Some notes on conditioned suppression and reinforcement schedules

Two pigeons were trained on an FR 150 schedule of reinforcement. An Estes-Skinner conditioned suppression procedure was then superimposed on this performance at varied intervals. If the CS occurred during the early stages of the ratio run, complete suppression resulted. If the CS occurred during the later stages of the run, the birds continued to respond until the reinforcement was obtained, which was then followed by complete suppression.     

Some effects of the conditioned suppression paradigm on operant discrimination performance

Three experiments were conducted with rats to determine the effects of electric shock on responding during an operant discrimination. In two of these experiments, a conditioned suppression procedure was superimposed upon a stimulus signalling the availability of food reinforcement (S(D)). Response rates were greatly suppressed, not only in the warning signal periods which preceded each shock, but in the presence of S(D), and the stimulus signalling the unavailability of reinforcement (S(Delta)) as well. A third experiment, in which a very mild shock was used without a warning signal, demonstrated an increased response rate in S(D) and S(Delta), although this effect was rather unsystematic. In a similar study, Hearst (1965) found an increased rate in S(Delta) independent of any change in the S(D) rate. The present study failed to obtain Hearst's effect but illustrated a suppressive effect with a similar procedure.     

Positive conditioned suppression: conditioned suppression using positive reinforcers as the unconditioned stimuli

Research has revealed the phenomenon of conditioned suppression in which the rate of responding is reduced during a stimulus that is paired with noncontingent shock. The present study replicated this procedure, but used noncontingent positive reinforcers instead of the aversive shock. The lever-pressing responses of rats were reinforced with food or water. While the rats were responding, a stimulus was occasionally presented and paired with the delivery of a noncontingent positive reinforcer, which was either food, water, or brain stimulation for different rats. The result was a reduction in the rate of responding during the conditioned stimulus. This finding shows that conditioned suppression occurs during a signal for reinforcing as well as aversive stimuli.     

Summation of conditioned suppression

Four rats were trained to suppress responses in the presence of two separately presented stimuli that signalled shock in a conditioned-suppression paradigm. The two stimuli that signalled shock were then presented simultaneously to evaluate the effect of stimulus compounding on conditioned suppression. Two rats were tested by presenting the compound conditioned stimulus while conditioned suppression was being maintained to the individual conditioned stimuli. The other two rats were tested by giving them random presentations of the compound conditioned stimulus and the single conditioned stimuli during extinction of conditioned suppression. All four rats showed greater suppression to the compound stimulus than to either stimulus presented alone.     

Habituation of conditioned suppression

Habituation of a conditioned emotional response was investigated using a procedure which eliminated contaminating temporal discriminations. Three rats were trained to bar press on a random interval 60 sec schedule of milk reinforcement and variable duration tone-shock pairings were superimposed upon this baseline. Very little recovery from conditioned suppression was found over 60 sessions of testing and no systematic differences were found after a month's “vacation” from the procedure. Analysis of responding within the CS period showed uniform suppression. The data are discussed in terms of stimulus predictability.     

Effects of response pacing on conditioned suppression

In this experiment, which employed a balanced design with two rat subjects, the frequency of reinforcement remained constant while the rate of operant responding was varied by means of a response pacing technique. At each of three response rates, 1-min. periods of noise were presented, and, as these periods ended, a slight unavoidable shock was delivered to the rat. This procedure resulted in suppression of the operant responding during the periods of noise. This behavioural change was measured by a suppression ratio, essentially a comparison of the response rates in the presence and absence of the noise. The suppression ratios varied in a systematic way during the experiment, denoting most conditioned suppression when the baseline rate of responding was high, and least suppression when this was low. It is therefore concluded that response rate in one factor determining the degree of conditioned suppression in this controlled experiment. The conclusion is corroborated by absolute measures of responding during the pre-shock periods of noise.     

Motivational properties of conditioned suppression

Two experiments were performed to investigate the interaction of baseline appetitive drive and incentive on the conditioned suppression of instrumental behavior exhibited in the presence of a preaversive stimulus. In one experiment, suppression of lever pressing of rats working on an intermittent food reinforcement schedule was considerably enhanced following partial satiation with food. In a second experiment, using a similar baseline, suppression was shown to be diminished by an increase in concentration of the baseline incentive. These results are consistent with the hypothesis that the instrumental suppression of the conditioned emotional response (CER) is a consequence of an algebraic interaction of hunger with fear.     

