Training a new response using conditioned reinforcement

Some of the most frequently used methods in the study of conditioned reinforcement seem to be insufficient to demonstrate the effect. The clearest way to assess this phenomenon is the training of a new response. In the present study, rats were exposed to a situation in which a primary reinforcer and an arbitrary stimulus were paired and subsequently the effect of this arbitrary event was assessed by presenting it following a new response. Subjects under these conditions emitted more responses compared to their own responding before the pairing and to their responding on a similar operandum that was available concurrently that had no programmed consequences. Response rates also were higher compared to responding by subjects in similar conditions in which there was no contingency (a) between the arbitrary stimulus and the reinforcer, (b) between the response and the arbitrary stimulus or (c) both. Results are discussed in terms of necessary and sufficient conditions to study conditioned reinforcement.     

Reinforcer devaluation by extinction depends on the food restriction protocol

A common feature of reinforcer devaluation studies is that new learning induces the devaluation. The present study used extinction to induce new learning about the conditioned reinforcer in a heterogeneous chain schedule. Rats pressed a lever in a heterogeneous chain schedule to produce a conditioned reinforcer (light) associated with the opportunity to obtain an unconditioned reinforcer (food) by pulling a chain. The density of food reinforcement correlated with the conditioned reinforcer was varied in a comparison of continuous and variable-ratio reinforcement schedules of chain pulling; this had no noticeable effect on conditioned reinforcer devaluation produced by extinction of chain pulling. In contrast, how rats were deprived appeared to matter very much. Restricting meal duration to 1h daily produced more lever pressing during baseline training and a greater reductive effect of devaluation on lever pressing than restricting body weight to 80% of a control rat's weight, which eliminated the devaluation effect. Further analysis suggested that meal-duration restriction may have produced devaluation effects because it was more effective than weight restriction in reducing rats' body weights. Our results exposed an important limitation on the devaluation of conditioned reinforcers: slight differences in food restriction, using two commonly employed food-restriction procedures, can produce completely different interpretations of reinforcer devaluation while leaving reinforcer-based learning intact.     

Central cholinergic influence on self-administration of morphine and amphetamine

Atropine and methylatropine were tested in rats for an ability to alter the reinforcing action of intravenous morphine sulfate and d-amphetamine sulfate (60 μg/kg/injection). Atropine blocked the self-administration of morphine, but methylatropine did not. Similarly, atropine but not methylatropine prevented the establishment of a conditioned reinforcer based on passive intravenous infusions of morphine. Self-administration of d-amphetamine was enhanced by atropine but not by methylatropine. The results indicate that a central cholinergic system exerts an influence on the brain mechanisms which are affected by morphine or d-amphetamine to produce positive reinforcement.     

The role of contextual conditioning in the effect of reinforcer devaluation on instrumental performance by rats

Different groups of rats received different amounts of training to lever press for a food reinforcer before an aversion was conditioned to the food. This devaluation of the reinforcer reduced responding in both subsequent extinction and reinforced tests of responding to a degree that was independent of the amount of instrumental training. Moreover, interpolating context extinction between aversion conditioning and the extinction test reduced the magnitude of the devaluation effect, thereby indicating that Pavlovian contextual conditioning may play a role in the instrumental devaluation effect.     

Effects of an extinguished CS on competition with another CS

Three experiments were conducted using a conditioned taste aversion procedure with rats to examine the effect of nonreinforced presentations of a conditioned stimulus (CS) on its ability to compete with a target stimulus for manifest conditioned responding. Two CSs (A and B) were presented in a serial compound and then paired with the unconditioned stimulus. CS A was first paired with the US and then presented without the US (i.e., extinction) prior to reinforced presentation of the AB compound. Experiment 1 showed that A was poor at competing with B for conditioned responding when given conditioning and extinction prior to reinforcement of AB relative to a group that received both A and B for the first time during compound conditioning. That is, an extinguished A stimulus allowed greater manifest acquisition to B. Experiment 2 found that extinction treatment produced a poor CR to the pretrained and extinguished CS itself following compound conditioning. Experiment 3 found that interposing a retention interval after extinction of A and prior to compound conditioning enhanced A's ability to compete with B. The results of these experiments are discussed with regard to different theories of extinction and associative competition.     

