Unconditioned Stimulus Intensity Research Articles

Duration of retrograde amnesia induced by tetrodotoxin inactivation of the parabrachial nuclei is inversely related to the intensity of footshock in rat's passive avoidance response

Previous work has demonstrated that in rats post-trial bilateral functional blockade of the parabrachial nuclei by local injection of tetrodotoxin (10 ng in 1 microliter) partially disrupts retention of an overtrained passive avoidance response. The time-course of functional blockade disrupting effects on passive avoidance response has been studied by altering both the acquisition-tetrodotoxin injection interval and footshock intensity as independent variables. When week footshocks (0.8 mA) were delivered, functional ablation of the parabrachial nuclei was still effective when induced up to 8 days after acquisition training. On the other hand, when rats were shocked with the stronger stimuli (1.2 mA), 2 days after acquisition functional ablation was no longer effective. The results are discussed in terms of unconditioned stimulus (US) intensity and engram consolidation.

Analysis of response systems in Pavlovian conditioning reveals rapidly versus slowly acquired conditioned responses: Support for two factors, implications for behavior and neurobiology

A review of the literature on aversive Pavlovian (classical) conditioning was conducted to determine whether various conditioned responses (CRs) develop at the same or at different rates. Statistical analyses revealed a bimodal distribution of the rates of acquisition of various types of CRs. Rapid acquisition (M = 5.7 trials to first consistent CR) occurs for conditioned suppression and changes in galvanic skin response, blood pressure, respiration, pupil size, and heart rate. Slower acquisition (M = 71.3 trials) characterizes nictitating membrane, eyelid, and flexion CRs. Differences in conditioned stimulus intensity, unconditioned stimulus intensity, intertrial interval, and interstimulus interval between the two groups cannot explain the dichotomy. Studies of concurrent measurement of more than one type of CR further support the “fast/slow” CR distinction. The findings support two-factor theories of Pavlovian conditioning. The results are discussed with regard to various two-factor learning theories, and the implications for behavioral and neurobiological studies of learning are considered.

Associative regulation of Pavlovian fear conditioning: Unconditioned stimulus intensity, incentive shifts, and latent inhibition.

Associative regulation of Pavlovian fear conditioning: Unconditioned stimulus intensity, incentive shifts, and latent inhibition.

Associative regulation of Pavlovian fear conditioning: unconditional stimulus intensity, incentive shifts, and latent inhibition.

Conditional stimuli (CS) associated with painful unconditional stimuli (US) produce a naloxone-reversible analgesia. The analgesia serves as a negative-feedback regulation of fear conditioning that can account for the impact of US intensity and CS predictiveness on Pavlovian fear conditioning. In Experiment 1 training under naloxone produced learning curves that approached the same high asymptote despite US intensity. Shifting drug treatment during acquisition had effects that paralleled US intensity shifts. In Experiment 3 naloxone reversed Hall-Pearce (1979) negative transfer using a contextual CS, indicating that conditional analgesia acquired during the CS-weak-footshock phase retards acquisition in the CS-strong-footshock phase. Experiment 5 used a tone CS in both a latent-inhibition and a negative-transfer procedure. Only negative transfer was blocked by naloxone. Therefore, negative transfer but not latent inhibition is mediated by a reduction of US processing.

Effects of MDA, CS intensity, and UCS intensity on the rabbit’s conditioned nictitating membrane response

