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Out of Control

Centralized communication is not the only problem with a central brain. Maintaining a central memory is equally debilitating. A shared memory has to be updated rigorously, timely, and accurately -- a problem that many corporations can commiserate with. For a robot, central command's challenge is to compile and update a "world model," a theory, or representation, of what it perceives -- where the walls are, how far away the door is, and, by the way, beware of the stairs over there.

What does a brain center do with conflicting information from many sensors? The eye says something is coming, the ear says it is leaving. Which does the brain believe? The logical way is to try to sort them out. A central command reconciles arguments and recalibrates signals to be in sync. In presubsumption robots, most of the great computational resources of a centralized brain were spent in trying to make a coherent map of the world based on multiple-vision signals. Different parts of the system believed wildly inconsistent things about their world derived from different readings of the huge amount of data pouring in from cameras and infrared sensors. The brain never got anything done because it never got everything coordinated.

So difficult was the task of coordinating a central world view that Brooks discovered it was far easier to use the real world as its own model: "This is a good idea as the world really is a rather good model of itself." With no centrally imposed model, no one has the job of reconciling disputed notions; they simply aren't reconciled. Instead, various signals generate various behaviors. The behaviors are sorted out (suppressed, delayed, activated) in the web hierarchy of subsumed control.

In effect, there is no map of the world as the robot sees it (or as an insect sees it, Brooks might argue). There is no central memory, no central command, no central being. All is distributed. "Communication through the world circumvents the problem of calibrating the vision system with data from the arm," Brooks wrote. The world itself becomes the "central" controller; the unmapped environment becomes the map. That saves an immense amount of computation. "Within this kind of organization," Brooks said, "very small amounts of computation are needed to generate intelligent behaviors."

With no central organization, the various agents must perform or die. One could think of Brooks's scheme as having, in his words, "multiple agents within one brain communicating through the world to compete for the resources of the robot's body." Only those that succeed in doing get the attention of other agents.

Astute observers have noticed that Brooks's prescription is an exact description of a market economy: there is no communication between agents, except that which occurs through observing the effects of actions (and not the actions themselves) that other agents have on the common world. The price of eggs is a message communicated to me by hundreds of millions of agents I have never met. The message says (among many other things): "A dozen eggs is worth less to us than a pair of shoes, but more than a two-minute telephone call across the country." That price, together with other price messages, directs thousands of poultry farmers, shoemakers, and investment bankers in where to put their money and energy.

Brooks's model, for all its radicalism in the field of artificial intelligence, is really a model of how complex organisms of any type work. We see a subsumption, web hierarchy in all kinds of vivisystems. He points out five lessons from building mobots. What you want is:

  • Incremental construction -- grow complexity, don't install it

  • Tight coupling of sensors to actuators -- reflexes, not thinking

  • Modular independent layers -- the system decomposes into viable subunits

  • Decentralized control -- no central planning

  • Sparse communication -- watch results in the world, not wires

When Brooks crammed a bulky, headstrong monster into a tiny, featherweight bug, he discovered something else in this miniaturization. Before, the "smarter" a robot was to be, the more computer components it needed, and the heavier it got. The heavier it got, the larger the motors needed to move it. The heavier the motors, the bigger the batteries needed to power it. The heavier the batteries, the heavier the structure needed to move the bigger batteries, and so on in an escalating vicious spiral. The spiral drove the ratio of thinking parts to body weight in the direction of ever more body.

But the spiral worked in the other direction even nicer. The smaller the computer, the lighter the motors, the smaller the batteries, the smaller the structure, and the stronger the frame became relative to its size. This also drove the ratio of brains to body towards a mobot with a proportionally larger brain, small though its brain was. Most of Brooks's mobots weighed less than ten pounds. Genghis, assembled out of model car parts, weighed only 3.6 pounds. Within three years Brooks would like to have a 1-mm (pencil-tip-size) robot. "Fleabots" he calls them.

Brooks calls for an infiltration of robots not just on Mars but on Earth as well. Rather than try to bring as much organic life into artificial life, Brooks says he's trying to bring as much artificial life into real life. He wants to flood the world (and beyond) with inexpensive, small, ubiquitous semi-thinking things. He gives the example of smart doors. For only about $10 extra you could put a chip brain in a door so that it would know you were about to go out, or it could hear from another smart door that you are coming, or it could notify the lights that you left, and so on. If you had a building full of these smart doors talking to each other, they could help control the climate, as well as help traffic flow. If you extend that invasion to all kinds of other apparatus we now think of as inert, putting fast, cheap, out-of-control intelligence into them, then we would have a colony of sentient entities, serving us, and learning how to serve us better.

When prodded, Brooks predicts a future filled with artificial creatures living with us in mutual dependence -- a new symbiosis. Most of these creatures will be hidden from our senses, and taken for granted, and engineered with an insect approach to problems -- many hands make light work, small work done ceaselessly is big work, individual units are dispensable. Their numbers will outnumber us, as do insects. And in fact, his vision of robots is less that they will be R2D2s serving us beers, than that they will be an ecology of unnamed things just out of sight.

One student in the Mobot Lab built a cheap, bunny-size robot that watches where you are in a room and calibrates your stereo so it is perfectly adjusted as you move around. Brooks has another small robot in mind that lives in the corner of your living room or under the sofa. It wanders around like the Collection Machine, vacuuming at random whenever you aren't home. The only noticeable evidence of its presence is how clean the floors are. A similar, but very tiny, insectlike robot lives in one corner of your TV screen and eats off the dust when the TV isn't on.

Everybody wants programmable animals. "The biggest difference between horses and cars," says Keith Hensen, a popular techno-evangelist, "is that cars don't need attention every day, and horses do. I think there will be a demand for animals that can be switched on and off."

"We are interested in building artificial beings," Brooks wrote in a manifesto in 1985. He defined an artificial being as a creation that can do useful work while surviving for weeks or months without human assistance in real environment. "Our mobots are Creatures in the sense that on power-up they exist in the world and interact with it, pursuing multiple goals. This is in contrast to other mobile robots that are given programs or plans to follow for a specific mission." Brooks was adamant that he would not build toy (easy, simple) environments for his beings, as most other robotists had done, saying "We insist on building complete systems that exist in the real world so that we won't trick ourselves into skipping hard problems."

To date, one hard problem science has skipped is jump-starting a pure mind. If Brooks is right, it probably never will. Instead it will grow a mind from a dumb body. Almost every lesson from the Mobot Lab seems to teach that there is no mind without body in a real unforgiving world. "To think is to act, and to act is to think," said Heinz von Foerster, gadfly of the 1950s cybernetic movement. "There is no life without movement."