A Review of the Empirical Laws of Basic Learning in Pavlovian Conditioning

Abstract

Contemporary learning research has provided multiple paradigms that have benefited not only researchers in the field, but also applied theorists and practitioners. However, the emphasis on theory development has made the learning literature almost impenetrable to nonexperts. In the present paper, we attempt to summarize not the different theoretical perspectives that have been proposed to explain different instances of learning , but the empirical relationships that testing of such theories has uncovered. Because the empirical relationships we summarize here hold across preparations and species, we suggest that such relationships should be understood as the empirical laws of basic learning. The focus of our review is the Pavlovian conditioning tradition, but most of these relationships also apply to instrumental learning and causality learning. We hope that the relatively novel organization we present here helps researchers and practitioners to directly incorporate these empirical principles into their current theoretical framework, whatever it may be. The study of behavioral change can be traced as far back as civilization itself. The works of Aristotle, Plato, Kant, and Hume (among others) reflect the philosophical roots of the study of behavior change. However, the rigorous scientific study of behav-ioral change started only about 120 years ago with the work of Ebbinghaus (1885/1913), Thorndike (1898), and Pavlov (1927), among others. These early scientific endeavors were largely driven by empirical phenomena, although theorizing was also evident. For example, Pavlov suggested that different stimuli were represented as "centers" in the brain, which were linked either by nature (as in the case of an unconditioned stimulus, US, and an unconditioned response, UR) or by experience (as in the case of a conditioned stimulus, CS, and a US). Similarly, Thorndike's (1911) Strong Law of Effect posited that there is no learning without reinforcement because reinforcers are required to engage the learning mechanism. A problem with these theoretical interpretations was that many researchers viewed Pavlov's and Thorndike's theoretical accounts as definitions of learning. Thus, Pavlov's stimulus substitution view cemented the belief that, in classical conditioning, learning occurs only if the US can elicit a response without learning, overlooking phenomena such as second-order conditioning (e.g., Pavlov, 1927) and sensory precondition-ing (Brogden, 1939; see below). Similarly, Thorndike's (1911) Strong Law of Effect cemented the belief that no learning could occur in the absence of reinforcement, which obviates situations in which learning occurs without apparent shifted reinforcement (e.g., song learning by birds). Thus, on many occasions, the focus from the