[fwd] Second Sight: New Scientist article on artificial vision

From: Lloyd G. Rasmussen (lras@loc.gov)
Date: Mon Dec 02 2002 - 06:53:13 PST


I haven't forwarded magazine articles to this list in a long time. Six
years ago, at the summer meeting of the R&D committee, I stated that we
would be seeing a lot of work on vision substitution over the next 25
years, and it would begin to impact our research agenda, our thinking about
the roles of rehabilitation, attitudes toward blindness and vision, the
medical model of rehabilitation funding, etc. The research is coming on at
a tremendous rate, and this year we have seen a great amount of publicity
touting the virtues of current surgeries and plans.

This article was posted on the "seeing with sound" mailing list, where the
main topic of discussion is the vOICe, a Windows program which converts all
kinds of visual images into sound patterns. The list moderator posts many
articles like this one, to his list. They should be available in the
archives on Topica. I am forwarding this one because it covers several of
the projects and the obstacles they face.

I'm not "hoping for a cure," but I'm not laughing anymore, either.

>X-Original-To: seeingwithsound@topica.com
>From: Peter Meijer <Peter.B.L.Meijer@philips.com>
>Resent-From: "Lloyd Rasmussen" <lras@sprynet.com>
>Subject: Re: [The vOICe] Second Sight: New Scientist article on artificial
vision
>Date: Wed, 27 Nov 2002 23:42:19 +0100
>
>Hi All,
>
>For your information. The article about artificial vision
>from this week's print edition of the New Scientist (the
>November 23, 2002 issue) is now appended.
>
>Best wishes,
>
>Peter Meijer
>
>
>Seeing with Sound - The vOICe
>http://www.seeingwithsound.com/winvoice.htm
>
>
>Second Sight. Artificial vision is promising to deliver sight to
>blind people, but will the technology ever work? Duncan Graham-Rowe
>says there's more to making implants than meets the eye.
>
>By Duncan Graham-Rowe.
>
>WHEN Delvin Kehoe looked at himself in the mirror earlier this
>year, he was appalled by what he saw. Instead of the smiling face
>of a man in his 30s, he was greeted instead by the grimace of a
>59-year-old. But Kehoe was not suddenly feeling his age, nor even
>reviving from a long coma. He was simply seeing his reflection
>for the first time in 20 years.
>
>His is one of several miracle tales sweeping the ophthalmological
>community. Years after losing their sight to a degenerative
>disease - in Kehoe's case, retinitis pigmentosa - patients have
>been given an eye implant that restores their vision. These
>'visual prosthetics' work by artificially stimulating the retina
>with electrical signals that are fed down the optic nerve into
>the visual cortex. Of the 20 people who have received such
>implants worldwide, some claim that they deliver such clear and
>detailed images that they can not only see their reflections, but
>can make out objects as tiny as ants on a pavement. One man even
>felt confident enough to drive his car, albeit on private
>property.
>
>But if the implants really work that well, why aren't millions of
>blind people lining up for them? The truth is that, despite the
>compelling stories, many researchers are starting to question how
>well the current technology really works. For every Delvin Kehoe,
>there are several others whose visual prosthetics deliver little
>more than dots and fuzzy patches. For these people, the
>environment around them resembles at best a game of space
>invaders, full of grainy, dotted images that bear little
>resemblance to reality.
>
>Now one researcher is proposing a fundamental rethink of the
>design principles used in existing retinal implants. Kwabena
>Boahen, a bioengineer at the University of Pennsylvania, says
>that instead of merely stimulating the retina we should be
>simulating it. He's created an artificial retina that copies the
>function of a real one down to the firing of individual neurons.
>Although he has yet to try his implant in a person, he's
>confident that his design can one day deliver full natural vision
>to blind people.
>
>There are many reasons for doubting that current technology can
>produce anything like natural vision. All the implants undergoing
>trials at the moment are based on the 1950s discovery that
>stimulating the retina with electrical pulses produces
>phosphenes, or vision sensations, even in blind people. In most
>cases, people become blind because their retinas no longer sense
>light, but the rest of their visual processing system - neurons
>in the retina, optic nerve and visual cortex in the brain -
>works fine. If an implanted chip can stimulate enough meaningful
>phosphenes in the brain, the theory goes, blind people will be
>able to see again.
>
>But how do you design the implant so people get useful phosphenes?
>There is no clear consensus. Perhaps the most obvious technique,
>called the epiretinal approach, is to cover the surface of the
>retina with an array of electrodes, each of which can stimulate
>the ganglion nerve cells underneath it to fire. The electrodes
>receive their signals from a transmitter that monitors visual
>information through a camera on the patient's glasses.
>
>But critics of this approach do not like the implicit assumption
>that ganglion cells are simple on-off switches. In a healthy
>retina, these cells do not receive signals directly from
>photoreceptors. The photoreceptors pass their information to
>layers of other cell types - bipolar, amacrine and horizontal
>cells - which then process it and relay it to the ganglions. In
>the epiretinal chips, by contrast, there's no pre-processing.
>'It's truly artificial,' says Mark Humayun, whose team at the
