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BIONICS
CONTENTS
1) Introduction
2) Classification
3) Human computer interface
4) Evolution
5) Artificial limb
6) Artificial Heart
7) Artificial Eye
8) Cochlear Implant
9) Limitations of bionics
10) Future of bionics
INTRODUCTION
Bionics means the replacement or enhancement of organs or other body parts by mechanical versions. Bionic implants differ from mere prostheses by mimicing the original function very closely, or even surpassing it. Bionics' german equivalent "Bionik" takes a somewhat broader scope in that it tries to develop engineering solutions from biological models. This approach is motivated by the fact that biological solutions will always be optimized by evolutionary forces. A classical example is the development of dirt- and water-repellent paint (coating) from the observeration that the surface of the lotus flower plant is practically unsticky for anything. While the technologies that make bionic implants possible are still in a very early stage, a few bionic items already exist, the best known being the cochlear implant, a device for deaf people. Some versions come quite close to "normal" hearing; they can even work better than natural ears at background noise filtering.Bionics are a common element of science fiction, with The Six Million Dollar Man as the probably best-known example.
There was a time when Bionics was the stuff of science fiction. "We have the technology" was the theme of a popular TV series, creative writers produced fantastic stories of mechanized men, people imagined replacing body parts, improving the quality of life, revolutionizing medicine with far flung ideas like prosthetic arms, legs, mechanical eyes and ears. There's no limit to what man has imagined. But often when people ponder these possibilities they look at them as just that, possibilities. Not everyone realizes that science fiction is quickly becoming scientific fact! Our ultimate goal is to one day discover that faint flashing light, that ray of hope for Christopher Reeves, and the numerous other disabled who would be helped by the chance to walk, see, hear, and function
like an able bodied person. This ultimate goal is to be able to connect any mechanical body part to the human brain, and have it function as a normal human organ.
The groundwork is already set for making such a possibility become a reality.Prosthetics was the first movement in this direction, allowing the brain to send signals to an artificial limb. Cochlear implants are looked at as an intermediate step. They are already in place and some of the mysteries behind them have been solved. Unlike prosthetics, Cochlear implants rely on the brain being able to both send and receive signals. Implanted electrodes stimulate nerve endings, which then allow communication with the brain. A final step is the development of the artificial eye, which when fully discovered will mean that the electrical signals can be connected directly to the nerves, which in turn will send it straight to the brain.
So if all this is in place, why can't we just hook it up to the brain? Although the groundwork has been laid, and the principles which will be necessary to fully understand and carry out this final task have been
determined, there are still a lot of unknowns to be resolved with new theories and testing. Scientists are still trying to fully comprehend the processes of the brain which are a part of every human task.
CLASSIFICATION OF BIONIC SYSTEM
Design Lessons From Mother Nature
Bionics and the related fields of biomechanics and biomimetics can teach us how Mother Nature performs integrated systems design. We present here some basic resources and information about bionics and its relationship to design.Note that there are two broad classes of bionic systems, more examples of which may be found in the Taxonomy of Bionic Systems.
Analogic synthetic bionic systems
These are technical systems based on biological principles. The classic example is developing radar from the study of bat echo location principles. This is what many designers think of as bionics. Examples range from "cold light" devices based on bioluminescent marine animals, to tensile structures based on spider webs, to solar arrays that track the sun like sunflowers, to irridescent art forms based on the keratin structure in bird feathers that refracts light. There are, of course, many many other examples.
Composition synthetic bionic systems
These are systems that contain both technical and biological components. This can serve as a design paradigm for analyzing relationships between the artificial and natural as whole systems. A person driving a car or wearing glasses, human-computer interaction (HCI), the city and its surrounding ecosystem, crocodiles that swallow rocks as ballast, and the cyborgs of science fiction are all bionic systems of this sort.