Environmental enrichment decreases responding for visual novelty

Previous research has demonstrated that rats reared in an enriched condition (EC) with novel objects and social partners self-administer less amphetamine compared to rats raised in an isolated condition (IC). However, it is unclear if the enrichment-induced decrease in stimulant self-administration generalizes to non-drug rewards such as those provided by novel environmental stimuli. In the current study, EC, IC, and social condition (SC) rats were raised from 21 to 51 days of age before being tested in a two-lever operant conditioning chamber in which responding on one lever (active lever) resulted in illumination of a cue light. In Experiment 1, rats were initially assessed for baseline responding (no contingency) and then the contingent light was introduced. EC rats responded less than IC rats for the contingent light stimulus; however, EC rats also displayed a lower rate of baseline responding. In Experiment 2, rats were trained initially to lever press for a sucrose reward to decrease differences in baseline responding. While sucrose pretraining decreased baseline response differences between groups, EC rats still responded less for the contingent light stimulus than IC or SC rats. These results suggest that environmental enrichment decreases the incentive value of visual novelty.     

Resistance to extinction and behavioral momentum

In the metaphor of behavioral momentum, reinforcement is assumed to strengthen discriminated operant behavior in the sense of increasing its resistance to disruption, and extinction is viewed as disruption by contingency termination and reinforcer omission. In multiple schedules of intermittent reinforcement, resistance to extinction is an increasing function of reinforcer rate, consistent with a model based on the momentum metaphor. The partial-reinforcement extinction effect, which opposes the effects of reinforcer rate, can be explained by the large disruptive effect of terminating continuous reinforcement despite its strengthening effect during training. Inclusion of a term for the context of reinforcement during training allows the model to account for a wide range of multiple-schedule extinction data and makes contact with other formulations. The relation between resistance to extinction and reinforcer rate on single schedules of intermittent reinforcement is exactly opposite to that for multiple schedules over the same range of reinforcer rates; however, the momentum model can give an account of resistance to extinction in single as well as multiple schedules. An alternative analysis based on the number of reinforcers omitted to an extinction criterion supports the conclusion that response strength is an increasing function of reinforcer rate during training.     

Resistance to extinction, generalization decrement, and conditioned reinforcement

This study investigated generalization decrement during an extinction resistance-to-change test for pigeon key pecking using a two-component multiple schedule with equal variable-interval 3-min schedules and different reinforcer amounts (one component presented 2-s access to reinforcement and the other 8s). After establishing baseline responding, subjects were assigned to one of the two extinction conditions: hopper stimuli (hopper and hopper light were activated but no food was available) or Control (inactive hopper and hopper light). Responding in the 8-s component was more resistant to extinction than responding in the 2-s component, the hopper stimuli group was more resistant to extinction compared to the Control group, and an interaction between amount of reinforcement, extinction condition, and session block was present. This finding supports generalization decrement as a factor that influences resistance to extinction. Hopper-time data (the amount of time subjects spent with their heads in the hopper) were compared to resistance-to-change data in an investigation of the role of conditioned reinforcement on resistance to change.     

Stimulus change dis-habituates operant responding supported by water reinforcers

The present experiment examined whether habituation contributes to within-session decreases in operant responding for water reinforcers. The experiment asked if this responding can be dishabituated, a fundamental property of habituated behavior. During baseline, rats’ lever pressing was reinforced by water on a variable interval 15-s schedule. During experimental conditions, rats responded on the same schedule and a new stimulus was introduced for 5 min at 15, 30 or 45 min into the 60-min session. The new stimulus was extinction, continuous reinforcement or flashing lights in different conditions. Rate of responding primarily decreased within the session during baseline. Introducing a new stimulus sometimes suppressed (extinction, continuous reinforcement) and sometimes increased (flashing lights) responding while it was in effect. The new stimulus increased responding after it ended and before it was presented in the session. The results are incompatible with the idea that non-habituation satiety factors (e.g., cellular hydration and blood volume) contributed to within-session changes in responding. These satiety factors should increase with increases in consumption, decrease with decreases in consumption and remain constant with constant consumption of water. Nevertheless, all stimulus changes increased operant responding for water. These results support the idea that habituation contributes to within-session decreases in responding for water reinforcers.     

