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.     

The effect of UCS inflation and deflation procedures on 'fear' conditioning

Davey (1992: Classical conditioning and the acquisition of human fears and phobias: a review and synthesis of the literature. Advances in Behaviour Research and Therapy, 14, 29-66) hypothesized that subjective revaluation of an unconditioned stimulus (UCS) would determine the strength of the autonomic conditioned response (CR) in the fear conditioning paradigm. The purpose of the present study was to examine the effect of UCS aversiveness on the CR strength in the fear conditioning paradigm. The UCS aversiveness was controlled by the UCS intensity; that is, the UCS intensity was increased for the inflation group or decreased for the deflation group. Thirty subjects were randomly assigned to the inflation or the deflation group, and they participated under both experimental and control conditions. All subjects went through the pretest, the acquisition of classical conditioning, the UCS intensity operation, and the test sessions. The indices of the CR were skin conductance responses (SCRs) and a subjective aversion to the conditioned stimulus (CS). The main results were as follows. (1) The CR strength measured by SCR was increased by the UCS inflation and decreased by the UCS deflation. (2) The subjective aversiveness of the CS was not sensitive to both manipulations of UCS intensity. These results suggested that the autonomic CR strength might be influenced by the subjective revaluation of UCS, as Davey (1992) described. The result from the test of the subjective aversiveness of the CS, however, could not support Davey's model. The difference between expressions of the SCR and the subjective aversiveness of the CS might be caused by different learning systems.     

Effects of UCS intensity and postpeak acquisition trials on classical conditioning of the SCR

The present study examined the effects of UCS intensity and number of postpeak acquisition trials on classical conditioning and extinction of the SCR. A 2 × 3 design was employed in which subjects received either a 1, 2, or 4 mA shock UCS and either two or 16 acquisition trials beyond the peak CR. While conditioning was demonstrated during acquisition, there was no relationship between strength of conditioning and intensity of UCS. The phenomenon of stronger resistance to extinction following fewer acquisition trials (e.g., two past the peak CR) than with many (e.g., 16 past the peak CR) was demonstrated only for the groups that were conditioned with the 4 mA UCS. Resistance to extinction varied positively with UCS intensity, but only for the subjects who received two postpeak acquisition trials. Sixteen trials beyond the peak CR resulted in the UCS intensity having little or no effect on resistance to extinction.     

Consequences of response-contingent change in unconditioned stimulus intensity upon the rabbit (Oryctolagus cuniculus) nictitating membrane response.

In a between-groups design, an instrumental contingency was superimposed on classical conditioning of the rabbit nictitating membrane response. Subjects were exposed to a tonal conditioned stimulus (CS) and, if no conditioned response (CR) occurred, a 5.0-ma. paraorbital electric shock unconditioned stimulus (US). USs of 5.0, 3.3, 1.7, and 0.0 ma., respectively, were contingent on occurrence of a CR in the CS-US interval for subjects in the 4 groups of the experiment. The group exposed to contingent US omission differed from the other 3 groups in percentage CR, onset latency, amplitude, and 2 indices of CR form, and those 3 groups generally did not differ significantly among themselves on these dependent variables. Results were interpreted to be contrary to "law of effect" formulations of classical conditioning.     

Biasing the development of response topography with nonspecific positive and negative evocative verbal stimuli

Conditioned response (CR) rate and development of CR latency, rise time, and airpuff attenuation were examined for V- and C-form responders using two nonspecific command words, do and don't, as conditioned stimuli (CSs) in single-cue, double-cue, and differential eyelid conditioning. In both single-cue and differential conditioning, regardless of the command word used to signal the unconditioned stimulus (UCS), the Vs produced a higher response rate and learned a better UCS-attenuating response topography than the Cs. However, in a double-cue conditioning paradigm in which both command words were presented alone on different trials and reinforced, response latency was longer and puff attenuation poorer among Vs than when the UCS was signaled by a unique cue. In contrast, adding a second reinforced cue actually enhanced the development of puff-avoidant CR topographies among Cs compared to single-cue conditioning. These results and others indicate that response topography development is to some extent a labile process that can be biased toward either good or poor puff-avoidant properties and that the factors responsible for influencing CR topography differ for Vs and Cs.     

