Sign-tracking behavior in aversive conditioning: Its acquisition via a Pavlovian mechanism and its suppression by operant contingencies

When rats are presented with Pavlovian backward pairings in which shock is the unconditioned stimulus (US) and an elevated platform the conditioned stimulus (CS), they show a strong tendency to approach the platform. Attempts were made at evaluating the nature of the associative mechanisms responsible for the acwuisition and maintenance of the approach behavior. In Experiment 1, following a baseline period when platform presentations were given in the absence of shocks, first (training I), approach to the platform was prevented and subjects were exposed to either backward, forward, or random presentations of shock and platform: this procedure attempted to minimize the effects of response learning on the acquisition of approach behavior. Then (training II), all subjects received backward shock-platform pairings and had access to the platform. Approach to the platform was stronger in animals previously exposed to backward pairings than in the animals of the other two groups. Also, animals preexposed to forward platform-shock pairings showed suppression of approach behavior on the first trial of training II relative to their performance on the last trial of baseline. These data suggest that a stimulus-reinforcer learning mechanism alone is sufficent for the acquisition of approach. Experiments 2a and 2b evaluated the effects of “punishing” operant contingencies on Pavlovian-produced approach behavior. The results showed that approach can be eliminated, but only after repeated exposure to an operant contingency which consisted of the immediate closure of the platform upon approach responding. These data suggest that approach behavior produced by Pavlovian contingencies can be modified by operant contingencies. Taken together, these data provide additional support for a sign-tracking notion in aversive conditioning.     

Signal duration and suppression of operant responding by free reinforcement

Pigeons were trained on a VI (variable interval) schedule of food presentation with a superimposed schedule of response-independent food. Substantial suppression of the operant response rate occurred when the free food was presented without a signal. When the free food was preceded by a short (4 sec) signal, the degree of suppression was similar to that with unsignaled free food. But when the signal was lengthened to 12 sec, the degree of suppression was substantially reduced. Experiment 3 assessed the effect of signal duration using a baseline schedule of delayed reinforcement, in which contingent reinforcers were themselves preceded by a signal. The signal preceding the free reinforcers was then either the same as or different from this contingent signal. Signal duration effects occurred only when the two types of signals were different. These differences as a function of signal duration have implications for both “context-blocking” and “comparator” interpretations of the effects of noncontingent reinforcement in both Pavlovian and operant procedures.     

Selective sensitivity of schedule-induced activity to an operant suppression contingency.

The sensitivity of pigeons' schedule-induced activity to operant consequences was studied in two experiments. During a 30-s interval between food presentations, a keylight stimulus brightened incrementally. Stable terminal key pecking and interim locomotor activity developed. An operant "setback" contingency was applied to activity. The contingency arranged for locomotor movements (detected by a nine-panel floorboard) to be followed by a resetting of the keylight brightness to a dimmer value and a 1-s delay of reinforcement (for individual responses). Experiment 1 showed that activity patterns were highly sensitive to their operant consequences. Accompanying key-peck rates were only transiently affected. In Experiment 2, the setback contingency was imposed during restricted portions of the trial, and differential operant control of activity was demonstrated. However, birds in this study produced higher rates of key pecking as activity rates were reduced. These results suggest that although schedule-induced activity arises in response to the temporal arrangement of stimulus events, this behavior may retain considerable sensitivity to response-consequence relations.     

Social reinforcement of operant behavior in rats: a methodological note.

An apparatus was developed to study social reinforcement in the rat. Four Long-Evans female rats were trained to press a lever via shaping, with the reinforcer being access to a castrated male rat. Responding under a fixed-ratio schedule and in extinction was also observed. Social access was found to be an effective reinforcer. When social reinforcement was compared with food reinforcement under similar conditions of deprivation and reinforcer duration, no significant differences were observed.     

Suppression of operant vs consummatory behavior

The magnitude and variability of conditioned suppression of bar pressing and dipper licking were compared. In two steady-state experiments, suppression of bar pressing was more profound and more stable from day to day. The two measures of suppression were uncorrelated as indexed by Pearson product-moment correlation coefficients computed for adjacent trials. Correlations within measures (internal consistency) were somewhat higher for the bar-press system except when a high proportion of rats completely suppressed on one of the correlated trials. In a transient state experiment in which possible adventitious punishment of both response systems was eliminated, suppression of bar pressing was again more profound and considerably slower to extinguish.     

Control of tantrum behavior by operant techniques during experimental verbal training

A technique of controlling undesirable or disruptive behavior during an ongoing program of verbal training with a retardate is described. The technique required that the stimulus materials of the verbal training program be graded according to difficulty, i.e., in terms of the length and complexity of the stimulus materials. (This resulted in an initial grading of the stimulus materials into different levels of probability of reinforcement.) Changes by the experimenter from high-difficulty to low-difficulty stimuli for two trials contingent upon disruptive behavior increased the rate of that behavior; changes from low-difficulty to high-difficulty stimuli for two trials contingent upon disruptive behavior decreased its rate. Thus, contingent alternation of the stimulus materials of the ongoing training program controlled the frequency of undesirable behaviors within the experimental sessions. This technique may comprise an alternative to other procedures which require punishment or timeout from the ongoing program.     

