[AI] An ambitious plan to build a computer that works like the brain
ilovecold at gmail.com
Fri Aug 27 06:47:32 EDT 2010
Army of smartphone chips could emulate the human brain
An ambitious plan to build a computer that works like the brain
will use "bog-standard, off-the-shelf processors of fairly modest
by Paul Marks
IF YOU have a smartphone, you probably have a slice of Steve
Furber's brain in your pocket. By the time you read this, his
1-billion-neuron silicon brain will be in production at a microchip
plant in Taiwan.
Computer engineers have long wanted to copy the compact power of
biological brains. But the best mimics so far have been impractical,
being simulations running on supercomputers.
Furber, a computer scientist at the University of Manchester, UK, says
that if we want to use computers with even a fraction of a brain's
flexibility, we need to start with affordable, practical, low-power
"We're using bog-standard, off-the-shelf processors of fairly modest
performance," he says.
Furber won't come close to copying every property of real neurons,
says Henry Markram, head of Blue Brain. This is IBM's attempt
to simulate a brain with unsurpassed accuracy on a Blue Gene
supercomputer at the Swiss Institute for Technology, Lausanne. "It's a
worthy aim, but brain-inspired chips can only produce brain-like
functions," he says.
That's good enough for Furber, who wants to start teaching his
brain-like computer about the world as soon as possible. His first
goal is to teach it how to control a robotic arm, before working
towards a design to control a humanoid. A robot controller with even a
dash of brain-like properties should be much better at tasks like
image recognition, navigation and decision-making, says Furber.
"Robots offer a natural, sensory environment for testing brain-like
computers," says Furber. "You can instantly tell if it is being
Called Spinnaker - for Spiking Neural Network Architecture - the
brain is based on a processor created in 1987 by Furber and colleagues
at Acorn Computers in Cambridge, UK, makers of the seminal BBC
Although the chip was made for a follow-up computer that flopped, the
ARM design at its heart lived on, becoming the most common "embedded"
processor in devices like e-book readers and smartphones.
But coaxing any computer into behaving like a brain is tough. Both
real neurons and computer circuits communicate using electrical
signals, but in biology the "wires" carrying them do not have fixed
roles as in electronics. The importance of a particular neural
connection, or synapse, varies as the network learns by balancing the
influence of the different signals being received. This synaptic
"weighting" must be dynamic in a silicon brain, too.
To coordinate its 'neurons' the chip mimics the way real neurons
communicate using 'spikes' in voltage
The chips under construction in Taiwan contain 20 ARM processor cores,
each modelling 1000 neurons. With 20,000 neurons per chip, 50,000
chips will be needed to reach the target of 1 billion neurons.
A memory chip next to each processor stores the changing synaptic
weights as simple numbers that represent the importance of a given
connection at any moment. Initially, those will be loaded from a PC,
but as the system gets bigger and smarter, says Furber, "the only
computer able to compute them will be the machine itself".
Another brain-like behaviour his chips need to master is to
communicate coordinated "spikes" of voltage. A computer has no trouble
matching the speed at which individual neurons spike - about 10 times
per second - but neurons work in very much larger, parallel groups
than silicon logic gates.
In a brain there is no top-down control to coordinate their actions
because the basic nature of individual neurons means that they work
together in an emergent, bottom-up way.
Spinnaker cannot mimic that property, so it relies on a miniature
controller to direct spike traffic, similar to one of the routers in
the internet's backbone. "We can route to more than 4 billion
neurons," says Furber, "many more than we need."
While the Manchester team await the arrival of their chips, they have
built a cut-down version with just 50 neurons and have put the
prototype through its paces in the lab. They have created a virtual
environment in which the silicon brain controls a Pac-Man-like program
that learns to hunt for a virtual doughnut.
"It shows that our four years designing the system haven't been
wasted," says Furber. He hopes to have a 10,000-processor version
working later this year.
As they attempt to coax brain-like behaviour from phone chips, others
are working with hardware which may have greater potential.
The Defense Advanced Research Projects Agency, the Pentagon's
research arm, is funding a project called Synapse. Wei Lu of the
University of Michigan at Ann Arbor, is working on a way of providing
synaptic weights with memristors, first made in 2008 (New
Scientist, 3 May 2008, p 26).
Handily, their most basic nature is brain-like: at any one moment a
memristor's resistance depends on the last voltage placed across it.
This rudimentary "memory" means that simple networks of memristors
form weighted connections like those of neurons. This memory remains
without drawing power, unlike the memory chips needed in Spinnaker.
"Memristors are pretty neat," says Lu.
Their downside is that they are untested, though. "Synapse is an
extremely ambitious project," says Furber. "But ambition is what
drives this field. No one knows the right way to go."
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