Background stimuli and the inter-stimulus interval during pavlovian conditioning

An experiment was carried out to investigate the part played by background stimuli during Pavlovian conditioning. Groups of rats were presented with tone CSs and unavoidable footshock USs. Two components of the inter-stimulus interval, namely CS duration and the duration of a trace interval, were manipulated across groups. Subsequently subjects were tested for their reactions to background stimuli by being re-exposed to the training environment in the absence of both the CS and US. The degree to which rats failed to avoid this environment was found to relate to CS duration by an inverted U curve. The manipulation of the trace interval however did not significantly affect avoidance.     

Electrodermal pavlovian conditioning with prepared and unprepared stimuli

One-trial learning referred to by Guthrie has been suggested to occur in autonomic conditioning, if the conditional stimuli (CSs) are so-called prepared ones. To test this idea, half of 28 subjects were given spider or snake slides as “prepared” CSs, while the remainder were given neutral slides as “unprepared” CSs. A shock was employed as the unconditional stimulus (UCS), with a CS-UCS interval of 8 seconds. Electrodermal activity and probe reaction times were the dependent measures of conditioning, conceived in cognitive, information-processing terms as the learning of the CS/UCS contingency. Evidence for the usual CS/UCS contingency learning emerged in both indicators, and during both acquisition and extinction, but none for one-trial learning, perhaps because the UCS was insufficiently aversive.     

The pavlovian analysis of instrumental conditioning

An account was given of the development within the Russian literature of a uniprocess formulation of classical and instrumental conditioning, known as the bidirectional conditioning hypothesis. The hypothesis purports to offer a single set of Pavlovian principles to account for both paradigms, based upon a neural model which assumes that bidirectional (forward and backward) connections are formed in both classical and instrumental conditioning situations. In instrumental conditioning, the bidirectional connections are hypothesized to be simply more complex than those in classical conditioning, and any differences in empirical functions are presumed to lie not in difference in mechanism, but in the strength of the forward and backward connections. Although bidirectional connections are assumed to develop in instrumental conditioning, the experimental investigation of the bidirectional conditioning hypothesis has been essentially restricted to the classical conditioning operations of pairing two CSs (sensory preconditioning training), a US followed by a CS (backward conditioning training) and two USs. However, the paradigm involving the pairing of two USs, because of theoretical and analytical considerations, is the one most commonly employed by Russian investigators. The results of an initial experiment involving the pairing of two USs, and reference to the results of a more extensive investigation, leads us to tentatively question the validity of the bidirectional conditioning account of instrumental conditioning.     

Hippocampal lesions and pavlovian cardiovascular conditioning

New Zealand albino rabbits received either sham, cortical control, or hippocampal lesions and were subjected to differential Pavlovian conditioning in which tones of different frequencies served as conditional stimuli (CSs), and a brief paraorbital electric shock train served as the unconditional stimulus. Heart rate (HR), blood pressure (BP), and electromyographic (EMG) conditional responses (CRs) were recorded. Animals with cortical and hippocampal damage or animals with cortical damage alone revealed attenuated bradycardiac CRs, but HR CRs of the former two groups did not significantly differ. BP changes were minimal; reliable differences were not obtained between CS+ and CS?. However, these changes consisted of small but reliable depressor responses, which were not affected by either cortical or hippocampal lesions. Few EMG CRs were obtained. These data, combined with those of previous experiments, suggest that forebrain structures may modulate higher level processing of stimulus information, perhaps in terms of assessing the biological significance of such stimulation.     

The conditional emotional response as a model of pavlovian conditioning

Integrative Psychological and Behavioral Science - Many investigators have assumed that the conditional emotional response (CER) with its attendant response measure, response suppression, can be...     

Some recalcitrant views on the role of noncognitive S-R factors in human pavlovian autonomic conditioning

Either implicitly or explicitly, most workers in the last two decades have adopted the (imperialistic) view that conditioning is simply the learning of (cognitive) S-S relationships, and that (noncognitive) S-R factors are irrelevant. I shall remind us of some contrary evidence from human Pavlovian autonomic conditioning (HPAC), consideration of which may spoil our neat cognitive picture (representation?) of the world, but may also lead both to a better understanding of the conditioning phenomenon and to more genuinely useful applications of conditioning principles to behavioral (including psychophysiological) problems.     

