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The Use of Hierarchies for Action Selection

Several researchers of animal behavior, such as Tinbergen and Baerends, have proposed hierarchical mechanisms for action selection. Maes, among others, has argued against mechanisms of this type because of the top-down control and lack of robustness inherent in these hierarchical decision structures, or rigid switching mechanisms, in which decisions are made at every level. Two alternatives exist to these hierarchical decision structures: Maes and others have designed non-hierarchical action selection mechanisms, and Rosenblatt and Payton have outlined a hierarchical mechanism that does not make decisions at every level. In this article, use of the two types of hierarchies for action selection is discussed, and the Rosenblatt and Payton approach—with free flow of information, combination of evidence, and the ability to select compromise candidates—is supported. It is also argued that the problem of action selection is, by nature, intrinsically hierarchical, and so Rosenblatt and Payton-like hierarchies (free-flow hierarchies) are more suitable for action selection than non-hierarchical mechanisms. Evidence from observation of animal behavior and from computer simulation testing is used to lend support to these claims.