International Journal of Comparative Psychology

These introductory comments for the special issue on Pavlovian conditioning begin with a brief review of Rescorla’s (1988) influential paper outlining how trends in the study of Pavlovian conditioning changed the dominant view from an analysis of simple associations to an information seeking approach. I argue that current research trends in Pavlovian conditioning suggest possible ways of integrating the information-seeking approach with a more embodied, evolutionary approach. I briefly consider four trends reflected in the following papers that potentially add to our appreciation of how ecology and evolution are involved in conditioning: (1) Exploring an adaptive basis for Pavlovian conditioning; (2) Clarifying the relation of Pavlovian and operant conditioning; (3) Relating preexposure and sensory preconditioning to the organization of exposure learning; and, (4) Integrating models of Pavlovian conditioning.

Two experiments with rats examined latent inhibition of unconditioned stimulus (US) signal value. In Experiment 1, latent inhibition (LI) rats showed attenuated conditioning, compared to control (C) rats, when a single food pellet, delivered 10 min into a session, was followed by three additional pellets. In preexposure, one pellet had been delivered 10 min into the session (in Group LI), or placed into the magazine at the beginning of the session (in Group C). Experiment 2 replicated Experiment 1 and also showed that latent inhibition of US signal value resulted after conditioned stimulus (CS) - US training. Results from Experiment 2 suggest that, in Pavlovian conditioning, subjects learn a CS-US association and also learn that a US signals a subsequent US-free period. Implications for theories of latent inhibition are considered.

Three experiments examined the role of CS (conditioned stimulus) duration in the unconditioned stimulus (US) preexposure effect. Rats received preexposure to unsignalled food pellets that were delivered on a fixed-time 90-s schedule and magazine entry responses were recorded. In Experiment 1, there was no evidence of retardation of conditioning to a 15- or 60-s CS when rats that received US preexposure were compared to unexposed control groups. Experiment 2 revealed a US-preexposure effect with a 90-s CS, but only when the rats were given a 31.5-min wait in the experimental chambers prior to the onset of US exposure. In Experiment 3, it was discovered that the magnitude of US preexposure was related to CS duration, with longer CS durations demonstrating progressively greater retardation in conditioning. The results are discussed in light of recent time-based accounts of classical conditioning.

Experiments designed to study latent inhibition typically use as a control condition a group of animals preexposed to the training context, but not to the conditioned stimulus (i.e., the context control). Experiments using the rat autoshaping preparation demonstrate that nonreinforced preexposure to the context facilitates subsequent conditioning to a discrete stimulus, particularly with large reinforcers (Experiment 1) and dramatically enhances performance under the unfavorable conditions posed by massed training (Experiment 2). Furthermore, it is nonreinforced preexposure to the training context, and not to a nontraining context, that enhances autoshaping performance (Experiment 3). The facilitatory effect of nonreinforced preexposure to the training context questions the exclusive use of the context control in latent inhibition experiments and suggests that findings based on such comparisons need to be reevaluated.

Pavlovian associative processes appear to be intimately involved in the acquisition of simultaneous discriminations by pigeons. We have found evidence that in a simultaneous discrimination, value transfers from the positive stimulus (S+) to the negative stimulus (S-) and the basis of that transfer appears to be the higher-order association of the S- with the reinforcer, by way of the S+. Furthermore, the association between the S+ and the S- appears to be bidirectional, occurring in the form of a within event association. In addition, it appears that when pigeons have extended experience with the consequences of responding to the Sstimulus, contrast (the opposite of value transfer) develops between the two (e.g., increasing the value of one, decreases the value of the other). Finally, I suggest that versions of simultaneous discriminations may provide a useful model of several Pavlovian conditioning phenomena including, higher-order conditioning, withinevent conditioning, postconditioning devaluation effects, inhibitory conditioning, potentiation, and perhaps also overshadowing.

Pigeons were studied on a two-component multiple schedule in which key pecking was reinforced on a variable interval (VI) 2-min schedule in both components. In separate phases additional food was delivered on a variable-time (VT) 15-s schedule (response independent) or a VI 15-s schedule (response dependent) in one of the components. In addition to rate, duration of key pecks was measured in an attempt to differentiate the biological and economic effects on key pecking. When components alternated frequently (every 10 s), all pigeons key pecked at a much higher rate during the component with the additional food deliveries, whether response dependent or independent. When components alternated infrequently (every 20 min), pigeons key pecked at high rates at points of transition into the component with the additional food deliveries. Rate of key pecking decreased with time spent in the 20-min component when the additional food was response independent whereas rate of pecking remained elevated when the additional food was response dependent. The additional food deliveries, whether response-independent or response-dependent, however, had no consistent effect on the pigeon's key-peck duration. That is, there were no systematic or reliable shifts in peck duration as would be predicted if short-duration pecks were biologically based. Despite the fact that we were unable to “tag” the biological effect in terms of key-peck duration, the finding that the delivery of response-independent food has different, but predictable effects on responding suggests that animal learning principles can be integrated with species-typical, biological considerations without the need to propose constraints that limit general laws of learning.

We explored whether the opportunity to learn about the arrival of food, a scarce resource, might facilitate subordinates’ food-stealing attempts―and dominants’ strategies to prevent stealing―in two species, namely green anole lizards (Anolis carolinensis) and firemouth cichlid fish (Thorichthys meeki). Following establishment of a dominance hierarchy, each group was randomly assigned to one of two treatment conditions, either a learning treatment in which a signal preceded the appearance of food, or a control treatment in which both signal and food appeared at randomly determined times. Dominants and subordinates of both species learned to anticipate food arrival using learned cues, which in turn changed their social dynamic. In anoles, learning enabled subordinates to steal food more effectively, and both dominants and subordinates to capture it more quickly. Alternatively, learning enabled dominant cichlids to protect their food more successfully by mounting a more aggressive defense. These results suggest that learning could play an important role in the competition for a scarce resource amongst many animals that form dominance hierarchies.

The literature on human sexual deviations is replete with case studies and behavior therapies that demonstrate successful treatment of maladaptive sexual behavior acquired through Pavlovian conditioning. Ironically, the empirical research with humans in this area is limited and plagued by methodological confounds. Nonhuman animal studies have provided some information about the mechanisms of the role of Pavlovian conditioning in sexual arousal/behavior but have not been well coordinated with clinical research. The present paper serves to highlight the major empirical findings and theories of these two disparate bodies of literature, briefly discuss how they have emerged over time, and finally discuss their overlap and make connections between animal and human research on sexual arousal.

An appetitive conditioning experiment with rats assessed the predictions of a new performance-based account of associative learning called the computational comparator hypothesis (Murphy, Baker, & Fouquet, 2001a, 2001b). A between-subjects design was used in which the stimuli A or B were separately trained either as excitors or as inhibitors prior to and during a relative validity treatment. During relative validity training, X was reinforced when presented with A but was not reinforced when presented with B. In test, responding to X in extinction was lower when A or B had been separately trained as excitors than as inhibitors. Thus, contrary to the computational comparator hypothesis, responding to X was affected by more than just inhibitory training of A. Better fits to the data were obtained by Pearce’s configural theory (Pearce, 1987, 1994) and the extended comparator hypothesis (Denniston, Savastano, & Miller, 2001) than by the elemental theory of Rescorla and Wagner (1972) or the computational comparator hypothesis.

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.