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 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