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Out of Control

In the 1940's, a trio of legendary animal watchers in Europe -- Konrad Lorenz, Karl von Frisch, and Niko Tinbergen -- began describing the logical underpinnings of animal behavior. Lorenz shared his house with geese, von Frisch lived among honeybee hives, and Tinbergen spent his days with stickleback perch and sea gulls. By rigorous and clever experiments the three ethologists refined the lore of animal antics into a respectable science called ethology (roughly, the study of character). In 1973, they shared a Nobel prize for their pioneering achievements. When cartoonists, engineers, and computer scientists later delved into the literature of ethology, they found, much to their surprise, a remarkable behavioral framework already worked out by the three ethologists, ready to be ported over to computers.

At the core of ethological architecture dwells the crucial idea of decentralization. As formalized in 1951 by Tinbergen in his book The Study of Instinct, the behavior of an animal is a decentralized coordination of independent action (drive) centers which are combined like behavioral building blocks. Some behavioral modules consist of a reflex; they invoke a simple function, such as: pull away when hot, or blink when touched. The reflex knows nothing of where it is, what else is going on, or even of the current goal of its host body. It can be triggered anytime the right stimulus appears.

A male trout instinctually responds to the following stimuli: a female trout ripe for copulation, a nearby worm, a predator approaching from behind. But when all three stimuli are presented simultaneously, the predator module always wins out by suppressing feeding or mating instincts. Sometimes, when there is a conflict between action modules, or several simultaneous stimuli, management modules are triggered to decide. For instance, you are in the kitchen with messy hands when the phone rings at the same time someone knocks on the front door. The conflicting drives -- jump to the phone! no, wipe hands first! no, dash to the door! -- could lead to paralysis unless arbitrated by a third module of learned behavior, perhaps one that invokes the holler, "Please wait!"

A less passive way to view a Tinbergen drive center is as an "agent." An agent (whatever physical form it takes) detects a stimuli, then reacts. Its reaction, or "output" in computer talk, may be considered input by other modules, drive centers, or agents. Output from one agent may enable other modules (cocking a gun's hammer) or it may activate other modules already enabled (pulling the trigger). Or the signal may disable (uncock) a neighboring module. Rubbing your tummy and patting your head at the same time is tricky because, for some unknown reason, one action suppresses the other. Commonly an output may both enable some centers and suppress others. This is, of course, the layout of a network swamped with circular causality and primed to loop into self-creation.

Outward behavior thus emerges from the thicket of these blind reflexes. Because of behavior's distributed origin, very simple agents at the bottom can produce unexpectedly complex behavior at the top. No central module in the cat decides whether the cat should scratch its ear or lick its paw. Instead, the cat's conduct is determined by a tangled web of independent "behavioral agents" -- cat reflexes-cross-activating each other, forming a gross pattern (called licking or scratching) that wells up from the distributed net.

This sounds a lot like Brooks's subsumption architecture because it is. Animals are robots that work. The decentralized, distributed control that governs animals is also what works in robots and what works for digital creatures.

Web-strewn diagrams of interlinked behavior modules in ethology textbooks appear to computer scientists as computer logic flow charts. The message is: Behavior is computerizable. By arranging a circuit of subbehaviors, any kind of personality can be programmed. It is theoretically feasible to generate in a computer any mood, any sophisticated emotional response that an animal has. Film creatures will be driven by the same bottom-up governance of behavior running Robbie the Robot -- and the very same scheme borrowed from living songbirds and stickleback fish. But instead of causing pneumatic hoses to pressurize, or fishtails to flick, the distributed system pumps bits of data which move a leg on a computer screen. In this way, autonomous animated characters in film behave according to the same general organizational rules as real animals. Their behavior, although synthetic, is real behavior (or at least hyperreal behavior). Thus, toons are simply robots without hard bodies.

More than just movement can be programmed. Character -- in the old-fashioned sense of the word -- can be encapsulated into bit code. Depression, elation, and rage will all be add-on modules for a creature's operating system. Some software companies will sell better versions of the fear emotion than others. Maybe they'll sell "relational fear" -- fear that not only registers on a creature's body but trickles into successive emotion modules and only gradually dissipates over time.