Dominance,the bidirectional hypothesis,and Pavlovian backward conditioning in the US-US paradigm

Based upon considerations raised by Soviet research, the role of relative stimulus intensity, or dominance, in the unconditioned stimulus-unconditioned stimulus (US-US) paradigm was investigated under circumstances presumed favorable to the backward conditioned response (CR). Using the classically conditioned forelimb response of the cat, a brief shock (USD delivered to one forepaw preceded a shock (US2) to the opposite forepaw in paired conditioning fashion; subjects in the control group received explicitly unpaired presentations of the stimuli. Conditioning in both the forward and backward directions was evaluated by the appearance of contralateral CRs on test trials to each of the USs. In Experiment 1, a ratio of the intensities between US1 and US2 of 100:80 was used to create a relative dominance in favor of the backward CR. In addition, to evaluate the suggestion that the appearance of the backward CR is retarded in the Pavlovian paradigm, overtraining was provided to a forward conditioning criterion of 200%. In Experiment 2, the cats were exposed to successive reductions in the intensity of US2 to verify manipulations of dominance reportedly involved in the reactivation of a latent backward CR. Although forward conditioning was readily established to USl, there was no evidence of back-ward conditioning to US2 under any of the conditions.     

Outcome-specific conditioned inhibition in Pavlovian backward conditioning

In the present experiments, the outcome specificity of learning was explored in an appetitive Pavlovian backward conditioning procedure with rats. The rats initially were administered Pavlovian backward training with two qualitatively different unconditioned stimulus conditioned-stimulus (US-CS) pairs of stimuli (e.g., pellet --> noise or sucrose --> light), and then the effects of this training were assessed in Pavlovian-to-instrumental transfer (Experiment 1) and retardation-of-learning (Experiment 2) tests. In the transfer test, it was shown that during the last 10-sec interval, the CSs selectively reduced the rate of the instrumental responses with which they shared a US, relative to the instrumental responses with which they did not share a US. The opposite result was obtained when the USs (in the absence of the CSs) were presented noncontingently. In the retardation test, conditioned magazine approach, responding to the CSs was acquired more slowly when the stimulus-outcome combinations in the backward and the forward conditioning phases were the same, as compared with when they were reversed. These results are collectively in accord with the view that Pavlovian backward conditioning can result in the formation of outcome-specific inhibitory associations. Alternative views of backward conditioning are also examined.     

Effects of a backward conditioning procedure following acquisition on extinction of conditioned suppression

A one-trial-a-day procedure was used to investigate the effects of US-CS pairings on extinction of conditioned suppression of licking by rats. Following acquisition trials, response suppression was immediately eliminated when US preceded CS, but it reappeared during subsequent CS-alone presentations. Ss that received backward pairings reached a significant level of extinction one trial before Ss that received conventional extinction trials.     

Outcome-selective effects of intertrial reinforcement in a Pavlovian appetitive conditioning paradigm with rats

The outcome-selective effects of presenting intertrial unconditioned stimuli (USs) in a rat appetitive conditioning paradigm were examined in two experiments. In both experiments, two stimuli were paired with different outcomes, while one of these outcomes was also presented in the intertrial interval (A+, B*, +). Two measures of learning, stimulus-elicited magazine approach and Pavlovian-to-instrumental transfer, were used to examine these effects. The presence of freely occurring outcomes in the intertrial interval (ITI) was observed to interfere more with the learning of a new association (Experiment 1) and to degrade more an already established association (Experiment 2) when the conditioned stimulus had been paired with the same outcome as that occurring in the ITI. An outcome-selective effect of ITI USs distinguishes among accounts of contingency based on general performance, attentional, and motivational mechanisms from those based on more specific associative mechanisms. Overall, the data highlight the importance of specific encoding processes in the analysis of associative learning.     

CS modality effects in one-trial backward and forward excitatory conditioning as assessed by conditioned suppression of licking in rats

Rats received a single 4-sec 1-mA grid-shock US either preceded or followed by a 4-sec tone or light CS. Conditioning was later assessed by comparing the amount of lick suppression evoked by the forward- or backward-paired CS versus an explicitly unpaired CS. The backward-paired CS produced more suppression than the unpaired CS only when both were tone; the light evoked strong suppression whether paired or not. In the forward procedure, tone produced more suppression when paired and less when unpaired than did light; conditioning thus appeared stronger with the tone. In one experiment, observations showed that rats froze during the forward-paired tone but not during the light. Increasing CS duration from 4 to 12 sec had no effect for the forward-paired light but increased freezing to the forward-paired tone. Another experiment showed similar unconditioned suppression to tone and light but faster habituation to tone. Problems that these results create for interpreting evidence for excitatory backward conditioning in the conditioned suppression procedure are discussed.     

