The effectiveness of electric shock and foul odor as unconditioned stimuli in classical aversive conditioning

In a partial replication of an earlier study, eighty undergraduate volunteers were assigned to the eight cells of a three between- and two within-group experimental design. One factor was the nature of the UCS—faradic shock or a carefully-timed blast of pyridine vapor; the second factor was the UCS contingency—the UCS being contingent upon the CS or randomly interspersed; the third factor was the nature of the CS—all CSs were compounds of colored, flavored liquids, with the discriminable dimension being either color or taste. The two within-subjects factors were the successive presentation of either the CS+ of the CS? over trials in a standard classical conditioning format. The outcome measures were sip-size, order of preference, and semantic differential ratings. It was found that the foul odor UCS resulted in no aversive conditioning with either color or taste cues. Where shock was the UCS, color, but not taste, became aversive. While lending no direct support to cue-appropriateness concepts, the results reveal the complexity of cue utilization in human aversive conditioning.     

Reexamination of contextual conditioning with massed versus distributed unconditioned stimuli

Sprague-Dawley rats were placed in the black compartment of a 2 compartment choice apparatus and received a series of unsignaled footshocks at fixed intertrial intervals (ITIs), with ITI duration varied across groups. Contextual conditioning was assessed using place preference and freezing tests. In Experiments 1 and 3, time spent in the unshocked, white compartment in a preference test decreased monotonically with increasing ITI. In Experiment 2, less freezing occurred in the 3-s than in the 60-s groups. An inverted U-shaped relationship between ITI and freezing emerged when a full range of ITIs was used in Experiment 3. The results have implications for the learning-performance distinction and suggest that short ITIs may promote contextual conditioning.     

Evaluative conditioning in the picture-picture paradigm with random assignment of conditioned stimuli to unconditioned stimuli

Human participants were allocated to 1 of 3 groups. In the conditioning group, each conditioned stimulus (CS)-unconditioned stimulus (US) pair was presented 7 times during the acquisition phase. Participants who were assigned to the extinction group saw 5 additional presentations of each CS in isolation after the 7 presentations of each CS-US pair. In the latent inhibition group, the CS-only trials were presented before the CS-US trials. Overall, a significant evaluative conditioning effect was observed. This effect cannot be dismissed on the basis of the arguments developed by A. P. Field and G. C. L. Davey (1997, 1998, 1999), and the results thus provide strong evidence for the associative nature of evaluative conditioning. The results are also in line with other findings, which showed that evaluative conditioning is resistant to extinction.     

Blocking and unconditioned response diminution in human classical autonomic conditioning

Four experiments examined blocking and UR diminution in human SCR conditioning. In Experiment 1, CS_X was conditioned in compound with previously conditioned CS_A, in one group, or in a compound with another novel stimulus, CS_N, in an additional group. UR diminution occurred, but there was no post-compound difference in CRs in the two groups and no difference in responding to CS_X and CS_A following equal training on each, i.e., no blocking. The correlation between blocking and UR diminution was not significant. In Experiment 2, two groups received a blocking procedure, but one was tested on CS_X and one on CS_A. UR diminution occurred, but there were no post-compound CR or UR differences. There was again no within-subjects blocking effect. The correlation between blocking and UR diminution was not significant, but this correlation was significant when data from Experiments 1 and 2 were combined. In Experiment 3, a differential conditioning procedure was used, followed by reinforcement of two compounds, one with CS_A+ and one with CS_A-. One subgroup was tested on CS_A+ and CS_A- with reinforcement; another was tested without reinforcement. UR diminution occurred, and there was significant blocking, but only after two nonreinforced tests. Blocking and UR diminution were significantly correlated. In Experiment 4, four groups received compound conditioning after initial training with CS_A. The compound contained CS_X and CS_A for three groups and two novel CSs for the fourth. Ten nonreinforced test trials were run. The three blocking groups received two CS_As plus eight CS_Xs, four CS_As plus six CS_Xs, or all CS_Xs. The fourth group received ten nonblocked CS_Xs. CR magnitude to blocked CS_X was significantly smaller than to nonblocked CS_X during the last six test trials, but not initially. Blocking and UR diminution were not correlated, in disagreement with the first three studies. The results indicated that repeated nonreinforced test trials are needed for blocking to be observed in this preparation. The proposition that blocking and UR diminution are both due to reduced processing of the US received only partial support.     