HUMAN COMPUTER INTERFACE
The development of sensory prostheses, cochlear implants, and artificial vision connecting any mechanical body part to the brain. Before this can happen, have proven to be three large steps leading up to the ultimate goal of however, a very deep understanding of all three steps, including solving the unknowns about each is a must. Since one step leads to the next, every unknown causes even larger problems in approaching the final solution. There are unknowns in all areas of bionics research, and this was already examined in each step's section. These unknowns combine, however, into several
large mysteries, which when solved will provide the key for advancing into a whole new world of bionics.
The first major puzzle is fully understanding the complex functioning of the brain. Scientists are continually struggling to identify how the brain decodes the messages of the nervous system into an understandable set of instructions, and likewise how the brain interprets signals such as sound characteristics. Part of this difficulty is caused by the uniqueness of each person's brain. The
brain is unique in its ability to continually reroute signals through the complex networks of cells, bypassing damaged or occupied paths. This means that even within the same person, the path a signal travels to the brain could vary with time. It is therefore nearly impossible to come up with a true model of how the brain functions that will work for everyone. Research is progressing, and the development of the cochlear implant and artificial vision, which are attempting to determine how the brain interprets these artificial signals, only adds to the hope that within the near future a break-through will occur.
The second major mystery is the biocompatibility of machines with the human body. It is unknown how machines will act and how they could best be connected to body. One of the problems that is often encountered is corrosion of the mechanical parts. Although this has been fixed in many situations, such as the corrosion of the artificial eye chips, it is unknown the long term effect of such mechanical hookups. Similarly, scientists are trying to figure out the maximum amount of electronics that can be implanted in the body. In the cochlear implant, for example, if a way to implant a greater number of electrodes into
the ear is discovered, it will work much more efficiently. Research is being conducted to find the best way to hook a machine to the body, with the smallest possibility of side effects.
The groundwork is in place. The faint flashing light can be seen in the distance, and for now Christopher Reeves and the numerous others who could be helped by bionics, wait. They hope that one day the mysteries will be solved and that faint flashing light will come into view?and it WILL be the entrance to a safe harbor. We are waiting for the day when they can get up and walk home.
Recent experiments involving direct electrical stimulation of the brain have enabled blind people to "see" simple light patterns, but our experts agree that researchers have a long way to go before technology can provide near-normal sight to the blind. Jenkins thinks that jacking into the visual cortex may eventually enable "letter recognition or limited form identification," but even that is probably 20 years away. Humphrey notes that the cere-bral cortex is extremely complex; leads to the brain from a videocamera would have to be perfectly placed to yield useful results. Even if this level of precision is
achieved, he believes, technological limita-tions would prevent the image from having useful color: "The details would be crude - like a neon sign - and motion would not be reproduced faithfully."
Since the 1970s, companies have developed "myoelectric" limbs that are actuated by electrical signals transmitted from underlying muscles to the surface of the skin. The next step is to interface motor nerves with sensors in the artificial limb - enabling a prosthetic to respond to brain signals. Humphrey says that his laboratory has controlled a robotic wrist using cerebral recordings of a monkey
moving its wrist. What's preventing this tech-nology from entering into clinical trials? "Small movements of the recording electrodes in the cerebral cortex damage the tissue, weakening the signal over time," Humphrey says. Even if that and other problems are solved, Loeb adds, "only a small number of patients with high, bilateral amputations are seriously enough handicapped after being fitted with existing prosthetic technology" to justify the expense and invasiveness of neural interfaces.
According to the experts we spoke to, cochlear implants - electrodes implanted in the cochlea to stimulate auditory nerves - are the most successful bionic prosthetic to date. In fact, a high percentage of patients report that implants already provide fidelity close to that of normal ears - enabling them to talk
comfort-ably on the phone, for example. "They hear very well: they enjoy their recovered communication skills and the ability to recognize the various environmental sounds that we all take for granted," Jenkins says. In agreement, Durfee comments, "It's not clear if the market is ready to go beyond what is
required for 'functional hearing.'" Whether that's true or not, "We have a way to go before the complex nuances of a Mozart concerto can be appreciated," Humphrey says.