The first experiment in a previous series of investigations in which we were concerned with assessing the dose effects of (+)-3,4-methylenedioxyamphetamine (MDA) on classical conditioning of the rabbit’s nictitating membrane response revealed an enhancement of conditioning to a light conditioned stimulus (CS) and an impairment in conditioning to a tone CS. A second study revealed that MDA’s effects on conditioning could not be attributed to the drug’s effects on nonas-sociative contributors to response occurrence. Accordingly, in several subsequent investigations we sought to localize MDA’s conditioning effects in the organism’s processing of the CS. These studies revealed that MDA attenuated tone-CS intensity and the tone CS’s unconditioned excitatory properties. The final study in the series revealed that MDA enhanced the frequency of unconditioned response (UCRs) across a range of unconditioned stimulus (UCS) intensities. These simple effects of MDA on the processing of the CS and UCS/UCR would, on the basis of empirical and theoretical considerations, accoount for the drug’s effect on conditioning. As yet, however, an assessment of the possible interactive effects of MDA’s CS and UCS/UCR effects on conditioning has not been made. Accordingly, to provide one means for assessing whether or not MDA interacted with CS and UCS intensity, in the present study we employed a between-groups MDA dosage manipulation and within-group CS and UCS intensity manipulation. Consistent with theoretical expectations was a pattern of responding that yielded a robust MDA dosage × CS intensity × UCS intensity interaction.

Effects of MDA on classical conditioning of the rabbit nictitating membrane response

In Experiment 1, classical conditioning of the rabbit's nictitating membrane response (NMR) was accomplished by pairing tone and light conditioned stimuli (CSs) with a shock unconditioned stimulus (UCS). MDA impaired the acquisition of conditioned responses (CR) to a tone-CS, while significantly enhancing CR acquisition to a light-CS. Experiment 2, employing explicitly unpaired CS, UCS training, revealed no reliable effects of MDA upon nonassociative processes. Subsequent efforts determined if MDA's CR acquisition effects resulted from alterations in sensory processing of the CS, UCS, and/or UCR motor functioning. Specifically, it was determined that MDA: (a) increased the tone-CS intensity threshold for eliciting CRs (Experiment 3); (b) attenuated the tone-induced reflex modification of the unconditioned NMR (Experiment 4); and (c) enhanced UCR frequency at varying UCS intensities (Experiment 5). It was concluded that MDA's effect upon CR acquisition reflected the drug's effects upon CS and UCS/UCR processing and thereby altered the ability of these components of conditioning to enter into associative learning.

A human laboratory test of eysenck's theory of incubation: A search for the resolution of the neurotic paradox

A number of recent attempts have been made by neobehaviorists to resolve the “neurotic paradox” by incorporating a nontraditional learning principle. Eysenck's concept of “incubation” represents one of these attempts and is the subject matter of this paper. Incubation theory states that under certain conditions exposure to a fear-provoking conditioned stimulus (CS) can result in a substained growth of fear. This concept is used to explain extreme avoidance (symptom) maintenance in extinction. To test this theory, three conditions identified by Eysenck and considered critical to the development of incubation were manipulated in a classical conditioning paradigm: unconditioned stimulus (UCS) intensity, duration of CS exposure, and individual differences in neuroticism/introversion. Both physiological and self-report fear measures were taken. Results indicated that, contrary to incubation theory, fear extinguished in all groups. Long durations of CS exposure were found to be more effective than brief exposure in reducing fear of highly fearful subjects. Clinical implications for therapies using fear exposure such as flooding and implosion were discussed, as well as the resolution of the neurotic paradox via established learning principles.

Anaphylactic shock-induced conditioned taste aversion: II. Correlation between taste aversion and indicators of anaphylactic shock

Previous studies (V. J. Djurić, B. M. Marković, M. Lazarević, & B. D. Janković, 1987, in B. D. Janković, B. M. Marković, & N. H. Spector (Eds.), Neuroimmune interactions, pp. 561–568, New York: New York Acad. Sci.; B. M. Marković, V. J. Djurić, M. Lazarević, & B. D. Janković, 1988, Brain Behav. Immun. 2, 11–23) have shown that rats learn to associate the taste of saccharin with the induction of anaphylactic shock, thus exhibiting conditioned taste aversion (CTA) toward an otherwise preferred saccharin solution. The present experiment investigates the effect of unconditioned stimulus intensity (the amount of antigen used for the induction of shock) on CTA. Rats were sensitized to ovalbumin and subjected to a conditioning trial in which the conditioned stimulus (CS; saccharin solution given orally) signaled the presentation of the unconditioned stimulus (US; shocking doses of ovalbumin ranging from 0.5 to 3 mg given intraperitoneally). Behavioral signs, hematocrit, and rectal temperature were used for evaluation of anaphylactic shock. Twenty-four hours after the conditioning trial, rats were subjected to a two-bottle preference test between saccharin solution and water. Multiple regression statistical analysis revealed significant correlations among saccharin preference ratio, dose of antigen used for the induction of shock, behavioral signs of shock, rise in hematocrit, and fall in rectal temperature. A dose-dependent relation among saccharin preference ratio and physiological indicators of shock suggests that conditioned anaphylactic shock-induced avoidance behavior is functionally related to homeostatic factors involved in immune reactivity.

