Food-paired stimuli as conditioned reinforcers: effects of d-amphetamine.

Seven pigeons were studied in two experiments in which key pecks were reinforced under a second-order schedule wherein satisfaction of variable-interval schedule requirements produced food or a brief stimulus. In the second part of each session, responses produced only the brief stimulus according to a variable-interval schedule (food extinction). For the 4 pigeons in Experiment 1, the response key was red throughout the session. In separate phases, the brief stimulus was either paired with food, not paired with food, or not presented during extinction. d-Amphetamine (0.3 to 10.0 mg/kg) dose-dependently reduced food-maintained responding during the first part of the session and, at intermediate dosages, increased responding during the extinction portion of the session. The magnitude of these increases, however, did not consistently depend on whether the brief stimulus was paired, not paired, or not presented. It was also true that under nondrug conditions, response rates during extinction did not differ reliably depending on pairing operations for the brief stimulus. In Experiment 2, 3 different pigeons responded under a procedure wherein the key was red in the component with food presentations and blue in the extinction component (i.e., multiple schedule). Again, d-amphetamine produced dose-related decreases in responding during the first part of a session and increases in responding in the second part of the session. These increases, however, were related to the pairing operations; larger increases were observed when the brief stimulus was paired with food than when it was not or when it was not presented at all. Under nondrug conditions, the paired brief stimulus controlled higher response rates during extinction than did a nonpaired stimulus or no stimulus. These findings suggest that d-amphetamine can enhance the efficacy of conditioned reinforcers, and that this effect may be more robust if conditioned reinforcers occur in the context of a signaled period of extinction.     

Attenuation of latent inhibition after compound conditioning

Using a conditioned suppression procedure with rats, three experiments examined the effects of compound conditioning on the degree of latent inhibition. Experiment 1 suggested that latent inhibition of the preexposed target was not enhanced but rather attenuated when a second stimulus was presented in compound conditioning. Experiment 2 showed that a similar result was obtained when, in subjects given only compound conditioning, the salience of the target was reduced to the level where it was overshadowed by the second stimulus. Experiment 3 proved that addition of the second stimulus only during preexposure, or during both preexposure and conditioning, did not attenuate the latent inhibition to the target. These results are difficult to explain by any model of Pavlovian conditioning which assumes that both latent inhibition and overshadowing effects are a consequence of acquisition deà cit; other possible accounts are discussed.     

Conditioned reinforcement dynamics in three-link chained schedules.

In two experiments rats were trained on three-link concurrent-chains schedules of reinforcement. In Experiment 1, additional entries to one terminal link were added during one of the middle links to a baseline schedule that was otherwise equal for the two chains, and, depending on the condition, these additional terminal-link presentations ended either in food or in no food. When food occurred, preference was always in favor of the chain with the additional terminal-link presentations (which also entailed a higher rate of reinforcement). When no food occurred at the end of the additional terminal links, the outcome depended on the nature of the stimuli associated with these additional terminal links. When stimuli different from the reinforced baseline terminal links were used for the no-food terminal links, preference was against the choice alternative that led to the extra periods of extinction. When the same stimulus was used for the two kinds of terminal links, preference was near indifference, that is, significantly greater than when different stimuli were used. In Experiment 2, rats learned repeated reversals of a simultaneous discrimination under a three-link concurrent-chains schedule, in which the food or no-food choice outcomes were delayed until the end of the chain. Different conditions were defined by the point in the chain at which differential stimuli occurred. When the middle and terminal links provided no differential stimuli, discrimination was acquired more slowly than when differential stimuli occurred in both links. When differential stimuli occurred in the middle but not the terminal links, acquisition rates were intermediate. Both experiments together show that the effects of stimuli in a chain schedule are due partly to the time to food correlated with the stimuli and partly to the time to the next conditioned reinforcer in the sequence.     

I. V. Zavadskii and the beginnings of behavioral pharmacology: an historical note and translation.

I. V. Zavadskii, who worked in Pavlov's laboratory between 1907 and 1909, performed a study that has many of the characteristics of modern behavioral pharmacology. He studied the effects of alcohol, morphine, cocaine and caffeine on the conditioned salivary reflex. A translation of his paper and some brief comments on his life are presented.     

