Hi All,
Please find a very interesting article on artificial vision systems
currently under development. It is my firm belief that these systems will
start to be commonplace in the next five years. The article appears in
today's EE Times.
Chips unravel vision mysteries.
By R. Colin Johnson, EE Times, July 30, 2003.
PORTLAND, Ore. - Enabling the blind to see again
is moving beyond the realm of Biblical prophecy as
researchers around the world tackle the problem
head-on. Recently, several researchers showed off
artificial retina prototypes at the International
Joint Conference on Neural Networks that are
bringing human applications for machine vision
closer to reality.
A Japanese team built a three-chip set "that
performs the analog functions of a real retina,"
said Tetsuya Yagi, a physician and professor in the
Electronic Engineering department at Osaka
University. His work with fellow engineer Seiji
Kameda is part of Japan's five-year "artificial
vision system" effort at the New Energy and
Industrial Technology Development Organization
(NEDO) and Nidek Co. Ltd.
Most current prosthesis efforts to cure blindness
concentrate on using a video camera - a CCD chip
with lens - and a DSP. Together, they transform
pixels into a pattern of electrical stimulation
that can be delivered by electrodes to either
remaining retinal cells, the optic nerve or the
visual cortex itself.
Most recently, the University of Southern
California successfully implanted a 16-electrode
retinal array that gave partial sight to patients
blinded by retinitis pigmentosa, which leaves
"bipolar" retinal cells intact.
That approach works as long as the video camera and
DSP are mounted on a pair of glasses connected to a
belt-pack with DSP and batteries. However Yagi's
research looks to the day when any kind of
blindness can be corrected with an implantable chip
that would replace any defective layer from the
retina, to the optic nerve, to the wiring of the
brain itself.
"We use analog chips [instead of digitizing a video
signal and using a DSP] because analog uses so very
little energy to operate and, more importantly,
does not generate heat, which is very important
when we start engineering implants," said Yagi.
Yagi's current chip provides a 184-pixel (40 x 46
pixels) image. It was fabricated in 0.6-micron CMOS
using double-polysilicon and three metal layers on
a 8.9 mm2 die. It and a second analog chip mimic two
of the five layers between the eye and the brain.
Yagi said he already has the other layers in sight.
The next one is already on the drawing board.
Nor is he alone. Labs around the world are aiming
to decode the neural patterns of electrical
stimulation on each visual processing layer so that
dead cells can eventually be bypassed with
specialized electronics that precisely replicate
the missing signals.
Visual circuitry computes higher-order visual
functions, such as edge detection. Hope is rampant
because the so-called retinal processing circuit is
among the few tissues of the nervous system where
the correlation between the physical structure and
electrical property is well understood.
The overall effect of the retinal processing
circuit is that without movement the signal goes
to neutral grey because of persistent negative
feedback. In the presence of motion the retinal
circuit delivers a smoothed and contrast-enhanced
image.
The chip circuitry replicates the first two layers
of the eye with three chips - two analog chips for
each layer plus an field-programmable gate array to
sequence them.
The first chip is an array of loosely coupled
photodiodes emulating the photoreceptor cell layer.
The second chip is a variable resistive network
emulating the horizontal cell layer. The second
chip also computes the difference between the two
layers to emulate the persistent negative feedback
of the horizontal layer.
A FPGA supplied control signals to sequence the
chip's processing tasks. Sample-and-hold circuits
stored analog values between the separate
computational layers, enabling analog voltage
levels to be transferred between chips.
"I plan to build the next layer on another parallel
operating chip, eventually connecting to the visual
cortex itself," said Yagi.
By carefully characterizing and replicating the
signal-processing capabilities at each layer of the
retinal processing circuit, Yagi and his Japanese
colleagues aim to someday help blind patients by
substituting prostheses for whatever part of the
visual circuitry is damaged.
Source URL:
http://www.eetimes.com/at/news/OEG20030730S0032
http://www.JoeLazzaro.Com
_______________________________________________
MCBtech mailing list
[log in to unmask]
http://jandjw.com/mailman/listinfo/mcbtech
http://www.JoeLazzaro.Com
-----------------------
Check out the EASI web:
http://www.rit.edu/~easi
Check EASI Courses and Clinics
To sign off this list
send e-mail to [log in to unmask] saying
signoff easi
|