Lifelong hyperarousal in the spontaneously hypertensive rat indicated by operant behavior

Instrumental conditioning techniques were used to obtain objective evidence of differences in behavioral arousal between the spontaneously hypertensive rat (SHR) and the normotensive ancestral Wistar Kyoto (WKY) strain. Subjective emotionality ratings previously indicated that the genetically hypertensive rats were more active and aggressive than their normotensive cousins. In a lengthy series of operant conditioning sessions using a small number of adult female SHR and WKY rats, hyperarousal in the SHR was confirmed by their significantly higher response outputs on either response contingent or time contingent schedules of reinforcement. Conditioned emotionality tests during this series of experiments also suggested hyperarousal and aggressiveness in the SHR, since the fear-conditioned stimulus suppressed bar-pressing in the SHR much less than in the WKY. Further experiments with young prehypertensive SHR rats provided the same evidence of hyperresponsivity in the SHR compared to the WKY strain. Furthermore, these young SHR failed to develop hypertension by the end of the study (14 weeks of age), while their nonconditioned SHR cousins had become clearly hypertensive by the same age. This suggests that factors related to the conditioning methods modified the development of high blood pressure in this animal model of essential hypertension.     

Menstrual cycle influences on operant behavior of female rhesus monkeys.

Nine female rhesus monkeys were paired with males throughout 63 menstrual cycles. The females' motivation to approach males was studied with an operant conditioning paradigm that required the female to press a lever 250 times to gain access to the male. Sexual behavior was scored during standard 60-min tests that followed the attainment of access (17 pairs, 1,440 tests). In the overall data, mean times to access were shortest at mid-cycle and longest just before and after the onset of menstruation, and a model-fitting method showed that 45% of cycles from individual pairs were significantly correlated with a V-shaped model of the overall pattern. Male sexual activity was highest at mid-cycle and lowest in the last quarter of the cycle, but the changes in access times could not be attributed entirely to the rewarding effects of the ejaculations. In the combined data from five females (9 pairs, 33 cycles), high estradiol levels and low progesterone levels were statistically associated with short access times and short ejaculation times. The overall effect was for operant performance and sexual activity to be synchronized and maximized in the periovulatory period of the menstrual cycle.     

Derived relational responding as generalized operant behavior

The major aim of the present study was to demonstrate that derived relational responding may be viewed as a form of generalized operant behavior. In Experiment 1, 4 subjects were divided into two conditions (2 in each condition). Using a two-comparison matching-to-sample procedure, all subjects were trained and tested for the formation of two combinatorially entailed relations. Subjects were trained and tested across multiple stimulus sets. Each set was composed of novel stimuli. Both Conditions 1 and 2 involved explicit performance-contingent feedback presented at the end of each block of test trials (i.e., delayed feedback). In Condition 1, feedback was accurate (consistent with the experimenter-designated relations) following exposure to the initial stimulus sets. When subjects' responding reached a predefined mastery criterion, the feedback then switched to inaccurate (not consistent with the experimenter-designated relations) until responding once again reached a predefined criterion. Condition 2 was similar to Condition 1, except that exposure to the initial stimulus sets was followed by inaccurate feedback and once the criterion was reached feedback switched to accurate. Once relational responding emerged and stabilized, response patterns on novel stimulus sets were controlled by the feedback delivered for previous stimulus sets. Experiment 2 replicated Experiment 1, except that during Conditions 3 and 4 four comparison stimuli were employed during training and testing. Experiment 3 was similar to Condition 1 of Experiment 1, except that after the mastery criterion was reached for class-consistent responding, feedback alternated from accurate to inaccurate across each successive stimulus set. Experiment 4 involved two types of feedback, one type following tests for mutual entailment and the other type following tests for combinatorial entailment. Results from this experiment demonstrated that mutual and combinatorial entailment may be controlled independently by accurate and inaccurate feedback. Overall, the data support the suggestion, made by relational frame theory, that derived relational responding is a form of generalized operant behavior.     

Enhancement of conditioned autonomic responses in monkey when preshock signals occasion operant suppression.

Classical pairings of a sound stilulus with shock elicited larger magnitude and more rapidly conditioned autonomic responses when subjects were responding on variable-interval schedules for food than when they were eating freely available food. The difference was not attributable to changes in control values of heart rate and blood pressure, or to alterations in motor activity, but appeared related to operant suppression.     

Aggression as a reinforcer: operant behavior in the mouse-killing rat

Two experiments examined mouse killing as a reinforcer of key pressing by rats that killed mice. In Experiment I, mouse-killing rats performed the key-pressing response when each press was reinforced with presentation of a mouse. Offered a choice between a key that yielded presentation of mice and one that did not, the rats preferred the key that yielded mice. When the contingency was reversed, the rats preferred the other key and continued to kill mice. In Experiment II, mouse-killing rats that did not kill rat pups performed a key-pressing response reinforced with presentation of mice on a variable-interval schedule. In tests for responding reinforced on that schedule with presentation of normal mice, anesthetized mice, dead mice, or rat pups, these rats that killed mice but not rat pups exhibited a decline in response rate when rat pups were the reinforcer. Altering the condition of the mice did not significantly affect performance.