Advanced bionic components may be within our grasp, but putting them all together in a real-life superpowered Steve Austin will probably remain the stuff of sci-fi. While a bionic person may be theoretically feasible, Humphrey says, "the major problem lies in overcoming tissue-material interfaces." And that's a biggie. Not only do artificial tendons and ligaments have to be connected to real ones, artificial muscles don't yet approach the size and power of human tissues. Our understanding of motor skills and the brain's sensory and perceptual abilities has really just begun. "Continued research in neuroscience and bioengineering will no doubt lead to improvements in man-machine interfaces
and func-tional replacements," Jenkins says, "but it will be a long, hard road filled with many failures and a few successes
A Brain-Computer interface is a staple of science fiction writing. Init's earliest incarnations no mechanism was thought necessary, as thetechnology seemed so far fetched that no explanation was likely. As morebecame known about the brain however, the possibility has become more realand the science fiction more technically sophisticated. Recently, thecyberpunk movement has adopted the idea of "jacking in", sliding "biosoft" chips into slots implanted in the skull (Gibson, W. 1984). Although such
biosofts are still science fiction, there have been several recent stepstoward interfacing the brain and computers. Chief among these aretechniques for stimulating and recording from areas of the brain with
permanently implanted electrodes and using conscious control of EEG to control computers. Some preliminary work is being done on synapsing neurons on silicon transformers and on growing neurons into neural networks on top of computer chips.
The most advanced work in designing a brain-computer interface has stemmed
from the evolution of traditional electrodes. There are essentially two main problems, stimulating the brain (input) and recording from the brain (output). Traditionally, both input and output were handled by electrodes pulled from metal wires and glass tubing. [] (Pickard 1979). Using conventional electrodes, multi-unit recordings can be constructed from mutlibarrelled pipettes. In addition to being fragile and bulky, the electrodes in these arrays are often too far apart, as most fine neuralprocesses are only .1 to 2 µm apart. [] It is difficult to permanently implant such arrays, and consequently it is difficult to directly study the brain as a function of animal behavior. []
Immediate applications of this include increasing the functionality of cochlear implants. By increasing the number of electrodes, the efficiency and specificity of the electrode-neuron interaction and the computational power driving the electrodes, speech recognition could be enhanced even
further than currently possible. This prefigures applications in which PCMs are used to input data from computers directly into normal people's auditory nerve, bypassing the actual production of sound by the computer. Such functionality would be relatively easy to add by including an input jack on the DSP chip of the implant. A similar application could be found in encoding visual stimuli directly into the optic nerve of blind people. This could then be adapted to present computer generated visual signals
divorced from real world input. The auditory and optic nerves are perhaps the most accessible methods of input to the brain. Memory structures in the brain itself are considerably less well understood. However it is not outside of the realm of possibility to directly include artificial memories through the use of advanced PCMs implanted in the brain. The problem of encoding information in a manner recognizable to the human brain would be difficult to surmount,especially given the possibility that data structures may be encoded differently by each person. [] It may be possible, then, to tailor such
neural nets to output data in a manner specific to one person's internal representations of memories. Although current technology is probably incapable of such a feat, because of the incredible amount of processing required, the combination of increased silicon chip speed and the use of complex neural nets built from neurons could make this possible.
The current approaches to interfacing the brain and computers described above offer very concrete examples of utility. Indeed, the potential for even currently available systems is still unrealized. However, it could be argued that they are hampered by inherent limitations. EEG based systems
have no possibility of input to the brain, and full comprehension of the human EEG may be out of reach by even the most advanced imaginable computers. Similarly, PCM recording or stimulating devices may be limited by both the size of the electrode arrays, the difficulty of implantation and by the complexity of the brain.
Despite optimistic projections, the brain's complexity may make it impossible to directly access from a computer. Even if these problems could be overcome, there are still problems involved with the very idea of implanting electrodes into the brain. The potential damage to biological structures may outweigh the tentative benefits of a direct computer interface, especially in higher cortical structures. Despite these conceptual difficulties, the prospect of extending the inherent capabilities of the organic brain allows the consideration of transcending the limitations imposed by the corporeal body. After all, computers were once science fiction, too.
