Classical Aversive Conditioning Research Articles

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.

Subjective estimates of shock probability following classical aversive conditioning with visual and gustatory conditioned stimuli

In two recent studies (Evans and Busch, 1974; Busch and Evans, in press) designed to explore the relevance of “cue appropriateness” concepts to aversion therapy, it was found that taste was a less effective CS than color. The major limitations of these studies were that conditioning was inferred from subjective ratings (although cross-validated by an unobtrusive but equally inferential performance measure), and the taste stimuli were rated more negatively in the pre-test than the color stimuli, thus creating possible ceiling effects. Quite apart from limitations in these particular studies, almost all cue appropriateness research contains methodological flaws; obvious ones are the failure to equate stimuli in different sense modalities for subjective intensity, or salience, and the failure to equate the ISIs when visual and gustatory elements of ingestible substances are the cues of interest. One of our studies (Busch and Evans, in press) partially resolved the timing problem, but in studies of visually-oriented college students the salience problem remains acute. It therefore seemed worthwhile to investigate whether, in the paradigm used in our laboratory, subjects simply attend less to taste cues than to color cues. In order to determine cue salience, a measure other than the development of CRs must be used. If an organism comes to give a CR to a certain stimulus, that is prima facie evidence of attention to, or if one prefers it, reception of, that stimulus, although generalization studies show the elements of the stimulus actually controlling the CR may not necessarily be the ones expected by the experimenter. Animal conditioning studies have shown, however, that the failure of CRs to emerge does not inevitably mean that the stimulus was ignored and an appropriate CR may appear if performance-related variables are manipulated. Similarly, humans may or may not show a CR and yet be able to verbalize correctly the contingency experienced during the conditioning. Thus for human Ss a cognitive expectancy measure should be able to reveal cue salience independent of the actual elaboration of a CR. We therefore repeated the Evans and Busch (1974) procedure and measured, instead of attitudinal changes to the CS, the Ss' perception of the contingency they had experienced.

Evaluation of informational control and preparatory response factors in classical aversive conditioning

Subjects performed in a differential eyelid conditioning paradigm with either airpuff or infraorbital shock as the UCS. The trial series included interpolated UCS-alone presentations, and subjects rated UCS aversiveness on all trials. Ratings of the airpuff, but not the shock UCS, were negatively correlated with the magnitude of anticipatory eyelid CRs, as predicted by preparatory response or law-of-effect models of classical conditioning. However, subjects showed no tendency to rate signaled (CS-UCS) trials as less aversive than unsignaled (UCS-alone) trials, and showed no significant preference for the signaled ucs. These results suggest that the operation of informational control and preparatory response factors is more complex than is assumed by available theories. Also, instrumental shaping and preparatory response mechanisms may not be involved in the acquisition of CRs.

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.

Classical aversive conditioning of heart rate in curarized rats at different blood gas levels.

In an effort to examine whether normal blood gas tensions were essential for conditioning, paralyzed rats received a classical aversive heart rate (HR) conditioning session while respirated at different peak expired CO2 values. After the session, arterial blood was drawn for analysis. That peak expired CO2 was effective in manipulating PCO2 was indicated by a significant correlation (r=0.594, df=17, P less than 0.05). In addition, only rats with blood gas values similar to those of anesthetized controls displayed a discriminated HR CR. These animals also had lower baseline HRs and greater HR variability. Further, 7 of the 9 rats with normal blood gas values were respirated at peak expired CO2 values from 5.0-5.1 per cent, and no animal ventilated within this range displayed abnormal values. These findings suggest that previous difficulties in obtaining calssical and operant conditioning in paralyzed animals may, in part, be attributable to inadequate ventilation.

Presidential Address, 1975. The cardiovascular-behavioral interaction--as it appears today.

ABSTRACTResearch is reviewed concerning the interrelationships among cardiodynamics, blood pressure control mechanisms, somatic activity, and the stimulus parameter of active vs passive coping. Emerging evidence suggests that with passive coping such as classical aversive conditioning, the heart is more under vagal control which is directionally linked with somatic activity, while blood pressure is more dominated by vascular processes. With active coping such as shock avoidance, the heart is under greater sympathetic control which is directionally independent of concomitant somatic activity, while cardiac influences on blood pressure become more dominant. Several current psycho physiological issues are discussed including the possible significance of these effects for cardiovascular disease processes.

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

Neuromuscular blocking drugs and heart rate changes after direct nerve stimulation and during classical conditioning in cats.

