an organ or organ system. Impairment: Loss or abnormality of cognitive, emotional, physiological, or anatomical structure or function, including all losses or abnormalities, not just those attributed to the initial pathophysiology. Modality-specific: A task that is specific to a single sense or movement pattern Orthosis: A modality-specific appliance that aids the performance of a function or movement by augmenting or assisting the residual capabilities of that function or movement. An orthopedic brace is an orthosis. Pathophysiology: Interruption or interference with normal physiological and developmental processes or structures Prosthesis: An appliance that substitutes for the loss of a particular function, generally by involving a different modality as an input and/or output channel. An artificial limb, a sensory substitution system, or an augmentative communication aid are prosthetic devices Residual function or residual capacity: Residual function is a measure of the ability to carry out one of more general tasks using the methods normally used. Residual capacity is a measure of the ability toto carry out these tasks using any means of performance. These residual measures are generally more subjective than other more quantifiable measures such as residual strength. Societal limitation: Restriction, attributable to social policy or barriers(structural or attitudinal), that limits fulfillment of roles, or denies access to services or opportunities that are associated with full participation References Clark, G.M., Y.C. Tong, and J.E. Patrick, 1990. Cochlear Prostheses, Churchill Livingstone, Edinburgh Goodenough- Trepagnier, C, 1994. Guest Editor of a special issue of Assistive Technology, 6(1), dealing with mental loads in augmentative communication. Kaczmarek, K.A., J.G. Webster, P Bach-y-Rita, and w.J. Tompkins, 1991. Electrotactile and vibrotactile displays for sensory substitution, IEEE Trans. Biomed. Engr, 38: 1-16 Klinke, R, 1983. Physiology of the sense of equilibrium, hearing and speech. Chapter 12 in Human Physiology (eds: R.E. Schmidt and G. Thews), Springer-Verlag, Berlin. Loeb, G E, 1985. The Functional Replacement of the Ear, Scientific American, 252: 104-111 Reswick, J. 1982. What is a rehabiliation engineer? in Annual Review of Rehabiltation, Vol. 2(eds. E L. Pan, T.E. Backer, C L. Vash), Springer-Verlag, New York. Robinson, C.J. 1993. Rehabilitation Engineering-an editorial, IEEE Transactions on Rehabilitation Engin Robinson, C], 1995. Rehabilitation Engineering, Science, and Technology, The Biomedical Engineering (O Bronzino, Editor), CRC Press LLC, Boca Raton, FL, pp. 2045-2054 Stein, R.B., D. Charles, and K B. James, 1988. Providing motor control for the handicapped: A fusion of modern neuroscience, bioengineering, and rehabilitation, Advances in Neurology Vol. 47: Functional Recovery in Neurological Disease,(ed. S.G. Waxman), Raven Press, New York. c 2000 by CRC Press LLC
© 2000 by CRC Press LLC Defining Terms [Note: the first five terms below have been proposed by the National Center for Medical Rehabilitation and Research (NCMRR) of the U.S. National Institutes of Health (NIH).] Activities of daily living (ADL): Personal activities that are done by almost everyone in the course of a normal day, including eating, toileting, combing hair, brushing teeth, reading, etc. ADLs are distinguished from hobbies and from work-related activities (e.g., typing). Appropriate technology: The technology that will accomplish a task adequately, given the resources available. Adequacy can be verified by determining that increasing the technological content of the solution results in diminishing gains or increasing costs. Disability: Inability or limitation in performing tasks, activities, and roles to levels expected within physical and social contexts. Functional limitation: Restriction or lack of ability to perform an action in the manner or within the range consistent with the purpose of an organ or organ system. Impairment: Loss or abnormality of cognitive, emotional, physiological, or anatomical structure or function, including all losses or abnormalities, not just those attributed to the initial pathophysiology. Modality-specific: A task that is specific to a single sense or movement pattern. Orthosis: A modality-specific appliance that