EVOLUTION
Welcome to the bionic age, when man-made devices can replace damaged limbs and organs. Already on the market are 100 percent mechanical hearts and heart parts, mechanical arms, legs, hands and cochlear implants that can benefit the nearly deaf. • On the near horizon are bionic eyes that restore at least partial vision, cochlear implants that allow hearing despite a damaged auditory nerve, and computer chips that permit the brain to control bionic limbs. • On the far horizon? Tissue engineering could make anything possible. In development are artificial blood, organs and other body parts, including the liver, pancreas, bladder, tendons and spinal cord. • In the field of pure bionics—the interface of human with machine—the focus has been on the heart, limbs, hands and eyes. Not only do they lend themselves to mechanical adaptation, they are also among the body parts most in demand.
ARTIFICIAL LIMB
Limbs That Live
In Moby Dick, Captain Ahab had a crude wooden leg. The "Six Million Dollar Man" on the ’70s TV series had super-powered legs. But the reality of artificial limbs lies somewhere in between.
Even the best prosthetic legs, for instance, have an artificial knee that swings free while the leg is moving and then locks when weight is put on it. The result? An awkward gait that’s obviously not natural.
Meanwhile, advances aim to do away with the awkwardness of artificial limbs. As one researcher says, "we want to develop limbs that feel like they are a part of a person’s body. In short, limbs that live."
One company, Otto Bock Orthopedics Industry in Germany, is using computer chips to make the knee of a prosthetic leg act more like a real one. Inside, a small battery-powered computer makes the knee seem anatomically perfect. Another company, Neural Signals of Atlanta, Georgia, has developed a brain implant that can communicate with an external computer. Called peripheral computer interface by its developer, Dr. Philip Kennedy, this computer system responds to human nerve impulses.When perfected, such capabilities will allow a patient’s brain to control a bionic limb. Already Kennedy has implanted his device in a quadriplegic man who was able to move a computer cursor just by thinking about it.
"Our hope is to let the patients interact with the world just by thinking," Kennedy says.
ARTIFICIAL HEART
New Hearts, Heart Helpers
Take the artificial heart, for example. About 2,000 people per year receive heart transplants. Yet 30,000 to 100,000 could benefit from a new heart. The problem is, there aren’t enough donor hearts to go around. The available organs are rationed by transplant committees who must decide if the patient is young enough, healthy enough and compliant enough to take care of the donated organ.
Total artificial hearts (TAH) and ventricular assist devices (VAD) that assist the damaged heart without replacing it, are the greatest hope there is of replacing the need for scarce donor hearts. They are also a tremendous mechanical challenge. A TAH must beat approximately 40 million times per year, and provide a reliable stream of blood that consists of 5 to 6 liters per minute. The current design goal for TAH is 90 percent reliability after five years, which is greater than the five-year survival rate for heart transplant patients. The most popular TAH is made by Abiomed Corporation of Danvers, Massachusetts. It is a combination of equipment that fits entirely in the chest and is powered by an energy system that sends electricity through the skin. This helps avoid infection that could enter the body through an incision if the heart was joined to the power supply by a cable. The AbioCor heart, as it is called, consists of a one-kilogram pump that mimics the function of the heart’s valves. Connected to that pump is a small computer and a battery pack that allows the patient freedom from his external power supply.
John Watson of the National Heart, Lung, and Blood Institute feels the AbioCor development and trials have gone very well. Two AbioCor hearts have been transplanted in the chests of patients who were too sick to get donor hearts. One patient, Robert Tools, lived 151 days with the mechanical heart before he died of a stroke possibly caused by a clot that developed on one of the AbioCor’s valves. A second patient, Tom Christerson, has survived more than 300 days, as of press time.This success led Time magazine to declare AbioCor "the invention of the year." Surprisingly, however, not all bionic heart experts agree. Dr. Robert Jarvik, whose pioneering device, the Jarvik-7 heart kept Barney Clark alive 112 days in 1982, says that "removing the natural heart is an obsolete approach."For him, VADs are the way to go. He has devised a thumb-sized pump that can be sewn inside a patient’s ventricle to help it perform the work of pumping. One of these was installed in the left ventricle of Houghton, who was within days of death when the tiny pump was put in his heart. Now he, like many other VAD users, is enjoying a quality life. There is also an added plus. If their hearts become stronger, there is a possibility that the VADs can be removed.