Blocking and unconditioned response diminution in human classical autonomic conditioning

This paper summarizes the results of three experiments on blocking and unconditioned response diminution in human SCR conditioning. Recent theories of conditioning propose that reduced processing of the unconditioned stimulus due to conditioning results in reduced unconditioned response magnitude and in blocking of conditioning of a second conditioned stimulus when it is in compound with the previously conditioned stimulus. In these experiments, clear evidence of diminution of the unconditioned response was obtained in all three studies, but blocking was found only in the third study, which employed a within-subject design and in which the blocking was observed only after at least one extinction trial on both the blocked and nonblocked stimuli. Order of testing was not a factor in this delayed blocking effect. These results do not support the view that blocking occurs because of reduced processing of the unconditioned stimulus in the unconditioned response diminution sense.     

Evaluative conditioning without directly experienced pairings of the conditioned and the unconditioned stimuli

Evaluative conditioning (EC) is the valence change of a stimulus (conditioned stimulus, CS) that is due to the previous pairing with another stimulus (unconditioned stimulus, US). We investigated whether EC can occur also when the CS-US pairings are not experienced directly by the participant but are implied by other events that the participant encounters. In two experiments, positive USs were presented in some trials and negative USs in other trials. Afterwards, participants were given information from which it was possible to conclude that CSs were covertly present during these trials. Finally, the valence of these CSs was registered using both implicit (Implicit Association Test, affective priming) and explicit measures (valence ratings). In line with the assumption that EC effects can be based on CS-US pairings that are not directly experienced, the valence of the CSs changed in the direction of the US with which they were covertly paired. This effect was observed both on explicit and on implicit measures. We argue that several aspects of our results are in line with propositional models of EC and fit less well with association formation models.     

Evaluative conditioning without directly experienced pairings of the conditioned and the unconditioned stimuli

Evaluative conditioning (EC) is the valence change of a stimulus (conditioned stimulus, CS) that is due to the previous pairing with another stimulus (unconditioned stimulus, US). We investigated whether EC can occur also when the CS–US pairings are not experienced directly by the participant but are implied by other events that the participant encounters. In two experiments, positive USs were presented in some trials and negative USs in other trials. Afterwards, participants were given information from which it was possible to conclude that CSs were covertly present during these trials. Finally, the valence of these CSs was registered using both implicit (Implicit Association Test, affective priming) and explicit measures (valence ratings). In line with the assumption that EC effects can be based on CS–US pairings that are not directly experienced, the valence of the CSs changed in the direction of the US with which they were covertly paired. This effect was observed both on explicit and on implicit measures. We argue that several aspects of our results are in line with propositional models of EC and fit less well with association formation models.     

Reflections on human pavlovian decelerative heart-rate conditioning with negative tilt as US: Alternative approaches

The negative-tilt preparation that has been reported since the late seventies is a specific form of Pavlovian conditioning that is of scientific interest and has potential applications. In this paper I reflect on the usefulness, to the development of this preparation, of two approaches to Pavlovian conditioning. One approach is the older S-R learning, stimulus-substitution paradigm exemplified by learning texts of the sixties. The other is the modern, Tolman-like view, according to which the phenomenon of Pavlovian conditioning is “now described as the learning of relations among events so as to allow the organism to represent its environment.” The three assumptions encapsulated by this approach are: (a) that only CS-US contingency relations are learned; (b) that teleological modes of explanations are adequate; (c) that the representational theory of knowledge is sound. Concerning Pavlovian conditioning in general, questions been raised in the literature for all three assumptions; they have not been adequately answered. Regarding the specific problem of developing the human Pavlovian heart-ratedecelerative conditioning with negative tilt as the US, I suggest that the cognitive approach has been much less helpful than the older, S-R, stimulus-substitution paradigm. Nevertheless, other literature clearly indicates that the cognitive, S-S approach has generated considerable interest and research, especially in preparations like the conditioned emotional response (CER), which are CS-IR ones in the sense that the effects on the CR are assessed indirectly through measuring an indicator or instrumental response (IR). Finally, even in CS-CR preparations like human GSR conditioning, it is important to study the cognitive, S-S learning process through using such dependent variables as continuously assessed subjective CS-US contingency.     

Short-term memory for "surprising" versus "expected" unconditioned stimuli in Pavlovian conditioning.

Rabbits were trained via a Pavlovian eyelid-conditioning regime to respond differentially to a conditioned stimulus (CSR) depending on whether or not that stimulus was preceded several seconds earlier by a preparatory stimulus consisting of an electric shock otherwise employed as an unconditioned stimulus (UCS). Following training, differential responding to CSR varied systematically with the interval between the preparatory stimulus and CSR, consistent with assumptions concerning decay of information in short-term memory. The major finding, however, involved the test effects of announcing the preparatory stimulus by either a conditioned stimulus with which it had otherwise been paired (CS+) or a conditioned stimulus with which it had otherwise been systematically unpaired (CS-). The greater differential responding to the following CSR in the latter case is taken to support the notion that a "surprising" UCS is more likely to be retained (rehearsed) in short-term memory than is an "expected" UCS.     