UCS revaluation and conditioning models of acquired fears

Recent developments in the study of Pavlovian conditioning in humans have suggested that the strength of a conditioned response (CR) is affected not only by associative processes that link the conditioned stimulus (CS) with the unconditioned stimulus (UCS), but also by processes which lead the individual to revalue the UCS itself. These latter processes can frequently lead to dramatic changes in CR strength independently of any experience with the CS-UCS contingency. This paper discusses a number of ways in which UCS revaluation can be effected in human subjects, and discusses their implications for conditioning models of acquired fears.     

Trace and delay eyeblink conditioning: contrasting phenomena of declarative and nondeclarative memory

We tested the proposal that trace and delay eyeblink conditioning are fundamentally different kinds of learning. Strings of one, two, three, or four trials with the conditioned stimulus (CS) alone and strings of one, two, three, or four trials with paired presentations of both the CS and the unconditioned stimulus (US) occurred in such a way that the probability of a US was independent of string length. Before each trial, participants predicted the likelihood of the US on the next trial. During both delay ( n =20) and trace ( n = 18) conditioning, participants exhibited high expectation of the US following strings of CS-alone trials and low expectation of the US following strings of CS-US trials a phenomenon known as the gambler's fallacy. During delay conditioning, conditioned responses (CRs) were not influenced by expectancy but by the associative strength of the CS and US. Thus, CR probability was high following a string of CS-US trials and low following a string of CS-alone trials. The results for trace conditioning were opposite. CR probability was high when expectancy of the US was high and low when expectancy of the US was low. The results show that trace and delay eyeblink conditioning are fundamentally different phenomena. We consider how the findings can be understood in terms of the declarative and nondeclarative memory systems that support eyeblink classical conditioning.     

The role of awareness in delay and trace fear conditioning in humans

Expression of conditional fear without awareness has been previously demonstrated during delay conditioning, a procedure in which the conditioned stimulus (CS) and unconditioned stimulus (UCS) overlap. However, less is known about the role of awareness in trace fear conditioning, where an interval of time separates the CS and UCS. The present study assessed skin conductance response (SCR) and UCS expectancy during delay and trace conditioning. UCS predictability was varied on a trial-bytrial basis by presenting perithreshold auditory CSs. Differential UCS expectancies were demonstrated only on perceived delay and trace trials. Learning-related SCRs were observed during both perceived and unperceived delay CSs. In contrast, differential SCRs were demonstrated only for perceived trace CSs. These data suggest that awareness is necessary for conditional responding during trace, but not delay, fear conditioning.     

Allocation of cognitive processing capacity during human autonomic classical conditioning

In each of two experiments, allocation of cognitive processing capacity was measured in college-student subjects during autonomic discrimination classical conditioning. A 7.0-sec delay paradigm was used to establish classically conditioned responses to a reinforced visual conditioned stimulus (CS+). Electrodermal responses were the primary measures of autonomic classical conditioning. Allocation of processing capacity was measured by monitoring performance on a secondary reaction-time (RT) task. The auditory secondary-task RT signal was presented before, and 300, 500, 3500, 6500, and 7500 msec following CS onset. The RT signal was also presented following properly and improperly cued shock unconditioned stimuli (UCSs). Significant discrimination classical conditioning was obtained in both experiments. Comparison with control subjects who did not receive the RT signals indicated that the presence of the RT signals did not interfere with the development of classical conditioning. Four principal findings were obtained with the secondary-task RT measure. First, RTs to signals presented during CS+ were consistently slower than RTs to signals presented during CS-. This finding indicates that greater capacity allocation occurred during CS+ than CS- and is consistent with recent cognitive interpretations of classical conditioning. Second, the largest capacity allocation (i.e., slowing of RTs) occurred 300 msec following CS+ onset. This finding is consistent with the notion that subjects are actively processing the signal properties of the CS+ at 300 msec following CS+ onset. Third, presentation of the UCS when improperly cued (following CS-) significantly increased capacity allocation, whereas presentation of the same UCS when properly cued (following CS+) did not affect capacity allocation. These findings indicate that subjects were actively prepared for the UCS following CS+ but not following CS- and that a surprising UCS elicits greater capacity allocation than does an expected UCS. Fourth, large electrodermal responders to the CSs exhibited patterns of capacity allocation during the CSs, particularly during the CS+, different from those of small electrodermal responders. In particular, they exhibited significantly longer RTs at 300 msec after CS+ onset than did the small responders, followed by a shortening of RT at 500 msec relative to the small responders. This finding suggests that large electrodermal responders devote greater processing capacity to significant environmental stimuli than do small responders and that their processing may begin and be completed more rapidly. All in all, the data indicate the complexity of the cognitive processes that occur during human classical conditioning and the usefulness of the secondary-task technique in integrating conditioning theories and psychophysiology with cognitive psychology.     