One-trial simultaneous and backward fear conditioning as reflected in conditioned suppression of licking in rats

In three experiments, groups of albino rats received one strictly simultaneous pairing of a 4-sec auditory conditioned stimulus (CS) and a 4-sec 1-mA shock unconditioned stimulus (US). Other groups received a backward pairing, in which the US began before the CS, or a forward pairing, in which the CS began before the US. Control groups received only the US or received both the CS and the US but widely separated in time. Later, the CS was presented while the rats licked a drinking tube for water, and CS-elicited suppression of licking was taken as an index of the Pavlovian conditioned response (CR). It was found that groups receiving a single forward or a single simultaneous pairing suppressed more than groups that had received a backward pairing; and the backward groups, in turn, suppressed more than the control groups. It appears, then, that excitatory fear conditioning, as reflected in conditioned suppression of licking in rats, can be produced in a single trial by both backward and simultaneous conditioning procedures.     

Differences in taste-potentiated odor aversions with O+/OT+ versus OT+/O+ conditioning: Implications for configural associations

The present research demonstrates a conditioning order effect difference: Odor-aversion conditioning is stronger following OT+/O+ conditioning than following O+/OT+ conditioning with specific odor (O) and taste (T) cues. When a weak odor cue was used in Experiments 1A and 1B, OT+/O+ conditioning produced significantly stronger odor aversions than did either O+/OT+ or O+/O+ conditioning, which did not differ. The same design was used in Experiment 2 with a strong odor, but the order effect difference was not replicated, suggesting that the order effect difference is specific to conditions that produce taste-potentiated odor aversions. The interpretation that O+/OT+ conditioning is weaker because of the absence of a taste-odor within-compound association was not supported in Experiments 3 and 4. Notably, using stimuli that supported potentiation in earlier experiments, in Experiment 4, we found evidence of a taste-odor within-compound association in the absence of potentiation. These results confirm that previous theories of potentiation (within-compound association model, sensory-and-gate channeling model) are not sufficient to produce potentiation. Instead, these results are interpreted in terms of taste-odor configural associations.     

One-trial excitatory backward conditioning as assessed by conditioned suppression of licking in rats: Concurrent observations of lick suppression and defensive behaviors

Twenty-eight male albino rats were given a single 4-sec 1-mA electric-grid-shock unconditioned stimulus (US). In the same session they received two 12-sec conditioned stimuli (CSs). One CS (explicitly unpaired) terminated 180 sec before the US began; the other (backward paired) began immediately after the US terminated. The CSs used were a 1000-Hz 85-dB tone and an 84-dB click; their roles were counterbalanced. Over the next 2 days, each CS was presented for 2 min while the rats drank from a water bottle. The backward-paired CS was found to suppress licking more than the explicitly unpaired CS. This suppression was accompanied by an increase in defensive behavior (freezing and freeze/nod) and by a decrease in other activity. The suppression did not seem to be due to a maintained or enhanced CS-orienting response reflex, nor could it be attributed to an adventitiously reinforced interfering operant. The results support the presumption made in previous reports that the lick suppression evoked by a backward CS reflected one-trial backward excitatory fear conditioning.     

The effects of signaling the US in backward conditioning: A shift from excitatory to inhibitory learning

The associative effects of “backward” US-CS pairings were compared when the pairing occasions were either consistently preceded by a well-trained CS+ or were unannounced. The investigation employed a conditioned emotional response procedure with rats, under conditions in which all subjects received the same schedule of shock USs, some signaled and others not, and the back-ward CS was arranged to follow either the former or the latter, in separate groups. The major finding was that although the backward CS became excitatory when it followed unsignaled USs, it became inhibitory when it followed signaled USs. This outcome, which is in line with prior findings of Wagner and Terry (1975), is in accordance with a “sometimes-opponent-process” model proposed by Wagner (1981). It is contrary to data reported by Fowler, Kleiman, and Lysle (1984) that may have resulted from a confounding of the different circumstances of backward conditioning with differences in the predictability of the US in the experimental context.     

One-trial backward excitatory fear conditioning in rats: Acquisition,retention, extinction,and spontaneous recovery

Water-deprived male albino rats received a single presentation of a 4-sec electric-grid-shock unconditioned stimulus followed by a 4-sec white-noise conditioned stimulus (a single backward conditioning trial.) Excitation conditioned to the noise was indexed in terms of the noise’s subsequent ability to suppress ongoing licking of a water tube. The main findings were: (1) Excitation was acquired and was retained over a 30-day retention interval; (2) although excitation was retained, it did not grow significantly stronger during the interval (there was no incubation effect); (3) excitation was extinguished by noise-alone trials; and (4) excitation showed more spontaneous recovery when extinction trials were separated by 29 days than when separated by only 1 day. Because these results are similar to those in the forward conditioning literature, they seem consistent with, but do not demand, the view that forward and backward excitatory conditioning involve similar learning processes. A current theory that embraces this view is opponent-process theory (Solomon & Corbit, 1974). We suggest that opponent-process theory can (1) account for existing backward conditioning data, (2) explain the phenomenon of incubation that has previously been described in the literature while simultaneously explaining its absence in the present study, and (3) integrate certain nonmonotonic acquisition phenomena that have appeared in both the forward and backward conditioning literatures.     

