210Bayesian formalizations of learning are a revolutionary advance over traditional approaches. Bayesian models assume that the learner maintains multiple candidate hypotheses with differing degrees of belief, unlike traditional models that assume the learner has a punctate state of mind. Bayesian models can account for some associative learning phenomena that are very challenging for traditional approaches. Perhaps more important, but even less prominent in the associative learning literature, is the fact that Bayesian models provide a foundation for models of active learning. Because Bayesian models represent degrees of belief across multiple hypotheses, the active learner can assess which possible probing of the environment is most likely to achieve beliefs that reduce uncertainty or make some hypotheses highly probable. Traditional models, by contrast, typically treat the learner as a passive recipient of information, and such models offer no predictions for how a real learner would actively probe its environment.This article is divided into two main parts. The first is a selective review of Bayesian models of associative learning. Two different Bayesian models are described in detail and compared with the traditional Rescorla-Wagner (1972) model. The behavior of the models is illustrated by applications to some well-known phenomena, such as backward blocking. The review also indicates how the specific models are situated in the larger space of all possible Bayesian models, which offers a remarkably liberating cornucopia of representational options for models of learning.The second part of the article focuses on active learning. Two different goals for active learning are reviewed, and the predictions of the two Bayesian models are presented. This article is the first application of active-learning formalisms to models of associative learning. The derivations and simulations demonstrate that different combinations of knowledge representations and active-learning goals generate different predictions, some of which are already informed by results in the literature. The broad framework that combines Bayesian models of passive learning with various goals for active learning is a gold mine for new research.
TRADITIONAL AND BAYESIAN THEORIESIn traditional cognitive models, the learner's knowledge at any given moment is represented as a specific state. For example, the learner may have an associative weight of 0.413 between "tone" and "shock," or the learner may know that the concept "cat" has a value of 0.289 on the scale of ferocity. When new information is delivered by the world, the values may change. For example, if another instance of shock preceded by a tone occurs, the associative weight might then increase to 0.582. On the other hand, if a cat snuggles up and purrs, that concept's ferocity value might decrease to 0.116. The punctate values comprise the totality of the learner's knowledge.Bayesian approaches assume a radically different mental ontology, in which the learner entertains an entire spectrum of ...