Variable-Interval Schedule Control Following Response Acquisition with Delayed Reinforcement

The Psychological Record - Four experimentally naive White Carneau pigeons acquired a key-peck response without specific response shaping or other training when such responding was reinforced...     

Free operant avoidance in rats under increased nitrogen pressures.

Rats performed on a free operant avoidance schedule with a response-shock interval of 20 sec. and a shock-shock interval of 2 sec. Avoidance response rates increased and shock frequency decreased when the rats were exposed to elevated pressures of both air and a nitrogen-oxygen mixture in a hyperbaric chamber. Increases in response rates were related to raised partial pressures of nitrogen at 89.0 psi and 111.3 psi. Conditional probabilities of interresponse times indicated that increases in response rates were not due to disruption of temporal discrimination. Increased avoidance rates under pressure suggested direct excitatory effects of high pressures of nitrogen.     

Conditioning of a free operant in Octupus cyaneus Gray

Operant conditioning was studied in six specimens of Octopus cyaneus Gray. An “arm-out-of-water” operant, in which the octopus inserted an arm up a feeding-tube breaking the water surface, proved susceptible to reinforcement schedules. An apparatus was developed that provided automated reinforcement and recording. Performance was studied under continuous reinforcement, fixed-ratio and variable-ratio schedules, and extinction conditions.     

Context specificity of operant discrimination performance in pigeons

In an experiment designed to investigate odors as potential retrieval cues in pigeons' memory (i.e., as conditional stimuli), 8 pigeons first learned to peck a red keylight (S+, reinforced) and not a blue one (S−, extinguished) in the presence of either a eucalyptus oil or isoamyl acetate odor. They were repeatedly switched between two chambers with the same odor to habituate any reaction to the switching that would be required for eventual testing for conditional control by the odors. Next, the birds learned the reversal (blue S+, red S−) in the presence of the alternative odor in one of these chambers. When the birds were then switched to the alternative chamber for additional training, although the odor was still appropriate to the reversal problem, behavior appropriate to the original training condition recurred. Testing indicated that reversal performance was specific to the one chamber in which it had been trained.     

Partial Reinforcement in Appetitive Pavlovian Conditioning with Rats

Four experiments examined the effects of a partial reinforcement schedule on extinction using appetitive Pavlovian conditioning. Extinction was slower after partial than after continuous reinforcement when the schedules were administered to different groups (Experiment 1). The opposite result was found in Experiments 2 and 3 when both schedules were presented to the same group in the same context. When the schedules were presented to the same group in different contexts, then extinction was again slower after partial reinforcement (Experiment 3). Experiment 4 demonstrated that a change of context facilitates extinction to a greater extent after conditioning with a partial reinforcement schedule than with a continuous one. The results are explained by assuming that the nonreinforced trials of a partial reinforcement schedule create an internal state that serves as a contextual cue.     

Backward Sensory Preconditioning When Reinforcement Is Delayed

In two experiments rats received an initial phase of training in which two neutral stimuli were presented as a serial compound (A-X). In a second phase, Awas established as a signal for a shock reinforcer, the shock being presented immediately after the termination of A (the immediate condition) or after a 5-sec interval (the trace condition). A final test phase showed that not only A but also X was capable of evoking conditioned suppression (a backward sensory preconditioning effect). The degree of suppression evoked by X was not correlated with that evoked by A. In both experiments the A trained with immediate reinforcement was more suppressive than that trained with the trace procedure, but in Experiment 1 the trace and immediate groups did not differ in the response they showed to X, and in Experiment 2 (which allowed a within-subject comparison) the trace procedure resulted in more suppression to X than did immediate conditioning of A. These results disconfirm the suggestion that the backward sensory preconditioning effect depends on the formation of an associative chain: X-A-shock. They are consistent with the proposal that the associatively activated representation of X is able to form a direct association with the reinforcer during A-shock training.     

Acquisition of a spatially defined operant with delayed reinforcement.

