  Brooks’s approach to robotics disavows the computational principles on which Shakey was designed, embracing instead a Gibsonian-inspired architecture. The result has been robots that exhibit far more versatility than Shakey ever displayed—robots that can roam cluttered environments, avoiding obstacles, setting goals for themselves, collecting soda cans for recycling, and more. Brooks’s “Creatures” run on what he calls a subsumption architecture. Rather than cycling through sense-model-plan-act sequences, Creatures contain arrays of sensors that are connected directly to behavior-generating mechanisms. For instance, the sensors on Brooks’s robot Allen were connected directly to three different kinds of behavior-generators: Avoid, Wander, and Explore. When sensors detected an object in Allen’s path, the Avoid mechanism would cause Allen to stop its forward motion, turn, and then proceed. The Wander generator would simply send Allen along a random heading, while the Explore generator would steer Allen toward a selected target. The three kinds of activity layers as Brooks called them, continually compete with each other. For instance, if Allen were Wandering and came across an obstacle, Avoid would step in and prevent Allen from a collision. Explore could inhibit Wander’s activation in order to keep Allen on course toward a target. From the competitive interactions of the three layers emerged unexpectedly flexible and seemingly goal-oriented behavior.