Pavlov and Thorndike pioneered the experimental study of animal learning and provided psychologists with powerful tools to unveil its underlying mechanisms. Today's research developments and theoretical analyses owe much to the pioneering work of these early investigators. Nevertheless, in the evolution of our knowledge about animal learning, some initial conceptions have been challenged and revised. We first review the original experimental procedures and findings of Pavlov and Thorndike. Next, we discuss critical research and consequent controversies which have greatly shaped animal learning theory. For example, although contiguity seemed to be the only condition that is necessary for learning, we now know that it is not sufficient; the conditioned stimulus (CS) also has to provide information about the occurrence of the unconditioned stimulus (US). Also, animals appear to learn different things about the same stimuli when circumstances vary. For instance, when faced with situations in which the meaning of a CS changes, as in the case of acquisition and later extinction, animals seem to preserve the original knowledge (CS-US) in addition to learning about the new conditions (CS-noUS). Finally, we discuss how parallels among Pavlovian conditioning, operant conditioning, and human causal judgment suggest that causal knowledge may lie at the root of both human and animal learning. All of these empirical findings and theoretical developments prove that animal learning is more complex and intricate than was once imagined. Copyright © 2009 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website.
Copyright © 2009 John Wiley & Sons, Ltd.