Michaela Macrae

Summation and configuration between and within sensory modalities in classical conditioning of the rabbit

Three experiments examined “atomistic” and “configurai” processes in stimulus compounding using the rabbit’s conditioned nictitating membrane response. Two conditioned stimuli (CSs) were trained separately and then tested together in a compound. Animals trained with CSs from different modalities—namely, tone and light—showed summation in both acquisition and extinction. That is, the probability of a response to the compound could be predicted by the statistical sum of responding to the CSs. In contrast, animals trained with CSs from the auditory modality, tone and noise, showed a level of responding to the tone + noise compound that was the same as that of the CSs, well under the level predicted by the statistical sum of responding to the CSs. In conclusion, atomistic processes appear to predominate in cross-modal compounding. Configurai processes may occur during compounding within the auditory modality, but atomistic alternatives—namely, common elements and selective attention hypotheses—may be able to explain the results.

Fundamental Behavioral Methods and Findings in Classical Conditioning

This chapter is intended to provide a solid foundation in the methods and findings of classical conditioning at a behavioral level. We take readers from an introduction to the basics of classical conditioning through to its more complex and recent findings that appear related to higher-order processes that are commonly labeled as attention, perception, and even cognition. Many textbook descriptions of classical conditioning give the mistaken impression that it is an area of completed science. In fact, the methods of classical conditioning have continued to evolve, and the range of important phenomena has continued to expand. Although this chapter primarily describes the empirical methods and outcomes of classical conditioning, we introduce important theoretical principles along the way. These principles have proven crucial in organizing research findings and in linking classical conditioning to other learning phenomena. In addition, our introduction to behavioral theory should help the reader place the phenomena described in this chapter in the context of the theories described in more detail in the next chapter (Brandon, Vogel, & Wagner, this volume).

Savings in animal learning: Implications for relapse and maintenance after therapy*

Savings are the proactive influences of prior learning on later learning even when the original behavior has been extinguished or forgotten. Therapists can capitalize on savings both to understand the sources of relapse and to maintain and extend therapeutic outcomes in the clients ordinary environment. This paper reviews recent findings from our laboratory that savings in animal learning are more extensive than previously thought. Not only can responding to an extinguished stimulus reappear spontaneously, but reacquisition of a conditioned response can also occur very rapidly. Moreover, once conditioning has taken place with one stimulus, subsequent acquisition of the same response to a completely novel stimulus will be accelerated. At the same time as this novel acquisition, the response to the original, extinguished stimulus also shows recovery that is distinct from generalization. We propose a neural network model that explains a wide range of savings and therefore illuminates a common mechanism that underpins both relapse and maintenance after therapy.

Savings after extinction in conditioning of the rabbit’s nictitating membrane response

The present experiments examined two forms of savings after the extinction of a conditioned response (CR) in the rabbit nictitating membrane preparation. Each experiment entailed three groups. First, a reacquisition (RAQ) group received initial conditioned stimulus-unconditioned stimulus (CS—US) acquisition, followed by CS-alone extinction, and then CS—US reacquisition with the same stimulus. Second, a cross-modal acquisition (CMA) group received initial acquisition and extinction with one stimulus but received its final stage of training with a stimulus from another modality. Third, a naive acquisition group (designated as REST) received only the final stage of CS—US training. In all three groups, tone and light were used as CSs in a counterbalanced fashion. In addition, the experiments tested whether the manipulation of contextual factors—namely, trial spacing and the number of trials per session—could influence the rates of acquisition in Groups RAQ and CMA after extinction. The experiments demonstrated that (1) reacquisition of the CR to the original CS was very rapid relative to Group REST, (2) cross-modal acquisition was also rapid relative to Group REST, and (3) in Group CMA, tests of the original CS showed concurrent recovery, which is a new phenomenon and is distinct from spontaneous recovery. However, the relative rates of acquisition after extinction appeared constant across the contextual manipulations. The results are discussed with respect to the relative stability of excitatory and inhibitory learning, as well as two alternative theories of savings after extinction.

Learning to Learn: Real-Time Features and a Connectionist Model

Two experiments used classical conditioning to examine transfer of response features specific to the warning interval between a conditioned stimulus (CS) and an unconditioned stimulus (US). Rabbits were given initial training with a stimulus (CSA) in one modality (tone) at a designated interval (e.g., 200 ms). In a second stage, the conditioned response (CR) to CSA was extinguished. Finally, training was shifted to a new stimulus (CSB) in another modality (light) at a new interval (e.g., 400 ms). Compared to rest controls, there was an enhanced rate of CR acquisition to CSB and a tendency for early CRs to CSB to reflect the CSA-US interval. However, the extinction procedure and the change in CS-US interval together reduced these two aspects of transfer across stimulus modalities. The findings are discussed in terms of their implications for theories of cross-modal transfer. A layered network with real-time features is offered.

