The contributions of this symposium on behavior systems are summarized and evaluated by considering two questions: (1) What is a behavior system? (2) What use to the learning theorist are behavior systems? Twoexamples of behavior systems from the classical ethological literature are compared with the behavior systems discussed in the symposium, and some similarities and differences in the type of analyses used are discussed. Analysis of the preorganized species-typical behavior systems relevant to the unconditioned stimuli or reinforcers in learning experiments can contribute performance rules and better understanding of the conditions and contents of learning. The organization of behavior systems can also provide important clues to the neural circuitry underlying behavior, and a behavior systems approach can raise novel questions concerning learning and behavioral development. Possible future directions for the behavior systems approach are briefly discussed.The contributors to this symposium deserve our thanks for reviewing in one place four successful and interesting research programs. Although these programs are diverse in the questions they ask and the methods they use, each of them has made extensive use of the notion that behavior is organized hierarchically into motivational systems. In his introduction, Timberlake (1994) claims that this approach can unify the disparate contemporary approaches to learning. Here, I briefly address Timberlake's claim by discussing two questions. First, what is a behavior system? Second, what use to the learning theorist are behavior systems?
What Is a Behavior System?Readers may be struck by the fact that each contribution to the symposium contains some sort of diagrammatic representation of a behavior system: fear in the rat (Fanselow, 1994), feeding in the rat (Timberlake, 1994), courtship in quail (Domjan, 1994, and dustbathing and feeding in chickens (Hogan, 1994). One thing these have in common is their hierarchical organization. Implicitly or explicitly, the lowest level of the hierarchy is a set of species-typical motor patterns. As both Hogan and Timberlake point out, the idea that species-typical behavior is organized into motivational systems of this general nature is at the core of classical ethology. Comparing the schemes for behavior systems presented here with some older ethological examples reveals some important similarities and differences and raises a few questions.