Two experiments investigated cardiovascular responses to several common neuromuscular blocking compounds. Experiment 1, employing 16 cats, assessed ganglionic transmission in sympathetic and parasympathetic systems controlling heart rate and blood pressure after d-tubocurarine chloride (d-T.C.), dimethyl d-tubocurarine iodide (D. d-T.I.), succinylcholine chloride (SC), or saline. Cardiovascular responses to sympathetic stimulation were essentially unaffected at drug levels that blocked evoked electromyograms; however, vagally evoked bradycardia and corresponding blood pressure decrease were blocked by d-T.C. and redduced by D. d-T.I. and SC. Experiment 2 compared heart responses of 12 cats under the same blocking compounds during differential classical aversive conditioning. Differential conditioned responses and unconditioned responses occurred under D. d-T.I., less under SC, but not under d-T.C. However, animals trained under d-T.C. and tested under D. D-T.I. showed differential conditioned responses.

Partial reinforcement effects in classical aversive conditioning in rabbits and human beings.

The partial reinforcement extinction effect (the PREE) in classical aversive conditioning was investigated in 2 experiments. In the first, the nictitating membrane responses of 120 rabbits were conditioned at a 250-msec. interstimulus interval (ISI) under continuous reinforcement, partial reinforcement with the unconditioned stimulus (US) omitted (Group PO), or partial reinforcement with the US delayed to 1,500 msec. (Group PD). These 3 groups were factorially extinguished under US-Omitted, US-Unpaired, or US-Delayed extinction regimens. A significant PREE was obtained, but only for PO training and US-Omitted extinction. The second experiment, employing human subjects in a masked eye blink conditioning task, produced parallel results. A general discrimination view of the classical PREE seems applicable, but one in which neither cognitive factors nor intertrial conditioning of reinforcement aftereffects play a significant role.

The effectiveness of visual and gustatory conditioned stimuli in human classical aversive conditioning with electric shock

Thirty-six undergraduate volunteers, divided into three equal groups, were given electric shock while sipping a colored, unflavored solution (Group I): a flavored, colorless solution (Group 2); or a colored, flavored solution (Group 3), in order to determine whether human Ss respond differentially to visual and gustatory cues when the UCS is aversive electric shock. Using a standard classical discrimination procedure, the CS + was blue water for Group 1, citric acid solution for Group 2, and blue citric acid solution for Group 3. For all groups the CS- was plain water, which was never paired with electric shock. The dependent variables were derived from Staats' A-R-D theory: attitudinal change (A) and a performance measure of sip-size taken during conditioning trials (D) both confirmed the hypothesis that taste can be an effective CS when the UCS is shock, in contrast to results typically obtained with rats where visual but not taste cues are effective with a shock UCS.

Classical conditioning of skeletal avoidance responses in two strains of rats.

Anticipatory skeletal responses can be directly elicited during classical aversive conditioning in the shuttlebox. Under the classical CS-UCS contingency Long-Evans rats shuttle at moderate rates, while Fischer344 rats display high rates of anticipatory responding, even though the instrumental avoidance contingency is absent. The classical contingency is also exceedingly important in determining the differences between these strains, as well as their initial and terminal rates of anticipatory responding, when the avoidance contingency is present.

Cardiovascular changes following DOCA/NaCl or conditioning in 6-hydroxydopamine-treated rats

Two intracisternal injections of 200 μg 6-hydroxydopamine reduced brain catecholamine levels 90% and significantly lowered resting heart rate and blood pressure. In a classical aversive conditioning paradigm, 6-hydroxydopamine-treated rats displayed little or no conditioned heart rate response in anticipation of shock, but a potentiated unconditioned response to shock itself. The alteration in heart rate responses may have been due in part to alterations in general activity. Although 6-hydroxydopamine treatment did not abolish the hypertension caused by DOCA/NaCl treatment following uninephrectomy, the increase in blood pressure was significantly less than the blood pressure increase in control rats receiving this treatment. The 6-hydroxydopamine treatment, however, concomitantly reduced the amount of NaCl consumed after DOCA. Since peripheral tyrosine hydroxylase activity and amine levels were not significantly altered by 6-hydroxydopamine treatment, the alterations in cardiovascular responses following 6-hydroxydopamine must result from its central actions. Although 6-hydroxydopamine administration markedly altered the cardiovascular responses to conditioned stimuli, shock, and DOCA/NaCl treatment, it is difficult to ascribe these alterations to ablation of central catecholamine fibers participating directly in cardiovascular control. The link between destruction of catecholamine fibers and changes in cardiovascular responses may be secondary to changes in activity or ingestive behavior.