Insensitivity to stimulus validity in human pavlovian conditioning

Four experiments investigated the role of information value, or stimulus validity, in human electrodermal conditioning. Conditioned stimuli (CSs) were long, variable duration (10-50-sec) slides or sounds, the unconditioned stimulus (US) was shock, and the primary measures were change in tonic skin conductance level and self-report expectancy of shock. In Experiment 1 electrodermal responding to a target stimulus was marginally lower in a blocking group than in a superconditioning group. This difference failed to occur in Experiment 2, despite increased sensitivity of the electrodermal measure. Explicit instructions to pay attention to the relationship between each stimulus and shock improved learning, but did not lead to group differences (Experiment 3). In Experiment 4 expectancy ratings in a blocking group were lower than in an overshadowing group, but no electrodermal differences occurred. The results were interpreted in terms of non-additive learning processes such as occasion-setting, in addition to a general lack of transfer of learning about a stimulus from one context to another (element to compound or vice versa). It was suggested that sensitivity to stimulus validity might be observed if conditioning were embedded in a causally familiar task, as in contingency judgement research.     

Aversion conditioning and enhanced neophobia: role of test stimuli

In Experiment 1, 100 rats (Rattus norvegicus) received 10% sucrose or 5% casein hydrolysate followed, after 10 min, by a LiCl or saline injection or, after 12 h, by a LiCl injection. Subsequently, rats received aversion testing to the CS or neophobia testing to the opposite novel flavor. Aversion effects were reliably greater to casein than to sucrose. However, conditioning with sucrose yielded a reliably greater increase in neophobia to casein (relative to controls) than conditioning with casein yielded to sucrose. In Experiment 2, 60 rats received distilled water followed, after 10 min, by LiCl or saline injection or, after 12 h, by LiCl injection. Aversion effects occurred to distilled water. Neophobia testing to casein and sucrose showed that, relative to controls, neophobia increased reliably more to casein. The results of Experiments 1 and 2 were not attributable to differences in baseline intakes between casein and sucrose flavors. Together, these experiments indicated that the demonstration of conditioning-enhanced neophobia may depend more on the characteristics of the neophobia test flavor than on the strength of aversion established because of CS characteristics.     

Differential acetylcholine release in the prefrontal cortex and hippocampus during pavlovian trace and delay conditioning

Pavlovian trace conditioning critically depends on the medial prefrontal cortex (mPFC) and hippocampus (HPC), whereas delay conditioning does not depend on these brain structures. Given that the cholinergic basal forebrain system modulates activity in both the mPFC and HPC, it was reasoned that the level of acetylcholine (ACh) release in these regions would show distinct profiles during testing in trace and delay conditioning paradigms. To test this assumption, microdialysis probes were implanted unilaterally into the mPFC and HPC of rats that were pre-trained in appetitive trace and delay conditioning paradigms using different conditional stimuli in the two tasks. On the day of microdialysis testing, dialysate samples were collected during a quiet baseline interval before trials were initiated, and again during performance in separate blocks of trace and delay conditioning trials in each animal. ACh levels were quantified using high-performance liquid chromatography and electrochemical detection techniques. Consistent with our hypothesis, results showed that ACh release in the mPFC was greater during trace conditioning than during delay conditioning. The level of ACh released during trace conditioning in the HPC was also greater than the levels observed during delay conditioning. While ACh efflux in both the mPFC and HPC selectively increased during trace conditioning, ACh levels in the mPFC during trace conditioning testing showed the greatest increases observed. These results demonstrate a dissociation in cholinergic activation of the mPFC and HPC during performance in trace but not delay appetitive conditioning, where this cholinergic activity may contribute to attentional mechanisms, adaptive response timing, or memory consolidation necessary for successful trace conditioning.     

Perseveration of cardiac-rate effects in the rhesus monkey following pavlovian conditioning

The effects of Pavlovian conditioning on diurnal cardiac rate were studied in four rhesus monkeys. A three-hour conditioning period, consisting of 18 CS-UCS pairings with UCS an aversive tail-shock, produced cardiac-rate elevation which persisted for as long as 12 hours after the session.     

