|
07/17/2001
Artificial Senses and Sensors
Members of my generation are often amazed, shocked and/or
horrified to see or hear of the locations at which ornaments are
attached to the bodies of many of the younger, and some not so
younger, generation. These body adornments are attached to the
personage through holes made by piercing the particular part of
the body. It personally makes me shudder to even think of
piercing any part of my body, even the ear, let alone some of the
other areas. And the tongue piercers really turn me off. How
one can live with a ring or pearl stuck in your tongue is beyond
me. You can imagine my fascination when I saw an article that
mentions an electronic device that interfaces gold electrodes with
the tongue, not as jewelry but as a device to enhance one of our
senses.
If you had been at the meeting of The Electrochemical Society in
Washington last March, you might conclude incorrectly that this
device is an "electronic tongue". At that meeting, there were
over 50 papers presented on the electronic tongue and the
electronic nose. I hadn''t realized the extent of the effort to mimic
the tongue and the nose and the variety of uses to which either
might be put. At the meeting, for example, there were papers
dealing with the electronic tongue as a tool for sorting various
types of fish, say freshwater from saltwater species, as well as to
detect spoilage in the fish. Another paper concerned the use of
the electronic tongue to determine the sensory characteristics of
tomato juice. This application presumably could help assure the
proper blend of tomatoes for better tasting juice and greater
customer acceptance of a company''s product.
While the electronic tongue is typically applied to checking
solids and liquids, the electronic nose does more sniffing of the
vapors and gases surrounding the material or environment being
tested. The electronic nose papers at the meeting dealt with
applications ranging from detection of noxious materials in the
air to medical applications such as the analysis of breath as a
possible tool for diagnosis of diseases such as lung cancer. Less
life threatening applications might be found in enhancing the
bouquet of your favorite wine.
These electronic noses and tongues typically consist of an array
of sensors, each of which has been tailored to detect and quantify
certain substances. Taking the outputs of these sensors, a silicon
chip can be programmed to analyze the overall pattern of the
ingredients and determine whether the results are normal or
warrant further attention. While for many applications the
electronic versions of the nose or tongue do a good job, there''s
still a long way to go before either one approaches the
capabilities of their living counterparts.
Our senses of smell and taste are pretty important and certainly
provide us with the ability to smell the roses and to savor our
food and drink. On the other hand, the senses of hearing and
sight rank higher in my opinion as the ones that I would most
like to keep if I had to make a choice. While the electronic nose
and tongue research is aimed at artificially making copies of the
nose and tongue, the work on artificial hearing and sight is most
often dedicated to the rejuvenation of the capabilities of the ear
or the eye when they''ve lost, or perhaps never had, the ability to
function properly.
When it comes to the fields of artificial hearing and sight, clearly
the field of artificial hearing is the most advanced. The
improvement in hearing aids over the past decades has been
stimulated by the introduction of the zinc-air batteries and by the
miniaturized circuitry in the devices. However, for many cases,
conventional hearing aids don''t suffice. In certain of these cases,
the cochlear implant now is the treatment of choice. Some
25,000 have been implanted. Normally, hair cells in the
cochlea, a section of the inner ear resembling the spirally wound
snail, pick up the sound waves. The hair cells change the sound
waves into electrochemical signals that go to the auditory nerve
fibers at the base of the hair cells. Then it''s on to the brain.
Lose or damage the hair cells and deafness results.
With a cochlear implant, the sound from a microphone is fed to a
sound processor, typically worn around the belt. The processor
translates the sound into coded impulses. These coded pulses are
sent to a transmitting coil that is held magnetically on the skull
just above an implanted device that sends the signal on to the 20-
odd electrodes implanted in the cochlea. These electrodes
stimulate the auditory nerve fibers and the signal travels down
the auditory nerve to the brain. Scientists still don''t know how
even the modest degree of hearing restored by the cochlear
implant is achieved from the limited amount of information sent
to the brain by the implanted device. After writing this
paragraph, I found in our Sunday paper and article about a 38-
year-old man in our town who has been deaf since birth. He just
received a cochlear implant and is delighted he can now hear the
rustle of the trees in the wind and his daughter''s voice.
