Introduction

Research on associative learning has undergone considerable change during the last 30 years. The conceptual framework has shifted from the notion that associative learning, and particularly Pavlovian conditioning, involves the formation of new stimulus–response connections to a position that asserts that the conditioned response is an indication that the organism has acquired new information (Mackintosh, 1983). Within this information-processing framework, there is an emphasis on the unexpectedness of the unconditional stimulus (Rescorla & Wagner, 1972), the extent to which the conditioned and unconditioned stimuli are primed in a short-term memory store (Wagner, 1978), the relative predictive accuracy of all cues (Mackintosh, 1974), the type of processing (automatic or controlled) that is devoted to the conditioned stimulus (CS) (Pearce & Hall, 1980; Dawson & Schell, 1985), and the nature of the attentional process underlying the processing of conditioned and unconditioned stimuli (Öhman, 1983, 1992).