Cambrian Intelligence: The Early History of the New AI by Rodney A. Brooks

MIT Press, 1999. $60.00/£39.95 (hbk), $25.00/£16.50 (pbk) (xii+199 pages)ISBN 0-262-02468-3 (hbk)ISBN 0-262-52263-2 (pbk)This small and fascinating book, a collection of papers written by Rodney Brooks (one is co-authored with his former student Maja Mataric), chronicles the development and rise to prominence of the key ideas of behavior-based robotics. The eight papers in the book are organized into two groups, the first consisting of technical papers and the second of more philosophical discourses on the implications of the ‘New AI’. From a technical point of view, the new AI rejects the more traditional view of ‘intelligence’ as a sequential sense–plan–act process that interposes cognition between perception and action. Rather, it suggests that intelligent behavior is produced by the direct coupling of perception and action, and later perception–action couplings interacting through the world. A control system for a mobile robot, then, is produced by building layers of behaviors connecting perceptions of the world to actions performed in the world. This approach to building intelligent robots, generally known as behavior-based robotics, has received increasing acceptance in the robotics community.One of the key issues in the new AI is that robotics makes sense only when the robots are embodied and situated in the world. ‘Embodiment’ implies that the robots are physical, real entities and have bodies, so they can experience the world directly and affect it by their actions. This further means that the robot builder must take into account the physical reality of the world, including such issues as friction and inertia, the fact that no two wheels of a robot are identical and that a truly autonomous robot must be able to perform useful tasks in an unstructured and uncertain world. ‘Situatedness’ implies that the robots are situated, and act, in the world; that they must deal with the reality of the world and not abstractions or verbal descriptions.It might be difficult to believe how slowly these ideas were accepted by the artificial intelligence community. The prevailing view of intelligent robotics was the one used in the construction of ‘Shakey’ at Stanford Research Laboratories in the early 1980s. This robot moved in an artificial and simple world of large colored blocks, smooth and light colored background walls and no obstacles. The robot worked sequentially: it observed the world using a vision system, it then processed the perceived images to construct a map of the world and plan an action, and then it moved a short distance. This sense–plan–act paradigm is in marked contrast with the subsumption architecture discussed throughout the papers in this book, where increasingly complex behaviors are layered on top of simpler ones, which they subsume as needed. (Subsuming implies the assumption of the existence of, and utilizing, ‘lower’ behaviors, arbitrating between layers if necessary.) A behavior may consist of exploring the environment, subsuming but not eliminating a ‘lower’ behavior that avoids obstacles. This architecture is analogous to that used by humans; that is, we can ask a student to take a book to the next office, but we need not say explicitly ‘and do not bump into chairs or other people on your way’, because this basic behavior continues to operate, in parallel with the delivery task.It is also characteristic of this approach to robotics that the behaviors operate as a completely distributed system of simple machines, with no central controllers. Nevertheless, it is possible for such robots to evolve changing goals over time and to build maps over their distributed network. This aspect of behavior-based systems (described in Chapter 3) challenged the notion, prevalent previously, that behavior-based systems were only capable of purely reactive behaviors. Another chapter in the first part of this book describes the development of ‘Genghis’, the first walking machine designed using the subsumption architecture. (Our robotics group at the University of Southern California was so inspired by Genghis that my students designed and built an analogous behavior-based six-legged walking machine, that we affectionately named Rodney).The second part of the book deals with the philosophy of this new approach to AI and robotics. In these chapters, the author puts the argument for his view of intelligence and explains why it can only be manifested in embodied, situated machines. There are extensive discussions with other AI researchers (sometimes quite pointed) on the author’s view of the failure of traditional AI approaches based on the ‘symbol system hypothesis’, and on the importance of grounding intelligence on physical interaction with the environment. When criticized for the inability of his robots to achieve certain goals, Brooks argues that elephants are not critized for being unable to play chess and chess-playing machines are not criticized for their inability to perform abstract symbol manipulation. Hence, behavior-based robots should be judged by their ability to perform tasks in a world that, after all, was not specifically designed for them. The fundamental arguments are laid out most clearly in the last chapter of the book (entitled ‘Intelligence without Reason’), which is a critique of traditional AI and its approach to intelligence.Let me conclude this review of this important book with a personal note. The first paper in the book (originally presented in 1985 and published in 1986), lays out the basic ideas of this simple, non-mathematical approach to designing control systems for mobile robots. Brooks points out that this paper, which was severely criticized for its lack of mathematical rigor, is his most cited paper. I was editor of the IEEE Journal of Robotics and Automation (later called Transactions on Robotics and Automation) at the time when this paper was submitted for publication, and indeed, the reviews were highly critical. Now that 15 years have passed, I can admit that I was personally so impressed by the paper and its importance for the future of robotics, that I overrode the reviewers’ recommendations and published it. Clearly, I was right to do so, and I am delighted to have had this small role to play in the development of the ‘new AI’.