Two-phase model analysis of the effects of interstimulus interval and masking task in human aversive classical conditioning

Three levels (.5, 1.0, and 2.0 sec) of interstimulus interval (ISI) and presence vs absence of a masking task were manipulated in a human eyelid reflex conditioning situation. Through the use of a two-phase model of conditioning performance, it was concluded that (1) increasing the ISI and introducing a masking task increased the duration of Phase 1, (2) as ISI increased, the amount of conditioning decreased, (3) the trial-by-trial rate of change in response probability increased as a function of ISI, and (4) the masking task reduced operator limits. It was also noted that the typical ISI function is composed of rate effects at short ISis and conditioning limit effects at long ISIs and that the larger 0 at larger ISis does not follow from a model of the stimulus trace hypothesis.

The relationship between electrodermal and digital vasomotor responses in aversive classical conditioning

Thirty-two subjects, exposed to a tone CS, shock UCS simple delayed conditioning paradigm with an interstimulus interval of 8 sec, were compared in skin conductance and finger pulse volume responses to a sensitization control group of 32 subjects given unpaired CS—UCS presentations. Magnitude, probability and amplitude of anticipatory and UCS omission responses were measured. Significant conditioning effects for both these types of response were observed using magnitude and probability measures of the two effector systems. Between-subject correlations showed significant positive relationships between vasomotor and electrodermal CS responses in the sensitization group and early in conditioning training. Later in training, however, this relationship disappeared, indicating a learned dissociation of the response systems during classical conditioning. Within-subject correlations showed that the two response systems developed quite independently over trials.

Multiple somatic measures and heart rate during classical aversive conditioning in the cat.

Multiple somatic measures and heart rate during classical aversive conditioning in the cat.

A two-phase model account of aversive classical conditioning performance in humans and rabbits

A two-phase model was applied to classical conditioning performance in man and rabbits. During phase 1, response probability remained constant. During phase 2, response probability generally increased, although one operator was sufficient for a majority of Ss and two operators were required for a minority of Ss. The latter Ss exhibited increases in responding after a CR trial and decreases in responding after a non-CR trial. The pattern of parameters was similar for man and rabbits. In man, increases in UCS intensity resulted in a decrease in the duration of phase 1 and an increase in the limit of the operators for those Ss requiring more than a single operator to describe performance during phase 2. The value of employing a model to describe the data and understand the effects of independent variable manipulation was discussed.

Auditory and autonomic tests of the preparatory-adaptive-response interpretation of classical aversive conditioning.

Auditory and autonomic tests of the preparatory-adaptive-response interpretation of classical aversive conditioning.

Alterations in cardiac contractility during classical aversive conditioning in dogs: methodological and theoretical implications.

ABSTRACTAn investigation of sympathetic influences on the heart was undertaken in dogs using classical aversive conditioning procedures. For this purpose, heart rate and cardiac contractile changes were measured, the latter using techniques assessing the rate of change or slope at which either the muscles of the left ventricle contract, or blood is accelerated in the ascending aorta, or the pulse pressure wave ascends from diastole to systole. Sympathetic influences were found to be more clearly manifest in contractile rather than heart rate changes as indicated by the greater attenuating influence of beta‐adrenergic blockade on anticipatory and unconditioned responses. Anticipatory sympathetic influences on the heart were commonly acute, becoming minimal upon repeated exposure to the aversive procedures. The rate of change or slope measures appear to detect sensitively extrinsic sympathetic influences on contractility. They are minimally influenced by intrinsic effects on contractility such as heart rate as well as non‐contractile events such as diastolic blood pressure. The slope of the ascending limb of the pulse pressure wave appears to offer a means of assessing contractility in human Ss.

Central effects of atropine upon aversive classical conditioning in rabbits.

Rabbits were given classical discrimination conditioning with one of two tones followed by shock. In Experiment I, 40 rabbits were trained under saline, 10, 18 or 26 mg/kg atropine sulfate or 18 mg/kg methylatropine. Six rabbits in Experiment 2 were conditioned, then given further sessions with saline, and 18, 26 and 34 mg/kg atropine sulfate and methylatropine. In Experiment 3, 18 rabbits were conditioned and then given two extinction sessions under saline or 34 mg/kg atropine sulfate or methylatropine followed by extinction under saline. Chief findings were (a) atropine sulfate but not methylatropine disrupted acquisition and maintenance of conditioned eyeblinks, (b) neither drug affected unconditioned blinks, (c) fewer blinks occurred in extinction under atropine sulfate than under methylatropine or saline, (d) rabbits extinguished under atropine sulphate showed higher percentages of eyeblinks when tested without drug. Disruptions in performance of learned eyeblink responses appeared to be due to drug interference with central cholinergic transmission.

Heart-rate conditioning to a pure tone in the guinea pig

Classical aversive conditioning of heart rate to a pure tone stimulus in the guinea pig was demonstrated. The CR (a decrease in heart rate) was easily established within 20 trials and appears to be both stable over time and under strict stimulus control. A nonpaired control group showed no indications of conditioning and, in fact, had a small increase in heart rate to the CS.