The effect of UCS intensity in classical and avoidance GSR conditioning

This study compared GSR avoidance and yoked-control conditioning procedures. Classical conditioning at two UCS intensities was followed by extinction and, two months later, by an avoidance session. Matching of Ss was based on GSR responsiveness and classical conditioning in the first session. The strong UCS led to more rapid reduction in CR latency (due to an increase in number of Ss responding) in the first session, and there was a tendency for maximum CR magnitude to occur in fewer trials with the strong UCS. No UCS-intensity difference in level of responding to the CS or UCS was found in the first session. A greater amount of spontaneous recovery in the second session was found in the strong UCS group. The avoidance and yoked control groups did not differ in CR magnitudes, latencies, or frequencies, nor in UCR magnitudes in the second session. They did differ significantly in the rate of decline in intertriai responses, the decline being more rapid in the avoidance condition.     

Classical heart-rate conditioning in the rat: The influence of curare and various setting operations

Conflicting reports concerning the success of classical conditioning of heart rate (HR) in curarized animals led to an experiment using a transfer design in which rats were classically conditioned either under curarized or restrained conditions. These conditions were then reversed for each group, giving a Curarized-Restrained (C-R) and a Restrained-Curarized (R-C) group. Results indicated that curare inhibits the conditional and unconditional HR response both during initial acquisition and after asymptotic levels of a HR CR have been attained. In addition, the C-R group did not acquire a CR during their later non-curarized restrained conditioning sessions, implying an inhibitory transfer from their earlier conditioning under curare. The UCRs during this period were normal for restrained rats. Analogous experimental“setting operations” prior to restrained conditioning were then explored by a second experiment which attempted to replicate the inhibitory transfer effect. The experimental operations investigated included: (1) restrained conditioning to investigate conditioned inhibition possibilities; (2) pseudo-conditioning types of randomized CS and UCS non-paired presentations to investigate associative vs. non-associative explanations; (3) CS-Only presentations to investigate possibilities that curare creates a blockage to the UCS, thus creating an inhibiting habituation to the CS; and (4) a group receiving curarization sessions, but no conditioning, to test the drug-only transfer effects. Results from the first and second experiments together indicated no inhibitory transfer effects under any prior experimental conditions except for those animals receiving classical conditioning while curarized. Only the CS-O group demonstrated any other kind of significant transfer effect; in this case a positive transfer accelerating later conditioning due to prior CS habituation sessions. These findings were discussed within the context of existing reports of curarized conditioning and setting operation effects on later conditioning, and various potential explanations and interpretations were explored.     

Galantamine facilitates acquisition of a trace-conditioned eyeblink response in healthy, young rabbits

