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Abstract
From a functional perspective, Pavlovian conditioning involves learning about conditioned stimuli (CSs) that have a pre-existing relation to an unconditioned stimulus (US) rather than learning about arbitrary or neutral CSs. In addition, the most important product of learning involves changes in how the organism responds to the US, not in how it responds to the CS, because the US is the more biologically relevant stimulus. These concepts are illustrated using examples from a variety of behavioral and physiological situations including caloric intake and digestion, breast feeding, poison-avoidance learning, eyeblink conditioning, sexual conditioning, fear conditioning, aggression, and drug tolerance and sensitization.
Key Words naturalistic conditioned stimuli, ecological learning, object learning, conditioned modifications of unconditioned behavior, adaptive significance of learning
INTRODUCTION
Pavlovian conditioning is one of the oldest and most extensively studied learning paradigms. The paradigm basically involves two stimuli. The unconditioned stimulus (US) elicits vigorous responding without any special prior training, or unconditionally. Because of that, the US originally was labeled the unconditional stimulus (Gantt 1966). In contrast, the conditioned stimulus (CS) elicits little more than an orienting response at first. The effectiveness of the CS depends, or is conditional, upon its pairings with the unconditioned stimulus. Hence, the CS originally was called the conditional stimulus. Learning is identified by the emergence of new responses to the CS, called conditioned responses or CRs. Because the development of conditioned responding depends on the pairing of the CS and US, the learning is considered to involve the establishment of an association between the CS and the US. This has made Pavlovian conditioning a favorite paradigm for the study of associative learning. Staddon (1983), for example, characterized Pavlovian conditioning as "the prototype for all signal learning" (p. 103).
The associative tradition encouraged investigators to use conditioned stimuli that are initially unrelated to, or arbitrary, with respect to the US. In fact, the initial independence of the CS and US has been incorporated into the definition of Pavlovian conditioning. Authors have characterized the CS as "arbitrary" (Bower & Hilgard 1981, p. 49) or "neutral" (Anderson 1995, p. 10; Papini 2002, p. 491; Shettleworth 1998, p. 109; Staddon 1983, p. 102) with respect to the US.
The view that Pavlovian conditioning involves learning about neutral or arbitrary cues that...