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Laboratory rats trained upon a table top with randomly positioned reinforcement containers showed significantly a greater tendency to alternate in a Y-maze than animals trained on a straight runway. The type of deprivation, either food or water, did not have an effect. The differences in alternation disappeared with repeated trials on the Y-maze.
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In Exp I, three pigeons were trained on an observing response procedure where observing responses produced a stimulus correlated either with FI or with FR. Stimulus duration was 30 sec. During FR, the subjects completed the ratio before the stimulus terminated. During FI, the subjects usually observed the stimulus only once. Observing responses occurred immediately after food reinforcement. In Exp II, stimulus duration was shortened to 5 sec and the FR for food was increased. The results were similar to those of Exp 1. During most FIs and FRs, only one observing response occurred. The results of both experiments could be interpreted in a response competition framework. Immediately after food reinforcement, observing behavior is strong. When behavior on the food key begins it competes with further observing behavior.
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Administration of antimuscarinic drugs induces amnesia of aversively motivated behaviors. However, when relatively high intensities of footshock are used during training (over-reinforcement), animals become protected against such amnesic state. Moreover, the protective effect is established in a none-or-all fashion, i.e., within a series of increasing intensities a minute augmentation of footshock intensity is sufficient to reach the protective threshold. In the present experiment it was found that very low intensities of aversive stimulation (under-reinforcement), sufficient to produce learning, also protected animals from scopolamine-induced amnesia. These results suggest that acetylcholine is critically involved in memory consolidation of passive avoidance, but only within a limited range of training intensities.
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Rats were trained on a discrete-trial probability learning task. In Experiment 1, the molar reinforcement probabilities for the two response alternatives were equal, and the local contingencies of reinforcement differentially reinforced a win-stay, lose-shift response pattern. The win-stay portion was learned substantially more easily and appeared from the outset of training, suggesting that its occurrence did not depend upon discrimination of the local contingencies but rather only upon simple strengthening effects of individual reinforcements. Control by both types of local contingencies decreased with increases in the intertrial interval, although some control remained with intertrial intervals as long as 30 s. In Experiment 2, the local contingencies always favored win-shift and lose-shift response patterns but were asymmetrical for the two responses, causing the molar reinforcement rates for the two responses to differ. Some learning of the alternation pattern occurred with short intertrial intervals, although win-stay behavior occurred for some subjects. The local reinforcement contingencies were discriminated poorly with longer intertrial intervals. In the absence of control by the local contingencies, choice proportion was determined by the molar contingencies, as indicated by high exponent values for the generalized matching law with long intertrial intervals, and lower values with short intertrial intervals. The results show that when molar contingencies of reinforcement and local contingencies are in opposition, both may have independent roles. Control by molar contingencies cannot generally be explained by local contingencies.
The inferior colliculus has been implicated in aversive or anxiogenic aspects of defensive behavior. Animals learn to turn off electrical stimulation applied to the inferior colliculus. The purpose of the present study was to determine (1) whether this aversion induced by electrical stimulation can be conditioned to a conditioned stimulus (CS, light) and (2) whether pre-exposure to the CS will diminish the extent of such conditioning, i.e. whether latent inhibition can be established with this paradigm. Rats were placed inside an open field, and thresholds for the escape response to electrical stimulation of the inferior colliculus were determined. The rats were then placed inside a shuttle box and submitted to a two-way avoidance paradigm. Electrical stimulation of the inferior colliculus at the escape threshold was used as negative reinforcement and shuttle box illumination as the CS. The rats quickly learned to avoid or terminate the inferior-colliculus stimulation. Furthermore, the performance of the animals in this paradigm was significantly disrupted when they were pre-exposed to 50 presentations of the CS before the session. These data suggest that the inferior colliculus has neural substrates for supporting associative learning and latent inhibition.
A group of severely retarded institutionalized adults was exposed to three different types of instructional procedures (imaginal instruction, verbal instruction, no instruction) and three types of reinforcement procedures (no reinforcement, reinforcing correct responses, reinforcing all responses) in learning concepts through modeling. Concept acquisition was tested, using Leiter-type items, in direct imitation as well as in a generalization task. In both imitation and generalization conditions, imaginal instructions were more effective than verbal instructions, which in turn were more effective than no instructions. The study of modeling procedures, especially with regard to the use of imagery, is called for in order to investigate the processes involved in their effectiveness with a severely retarded population.
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BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) affects up to 10% of school-age children. The impulsivity which is seen as its core feature persists over years, yet experimental measures of impulsivity can be altered in a single session. In this study, we tested the theory that both the persistence and the variability of impulsivity could be the result of abnormalities in learning mechanisms and environment. METHOD: We extended an existing model of the role of dopamine in operant conditioning to address the delayed response time task, which is one of the standard tests for impulsivity in ADHD. In this task, subjects choose between immediate responding for a small reinforcer and later responding for a larger one. We studied the influence on impulsivity of four key parameters of the model: The learning rate, discount factor, brittleness, and action bias. RESULTS: The behavior of the model is broadly comparable with electrophysiological (monkey) and behavioral (ADHD and normal) data. Variations in any of the parameters can cause impulsivity. All parameters except the discount factor show inverted U-shaped curves for their effects on impulsivity, suggesting, for example, how either hyper- or hypofunctioning of dopamine can cause impulsivity. The model suggests how decision making can be affected by environmental unpredictability, and thus offers an account of one aspect of the natural history of ADHD. CONCLUSIONS: Some types of ADHD may be caused by specific deficits in reinforcement learning and in the use of learned lessons. Environmental factors can interact with these deficits to delay maturation.
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For rats in a T-maze, nonreinforced trials were interspersed with reinforced trials to insure that .67 of all reinforcements would be dispensed on the more frequently reinforced side. At asymptote , the proportion of responses to the more frequently reinforced side was .67.
Parameters were identified for the rat which both made drinking more probable than running and running more probable than drinking. In the same subjects, depending upon which parameters were used, running reinforced drinking and drinking reinforced running. This relationship suggests that a "reward" is simply any response that is independently more probable than another response.
The progressive ratio schedule requires the subject to emit an increasing number of responses for each successive reinforcement. Eventually, the response requirement becomes so large that the subject fails to respond for a period of 15 min and thereby terminates the session. This point is arbitrarily defined as the "breaking point" of the subject's performance. The measure is quantified in terms of the number of responses in the final completed (i.e., reinforced) ratio run of the session. Previous work has shown that this measure varies as a function of several motivational variables and may thus be useful as an index of reinforcement strength. The present study is an extension of that work. The subjects were four rats. In the first experiment, the effects of the size of the increment by which each ratio run increased were studied. In two additional experiments, the volume of a liquid reinforcer was varied using both large and small ratio increments. The results indicate that the number of responses in the final completed ratio run increases as a function of the size of the ratio increment. However, the number of reinforcements obtained by the animals per session declines sharply. When large ratio increments are used, the number of responses in the final ratio increases as a function of the volume of the reinforcer, but when small increments are used, progressive satiation results in a decline in performance with the larger volumes of liquid.
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