Two experiments investigated the role of an immediate, response-produced auditory stimulus during acquisition, via delayed reinforcement, of a response selected to control for possible unprogrammed, operandum-related sources of response feedback. Experimentally naive rats were exposed to a delayed-food reinforcement condition, specifically a tandem fixed-ratio 1 differential-reinforcement-of-other-behavior 30-s schedule. The response was defined as breaking a photocell beam located near the ceiling at the rear of the operant conditioning chamber. In Experiment 1, rates of photobeam breaking by each rat increased from near zero, regardless of the presence or absence of a tone that immediately followed the response initiating the delay interval. Though not essential, the tone facilitated response acquisition and resulted in more efficient response patterns at stability. Experiment 2 demonstrated that photobeam-breaking response rates under the delayed reinforcement contingency exceeded those in a preceding baseline condition in which no food was delivered. In addition, upon introduction of the delayed reinforcement procedure, correspondence between response patterns and the requirements of the reinforcement schedule increased over baseline levels in the absence of a food contingency. Together with a previous report of Lattal and Gleeson (1990), the present results suggest that response acquisition with delayed reinforcement is a robust phenomenon that may not depend on a mechanically defined response or an immediate external stimulus change to mediate the temporal gap between response and reinforcer.     

Acquisition and transfer of occasion setting in operant feature positive and feature negative discriminations

The acquisition and transfer of stimulus control in discrete-trial operant feature positive and feature negative discriminations was examined in two experiments with rats. When the feature and target cues were presented simultaneously on compound training trials, the feature appeared to acquire simple excitatory or inhibitory control, which readily transferred to other target cues and which was substantially reduced by post-training counterconditioning. Conversely, when the feature preceded the target during training, the feature's control was relatively more specific to responding in the presence of its original target and less influenced counterconditioning. These results are comparable to outcomes of analogous experiments (previously reported) that used Pavlovian conditioning procedures.     

Differential Conditioning Based on a Difference in the Predictability of Reinforcement

A Pavlovian procedure containing a set of several alternative reliable trial stimuli and a set of several alternative unreliable trial stimuli was used to determine if reliability of outcome, per se, would differentially condition additional trial stimuli that either preceded or followed those original trial stimuli in a serial conditioning paradigm. The reinforcing effectiveness of the antecedent stimuli themselves was later tested in a higher-order conditioning design. It was found that different rates could be established to the different antecedent stimuli in the absence of a difference in the probability of reinforcement. Further, stimuli paired with those antecedent stimuli in the higher-order conditioning test also exhibited a difference in rate. It was concluded that a combination of a stimulus that is always followed by food and another that is never followed by food are, in net, a more effective reinforcer than a common stimulus that has the same overall probability of reinforcement but which is followed by both outcomes.     

Free operant avoidance as a function of the response-shock=shock-shock interval

Two temporal parameters of free operant or Sidman avoidance behavior are the interval by which responses postpone shocks (Response-Shock interval) and the interval between shocks when no responses occur (Shock-Shock interval). Avoidance behavior was examined in three white rats under conditions where the Response-Shock and Shock-Shock intervals were always equal. With intervals from 10 to 60 sec response rates and shock rates were similar, decreasing, negatively accelerated functions of increasing Response-Shock=Shock-Shock interval. Over this range, response and shock rates were linearly related to the reciprocal of the Response-Shock=Shock-Shock interval. It was shown, however, that this relation cannot hold at extremely long intervals. Both the ratio of responses emitted to shocks received and the percentage of shocks possible which were avoided increased at long Response-Shock=Shock-Shock intervals. These findings may be related to the fact that long intervals provide optimal conditions for conditioning avoidance behavior in the rat.     

Choice As A Function Of Reinforcement Ratios In Delayed Matching-to-sample

Pigeons were studied in two experiments using a delayed matching-to-sample task. In Experiment 1, 4 subjects were exposed to a task in which the proportion of reinforcement associated with matching and nonmatching, and the overall proportion of reinforcement associated with selecting each choice, regardless of the sample stimulus, were varied. Choice was sensitive to both proportions. A least squares regression analysis showed that Wixted's (1989) proportions of reinforcement model closely fit the data from Experiment 1; however, the model failed to make accurate qualitative predictions for some test conditions. In Experiment 2, 4 subjects were exposed to a delayed matching-to-sample task in which the retention intervals and the reduction in delay to reinforcement signaled by the onset of the sample stimulus were independently varied. When the retention interval was short and when the delay-reduction value of the sample stimulus was high, the sample exerted greater control over choice; the control by the overall proportion of reinforcements for selecting each choice stimulus was correspondingly low. Conversely, when the retention interval was long and the delay-reduction value of the sample stimulus was low, the sample exerted relatively less control over choice; control by the overall proportion of reinforcements obtained for selecting each choice stimulus was correspondingly high. A signal detection analysis found that sensitivity to reinforcement varied directly with retention interval. Data were also consistent with misallocation models. No evidence was found to suggest that pigeons ignore the rate at which selecting individual choice stimuli is reinforced, as has been reported in studies with human subjects.     

