The Behavior Language; User's Guide

The Behavior Language is a rule-based real-time parallel robot programming language originally based on ideas from [Brooks 86], [Connell 89], and [Maes 89]. It compiles into a modified and extended version of the subsumption architecture [Brooks 86] and thus has backends for a number of processors including the Motorola 68000 and 68HCll, the Hitachi 6301, and Common Lisp. Behaviors are groups of rules which are activatable by a number of different schemes. There are no shared data structures across behaviors, but instead all communication is by explicit message passing. All rules are assumed to run in parallel and asynchronously. It includes the earlier notions of inhibition and suppression, along with a number of mechanisms for spreading of activation

Intelligence Without Reason

Computers and Thought are the two categories that together define Artificial Intelligence as a discipline. It is generally accepted that work in Artificial Intelligence over the last thirty years has had a strong influence on aspects of computer architectures. In this paper we also make the converse claim; that the state of computer architecture has been a strong influence on our models of thought. The Von Neumann model of computation has lead Artificial Intelligence in particular directions. Intelligence in biological systems is completely different. Recent work in behavior-based Artificial Intelligenge has produced new models of intelligence that are much closer in spirit to biological systems. The non-Von Neumann computational models they use share many characteristics with biological computation

A Mobile Robot Project

We are building a mobile robot which will roam around the AI lab observing and later perhaps doing. Our approach to building the robot and its controlling software differs from that used in many other projects in a number of ways. (1) We model the world as three dimensional rather than two. (2) We build no special environment for our robot and insist that it must operate in the same real world that we inhabit. (3) In order to adequately deal with uncertainty of perception and control we build relational maps rather than maps embedded in a coordinate system, and we maintain explicit models of all uncertainties. (4) We explicitly monitor the computational performance of the components of the control system, in order to refine the design of a real time control system for mobile robots based on a special purpose distributed computation engine. (5) We use vision as our primary sense and relegate acoustic sensors to local obstacle detection. (6) We use a new architecture for an intelligent system designed to provide integration of many early vision processes, and robust real-time performance even in cases of sensory overload, failure of certain early vision processes to deliver much information in particular situations, and computation module failure.MIT Artificial Intelligence Laborator

Planning is Just a Way of Avoiding Figuring Out What To Do Next

The idea of planning and plan execution is just an intuition based decomposition. There is no reason it has to be that way. Most likely in the long term, real empirical evidence from systems we know to be built that way (from designing them like that) will determine whether its a very good idea or not. Any particular planner is simply an abstraction barrier. Below that level we get a choice of whether to slot in another planner or to place a program which does the right thing. Why stop there? Maybe we can go up the hierarchy and eliminate the planners there too. To do this we must move from a state based way of reasoning to a process based way of acting.MIT Artificial Intelligence Laborator

MIT Mobile Robots - What's Next?

The MIT Mobile Robot Project began in January of 1985 with the objective of building machines that could operate autonomously and robustly in dynamically changing environments. We now have four working robots, each progressively more intelligent and sophisticated. All incorporate some rather novel ideas about how to build a control system that can adequately deal with complex environments. The project has also contributed some innovative and creative technical solutions in terms of putting together sensors, actuators, power supplies and processing power into whole systems that actually work. From our experiences over the past two and a half years, we have gained insight into the real issues and problems and what the goals should be for future robotics research. This paper gives our perspectives on mobile robotics: our objectives, experiences, mistakes and future plans.MIT Artificial Intelligence Laborator

Low computation vision-based navigation for a Martian rover

Construction and design details of the Mobot Vision System, a small, self-contained, mobile vision system, are presented. This system uses the view from the top of a small, roving, robotic vehicle to supply data that is processed in real-time to safely navigate the surface of Mars. A simple, low-computation algorithm for constructing a 3-D navigational map of the Martian environment to be used by the rover is discussed

The effect of age on outcomes of coronary artery bypass surgery compared with balloon angioplasty or bare-metal stent implantation among patients with multivessel coronary disease. A collaborative analysis of individual patient data from 10 randomized trials.

OBJECTIVES: This study sought to assess whether patient age modifies the comparative effectiveness of coronary artery bypass graft (CABG) surgery and percutaneous coronary intervention (PCI). BACKGROUND: Increasingly, CABG and PCI are performed in older patients to treat multivessel disease, but their comparative effectiveness is uncertain. METHODS: Individual data from 7,812 patients randomized in 1 of 10 clinical trials of CABG or PCI were pooled. Age was analyzed as a continuous variable in the primary analysis and was divided into tertiles for descriptive purposes (≤56.2 years, 56.3 to 65.1 years, ≥65.2 years). The outcomes assessed were death, myocardial infarction and repeat revascularization over complete follow-up, and angina at 1 year. RESULTS: Older patients were more likely to have hypertension, diabetes, and 3-vessel disease compared with younger patients (p < 0.001 for trend). Over a median follow-up of 5.9 years, the effect of CABG versus PCI on mortality varied according to age (interaction p < 0.01), with adjusted CABG-to-PCI hazard ratios and 95% confidence intervals (CI) of 1.23 (95% CI: 0.95 to 1.59) in the youngest tertile; 0.89 (95% CI: 0.73 to 1.10) in the middle tertile; and 0.79 (95% CI: 0.67 to 0.94) in the oldest tertile. The CABG-to-PCI hazard ratio of less than 1 for patients 59 years of age and older. A similar interaction of age with treatment was present for the composite outcome of death or myocardial infarction. In contrast, patient age did not alter the comparative effectiveness of CABG and PCI on the outcomes of repeat revascularization or angina. CONCLUSIONS: Patient age modifies the comparative effectiveness of CABG and PCI on hard cardiac events, with CABG favored at older ages and PCI favored at younger ages