There are several types of VADs. The one developed by Jarvik has been nicknamed "flowmaker" because it has no artificial valves and no pulse. It simply helps blood flow through a weakened heart. A fine wire runs from the VAD in the heart to a power socket installed behind the ear. A battery is then worn on the belt and connects to the socket. A control dial allows the recipient to set the device for "rest," "sleep" and "exercise."Houghton felt so good after his VAD implant that he told BBC News that he was doing things he shouldn’t be. "If you’re on the Titanic you might as well enjoy yourself."
ARTIFICIAL EYE
Now the Eyes Have It
Overcoming blindness with bionics has been a realistic goal for 50 years. As early as 1956, a patent application was filed for a light-sensitive selenium cell that would restore the perception of light when implanted behind a blind person’s retina.Last year (2002), ophthalmologist Dr. Alan Chow did something just like that. With the approval of the Food and Drug Administration (FDA), Chow implanted tiny microchips into the retinas of six blind patients. Those chips, which Chow designed with his brother Vincent, an electrical engineer, contained 5000 solar cells on a disc the size of a pinhead. When exposed to light, the cells generated electricity that stimulated the optic nerve. Would that make the blind see again? Chow could only hope. One by one, Chow’s six patients reported substantial improvement in their vision. One man went from seeing nothing to being able to see his porch light. Another went from barely being able to see his hands in front of his face to seeing a flock of geese in the sky. It was not the telescoping vision of the Six Million Dollar Man. But for the six patients, it was a giant leap forward nevertheless. Researchers differ about how well Chow’s implants actually worked, but agree that bionic retinal implants will eventually restore sight. Scientists at North Carolina State University, University of North Carolina-Chapel Hill and Johns Hopkins University are continuing the research. However, experts estimate it will take at least two more decades for bionics to give us true, near-normal sight.
COCHLEAR IMPLANT
Experts say cochlear implants are the most successful bionic devices
Rush Limbaugh certainly agrees. A few months after signing a salary package that exceeded $200 million, the popular radio talk show host began to lose his hearing. On May 29th he told his stunned audience that an autoimmune disease had left him 100 percent deaf in his left ear and 80 percent deaf in his right. The man "with a gift on loan from God" could no longer hear his own program.
He continued his daily program, but there was a noticeable difference in its quality. Using a TelePromTer he read questions from his listeners, leaving uncomfortable gaps of silence between their questions and his answers. Finally, desperate to hear himself speak, he had a cochlear device surgically implanted in his right ear. A microelectric array stimulates the auditory nerve helping make up for the loss of the hair cells inside the cochlea, part of the inner ear that converts sound waves into electrical impulses that can then be read by the sound center of the brain. Cochlear implants have been around for more than 30 years and have shown steady improvement with the advance of electronics. Doctors at the House Ear Clinic in Los Angeles, where Limbaugh had his implant performed, estimate the success rate for cochlear implants at 99.6 percent. They estimate that Limbaugh will regain as much as 50 percent of the hearing.
During surgery, electrodes are implanted in the cochlea to replace the nerve cells that have been lost. Six weeks later, the patient is fitted with an external microphone that connects to the electrodes. The signal is then sent to the brain through the implanted wires and existing auditory nerve. Without a functioning auditory nerve, cochlear implants will not work. But the next generation of implants may change that. Doctors are looking at ways to connect a man-made device directly to the brainstem to eliminate the need to rely upon the auditory nerve. In the near future, bionics experts predict that surgeons will be able to plug into the brainstem with such precision that high-fidelity cochlear implants will be possible. In the meantime, though, Rush Limbaugh and his 20 million fans are happy. Without the cochlear implant, Limbaugh says, "it was tough toenails" for the radio show.
continue as a deaf person in the hearing world.