Direct and continuous measurement of relational learning in human pavlovian conditioning

Three experiments were conducted employing a continuous measure of conditional stimulus/unconditional stimulus (CS/US) contingencies as perceived by the subject (i.e., subjective contingency or SC). It is argued that direct measurement of relational learning, as indexed by SC, can lead to a better understanding of Pavlovian conditioning processes. The first two experiments applied this approach to a methodologic controversy, raising the debate from a procedure-based argument to testing what the subject actually learns about CS/US relationships. While the issue was not resolved, testable hypotheses for future research were generated from the data. The third experiment contrasted the contingency stimulus-stimulus (S-S) account of Pavlovian conditioning with an earlier stimulus-response (S-R) continguity-reinforcement account. In this experiment, both SC and skin resistance were measured. Evidence for the existence of both cognitive-propositional and response-learning processes in conditioning was obtained.     

Body temperature as a conditional response measure for pavlovian fear conditioning

On six days rats were exposed to each of two contexts. They received an electric shock in one context and nothing in the other. Rats were tested later in each environment without shock. The rats froze and defecated more often in the shock-paired environment; they also exhibited a significantly larger elevation in rectal temperature in that environment. The rats discriminated between each context, and we suggest that the elevation in temperature is the consequence of associative learning. Thus, body temperature can be used as a conditional response measure in Pavlovian fear conditioning experiments that use footshock as the unconditional stimulus.     

Hemispheric asymmetry and electrodermal activity in orienting and pavlovian conditioning paradigms

Three experiments on lateralization of electrodermal orienting and conditioned behavior are reported. The basic findings show effects of hemispheric asymmetry on initial magnitude and rate of habituation of phasic stimulus-elicited electrodermal responses. In summary, responses to verbal stimuli repeatedly flashed to the right visual half-field are larger than corresponding responses in the left half-field. Similarily, spatially relevant stimuli initially presented to the left half-field result in larger responses than when the same stimuli are repeatedly presented in the right half-field. In the auditory modality, data show asymmetrical control of responding to verbal material in a dichotic conditioning paradigm with greater resistance to extinction when the conditioned stimulus is initially fed only to the left hemisphere as compared to when it is fed only to the right hemisphere. It is argued that the present approach taps on basic mechanisms for the lateralization of attentional and associative functions.     

Pavlovian conditioning with proximal stimuli

This experiment was conducted with the objective of demonstrating that the effective stimuli in Pavlovian Conditioning are not environmental stimuli but internal physiological processes elicited by environmental input (proximal stimuli). In order to achieve the objective, afterimages in color vision were used: looking at a diffuse lightened circle after seeing a red circle yields an image of a green circle. A differential conditioning paradigm with two sequential compounds was run. In one group (G⁺B^?: n₁=10), a red circle followed by a green circle was paired with shock, whereas a red circle followed by a blue circle remained unpaired. A second group (G^?B⁺: n₂=10) received red-blue paired trials and unpaired red-green trials. Immediately after that training, subjects were tested with a new, never trained sequential compound: a red circle followed by a diffuse lightened circle. Furthermore, they were tested with the already trained compounds. Taking the environmental point of view, the never trained stimulus should elicit an orienting response lying inbetween the excitatory reaction to the paired stimulus and the inhibitory reaction to the unpaired stimulus. From the proximal point of view, the diffuse light should elicit an excitatory reaction in group G⁺B^? and an inhibitory reaction in group G^?B⁺. Electrodermal conditioned anticipatory and omission responses were measured. The results supported the proximal hypothesis. Hence, defining input in environmental terms may be the wrong way. Instead, in conceptualizing the stimulus in conditioning, the following should be considered: the processing organism itself is creating the effective stimuli.     

A model of pavlovian conditioning: Variations in representations of the unconditional stimulus

We present a model of Pavlovian excitatory conditioning in which associative strength and malleable central representations of unconditional stimuli determine the strength of conditional responding. Presentation of a conditioned stimulus acts through an experientially determined associative bond to activate a representation of the unconditional stimulus. The activation of the representation produces a conditioned response. A striking feature of the model is its ability to describe changes in conditioned response magnitude in terms of alterations of representations of the unconditional stimulus. Another is its acknowledgement of the capacity of associative bonds to survive behavioral extinction. The model describes much of the data reported from excitatory conditioning experiments and predicts counterintuitive phenomena. This work was supported by Natural Sciences and Engineering Research Council grant #U0262 awarded to the first author.