Time-dependent changes in conditioned suppression

Time-dependent changes in a response following aversive conditioning were investigated using a conditioned suppression procedure in a within-subjects design. Four groups of pigeons received Pavlovian conditioning “off the baseline”, immediately followed by an operant task. During the Pavlovian phase, two groups received a forward pairing of a tone with shock, one group received a backward pairing, and one group received a truly random pairing. One of the forward pairing groups also received a delay between the Pavlovian and operant phases. For all groups, key pecking was reinforced on a variable-interval schedule during the operant phase. Testing sessions were identical to training sessions, except that the tone used during Pavlovian conditioning was presented either 0, 15, 30, 45, of 60 minutes after the operant phase began. Testing sessions in which the Pavlovian phase was omitted were also included. The results showed suppression to change as a function of the retention interval, with maximum suppression occurring at intermediate intervals. This U-shaped function was obtained for 11 of the 12 pigeons in the forward-pairing groups and for three of the five in the truly random group. Pigeons in the background pairing group did not show changes in suppression as a function of the retention interval.     

Maintained generalization testing of conditioned suppression

This study concerns the use of a multiple stimulus discrimination procedure for producing data on the generalization of conditioned suppression. Four rats were maintained on a variable interval schedule of milk reinforcement in the presence of five stimuli varying in auditory click rate. When response rates were stable, electric shock was regularly paired with the termination of one of the click stimuli. For two rats the shock was paired with the slowest click rate, and for two rats shock was paired with the fastest click rate. The VI schedule remained in effect. Plots of the relative rates of response to each of the five stimuli yielded concave gradients for both animals suppressed at the slowest click rate, and flat gradients with a sharp drop at the warning stimulus for both animals suppressed at the fastest click rate. When the warning stimuli were reversed for both pairs of subjects, both gradient forms were reproduced. The present procedure was contrasted with procedures used by other investigators.     

Some notes on the nature of methodological indeterminacy

This paper is an attempt to extend the meaning of the concept of indeterminacy for the human sciences. The authors do this by coining the term methodological indeterminacy and arguing that indeterminacy is better understood when linked to specific methodological techniques. Paradoxically, while specific research techniques demonstrate that the issue of indeterminacy is complex, yielding the possibility of types and degrees, it does not eliminate the problem of translation first raised by Quine. However, the authors go on to argue that, from a research perspective, indeterminacy can and must be approached in such a way that it is possible to reduce cases of it, even though never completely eliminating it in the human sciences.     

One-trial conditioned suppression: effects of instructions on extinction

Two experimental groups of undergraduate volunteers received a single Pavlovian conditioning trial consisting of a paired presentation of a tone conditioned stimulus (CS) and a shock unconditioned stimulus (UCS). Control groups received either the CS alone or the UCS alone. Subjects from one experimental group were subsequently instructed that they would not receive further shocks, while the other experimental group received no such instructions. The CS alone was then presented once to all four groups while subjects were engaged in a button-pressing task maintained by slide reinforcement. During the latter phase, rate of button-pressing was measured. Classically conditioned suppression of button-pressing was obtained in the noninstructed experimental group but not in the instructed group. The results demonstrate that suppression can be a sensitive index of Pavlovian conditioning in humans but question the use of conditioned suppression as an adequate experimental analog of clinically observed anxiety-motivated behavior.     

Retrospective revaluation effects in the conditioned suppression procedure

In four experiments using the conditioned suppression procedure, rats received initial reinforced training with two compound stimuli, AX and BY, each compound consisting of one auditory and one visual element. After a second phase of training consisting of nonreinforced presentations of A, the suppression governed by X and Y was tested. In Experiment 1 X evoked slightly less suppression than Y (a mediated extinction effect). This outcome was obtained when the auditory cues served as Xand Y(Experiment 1a), when the visual cues served as Xand Y(Experiment 1b), and when the number of nonreinforced presentations of Awas increased (Experiment 1c) from 18 to 216. In Experiment 2, however, in which the initial training was given with serial compounds (i.e., A ⇒ X and B ⇒ Y) X evoked more suppression than Y (a recovery-from-overshadowing effect). It was argued that extinction of A engages two learning processes, one increasing the effective associative strength of its associate (X) and one reducing it, and that the balance between these two depends on the specific conditions of training.     

Generalization of conditioned suppression after differential training

In a modified conditioned suppression procedure, clicks at one frequency (danger signal) preceded shocks, while no shocks followed clicks at a different frequency (safe signal). During generalization tests, the maximal response rate was frequently shifted from the safe signal in the direction away from the danger signal, and the minimal response rate was frequently shifted in the opposite direction, away from the safe signal. There was considerable variability in the results from one animal to another. The generalization tests also suggested different generalization functions according to whether the danger signal was a lower or a higher frequency than the safe signal. The results also showed the development of systematic differences in response rate during and after the safe and danger signals, notably a relatively high rate at the beginning of the safe signal and after the danger signal.