Hall and Pearce negative transfer: Assessments in conditioned suppression and nictitating membrane conditioning experiments

Two experiments using a conditioned suppression procedure in the rat replicated the finding of Hall and Pearce (1979) that pairing a conditioned stimulus (CS) with a weak unconditioned stimulus (US) in Stage 1 produces negative transfer when US intensity is increased in Stage 2. Although the degree of negative transfer appeared to be independent of initial CS salience, it did depend on other factors. Specifically, weak suppression in Stage 1, or a postasymptotic decline in suppression in Stage 1, appeared crucial: strong suppression in Stage 1 unaccompanied by a postasymptotic decline resulted in positive, not negative, transfer. Experiments using the nictitating membrane response (NMR) conditioning procedure in the rabbit and a wide range of parameters failed to find evidence for negative transfer, but as a rule showed positive transfer instead. Because Kamin blocking, conditioned inhibition, and negatively accelerated learning curves are all readily obtained with the rabbit NMR procedure, the strong possibility exists that the mechanisms responsible for these effects differ from those responsible for the Hall-Pearce negative transfer phenomenon.

Alleviation of response suppression to conditioned aversive stimuli by lesions of the dorsal noradrenergic bundle

Rats with neurotoxic lesions of the dorsal ascending noradrenergic bundle (DB) were compared with sham-operated (SH) controls on the acquisition, steady state and extinction of response suppression maintained by a classical (conditioned suppression) or an instrumental (discriminated punishment) contingency. DB lesions interfered neither with the acquisition of the reference response of sucrose-rewarded barpressing nor with unconditioned responding to the overhead flashing light subsequently used as a signal of shock. The acquisition of discriminated response suppression was also unaffected by the lesion under both types of contingency. However, once discriminated suppression had stabilized, both the conditioned and the discriminative stimulus used were significantly less effective in maintaining suppression in DB animals than in SH controls provided that low intensity footshock (0.2 mA) was used as the unconditioned stimulus (UCS). Upon increase of UCS intensity (to 0.5 mA) normal suppression was observed in the DB group under both contingencies. Extinction of the classical contingency reinstated the difference between DB and SH performance: DB lesion resulted in significantly faster extinction of fear. In contrast, extinction of the discriminated punishment contingency was unaffected by the lesion, although generalized response suppression dissipated faster in the DB than in the SH animals trained under this condition. Our results offer no support for the reinforcement hypothesis of DB function (normal acquisition of barpressing and of discriminated suppression of barpressing); mixed support (greater initial generalization of suppression in DB animals) and contradiction (more rapid extinction of conditioned suppression in DB animals) for the attentional hypothesis; and weak support (reduced suppression and more rapid extinction of suppression in DB animals, but only within limited experimental parameters) for the anxiety hypothesis of DB function. Hence none of the extant theories of DB function offer a ready explanation of the pattern of results presented here. A simple interpretation which conforms with the sparsity of positive behavioural findings in the literature on DB lesions is that forebrain noradrenaline contributes to the detection and utilization of conditioned stimuli; but that this contribution is critical only for the detection of stimuli with low associative strength.