Previous work has demonstrated that drugs increasing brain concentrations of acetylcholine can enhance cognition in aging and brain-damaged organisms. The present study assessed whether galantamine (GAL), an allosteric modulator of nicotinic cholinergic receptors and weak acetylcholinesterase inhibitor, could improve acquisition and retention of an eyeblink (EB) classical conditioning task in healthy, young animals. We trained 24 rabbits (n = 8/group) in a 1000-msec trace Pavlovian EB conditioning paradigm in which a tone conditioned stimulus (CS) was presented for 500 msec, followed by a 500-msec trace period in which no stimuli were presented. A 100-msec corneal airpuff was the unconditioned stimulus (US). Acquisition sessions, consisting of 100 trials each, occurred daily for 10 consecutive days, followed by 3 d of extinction training. Animals were treated with one of three doses of GAL (0.0-3.0 mg/kg) prior to each session. Animals that received 3.0 mg/kg GAL showed significantly more EB conditioned responses (CRs) in fewer training trials than animals receiving either 1.5 mg/kg GAL or vehicle injections. GAL had no effect on CR performance during extinction. Pseudoconditioning control experiments, consisting of 200 explicitly unpaired tone-puff presentations indicated that GAL did not increase reactivity to the CS or US. These findings indicate that GAL may improve acquisition of moderately difficult associative learning tasks in healthy young organisms.     

对体液免疫反应的条件反射性调节

以饮糖精水作为条件刺激(conditioned stimulus,CS),腹腔注射免疫抑制剂环磷酰胺作为非条件刺激(unconditioned stimulus,UCS)训练Wistar大鼠,3天后腹腔注射卵清蛋白(ovalbunfin,OVA)抗原,观察再次单独条件刺激对原发性体液免疫反应的作用。结果发现．一次CU-UCS结合训练导致CS组大鼠对再现糖精水产生厌恶反应,外周血中抗OVA-IgG抗体水平显著低于UCS组。两次CS-UCS结合训练并多次给予条件刺激后,CS组大鼠抗OVA-IgG的条件性免疫抑制效应与一次CS-UCS结合训练及再次给予一次条件刺激的反应类同。这些结果证明条件刺激增强了环磷酰胺对动物原发性体液免疫反应的抑制作用．这种条件性体液免疫抑制作用是相对稳定和有限度的,不易受条件反射建立参数的影响。     

Acquisition of the classically conditioned eyeblink response in humans over the life span

Human subjects ranging in age from 18 to 85 years underwent classical conditioning of the eyeblink response to a tone conditioned stimulus (CS) and an air-puff unconditioned stimulus (UCS). There was a decline in percentage of conditioned responses with age. This decline was most noticeable in subjects over age 50. These conditioning deficits were not due to age-related changes in sensitivity to the tone CS or the air-puff UCS, nor could the conditioning deficits be attributed to an age-related decline in general cognitive abilities or to changes in spontaneous blink rates. The results are discussed in terms of using the classically conditioned eyeblink in humans in conjunction with the classically conditioned nictitating membrane response in rabbits as a model system for studying the neurobiology of age-related conditioning deficits.     

Attenuation of age-related conditioning deficits in humans by extension of the interstimulus interval

Young (17-22 years) and older (61-86 years) persons underwent classical conditioning of the eye-blink response to a tone conditioned stimulus (CS) and an airpuff unconditioned stimulus (UCS) at 1 of 3 interstimulus intervals (ISIs; 400, 650, and 900 ms). As in a previous study, older subjects conditioned more slowly and emitted fewer conditioned responses at the optimal 400-ms ISI. At longer ISIs, however, this age-related disruption of classical conditioning was attenuated. These differences in conditioning were not due to nonassociative factors, such as sensitivity to the tone CS or airpuff UCS or to differences in spontaneous blink rate, nor were they due to differences in general cognitive abilities. The results are discussed in terms of the role of temporal relationships between stimuli in conditioning across the life span.     

Mediodorsal thalamic lesions impair trace eyeblink conditioning in the rabbit

Rabbits received lesions of the mediodorsal nucleus of the thalamus (MDN) or sham lesions and were subjected to classical eyeblink (EB) and heart rate (HR) conditioning. All animals received trace conditioning, with a.5-sec tone conditioned stimulus, a .5-sec trace period, and a 50-msec periorbital shock unconditioned stimulus. Animals with MDN lesions acquired the EB conditioned response (CR) more slowly than sham-lesioned animals. However, previous studies have shown that MDN damage does not affect delay conditioning using either .5-sec or 1-sec interstimulus intervals. The lesions had no significant effect on the HR CR. These results suggest that information processed by MDN and relayed to the prefrontal cortex is required for somatomotor response selection under nonoptimal learning conditions.     