Reflections on human Pavlovian decelerative heart-rate conditioning with negative tilt as US: alternative approaches.

The negative-tilt preparation that has been reported since the late seventies is a specific form of Pavlovian conditioning that is of scientific interest and has potential applications. In this paper I reflect on the usefulness, to the development of this preparation, of two approaches to Pavlovian conditioning. One approach is the older S-R learning, stimulus-substitution paradigm exemplified by learning texts of the sixties. The other is the modern, Tolman-like view, according to which the phenomenon of Pavlovian conditioning is "now described as the learning of relations among events so as to allow the organism to represent its environment." The three assumptions encapsulated by this approach are: (a) that only CS-US contingency relations are learned; (b) that teleological modes of explanations are adequate; (c) that the representational theory of knowledge is sound. Concerning Pavlovian conditioning in general, questions been raised in the literature for all three assumptions; they have not been adequately answered. Regarding the specific problem of developing the human Pavlovian heart-rate decelerative conditioning with negative tilt as the US, I suggest that the cognitive approach has been much less helpful than the older, S-R, stimulus-substitution paradigm. Nevertheless, other literature clearly indicates that the cognitive, S-S approach has generated considerable interest and research, especially in preparations like the conditioned emotional response (CER), which are CS-IR ones in the sense that the effects on the CR are assessed indirectly through measuring an indicator or instrumental response (IR).(ABSTRACT TRUNCATED AT 250 WORDS)     

Reinforcement and the organization of behavior in golden hamsters: Pavlovian conditioning with food and shock unconditioned stimuli

The effects of Pavlovian conditioned stimuli (CSs) for food or shock on a variety of behaviors of golden hamsters were observed in three experiments. The aim was to see whether previously reported differences among the behaviors produced by food reinforcement and punishment procedures could be accounted for by differential effects of Pavlovian conditioning on the behaviors. There was some correspondence between the behaviors observed to the CSs and the previously reported effects of instrumental training. However, the Pavlovian conditioned responses (CRs) alone would not have predicted the effects of instrumental training. Moreover, CRs depended to some extent on the context in which training and testing occurred. These findings, together with others in the literature, suggest that the results of Pavlovian conditioning procedures may not unambiguously predict what system of behaviors will be most readily modified by instrumental training with a given reinforcer.     

Conditioned response-contingent delays of the unconditioned stimulus in human aversive conditioning.

Four groups of subjects were given either 0. 100, 500, or 1,000 msec delays of the unconditioned stimulus (UCS) contingent upon the occurrence of a conditioned response (CR) and were given a UCS 515 msec after conditioned stimulus (CS) onset when a CR did not occur. A fifth group received standard classical conditioning trials with an interstimulus interval of 515 msec. Overall performance decreased as CR-contingent UCS delay increased, with the classical conditioning group approximating the performance of the group receiving the 100-msec delay. The data were analyzed with the two-phase model of conditioning and the following results were obtained: The duration of Phase 1 of the model increased with contingent delay; operator limits associated with CR trials or with combined CR-CR (CR absent) trials decreased as a function of delay; and operator limits associated exclusively with CR trials were unaffected by the delay. Subjects receiving a contingent delay of 0 msec gave the shortest latency responses and exhibited reliable latency decreases across trials, suggesting an attempt to "beat" the UCS. The results were interpreted as contrary to what would be expected from low-of-effect theories which postulate that reinforcement results from a CR-UCS interaction, although they could be subsumed under a drive or an associative strength theory in which the aversive, or CR-supportive, strength of the UCS is assumed to be negatively correlated with contingent UCS delay.     

Pentylenetetrazole as an unconditioned stimulus for olfactory and contextual fear conditioning in rats

The association of five footshocks with a neutral odor is able to establish an olfactory fear conditioning in rats. The present study sought to investigate whether the systemic administration of pentylenetetrazole (PTZ; 3.75–15 mg/kg) would turn the coffee odor in a conditioned stimulus in the fear conditioning paradigm. The results showed that rats started to display risk assessment and avoidance after PTZ (15 mg/kg)–coffee odor pairing. When three mild footshocks (0.4 mA for 2 s) were delivered during this pairing, the conditioned response exhibited was greater than before. In both cases, however, pretreatment with the benzodiazepine midazolam (MDZ. 0.5 mg/kg i.p.) fully counteracted the expression of these defensive behaviors. Moreover, after being paired with 15 mg/kg of PTZ alone or combined with footshocks, the coffee odor was able to promote a new fear conditioning related to the context where it was re-exposed. The present findings point out the usefulness of PTZ as an unconditioned stimulus to promote fear conditioning to olfactory and contextual cues in rats.