Effects of US parameters on classical conditioning of cat hindlimb flexion

Unconditioned stimulus (US) intensity and duration were manipulated to determine their effects on cat hindlimb flexion conditioning. Seven consecutive days of acquisition training of a hindlimb flexor response to a tone conditioned stimulus (CS) were followed by 2 days of extinction. Eight animals in each of 12 groups received a 1-, 2-, 3-, or 4-mA, 60-Hz shock delivered to the right hindleg for 25, 50, or 100 msec as the US. Analysis of conditioned-response (CR) frequency indicated that conditioned responding was a positive function of both the intensity and duration of shock, although these variables did not interact with one another. CR latency and amplitude were decreased and increased, respectively, by increases in US intensity. The pattern of results reported here may support a contiguity notion of conditioning, and are discussed in the context of other conditioning preparations.

One-trial backward fear conditioning in rats as a function of US intensity

In a one-trial backward conditioning procedure, four groups of seven rats each received a 4-sec white noise conditioned stimulus (CS) immediately following a 4-sec electric grid shock unconditioned stimulus (US). For different groups the US intensity was.5, 1.0, 1.6, or 2.0 mA. A fifth group served as a sensitization control and received a single 4-sec, 2.0-mA US presentation, but no noise CS. All the rats were later presented the CS while licking a drinking tube for water, and CS-elicited suppression of licking was taken as an index of excitatory conditioning. The magnitude of this suppression was found to increase as a function of US intensity.

Cardiac conditioning in the rat: US intensity function and response constancy theory.

ABSTRACTThe classically conditioned cardiac response to electric shock was examined in five groups of 10 rats each. Twenty trials were presented each day for 10 days with either a 1 mA, 2 mA, 3 mA, 4 mA, or 5 mA subcutaneous shock as the unconditioned stimulus (US). Data were evaluated with reference to a general theory of autonomic activity termed Response Constancy theory. A mathematical derivative of the theory is a significant negative correlation between prestimulus levels and change scores, i.e. the Law of Initial Values. The theory predicts that degree of control exerted by a stimulus is reflected by the ability of the stimulus to produce a particular level of activity. Decreasing variability of conditioned heart rate was monotonically related to US intensity throughout, and negative correlations between prestimulus levels and change scores were observed in all groups. Magnitude of decelerative change was an inverted U‐shaped function of US intensity in acquisition, and a monotonic function of US intensity at asymptote.

Manipulation of response-contingent unconditioned-stimulus intensity in human eyelid conditioning: A two-phase model analysis

Four groups of human subjects were given 360 classical eyeblink conditioning trials. All groups received the same UCS (unconditioned stimulus) intensity on[Formula: see text] (nonconditioned response) trials but differed in the intensity presented on CR trials. Response probability increased as a positive function of UCS intensity on CR trials. Phase 1 of the two-phase model was longer when no UCS was presented on CR trials, but did not differ in duration among the remaining three groups. Most subjects could be described with a single operator in Phase 2, the operator limit increasing as a positive function of CR-contingent UCS intensity. For subjects requiring different operator limits on CR and[Formula: see text] trials, the latter was lower with high CR-trial intensities but higher with low CR-trialintensities. The results were interpreted to be more consistent with drive theory than with "law-of-effect" or two-factor theories.

Application of a drive and an associative theory to the effects of CR-contingent increments and decrements in unconditioned stimulus intensity

An analysis of data from classical aversive conditioning of the nictitating membrane of rabbits with the two-phase model was made in order to test predictions from Spence’s drive theory and the Rescorla-Wagner associative theory. While overall group means were ordered as expected from these theories, the interrelationships among estimates of parameters in the two-phase model showed that neither can account for more detailed analyses of the data. It was shown, for example, that the inferior performance of subjects receiving an avoidance treatment was not, as theoretically predicted, a result of the CR-contingent omission of the US leading to a decrement in response probability. Similarly, it was shown that increments in response probability followed trials on which the CR occurred even when CR-contingent US intensity was lower than that on non-CR trials, an effect which neither theory can predict since both are response independent. These two outcomes are opposite to what has been obtained in human aversive conditioning, which means that the two theories, while accounting for the behavior of one species, are of limited generality across species.