Context specificity of operant discriminative performance in pigeons: II. Necessary and sufficient conditions

Six experiments were performed to explore the necessary and sufficient conditions for producing context specificity of discriminative operant performance in pigeons. In Experiment 1, pigeons learned a successive discrimination (red S+/blue S−) in two chambers that had a particular odor present and between which they were frequently switched. The birds subsequently learned the reversal (blue S+/ red S−) in one of these chambers with a different odor present. When switched to the alternative chamber, although the odor and the reinforcement contingency were still appropriate to the reversal, performance appropriate to the original discrimination recurred in subjects for which the houselights were on during training and testing but not for those for which the houselights were off. This indicated the importance of visual contextual cues in producing context specificity. Experiment 2 showed that the frequent switching between boxes in initial training was of no consequence, presumably because the apparatus cues were highly salient to the subjects. Experiment 3 showed significantly less context specificity when odor cues were omitted. Experiment 4 showed that simply using a different reinforced stimulus in each phase of training was ineffective in producing context specificity. Experiment 5 showed that the generalization test procedure used in Experiment 4 was sensitive to context specificity when discrimination-reversal training was used with different odors in the two training phases. Experiment 6 replicated the results of Experiment 4, but then showed that when different odors accompanied the two training phases, context specificity was obtained with the single-stimulus paradigm. Thus in both single-stimulus and discrimination-reversal paradigms, redundant odor cues potentiated learning about apparatus cues.     

Scopolamine Selectively Disrupts the Acquisition of Contextual Fear Conditioning in Rats

Muscarinic cholinergic antagonism produces learning and memory deficits in a variety of hippocampal-dependent tasks. Hippocampal lesions produce both acquisition deficits and retrograde amnesia for contextual fear conditioning, but do not impact fear conditioning to discrete cues. In order to examine the effects of muscarinic antagonism in this paradigm, rats were given scopolamine (1 mg/kg) either before or for 3 days after a Pavlovian fear-conditioning session in which tones were paired with aversive footshocks. Fear to the context and the tone was assessed by measuring freezing in separate tests. It was found that pretraining, but not posttraining, scopolamine severely impaired contextual fear conditioning; tone conditioning was not affected under either condition (cf., Young, Bohenek, & Fanselow,Neurobiology of Learning and Memory,63,174–180, 1995).     

Human operant learning under concurrent reinforcement of response variability

This study asked whether the concurrent reinforcement of behavioral variability facilitates learning to emit a difficult target response. Sixty students repeatedly pressed sequences of keys, with an originally infrequently occurring target sequence consistently being followed by positive feedback. Three conditions differed in the feedback given to non-target sequences: concurrent positive feedback presented contingent on response variability, positive feedback presented non-contingently, or no reinforcement for any non-target responses (control condition). Contrary to the result of analogous rat studies, if anything, the participants in the control condition more readily learned to emit the target sequence than did the subjects in each of the other two conditions. It is argued that these contradictory findings are primarily caused by procedural differences, such as differences in the density of the reinforcement schedule applied to non-target behavior, rather than reflecting a true species difference.     

Zebrafish excel in number discrimination under an operant conditioning paradigm

Animal Cognition - Numerical discrimination is widespread in vertebrates, but this capacity varies enormously between the different species examined. The guppy (Poecilia reticulata), the only...     

Loss of Latent Inhibition of Contextual Conditioning Following Non-reinforced Context Exposure in Rats

Three experiments with rats demonstrated that preexposure to an experimental environment retarded the level of conditioned freezing observed on a test in that environment after it had been paired with mild footshock. Furthermore, Experiment 1 demonstrated that this latent inhibition effect could be abolished if preexposed rats were exposed to a second experimental environment following conditioning to the preexposed environment. Experiments 2 and 3 demonstrated that this second environment had to be similar, but not identical, to the preexposed environment, and that the influence of exposure to the second environment on latent inhibition could be abolished by exposure to that environment prior to footshock conditioning. These results are considered in terms of the Dickinson-Burke (1996) theory of retrospective revaluation, and their implications for experiments demonstrating a loss of latent inhibition across a delay are considered.