Artificial sight is another matter. Generally, the field has been
pretty low tech. The amazingly talented Benjamin Franklin
made a major advance in artificial sight when he came up with
the invention of bifocals. I''ll never forget the first day I got my
first pair of prescription eyeglasses, bifocals for reading and for
distance. They were also safety glasses, so I could get them free
at Bell Labs. I picked them up that afternoon, before taking the
bus home from work. I got off the bus wearing my new bifocals
and had the strangest feeling that I was as tall as Toulouse Latrec
and my briefcase seemed inches off the ground! I was in my 40s
at the time. Several years ago, my ophthalmologist told me I had
slight macular degeneration in one eye. Fortunately, it has not
worsened since that time and the lines in the standard grid are
just a tad wavy. Naturally, since macular degeneration is a
leading cause of blindness, any articles dealing with sight garner
a bit more attention from me than they might normally. The
August issue of Discover magazine contains such an article titled
"Artificial Sight" by Gregory Cerio.
Cerio himself has a keen interest in his subject, having suffered a
severe injury in one eye as a 4-year old child. As a result, he has
very poor vision in that eye and can hardly make out the biggest
letter on the standard eye chart. In the article, he discusses
current research on restoring sight to the blind and cites the hope
among these artificial sight researchers that the situation will be
analogous to the cochlear implant story. In other words, they
hope that the brain will be able to take a relatively small amount
of information fed to it by an artificial eye and make more of it
than one might expect. The first hurdle, and a huge one, is how
to get the information to the brain.
Workers at Johns Hopkins and a team at Harvard and MIT are
trying the approach of actually implanting an array of
microelectrodes in the eye. The input to the electrodes comes
from a camera that could be worn as a part of eyeglasses. The
camera''s output is fed to a processor that converts the signals to
radio waves for transmission to the chip. The implanted chip
then fires its electrodes. This stimulates the neural cells lying
beneath the retina and it''s on to the brain. Obviously, there are
problems. So far the Hopkins group has only left the chip in the
eye of a subject for 45 minutes, while the Harvard/MIT group
has been more aggressive, leaving it in some subjects for months.
The Hopkins workers are more concerned about the effect of the
eye on the chip than vice versa, with all that salty liquid inside
the eye. But having a foreign body like a silicon chip in the
fragile environment eye isn''t to be taken lightly!
Substituting a chip for a damaged retina is not the only approach,
however. Some workers, like Richard Norman at the University
of Utah, bypass the eye and go directly to the brain. This bypass
approach assumes that the brain can be tricked by inserting
directly into the brain an array of microelectrodes and sending
the visual signals directly to these electrodes. In 1995, the
National Institutes of Health actually did implant an array of 38
electrodes in the brain of a woman who had been blind for over
20 years. The results were mixed in that simple shapes were
constructed from impulses sent to the array of electrodes.
However, the results were variable and half the electrodes were
broken after a month or so of operation. The experiment was
terminated and deemed premature for humans at that point. The
Utah worker thinks he''s solved the breakage problem with a
different array design and hopes to implant a 100-electrode array.
Hopefully, the brain would construct roughly the equivalent of a
100-pixel image from the signals it receives.
Over the years, there has been work of another type. I''ve seen
reports of using arrays of electrodes on the skin to "see".
Workers in this field use the sensations and patterns that the
subject perceives on his or her skin to detect objects and shapes.
The hope is that the brain will learn to identify different patterns
in much the same way as it interprets the visual patterns from the
eye. There is a problem with skin. It has a high electrical
resistance and doesn''t conduct electrical signals very well.
Enter the tongue. In contrast to the skin, the tongue is chock full
of nerves and is immersed in saliva, a nicely conducting liquid.
According to a sidebar to the Cerio article, workers at the
University of Wisconsin are experimenting with a "patch" of
gold electrodes that is placed in contact with the tongue. It''s now
sort of like a tongue depressor. The subjects feel a tingling,
vibrating sensation and have used the device to find their way
through mazes and to decipher simple graphics, according to the
report. The investigators certainly don''t think you could sit on
your couch and "tongue" a TV program. However, for
recognizing shapes and moving around, "tonguing" (my term)
could be a simpler and less invasive approach to artificial sight.
So, for those who are tempted to pierce their tongue, I suggest
reconsideration of the idea. You don''t want to louse up your
tongue in case you need it someday to find your way around the
room!
Allen F. Bortrum
|