US preexposure: Effects on flavor aversions produced by pairing a poisoned partner with ingestion

If an unpoisoned rat drinks a flavored solution and then is exposed to another rat suffering from lithium poisoning, the unpoisoned rat will later exhibit a flavor aversion. This is called the poisoned partner effect (PPE). The present experiments showed that (1) the US preexposure effect applies to the PPE since, if the unpoisoned rat is preexposed to poisoned partners, the PPE is attenuated, (2) the magnitude of the PPE increases with the dose of poison, and (3) a poisoned partner accustomed to poisoning produces a slightly weaker PPE than a partner naive to poisoning. Two earlier findings were confirmed: (1) The PPE occurs because the poisoned partner is an aversive US, not because a learned aversion is transferred from one rat to another; and (2) the PPE is weaker than an aversion produced by poisoning itself.     

Effect of number of trials,interstimulus interval,and dishabituation during CS habituation on subsequent conditioning in a CER paradigm

Three experiments were conducted to investigate the influence of variables during habituation of a CS on a subsequent conditioning to that CS in a conditioned emotional response paradigm. Experiment I varied the number of habituation trials received before conditioning, and it was found that additional habituation trials resulted in a further attenuation of conditioning. Experiment II varied the interstimulus interval of the habituating stimulus, and it was found that the longer intervals produced the greater attenuation in conditioning. Experiment III examined the effect of interpolating another stimulus between habituation and conditioning (dishabituation), and it was found that the dishabituating stimulus augmented subsequent conditioning. It was concluded that manipulations during habituation training that produce the greatest decrement in response to a stimulus, when assessed under equivalent conditions for all animals, have the greatest attenuating effect on subsequent conditioning to that stimulus.     

Effects of repeated lithium injections on temperature,activity, and flavor conditioning in rats

Two experiments investigated the effects of lithium chloride on activity and rectal temperature in rats. Lithium injections, relative to saline injections in controls, caused decreases in both activity and temperature. Importantly, lithium’s effects did not diminish over the course of eight repeated injections, although preexposure to lithium did attenuate its conditioning effectiveness in a flavor-conditioning trial. The results support the idea that drug tolerance is not of great importance in the lithium-mediated US-preexposure effect in flavor conditioning.     

比色管色谱法测定食品中甜蜜素的探讨

采用比色管为顶空瓶，顶空气相色谱法测定食品中甜蜜素含量。样品在比色管中保温，用氢火焰离子化检测器检测，食品中甜蜜素的最低检出浓度为1.9mg／kg，在样品中加标浓度为0.2-0.4g／kg时，平均回收率为92.4％一97.6％，高、中、低三种浓度的变异系数均小于5％。     

Suppression of predatory behaviors in laboratory mice following lithium chloride injections or electric shock

The present study compared the relative effectiveness of electric-shock and lithium chloride (LiC1) injections in suppressing cricket killing and eating by mice. Male ICR mice were tested for cricket killing and eating. Mice that attacked and ate a cricket were punished (with electric shock or LiC1 injections) after killing and eating crickets. Control mice received saline injections, delayed shock, or delayed LiCl injections after attacking and eating crickets. LiCl injections and electric shock were both effective in suppressing cricket killing and eating. Shock suppressed both attack and eating responses, while LiCl injections suppressed eating responses more than attack responses.     

Multivariate analyses of performance in a DRL paradigm

Multivariate analyses were used to explore the interrelations between response measures used in a DRL-20 schedule. A principal components analysis revealed two major components which accounted for a majority of the variance in all measures. One component included responses, reinforcements, efficiency, and a decrease in short-latency interresponse times; it could be viewed as supporting the previous use of the construct inhibition in the interpretation of DRL results. The other component was primarily associated with increased responding in the first period in which reinforcement was available; it could be viewed as a measure of temporal discrimination. A discriminant function, with blocks of trials as the criterion, was used to obtain from IRT/OP data a single measure summarizing change in behavior as a function of experience. The discriminant function incorporated both of the above sources of variance. The findings indicate that currently used summary measures do not fully reflect changes that occur under the DRL schedule.     

眼跳任务转换中的反应系统可塑性

选取三年级大学生为被试,以朝向眼跳和反向眼跳为任务,采用EyelinkⅡ型眼动仪记录眼动数据,分别考察朝向眼跳和反向眼跳的重复任务与转换任务的成绩差异。结果表明,眼跳类型对重复和转换任务的成绩差异有影响,朝向眼跳条件下产生了转换代价,反向眼跳条件下产生了转换收益,结果支持任务转换的反应系统可塑观。