A comparison of the effects of discriminative and Pavlovian inhibitors and excitors on instrumental responding

In two experiments, the effects of Pavlovian or discriminative conditioned inhibitors on operant responding were investigated in rats. Experiment 1 found that a Pavlovian conditioned inhibitor for food suppressed food-reinforced lever pressing more than a non-differentially trained control stimulus did. Experiment 2 demonstrated that an operant discriminative inhibitor produced greater suppression of lever pressing than a Pavlovian conditioned inhibitor. Experiment 2 also found that compounding an operant discriminative stimulus (SD) for food-reinforced responding with another SD for food-reinforced responding resulted in more additive summation than when an SD was compounded with a Pavlovian conditioned excitor for food. The results of these experiments support two-factor theories that postulate that incentive and response discriminative processes summate algebraically when the processes are inhibitory or excitatory.     

The operant reserve: a computer simulation in (accelerated) real time

In Skinner's Reflex Reserve theory, reinforced responses added to a reserve depleted by responding. It could not handle the finding that partial reinforcement generated more responding than continuous reinforcement, but it would have worked if its growth had depended not just on the last response but also on earlier responses preceding a reinforcer, each weighted by delay. In that case, partial reinforcement generates steady states in which reserve decrements produced by responding balance increments produced when reinforcers follow responding. A computer simulation arranged schedules for responses produced with probabilities proportional to reserve size. Each response subtracted a fixed amount from the reserve and added an amount weighted by the reciprocal of the time to the next reinforcer. Simulated cumulative records and quantitative data for extinction, random-ratio, random-interval, and other schedules were consistent with those of real performances, including some effects of history. The model also simulated rapid performance transitions with changed contingencies that did not depend on molar variables or on differential reinforcement of inter-response times. The simulation can be extended to inhomogeneous contingencies by way of continua of reserves arrayed along response and time dimensions, and to concurrent performances and stimulus control by way of different reserves created for different response classes.     

Relapse processes after the extinction of instrumental learning: renewal, resurgence, and reacquisition

It is widely recognized that extinction (the procedure in which a Pavlovian conditioned stimulus or an instrumental action is repeatedly presented without its reinforcer) weakens behavior without erasing the original learning. Most of the experiments that support this claim have focused on several "relapse" effects that occur after Pavlovian extinction, which collectively suggest that the original learning is saved through extinction. However, although such effects do occur after instrumental extinction, they have not been explored there in as much detail. This article reviews recent research in our laboratory that has investigated three relapse effects that occur after the extinction of instrumental (operant) learning. In renewal, responding returns after extinction when the behavior is tested in a different context; in resurgence, responding recovers when a second response that has been reinforced during extinction of the first is itself put on extinction; and in rapid reacquisition, extinguished responding returns rapidly when the response is reinforced again. The results provide new insights into extinction and relapse, and are consistent with principles that have been developed to explain extinction and relapse as they occur after Pavlovian conditioning. Extinction of instrumental learning, like Pavlovian learning, involves new learning that is relatively dependent on the context for expression.     

Excitatory backward conditioning in an appetitive conditioned reinforcement preparation with rats

Four experiments were conducted to examine appetitive backward conditioning in a conditioned reinforcement preparation. In all experiments, off-line classical conditioning was conducted following lever-press training on two levers. Presentations of a sucrose solution by a liquid dipper served as an unconditioned stimulus (US) and two auditory stimuli served as conditioned stimuli (CSs); one was paired with the US in either a forward (Experiment 1a) or a backward (Experiments 1b, 2, and 3) relationship, and the other served as a control CS, which was not paired with the US. In testing, each lever-press response produced a presentation of one of the CSs instead of appetitive reinforcers. The response to a lever was facilitated, compared to the response to another lever, when the response produced the backward CS presentation as well as when it produced the forward CS presentation; that is, the backward CS served as an excitatory conditioned reinforcer.     