LIMITATIONS
Fantasy, Success and Failure
Is there a completely bionic man in our future? Doubtful, say most bionics experts. Although technology has come a long way toward melding man and machine, it still has a long way to go. The major problem, say the experts, is in " tissue-material interface." Machines need to interface with the organ of perception, the brain. Since our understanding of the brain has just begun, our understanding of how to connect mechanical devices to these workings is lagging even further behind.
"Continued research in neuroscience and bioengineering will no doubt lead to improvements," says William Jenkins , Ph.D., vice president for development at Scientific Learning Principles Corporation in an interview with Wired magazine. "But it will be a long, hard road filled with many failures and few successes."
Otto Bock Orthopedics Industry of Duderstadt, Germany, is using computer chips to help prosthetic knees behave more like real ones. The company's new C-Leg contains a lithium-ion battery and a microprocessor that measures the angle of the knee and the rate at which it's bending 50 times per second. The computer uses that information to project what the amputee is trying to do and adjusts valves to change the flow of fluid within hydraulic chambers inside the knee, increasing or decreasing resistance as necessary. "Every step an above-knee amputee takes, as he comes down he has to be concerned that the leg is stable," says Todd Anderson, a prosthetist at the Minneapolis branch of Otto Bock. "But if we could develop a prosthesis that does exactly what an anatomical leg does, theoretically the brain is already programmed to respond to that."
ARTIFICIAL LIMB LIMITATIONS
To match each individual's natu-ral gait, the C-Leg must be custom-programmed by a prosthetist when fitted. The Leg Lab is working on an auto-adaptive knee incorporating sensors that determine the correct operating parameters without any help. Researchers in the Smart Integrated Lower Limb program at Sandia National Laboratories in Albuquerque, New Mexico, aim to go further. They are working on prosthetics that measure not only knee position but also the forces exerted on the foot as it strikes the ground. Those inputs would allow a more accurate simulation of normal limb motion. "This isn't going to be the bionic man or anything like that; it's going to be something much simpler," says Diane Hurtado, the former manager of the Sandia project. Even a small improvement would mean a lot to amputees, because plenty of routine activities are beyond the scope of artificial legs. "Going from standing to walkin up a set of stairs requires your leg to completely change configuration," says Hurtado.
Hands are even more complicated. Most artificial replacements are little more than pincers covered with plastic shaped to look like skin. About all they can do is grasp and release. Human hands, by contrast, can pivot, twist, grasp, and pluck. Fingers are capable of moving in at least 22 different ways. Bill Craelius, an associate professor of biomedical engineering at Rutgers University, is testing a hand that restores some of that finesse by tapping into the ability of certain amputees to sense the limb they lost. If they try to move a missing finger in a particular way, the tendons in the residual arm move the way they would if the finger were still there. The Rutgers "myo-pneumatic" hand contains foam sensors that connect to truncated tendons. Changes in the shape of the tendons squeeze the sensors and transmit data to a computer chip that controls electronic actuators in the arm. "Our vision is the user is going to more or less adopt this thing as part of his body," says Craelius. Amputees testing the tendon-activated hand have been able to tap out words on a keyboard and to play the piano— slowly— as was demonstrated at the 1999 Discover Technology Awards expo in Orlando, Florida. A commercial version should be available later this year. So far Craelius's subjects can use three separate fingers. In the future he hopes to provide some wearers with five movable digits. Still, his approach will aid only the comparatively small number of patients who have tendon control. "We're a long way from really duplicating the human hand," he says. One major limitation of current prosthetics is that they rely on mechanical connections, which cannot match the intuitiveness of the body's own neural wiring. Attempts to control prostheses with electrical sensors on the skin have not had much success, mainly because it is difficult to distinguish among the many electrical changes that activate muscles. A number of researchers are therefore trying to tap straight into the nervous system, but that work remains at an early stage of development. Another problem is power. An ideal prosthetic should move on its own, but conventional motors are heavy and consume too much electricity. In the Leg Lab, Herr and his colleagues are experimenting with a robot driven by animal-derived muscle tissue that burns glucose, just like human muscle. An experimental "biomechatronic" fish built in the lab can propel itself with a tail driven by real muscle fibers. Herr thinks it may someday be possible to replace missing limbs with artificial skeletons powered by bioengineered muscle and hooked into the nervous system. Even current technology, Herr says, has some advantages over flesh and bone. His rock-climbing abilities have actually improved, because his lightweight prostheses fit into crevices where a human foot cannot. Still, most amputees yearn for a prosthesis that is far more intimate with the body. "If I can feel my ankles, or better still, if I can think and just move that foot around, it's going to be almost as if my legs were never amputated," he says.