Brain asymmetry and human electrodermal conditioning

Two experiments are reviewed that demonstrate effects of brain laterality on human classical conditioning. Pictures of facial emotional expressions were used as conditioned stimuli (CSs) together with shock as unconditioned stimulus (UCS). Bilateral electrodermal responses were recorded as dependent measures. In the first experiment, one group was conditioned to an angry face, and one group to a happy face. During extinction, the face-CSs were presented to the right hemisphere on half of the trials and to the left hemisphere on the other half of the trials. Results showed that the right hemisphere was superior in showing persisting effects of learning, and especially to the angry CS+. In the second experiment, lateralized presentations of the angry and happy faces were made during acquisition, with foveal presentations during extinction. Once again, the angry face elicited greater skin conductance responses (SCRs) during extinction in the group that had this stimulus presented to the right hemisphere during acquisition. It is concluded that emotional conditioning is differentially regulated by the two hemispheres of the brain.     

A comparison of pecking generated by serial, delay, and trace autoshaping procedures

Pigeons were exposed to serial, delay, and trace autoshaping procedures. In Experiment I, all conditioned stimuli (CSs) were changes in illumination of the response key. The number of trials to acquisition of the keypeck increased from serial, to 4-sec delay, 8-sec delay, and 8-sec trace procedures, in that order. In Experiment II, which used a longer intertrial interval, trials to criterion increased from 8-sec delay, to 28-sec delay, 8-sec trace, and 28-sec trace procedures, in that order. In Experiment III, two groups received serial procedures in which the first CS was either a tone or a houselight, and the second was a keylight. The tone group acquired the key peck more rapidly than the houselight group. Early in conditioning in these experiments, and when the conditioned stimulus was a change in the keylight, there was a short latency to the onset of pecking and pecking was directed at the CS. After extensive conditioning, or when the CS was relatively diffuse, pecking still occurred, but had a longer latency and was not reliably directed toward the conditioned stimulus.     

Neuronal unit activity in the abducens nucleus during classical conditioning of the nictitating membrane response in the rabbit (Oryctolagus cuniculus).

Neuronal unit activity was recorded from the abducens (6th nerve) nucleus, the "final common path," during classical conditioning of the nictitating membrane (NM) response in the rabbit, with the use of a tone conditioned stimulus, an air puff unconditioned stimulus (UCS), 250-msec interstimulus interval, and 60-sec intertrial interval. Animals were given 2 days of conditioning training (104 trials in eight blocks per day) and 1 day of extinction. Control animals were given comparable periods of stimulus presentations, explicitly unpaired. Activity of small clusters of units--"multiple unit" recording--was compared with the amplitude-time course of the NM response. Between-blocks comparisons of neural and behavioral responses indicated an essentially perfect correlation during acquisition of the conditioned response (Day 1, r = .99; Day 2, r = .98) and a slightly lower correlation during extinction (r = .93) for the conditioning animals. Within-blocks comparisons indicated a close correspondence between the histograms of unit activity and the amplitude-time course of the NM response for the conditioning animals in all phase of training and for the control animals in the UCS trial blocks.     

Concomitant Pavlovian conditioning of heart rate and leg flexion responses in the rat

Pavlovian conditioning was studied in male Fischer 344 rats using tones as the conditioned stimulus (CS) and footshock as the unconditioned stimulus (UCS). Different groups of animals received (a) contiguous CS-UCS pairings with a 0.5 sec CS, (b) contiguous CS-UCS pairings with a 4.0 sec CS, or (c) a random sequence of noncontiguous tones and shocks using either a 0.5 sec or a 4.0 sec CS. Heart rate (HR) and leg flexion (LF) responses were recorded. Leg flexion conditioning occurred only in the 0.5 sec contiguous group. Decelerative HR CRs occurred only in the 4.0 sec contiguous group. Accelerative HR changes occurred in the other two groups but were significantly greater in the 0.5 sec contiguous group. These results are similar to but not identical to those obtained during eyeblink or nictitating membrane conditioning in rabbits, and suggest that the topography of the Pavlovian HR CR is dependent on the simultaneous occurrence of other classically conditioned responses.