Effect of US identity on elimination and recovery of autoshaped responding with explicitly unpaired and degraded contingency extinction procedures

The depressive effects of noncontingent and explicitly unpaired food unconditioned stimuli (USs) and the recovery from those effects on autoshaped responding were examined in a series of experiments with pigeons. In Experiments 1 and 2, responding to a keylight conditioned stimulus (CS) previously paired with food was depressed equally by explicitly unpaired presentations of either that same food or a different food. Furthermore, responding recovered equally following removal of the explicitly unpaired foods. In contrast, Experiments 3 and 4 showed that noncontingent presentations of a food US depressed responding more to a keylight CS paired with that same food than to a keylight CS paired with a different food. Moreover, removal of the noncontingent foods led to complete recovery but more rapid extinction of responding to the same keylight relative to the different keylight. The implications of these results for understanding the mechanisms underlying depression and recovery of responding following degraded contingency and explicitly unpaired extinction procedures are discussed.     

Response-cost punishment via token loss with pigeons

Two experiments were conducted to investigate punishment via response-contingent removal of conditioned token reinforcers (response cost) with pigeons. In Experiment 1, key pecking was maintained on a two-component multiple second-order schedule of token delivery, with light emitting diodes (LEDs) serving as token reinforcers. In both components, responding produced tokens according to a random-interval 20-s schedule and exchange periods according to a variable-ratio schedule. During exchange periods, each token was exchangeable for 2.5-s access to grain. In one component, responses were conjointly punished according to fixed-ratio schedules of token removal. Response rates in this punishment component decreased to low levels while response rates in the alternate (no-punishment) component were unaffected. Responding was eliminated when it produced neither tokens nor exchange periods (Extinction), but was maintained at moderate levels when it produced tokens in the signaled absence of food reinforcement, suggesting that tokens served as effective conditioned reinforcers. In Experiment 2, the effect of the response-cost punishment contingency was separated from changes in the density of food reinforcement. This was accomplished by yoking either the number of food deliveries per component (Yoked Food) or the temporal placement of all stimulus events (tokens, exchanges, food deliveries) (Yoked Complete), from the punishment to the no-punishment component. Response rates decreased in both components, but decreased more rapidly and were generally maintained at lower levels in the punishment component than in the yoked component. In showing that the response-cost contingency had a suppressive effect on responding in addition to that produced by reductions in reinforcement density, the present results suggest that response-cost punishment shares important features with other forms of punishment.     

Segmentation and the pairing hypothesis

The effect of stimulus contiguity and response contingency on responding in chain schedules was examined in two experiments. In Experiment 1, four pigeons were trained on two simple three-link chain schedules that alternated within sessions. Initial links were correlated with a variable-interval 30s schedule, and middle and terminal links were correlated with interdependent variable-interval 30s variable-interval 30s schedules. The combined duration of the interdependent schedules summed to 60s. The two chains differed with respect to signaling of the schedule components: a two-stimulus chain had one stimulus paired with the initial link and one stimulus paired with both the middle and the terminal link, while a three-stimulus chain had a different stimulus paired with the each of the three links. The results showed that the two-stimulus chain maintained lower initial-link responding than the three-stimulus chain. In Experiment 2, four pigeons were exposed to three separate conditions, the two- and three-stimulus chains of Experiment 1 and a three-stimulus chain that had a 3s delay to terminal-link entry from the middle-link response that produced it. The two-stimulus chain maintained lower initial-link responding than the three-stimulus chain, as in Experiment 1, and a similar initial-link responding was maintained by the two-stimulus chain and the three-stimulus chain with the delay contingency. The results demonstrate that a stimulus noncontiguous with food can maintain responding that is sometimes greater than a stimulus contiguous with food, depending on the response contingency for terminal-link entry. The results are contrary to the pairing hypothesis of conditioned reinforcement.     

