Lecture #3 introduced the behaviour-based approach to AI.
Notes are available in four formats:
Chapter 2 in the textbook covers the same material as the lecture, so you should read through this if you have the textbook.
The classic article on the subsumption architecture is
Brooks, R. A., "Intelligence Without Representation", Artificial Intelligence Journal (47), 1991, pp. 139-159You should read it. For those more interested, a recent paper is:
Brooks, R.A., " From Earwigs to Humans", Robotics and Autonomous Systems, Vol. 20, Nos. 2-4, June 1997, pp. 291-304.