Conditioned reinforcement and choice

In a series of three experiments, rats were exposed to successive schedule components arranged on two levers, in which lever pressing produced a light, and nose-key pressing produced water in 50% of the light periods. When one auditory signal was presented only during those light periods correlated with water on one lever, and a different signal was presented only during those light periods correlated with nonreinforcement on the other lever, the former lever was preferred in choice trials, and higher rates of responding were maintained on the former lever in nonchoice (forced) trials. Thus, the rats preferred a schedule component that included a conditioned reinforcer over one that did not, with the schedules of primary reinforcement and the information value of the signals equated. Preferences were maintained when one or the other of the auditory signals was deleted, but were not established in naive subjects when training began with either the positive or negative signal only. Discriminative control of nose-key pressing by the auditory signals was highly variable across subjects and was not correlated with choice.     

Discriminated response and incentive processes in operant conditioning: a two-factor model of stimulus control

Understanding stimulus control generated in instrumental learning requires the direct investigation of discriminated response and reinforcer (incentive) processes acquired exclusively through the response-reinforcer contingencies operating on complex (multicomponent) baselines. Two series of stimulus-compounding studies accomplished this direct investigation. In one series, the independent variable was the relative reinforcement between schedule components; in the second series, it was relative response rate between components. Stimulus-compounding tests revealed that response and incentive processes enhanced each other when in agreement, counteracted each other when in opposition, and produced intermediate results when only one factor was operating. This pattern of results led to the conclusion that these factors were algebraically combining and to the development of a response/incentive matrix reflecting these dynamics. This two-factor analysis was extended to the peak-shift effect in stimulus generalization experiments and to the generation of inhibitory control. Two decades of stimulus compounding and peak-shift research were organized within this two-factor framework, extending this traditional approach to learning to active research areas heretofore not systematically considered in these terms.     

Variable shock-free times with informative and uniformative stimuli

Three rats were trained on a fixed-ratio escape procedure in which responding produced one of two equiprobable outcomes—a 10-second or 60-second shock-free period. Before the fixed-ratio requirement was satisfied, brief shocks were presented at irregular intervals averaging either 15 or 30 seconds. Two conditions, differing in the relationship between exteroceptive stimuli and the outcomes, were studied. In the uninformative (uncorrelated) condition, the same stimulus was presented during both outcomes. In the informative (correlated) condition, one stimulus was present during the 10-second outcome only; another stimulus was present during the 60-second outcome only. Subjects pressed faster in the uninformative condition than they did in the informative condition. The inadequacy of the information hypothesis in accounting for the findings is discussed, and an alternative hypothesis is offered.     

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.     

一般性注意资源限制对返回抑制的影响

通过探讨视空间和语义通道内的注意资源的限制对IOR的影响的4个实验,来验证“IOR的低级成分不受注意资源限制的影响和IOR的高级成分受注意资源限制的影响”的假设。实验1A和1B的结果表明,在基于空间位置的简单检测任务中,IOR的低级成分既不随语义通道内注意资源的减少而消减,也不随空间通道内注意资源的减少而消减。实验2A和2B结果表明,在基于客体特性的辨别任务中,IOR的高级成分既随语义通道内注意资源的减少而消减,又随空间通道内注意资源的减少而消减。因此,辨别任务中的IOR受一般性注意资源的限制。同时,实验结果还表明,IOR的高级成分对空间通道内的注意资源的需求要高于对语义通道内注意资源的需求     

对体液免疫反应的条件反射性调节

以饮糖精水作为条件刺激(conditioned stimulus,CS),腹腔注射免疫抑制剂环磷酰胺作为非条件刺激(unconditioned stimulus,UCS)训练Wistar大鼠,3天后腹腔注射卵清蛋白(ovalbunfin,OVA)抗原,观察再次单独条件刺激对原发性体液免疫反应的作用。结果发现．一次CU-UCS结合训练导致CS组大鼠对再现糖精水产生厌恶反应,外周血中抗OVA-IgG抗体水平显著低于UCS组。两次CS-UCS结合训练并多次给予条件刺激后,CS组大鼠抗OVA-IgG的条件性免疫抑制效应与一次CS-UCS结合训练及再次给予一次条件刺激的反应类同。这些结果证明条件刺激增强了环磷酰胺对动物原发性体液免疫反应的抑制作用．这种条件性体液免疫抑制作用是相对稳定和有限度的,不易受条件反射建立参数的影响。