The critical dimensions of the response-reinforcer contingency

Two major dimensions of any contingency of reinforcement are the temporal relation between a response and its reinforcer, and the relative frequency of the reinforcer given the response versus when the response has not occurred. Previous data demonstrate that time, per se, is not sufficient to explain the effects of delay-of-reinforcement procedures; needed in addition is some account of the events occurring in the delay interval. Moreover, the effects of the same absolute time values vary greatly across situations, such that any notion of a standard delay-of-reinforcement gradient is simplistic. The effects of reinforcers occurring in the absence of a response depend critically upon the stimulus conditions paired with those reinforcers, in much the same manner as has been shown with Pavlovian contingency effects. However, it is unclear whether the underlying basis of such effects is response competition or changes in the calculus of causation.     

60 Hz electric fields and incandescent light as aversive stimuli controlling the behavior of rats responding under concurrent schedules of reinforcement

Several reports have shown that animals will sometimes engage in behaviors that reduce their exposure to a 60 Hz electric field (E-field). The field, therefore, can function as an aversive stimulus. In other studies, the E-field at equivalent strengths failed to function as an aversive stimulus. The present experiment, using rats, demonstrates how factors other than field strength can influence whether a subject engages in behavior that reduces field exposure. The general design consisted of giving the rat a choice between two alternatives, one of which sometimes included an added stimulus. Each subject was trained to press each of two levers to obtain food. Pressing one lever was reinforced intermittently under a variable interval 2 min schedule (VI 2); pressing the other lever was reinforced by a second VI 2 schedule operating independently of the first. Under this concurrent schedule the rat spent 50% of the daily 50 min session responding to each of the levers, indicating that they were equally “valued.” Next, while the schedules remained in effect, the first response to one of the levers turned on a 100 kV/m E-field which remained on until the rat pressed the other lever. The time spent responding under the schedule associated with the field was reduced by about 5–10%. When the procedure was changed so that no lever presses produced food, i.e., extinction, but the added stimulus contingency remained, the rats spent even less time in the presence of the field. Similar outcomes were observed during both the concurrent food or extinction schedules when incandescent light was used. Thus, both an E-field and incandescent light functioned as aversive stimuli, but the magnitude of the aversiveness was small. Aversiveness depended not only on stimulus intensity, but also on behavioral factors. Bioelectromagnetics 19:210–221, 1998. © 1998 Wiley-Liss, Inc.     

Extinction of conditioned opiate withdrawal in rats in a two-chambered place conditioning apparatus

Conditioned opiate withdrawal contributes to relapse in addicts and can be studied in rats by using the opiate withdrawal-induced conditioned place aversion (OW-CPA) paradigm. Attenuation of conditioned withdrawal through extinction may be beneficial in the treatment of addiction. Here we describe a protocol for studying OW-CPA extinction using a two-chambered place conditioning apparatus. Rats are made dependent on morphine through subcutaneous implantation of morphine pellets and then are trained to acquire OW-CPA through pairings of one chamber with naloxone-precipitated withdrawal and the other chamber with saline. Extinction training consists of re-exposures to both chambers in the absence of precipitated withdrawal. Rats tested after the completion of training show a decline in avoidance of the formerly naloxone-paired chamber with increasing numbers of extinction training sessions. The protocol takes a minimum of 7 d; the exact duration varies with the amount of extinction training, which is determined by the goals of the experiment.     

Effect of amount of context extinction on revaluation of a target CS

In two experiments using rats in a conditioned lick suppression paradigm the effects of posttraining extinction of the conditioning context on responding to the target conditioned stimulus (CS) which had previously been paired with a footshock was examined in a neutral context. Experiment 1 replicated Marlin's [Learn. Motiv. 13 (1981) 526] observation that this treatment can reduce responding to the target CS. This finding is contrary to other reports that context extinction enhances responding to the target CS. Experiment 2 examined the amount of posttraining context extinction as a variable potentially controlling this effect. It found the mediated extinction effect following one, but not 10 h of context extinction.