>University of Southern California in Los Angeles gave one patient
>an epiretinal implant earlier this year.
>
>And this pre-processing step is a crucial element of vision. The
>ganglion cells use this network of cell layers to compare
>differences between the signals from nearby photoreceptors and
>only relay data on striking changes, such as a border to an area
>of fixed intensity or its motion across the field of vision. Less
>interesting information is ignored. So the signals that ganglion
>cells relay to the optic nerve are already partially processed.
>In a prosthetic that doesn't carry out this processing, the brain
>loses a source of useful information. This can lead to
>contradictory signals, if, for example, the chip directly
>stimulates a ganglion that normally only fires when it detects a
>border but also stimulates neighbouring cells in a way that
>indicates a region of constant brightness.
>
>It is a wonder, then, that Humayun's patient can see 16 dots of
>light in a four-by-four array corresponding to the locations of
>the electrodes on his retina. The resolution does improve
>slightly if the patient moves their head to scan the visual field
>but 'high resolution and near-natural vision is a long way off',
>says Humayun.
>
>Another technique, the subretinal approach, looks more promising.
>Here, the implant sits at the back of the retina and stimulates
>the bipolar cells. Because these are upstream of the ganglion
>cells, subretinal implants have the potential to tap into some of
>the processing power of those parts of the retina that are still
>working.
>
>Subretinal implants seem particularly promising because they would
>let the rest of the eye function as normal, allowing the lens to
>focus images directly onto photodiodes on the chip, which convert
>the light into electrical energy. But with this comes another
>difficulty.
>
>The electrodes must be separated by a large enough distance so
>that they don't interfere with each other's signal. As a result
>it is still not possible to address individual bipolar cells, and
>therefore large numbers of cells are stimulated simultaneously
>and resolution is lost, says Eberhart Zrenner, a
>neuro-ophthalmologist at the University of T bingen in Germany
>who is developing subretinal chips. He also says that subretinal
>chips do not incorporate a full understanding of how the bipolar,
>amacrine and horizontal cells process visual data. He does not
>expect the approach to do much more than provide blind people
>with some basic awareness of their surroundings. Their visual
>acuity will always fall a long way short of natural vision, he
>says, and will always be slightly distorted .
>
>However, Vincent and Alan Chow, whose company Optobionics in
>Wheaton, Illinois, implanted Kehoe's chip, claim to have taken
>subretinals further. Optobionics' chips contain 5000 photodiodes,
>so should in theory give at least three times the resolution of
>Zrenner's, probably enough to see your reflection in a mirror.
>
>But it is unclear to what extent Optobionics' successes are due to
>the implants. In May, the company reported that its chips have
>had an unusual and unexpected side effect. Rather than just
>stimulating groups of cells near each of the electrodes, their
>patients were experiencing improved vision in areas of the retina
>well beyond the physical reach of the chips. Previously damaged
>parts of their retinas were suddenly working again, even in
>places not covered by the chip.
>
>So what's going on? The Chows argue that the current generated by
>the chip is reactivating photoreceptors across large areas of the
>retina beyond the reach of the chip. While arguably this would
>not qualify the implant as a prosthetic, because the patients
>aren't directly using it to see, it would be a truly remarkable
>effect.
>
>But others working in the field prefer a different explanation
>that gives even less credit to the Optobionics chips. In many
>retinal diseases, including retinitis pigmentosa, it is not
>unusual for faulty photoreceptors to start working again, says
>Zrenner. This 'rescue effect' can be caused by the trauma of
>surgery itself. Tissue experts agree. 'The eye is very
>sensitive,' says Peng Tee Khaw, an expert in tissue repair at
>Moorfields Eye Hospital in London. 'The moment you fiddle around
>with it you get a release of all these growth factors. Even if
>you inject water into the eye you get rescue.'
>
>If the critics are right, Kehoe and fellow patients at Optobionics
>could have the same visual experiences if surgeons carried out
>dummy operations on their eyes where they didn't bother to
>implant the chips at all. Alan Chow disagrees. He says a healing
>effect triggered by the trauma of surgery couldn't last as long
>and be as robust as the results he has seen in his patients.
>
>Perhaps the most promising work in visual prosthetics, in terms of
>what the patient actually sees, has been from cortical
>stimulation, or stimulating the brain directly. William Dobelle,
>of his own Dobelle Institute in Commack, New York, believes that
>visual prosthetics should not just be developed for people with
>retinal diseases but for those who have suffered trauma to the
>eye or optic nerve. If a device is to cater for a wide range of
>causes of blindness, it will have to bypass the eye.
>
>Dobelle's technique involves implanting electrodes into the visual
>cortex. The electrodes then receive a video-like feed down a wire
>from a camera mounted on the patient's glasses. 'Initially the
>phosphenes appear almost randomly,' says Dobelle. But he improves
>the images by adjusting signals delivered to the electrodes while
>the patient describes what they're seeing. He also uses