aids the performance of a function or movement by augmenting or assisting the residual capabilities of that function or movement. An orthopedic brace is an orthosis. Pathophysiology: Interruption or interference with normal physiological and developmental processes or structures. Prosthesis: An appliance that substitutes for the loss of a particular function, generally by involving a different modality as an input and/or output channel. An artificial limb, a sensory substitution system, or an augmentative communication aid are prosthetic devices. Residual function or residual capacity: Residual function is a measure of the ability to carry out one of more general tasks using the methods normally used. Residual capacity is a measure of the ability to to carry out these tasks using any means of performance. These residual measures are generally more subjective than other more quantifiable measures such as residual strength. Societal limitation: Restriction, attributable to social policy or barriers (structural or attitudinal), that limits fulfillment of roles, or denies access to services or opportunities that are associated with full participation in society. References Much of this material also appeared in: Clark, G.M., Y.C. Tong, and J.F. Patrick, 1990. Cochlear Prostheses, Churchill Livingstone, Edinburgh. Goodenough-Trepagnier, C., 1994. Guest Editor of a special issue of Assistive Technology, 6(1), dealing with mental loads in augmentative communication. Kaczmarek, K.A., J.G. Webster, P. Bach-y-Rita, and W.J. Tompkins, 1991. Electrotactile and vibrotactile displays for sensory substitution, IEEE Trans. Biomed. Engr., 38:1–16. Klinke, R., 1983. Physiology of the sense of equilibrium, hearing and speech. Chapter 12 in Human Physiology (eds: R.F. Schmidt and G. Thews), Springer-Verlag, Berlin. Loeb, G.E., 1985. The Functional Replacement of the Ear, Scientific American, 252:104–111. Reswick, J. 1982. What is a rehabiliation engineer? in Annual Review of Rehabiltation, Vol. 2 (eds. E.L. Pan, T.E. Backer, C.L. Vash), Springer-Verlag, New York. Robinson, C.J. 1993. Rehabilitation Engineering — an editorial, IEEE Transactions on Rehabilitation Engineering, 1(1):1–2. Robinson, C.J., 1995. Rehabilitation Engineering, Science, and Technology, The Biomedical Engineering (J.O. Bronzino, Editor), CRC Press LLC, Boca Raton, FL, pp. 2045–2054. Stein, R.B., D. Charles, and K.B. James, 1988. Providing motor control for the handicapped: A fusion of modern neuroscience, bioengineering, and rehabilitation, Advances in Neurology, Vol. 47: Functional Recovery in Neurological Disease, (ed. S.G. Waxman), Raven Press, New York
ther Information Readers interested in rehabilitation engineering can contact RESNA - an interdisciplinary association for the advancement of rehabilitation and assistive technologies- at 1101 Connecticut Ave, N W, Suite 700, Wash ington, D. C. 20036. RESNA publishes a quarterly journal called Assistive Technology The U.S. Department of Veterans Affairs puts out a quarterly Journal of Rehabilitation Re-D. The January issue each year contains an overview of most of the rehabilitation engineering efforts occurring in the U.Sand Canada, with over 500 listings The IEEE Engineering in Medicine and Biology Society publishes IEEE Transactions on Rehabilitation Engi neering, a quarterly journal. The reader should contact the IEEE at P.O. Box 1331, 445 Hoes Lane, Piscataway, N]08855-1331 for further details c 2000 by CRC Press LLC
© 2000 by CRC Press LLC Futher Information Readers interested in rehabilitation engineering can contact RESNA — an interdisciplinary association for the advancement of rehabilitation and assistive technologies — at 1101 Connecticut Ave., N.W., Suite 700, Washington, D.C. 20036. RESNA publishes a quarterly journal called Assistive Technology. The U.S. Department of Veterans Affairs puts out a quarterly Journal of Rehabilitation R&D. The January issue each year contains an overview of most of the rehabilitation engineering efforts occurring in the U.S. and Canada, with over 500 listings. The IEEE Engineering in Medicine and Biology Society publishes IEEE Transactions on Rehabilitation Engineering, a quarterly journal. The reader should contact the IEEE at P.O. Box 1331, 445 Hoes Lane, Piscataway, NJ 08855-1331 for further details