Real-time processing of serial stimuli in classical conditioning of the rabbit's nictitating membrane response.

Real-time models contend that a conditioned stimulus (CS) gives rise to a cascade of hypothetical stimuli that govern conditioned responses (CRs) on a moment-by-moment basis. Experiments with the rabbit nictitating membrane response successfully extended these models to external stimuli. CSs were trained in sequence with an unconditioned stimulus (CSA-CSB-US). When the CSA-CSB interval was shortened, the CR was compressed; when the CSA-CSB interval was lengthened, the CR was broadened. Peaks appeared at 2 places, namely, 1 following CSA by a period equal to its CS-US interval and another following CSB by its CS-US interval. Outside the sequence, the individual CSs evoked CRs located between their respective CS-US intervals. When, however, the 2 CSs were trained separately, the CRs were appropriate to their respective CS-US intervals when tested alone or in sequence. The results are discussed in terms of the J.E. Desmond and J.W. Moore (1988) and S. Grossberg and N.A. Schmajuk (1989) models.

MK801 impairs acquisition and expression of conditioned responses in the rabbit nictitating membrane preparation

MK801 is a noncompetitive antagonist to N-methyl-D-aspartate (NMDA) receptors. MK801 (0.1 mg/kg IV) was given to rabbits during classical conditioning of their nictitating membrane response. Administration of MK801 before each training session impaired acquisition of a conditioned response (CR). When MK801 administration was suspended, responding remained at a low level. Control animals were given either MK801 after each training session (Experiment 1) or saline before each session (Experiment 2). The control animals showed high levels of CR acquisition. When the control animals were given the MK801 before a session, they showed a large deficit in responding. Responding returned to its former level when the original control condition was reinstated. In all the animals, tests for motor deficits caused by MK801 proved negative; the magnitude of the UR was not influenced by MK801 at either the beginning or end of training. In conclusion, it appears that MK801 impairs both the formation of associative linkages and the performance of established CRs. A reduction in CS salience caused by MK801 is the most parsimonious explanation of the data. There is a more complex, two-factor alternative that contends that MK801 directly hindered associative formation in the subjects trained with that drug and produced a state-dependent generalization decrement in responding when introduced to the control subjects.

Classical conditioning of the rabbit nictitating membrane response can be fast or slow: Implications for Lennartz and Weinberger’s (1992) two-factor theory

Classical conditioning of the rabbit’s nictitating membrane (NM) response usually requires several dozen trials for the first conditioned response (CR) to appear. However, as the number of trials is reduced to one per session, the rate of acquisition increases progressively, and the first CR appears in less than a dozen trials. This large and systematic variation in the rate of conditioning challenges recent conclusions by Lennartz and Weinberger (1992). They use the rabbit NM preparation as an example of a slow-conditioning, “specific” system that is distinct from a fast-conditioning, “nonspecific” system, such as heart rate.

MK-801 protects conditioned responses from extinction in the rabbit nictitating membrane preparation

MK-801 is a noncompetitive antagonist to N-methyl-d-aspartate (NMDA) receptors. MK-801 was given (0.05 or 0.10 mg/kg i.v.) to rabbits during extinction of a well-established conditioned response (CR) in the nictitating membrane preparation. The drug administration produced an immediate deficit in CR performance during extinction. However, when MK-801 administration was suspended, CRs reappeared immediately and showed no evidence of the previous extinction treatment. In addition, we confirmed previous findings that MK-801 impairs both the acquisition and the expression of CRs during CS—US training. A reduction in CS processing caused by MK-801 is the most parsimonious explanation of the data. There are also two-factor alternatives, which contend that MK-801 directly hinders associative formation and either directly blocks CR output or produces a state-dependent generalization decrement.

Conditioning and reflex modification of the rabbit nictitating membrane response using electrical stimulation in auditory nuclei.

Electrical brain stimulation (EBS) was applied to four nuclei in the auditory system, namely, the cochlear nucleus (CN), superior olive (SO), inferior colliculus, and medial geniculate. EBS was also applied to the pontine nuclei, which are the main relays for transmitting auditory conditioned stimuli (CSs) into the cerebellar pathways for conditioning of the nictitating membrane response (NMR). EBS of the CN, but no other site, yielded reflex modification, which was an increase in the unconditioned NMR to an airpuff unconditioned stimulus (US) when preceded by EBS. Throughout the experiment, EBS of the SO produced a distinctive distribution of NMRs, in which a high proportion had latencies less than 50 ms. When EBS was repeatedly paired with the airpuff US, conditioned responses (CRs) were acquired to comparable levels across all sites. At each site, response likelihood was an increasing function of the EBS parameters of pulse amplitude, pulse frequency, and pulse width. Combined with anatomical findings, these results indicate that multiple encodings of an auditory CS are sent to the pathways for the NMR.