The problem of maintaining independence between response rates and reinforcement probabilities when determining the effect of varying the response-reinforcement contingency upon free-operant behavior was solved by programming local reinforcement probabilities for response and no response on a second-by-second basis. Fifty-seven rats were trained to lever-press on schedules of water reinforcement involving different values of contingency. All rats were first trained on a high positive contingency and then shifted to less positive, zero, or negative contingencies. Under these conditions, rate of lever-pressing declined appropriately when the contingency between response and reinforcement decreased or was made negative. The decline in rate produced by a zero contingency cannot be attributed to extinction, since the probability of reinforcement given the occurrence of a response was the same as for the positive contingency from which the shift to zero was made. That is, there was no change in the opportunity for response-reinforcement contiguity. It was concluded that the technique of programming local reinforcement probabilities offers promise for more critical examinations of the effects of contingency upon free-operant behavior.
Rats in an experimental group were given 30 trials of dif ferential CER and then the CS+ and CS-were combined during CER extinction. The combination resulted in less suppression for the experimental group than shown by a control group which had a CS+ and a formerly random stimulus combined during extinction. This was interpreted as a demonstration of the active inhibitory properties of CS-.
Rats were givell differelltial cOllditiollillg to a tOile ( There are several ways of combining Pavlovian conditioning and instrumental training procedures in the control of instrumental responding. Rescorla & LoLordo (1965) trained dogs to jump to avoid shock on a Sidman schedule, and then they tested the dogs with brief presentations of a CS+ that had been paired with shock and a CS-that had been paired with absence of shock during Pavlovian conditioning. The CS+ was excitatory, increasing the jumping rate, but the CS-was inhibitory, actively suppressing the jumping. In this experiment both the Pavlovian US and the instrumental reinforcer were aversive.In contrast, the standard CER experiment combines an aversive Pavlovian conditioning procedure with an appetitive instrumental training procedure; and, in addition, most CER experiments have been non-discriminative, using a CS+ paired with shock but no contrasting CS-paired with absence of shock. Therefore, we are not yet certain whether the CS+ and CSof a Pavlovian fear conditioning procedure would have effects on appetitive instrumental responding analogous to those found by Rescorla and LoLordo for aversive instrumental responding. We know that a CS+ paired with shock will suppress appetitive instrumental responding. We have, however, only hints about the action of a CS-paired with absence of shock. Ray & Stein (1959) did differential conditioning with two tones of different f,;requency using the CER procedure. They found enhancement of instrumental responding to the presentation of the CS-after three months of differential conditioning.In the present study, the investigation of the inhibition of fear in the CER paradigm is improved by the use of a CS+ and CS-which are markedly different from each other. MethodSixteen albino rats were divided into a CER and a no-shock control group.Four automatically programmed Skinner boxes were used. Ss were given six 2 hr. daily sessions of VI-I min. training for water reward (under 21-1/2 hr. deprivation). On both the fifth and sixth day of VI training, Psychon. SCi., 1966, Vol. 5 (9) LYNN J. HAMMOND TEMPLE UNIVERSITY a flashing light (6 w bulb) and a tone (3000 cps) were each presented three times. Stimulus dUration was 3 min. No shock was presented on these days. This procedure was then continued for another 15 days for the control group. For the CER group, the stimuli were presented in the same fashion on these 15 days, but the tone (CS+) always terminated in a .5 sec., .72 ma, scrambled grid-shock. Thus the CER group received three tone-shock trials and three light-no-shock trials a day, for a total of 45 reinforced trials. ResultsSuppression ratios were calculated for the responses to the stimuli (AI A + B, where A is the rate during the 3 min. stimulus and B is the rate for the 3 min. immediately preceding the stimulus).The suppression ratios produced by the CS+ and CSfor the CER group on the two pre-test days and the 15 conditioning days are shown in Fig. 1. Also shown are the control group's ratios to the light on...
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