Modelling the acquisition of Pavlovian conditioning

Pavlovian conditioning is a fundamental learning process that allows animals to anticipate and respond to significant environmental events. This review examines the key properties of the relationship between the conditioned stimulus (CS) and unconditioned stimulus (US) that influence learning, focussing on the temporal proximity of the CS and US, the spacing of trials (pairings of the CS and US), and the contingency between the CS and US. These properties have been touchstones for models of associative learning. Two primary theoretical approaches are contrasted here. Connection strength models, exemplified by the Rescorla-Wagner model (Rescorla & Wagner, 1972), describe learning as trial-by-trial changes in the strength of an associative bond based on prediction errors. In time-based models of learning (e.g., Gallistel & Gibbon, 2000) animals encode and remember temporal intervals and rates of reinforcement. The integration of Information Theory into time-based models (Balsam & Gallistel, 2009) provides a mathematical framework for quantifying the effects of proximity, trial spacing, and contingency in terms of how much the CS reduces uncertainty about the US. The present paper incorporates a trial-by-trial Bayesian updating process into the information theoretic account to describe how uncertainty about the CS-US interval changes across conditioning. This Bayesian process is shown to account for empirical evidence about the way that responding changes continuously over conditioning trials.