FUTURE OF BIONICS
In 1974, we learned that Colonel Steve Austin, an astronaut whose arm, legs, and eye had been destroyed in an accident, could be rebuilt. "We have the technology. We have the capability to make the world's first bionic man," Oscar Goldman said on The Six Million Dollar Man TV series. More than 20 years later, Austin would wear a US$17 million price tag, which probably explains why he thrives only in reruns. But thanks to neu-roscience research and the miracle of microelectronics, astounding breakthroughs in prosthetics are on the horizon. Wired asked four experts about the future of bionics. Unfortunately, Lee Majors was not available for comment.
Artificial Vision
Bionic Limbs
Hi-Fi Cochlear Implants
Bionic Person
Durfee
2040
2020
2030
unlikely
Humphrey
2005
now
2050
Jenkins
2016
Loeb
2010
1998
Bottom Line
2013
Recent experiments involving direct electrical stimulation of the brain have enabled blind people to "see" simple light patterns, but our experts agree that researchers have a long way to go before technology can provide near-normal sight to the blind. Jenkins thinks that jacking into the visual cortex may eventually enable "letter recognition or limited form identification," but even that is probably 20 years away. Humphrey notes that the cere-bral cortex is extremely complex; leads to the brain from a videocamera would have to be perfectly placed to yield useful results. Even if this level of precision is achieved, he believes, technological limita-tions would prevent the image from having useful color: "The details would be crude - like a neon sign - and motion would not be reproduced faithfully."
Since the 1970s, companies have developed "myoelectric" limbs that are actuated by electrical signals transmitted from underlying muscles to the surface of the skin. The next step is to interface motor nerves with sensors in the artificial limb - enabling a prosthetic to respond to brain signals. Humphrey says that his laboratory has controlled a robotic wrist using cerebral recordings of a monkey moving its wrist. What's preventing this tech-nology from entering into clinical trials? "Small movements of the recording electrodes in the cerebral cortex damage the tissue, weakening the signal over time," Humphrey says. Even if that and other problems are solved, Loeb adds, "only a small number of patients with high, bilateral amputations are seriously enough handicapped after being fitted with existing prosthetic technology" to justify the expense and invasiveness of neural interfaces.
According to the experts we spoke to, cochlear implants - electrodes implanted in the cochlea to stimulate auditory nerves - are the most successful bionic prosthetic to date. In fact, a high percentage of patients report that implants already provide fidelity close to that of normal ears - enabling them to talk comfort-ably on the phone, for example. "They hear very well: they enjoy their recovered communication skills and the ability to recognize the various environmental sounds that we all take for granted," Jenkins says. In agreement, Durfee comments, "It's not clear if the market is ready to go beyond what is required for 'functional hearing.'" Whether that's true or not, "We have a way to go before the complex nuances of a Mozart concerto can be appreciated," Humphrey says.
Advanced bionic components may be within our grasp, but putting them all together in a real-life superpowered Steve Austin will probably remain the stuff of sci-fi. While a bionic person may be theoretically feasible, Humphrey says, "the major problem lies in overcoming tissue-material interfaces." And that's a biggie. Not only do artificial tendons and ligaments have to be connected to real ones, artificial muscles don't yet approach the size and power of human tissues. Our understanding of motor skills and the brain's sensory and perceptual abilities has really just begun. "Continued research in neuroscience and bioengineering will no doubt lead to improvements in man-machine interfaces and func-tional replacements," Jenkins says, "but it will be a long, hard road filled with many failures and a few successes
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