>algorithms to find the edges of objects in the camera image and
>ensure that light-dark boundaries appear in the phosphenes at the
>right point in the visual field.
>
>But in the 30 years Dobelle has been experimenting with human
>vision, the visual acuity of his patients has not improved beyond
>about 100 pixels. In comparison, normal visual acuity is at least
>10,000 times that. For all the sophistication of his software it
>is questionable whether he could ever match the efficiency of the
>retina in producing natural vision. His electrodes stimulate
>hundreds if not thousands of neurons simultaneously, but to get
>natural vision he'll need to increase the number of electrodes
>dramatically and find a way to prevent their signals from
>interfering with each other.
>
>Enter Boahen. He says the problem with existing prosthetics is
>that they are not based on any real understanding of how a
>healthy retina functions. Rather than merely relaying signals to
>the brain, the retina performs a huge amount of pre-processing.
>Instead of treating the retina purely as a light-detecting
>surface, Boahen says you have to think of it as part of the
>brain. Until we understand how the retina 'thinks' we'll never
>build good prosthetics.
>
>So Boahen has spent the past few years trying to fathom the
>colossal computations that go on in a healthy retina. To get a
>sense of how much processing the retina does, consider that there
>are nearly 130 million photoreceptors in each human retina, but
>only about a million neural pathways in the optic nerve. The eye
>couldn't possibly cram all the information it receives down such
>a narrow pipe. Instead, the retina filters and interprets the
>information and sends only the interesting stuff. 'Most of the
>time [ganglion] cells are not firing at all,' explains Boahen.
>'They only respond to changes.'
>
>Boahen is now developing a silicon device that tries to copy the
>function of all of these layers of cells. It's a tall order and
>many of those who are already implanting less complex chips can't
>shake the feeling Boahen is trying to run before he can walk. 'We
>don't want to over-engineer it,' says Humayun. Boahen's
>'retinomorphic chip' has several layers of different,
>interconnected 'cells' etched in silicon. Like their biological
>counterparts - the bipolar, amacrine, horizontal and ganglion
>cells - these silicon cells perform different and very specific
>signal processing functions.
>
>Boahen's chip already detects light and performs the same kind of
>edge and motion detection functions as a real retina, ultimately
>resulting in an electrical signal rather like that in a healthy
>optic nerve. 'We more or less have a complete retina model,' says
>Boahen. 'We have been able to develop outputs that match the
>outputs of the optic nerve.'
>
>Processing a great many signals in a device simultaneously is
>no mean feat. Silicon chips use roughly 100,000 times more
>components and connections to run a given set of computations
>than the human nervous system. That's because they run
>computational tasks one after the other, instead of running
>several in parallel like the brain can do.
>
>Wiring the retinomorphic chip to run enough computations without
>generating too much heat is a remarkable piece of engineering.
>Chips generate a lot of heat and biological tissue doesn't take
>too kindly to this. But Boahen has found a way to process
>thousands of signals in parallel by getting single transistors to
>behave like individual neuronal synapses. In chips, transistors
>normally behave as simple switches, digital on-offs that form
>simple binary logic circuits. Boahen's transistors produce
>analogue signals that are not simply on or off, but can be
>stronger or weaker as well. Over time, the transistors are
>relaying a waveform-like signal that is a function of the
>waveform inputs they get from the silicon cells.
>
>This solves the heat problem because, with the richer analogue
>signals, about 1000 times fewer transistors are needed to convey
>the same information. But Boahen could not implant the chip right
>now because in its current form the chip still does not match the
>resolution of the retina. With roughly 6000 photoreceptors
>feeding into about 1500 ganglion cells, its components need to
>shrink by a factor of about 10,000 to match the capabilities of a
>real retina. Although Moore's Law is on Boahen's side - every 18
>months the number of transistors chip makers can cram onto a chip
>doubles - one problem the chip industry won't solve is how to
>engineer the face of the chip so that it interfaces to living
>tissue at high resolutions.
>
>Solving these problems will take several years, which is no great
>comfort to people who are already coping with blindness, but
>Boahen believes his sophisticated chips will be worth the wait.
>He hopes that pioneers like Zrenner, Dobelle, Humayun and Chow
>will be using his technology when his first volunteers open their
>eyes to truly natural vision. This is not to criticise the effort
>that's gone into current technology - discovering what kind of
>stimulation gets different nerves to fire is important. The
>difference now is that Boahen's chip is talking the brain's
>language.
>
>Source URL:
>http://maelstrom.stjohns.edu/CGI/wa.exe?A2=ind0211&L=vicug-l&O=D&P=16214

Braille is the solution to the digital divide.
Lloyd Rasmussen, Senior Staff Engineer
National Library Service f/t Blind and Physically Handicapped
Library of Congress (202) 707-0535 <lras@loc.gov>
<http://www.loc.gov/nls>
HOME: <lras@sprynet.com> <http://lras.home.sprynet.com>
The opinions expressed here are my own and do not necessarily represent
those of NLS.



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