Abstract

Introduction In a famous experiment by Pavlov (1927), a dog was trained with the ringing of a bell (stimulus) followed by food delivery (reinforcer). In the first trial, the animal salivated when food was presented. After several trials, salivation started when the bell was rung. This finding suggests that the salivation response following the bell ring reflects anticipation of food delivery. A large body of experimental evidence led to the hypothesis that Pavlovian learning is dependent upon the degree of unpredictability of the reinforcer (Rescorla & Wagner, 1972; Dickinson, 1980). According to this hypothesis, reinforcers become progressively less efficient for behavioral adaptation as their predictability grows during the course of learning. The difference between the actual occurrence and the prediction of the reinforcer is usually referred to as the "error" in the reinforcer prediction. This concept has been employed in the temporal-difference model (TD model) of Pavlovi

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