Conditioned suppression of a positively reinforced shuttle response

Rats were trained to run up and down an alleyway for sucrose reinforcement a variable interval schedule. Differential aversive classical conditioning with auditory CSs was then conducted in a separate apparatus (off the baseline) prior to those CSS being presented while the subjects were responding for sucrose in the alleyway. Once the effects of the CSs had extinguished, shock was reintroduced following one CS but not the other (on the differential aversive classical conditioning). Both off the and on the conditioning resulted in conditioned suppression to the CS followed by shock, but little effect of the CS followed by no shock was found. In the on the phase, total suppression of baseline responding occurred at moderate US intensities, and this appeared to result from the subject avoiding the location at which he was last shocked. At lower values, both baseline response rate and relative suppression ratio were functions of US intensity. The results are discussed in relation to the effects found in similar experiments using avoidance baselines. Estes and Skinner (1941) found that food reinforced 1everpressing was suppressed by a conditioned stimulus (CS) that was followed by an unconditioned stimulus (US) of an electric shock. Such conditioned suppression of operant behavior by a preaversive CS has also been found using avoidance baselines (Bryant, 1972). However, Rescorla and Solomon (1967) were able to find support for their motivational account of operant classical interactions from a number of studies carried out in the Pennsylvanian laboratories (e.g., Rescorla & Lolordo, 1965; Rescorla, 1967). In general, these in­ volved training dogs to jump over a hurdle a Sidman

Effect of CS-US pairings on shock-elicited aggression as a function of US intensity

In two experiments with paired rats, the effect of superimposing CS-US pairings on a baseline of shock-elicited aggression was studied. Baseline shocks (3.0 mA, 0.125-sec duration) occurred at a rate of 20 shocks per min throughout each session. In Experiment I, each independent group of two pairs of subjects received (in addition to baseline shocks) US shocks of 1.0, 3.0, or 5.0 mA and 5-sec duration, each shock signalled by a 1-min CS. At all three US intensities, aggression increased during the CS. In Experiment II, pairs of subjects received each unconditioned stimulus intensity in a within-subjects design. This procedure revealed a direct relationship between rate of responding and unconditioned shock intensity.

The effects of unconditioned stimulus intensity on conditioned alpha blocking

The relationship between US intensity and conditioned alpha blocking was investigated in a between-group design employing 24 human subjects. In all cases, one of three different light intensities was paired with the same tone stimulus. The light intensities used were.602, 1.342, and 2.065 log fL. The three groups of eight subjects each received the same random sequence and number of stimulus trials in pseudoconditioning, conditioning, and extinction. In pseudoconditioning and extinction, there were 36 unpaired tone and light trials, and in conditioning there were 30 paired tone and light trials. It was found that there was an inverse relationship between light intensity and conditioned alpha blocking. The results were interpreted by extending Pavlov’s concept of ultramaximal inhibition.

Spinal conditioning: unconditioned stimulus intensity requirement

Spinal conditioning: unconditioned stimulus intensity requirement

Skin conductance response conditioning with CS intensities equal to and greater than UCS intensity

With .2-sec bursts of white noise as both conditioned stimulus (CS) and unconditioned stimulus (UCS), conditioning of first-interval skin conductance responses was obtained when the intensity of the CS equaled and exceeded that of the UCS. There was no evidence that second-interval response conditioning occurred. Nonspecific response frequencies were also affected by the variations in stimulus intensity, this raising some question about typical controls employed in SCR conditioning. There was some evidence that second interval responses were suppressed by the intense CS values. It was concluded that the existence of simple conditioning with a CS/UCS intensity ratio equal to or greater than unity was contrary to the Pavlovian proposition that a CS must be biologically less salient than the UCS in order for conditioning to occur. It was noted, however, that the suppression of second-interval responses might indicate that anticipatory CRs which are not confounded with orienting reflexes are prevented from exhibiting a conditioning effect when a high CS/UCS intensity ratio is employed.