Rate of conditioned reinforcement affects observing rate but not resistance to change

An evaluation of methods for studying the effects of conditioned reinforcement on human choice

Shahan et al. (2006) found that the relative rate of pigeons' pecking on two observing responses (i.e., responses that only produced an S+ or stimulus correlated with primary reinforcement) was well described by the relative rate of S+ delivery. Researchers have not evaluated the effects of S+ delivery rate in a concurrent observing response procedure with human subjects, so the necessary procedural modifications for studying the effects of conditioned reinforcement on human choice remain unclear. The purpose of the current study was to conduct an additive component analysis of modifications to the procedures of Shahan et al. (2006). We evaluated the additive effects of introducing response cost, a changeover response, and ordinal discriminative stimuli on correspondence with the results of Shahan et al. and the quality of fits of the generalized matching equation. When our procedures were most similar to those of Shahan et al., we observed low rates of observing and indifference between the two observing responses. For the group of subjects with whom all three additive components were included, we obtained the highest level of sensitivity to relative rate of S+ delivery, but the slope and R² of our fits of the generalized matching equation were still much lower than those obtained by Shahan et al. Potential reasons for these discrepancies, methods of resolving them, and implications for future research are discussed.

Resistance to change and relapse of observing

Four experiments examined relapse of extinguished observing behavior of pigeons using a two-component multiple schedule of observing-response procedures. In both components, unsignaled periods of variable-interval (VI) food reinforcement alternated with extinction and observing responses produced stimuli associated with the availability of the VI schedule (i.e., S+). The components differed in the rate of food arranged (Rich  = VI 30 s; Lean  =  VI 120 s). In Experiment 1, following baseline training, extinction of observing involved removal of both food and S+ deliveries, and reinstatement was examined by presenting either response-independent food or S+ deliveries. In Experiment 2, extinction involved removal of only food deliveries while observing responses continued to produce S+. Reinstatement was examined by delivering food contingent upon the first two food-key responses occurring in the presence of the S+. Experiment 3 assessed ABA renewal of observing by extinguishing food-key and observing responses in the presence of one contextual stimulus (i.e., B) and then returning to the original training context (i.e., A) during continued extinction. Experiment 4 examined resurgence by introducing food reinforcement for an alternative response during extinction, and subsequently removing that alternative source of food. Across experiments, relative resistance to extinction and relapse of observing tended to be greater in the component previously associated with the higher rate of primary reinforcement. Relapse of observing or attending to stimuli associated with primary reinforcement appears to be impacted by frequency of primary reinforcement in a manner similar to responding maintained directly by primary reinforcement.

Emergent stimulus relations depend on stimulus correlation and not on reinforcement contingencies

We aimed to investigate whether novel stimulus relations would emerge from stimulus correlations when those relations explicitly conflicted with reinforced relations. In a symbolic matching-to-sample task using kanji characters as stimuli, we arranged class-specific incorrect comparison stimuli in each of three classes. After presenting either Ax or Cx stimuli as samples, choices of Bx were reinforced and choices of Gx or Hx were not. Tests for symmetry, and combined symmetry and transitivity, showed the emergence of three 3-member (AxBxCx) stimulus classes in 5 of 5 human participants. Subsequent tests for all possible emergent relations between Ax, Bx, Cx and the class-specific incorrect comparisons Gx and Hx showed that these relations emerged for 4 of 5 the participants after extended overtraining of the baseline relations. These emergent relations must have been based on stimulus-stimulus correlations, and were not properties of the trained discriminated operants, because they required control by relations explicitly extinguished during training. This result supports theoretical accounts of emergent relations that emphasize stimulus correlation over operant contingencies.

Revisiting the role of bad news in maintaining human observing behavior

Results from studies of observing responses have suggested that stimuli maintain observing owing to their special relationship to primary reinforcement (the conditioned-reinforcement hypothesis), and not because they predict the availability and nonavailability of reinforcement (the information hypothesis). The present article first reviews a study that challenges that conclusion and then reports a series of five brief experiments that provide further support for the conditioned-reinforcement view. In Experiments 1 through 3, participants preferred occasional good news (a stimulus correlated with reinforcement) or no news (a stimulus uncorrelated with reinforcement) to occasional bad news (a stimulus negatively correlated with reinforcement). In Experiment 4 bad news was preferred to no news when the absence of stimulus change following a response to the bad-news option was reliably associated with good news. When this association was weakened in Experiment 5 the results were intermediate. The results support the conclusion that information is reinforcing only when it is positive or useful. As required by the conditioned-reinforcement hypothesis, useless information does not maintain observing.

Stimulus effects on local preference: stimulus-response contingencies, stimulus-food pairing, and stimulus-food correlation

Four pigeons were trained in a procedure in which concurrent-schedule food ratios changed unpredictably across seven unsignaled components after 10 food deliveries. Additional green-key stimulus presentations also occurred on the two alternatives, sometimes in the same ratio as the component food ratio, and sometimes in the inverse ratio. In eight experimental conditions, we varied the contingencies surrounding these additional stimuli: In two conditions, stimulus onset and offset were noncontingent; in another two, stimulus onset was noncontingent, and offset was response contingent. In four conditions, both stimulus onset and offset were contingent, and in two of these conditions the stimulus was simultaneously paired with food delivery. Sensitivity to component food ratios was significantly higher when stimulus onset was response contingent compared to when it was noncontingent. Choice changes following food delivery were similar in all eight conditions. Choice changes following stimuli were smaller than those following food, and directionally were completely determined by the food-ratio:stimulus-ratio correlation, not by the stimulus contingency nor by whether the stimulus was paired with food or not. These results support the idea that conditional reinforcers may best be viewed as signals for next-food location rather than as stimuli that have acquired hedonic value, at least when the signals are differential with respect to future conditions.

Resistance to change and frequency of response-dependent stimuli uncorrelated with reinforcement

Stimuli uncorrelated with reinforcement have been shown to enhance response rates and resistance to disruption; however, the effects of different rates of stimulus presentations have not been assessed. In two experiments, we assessed the effects of adding different rates of response-dependent brief stimuli uncorrelated with primary reinforcement on relative response rates and resistance to change. In both experiments, pigeons responded on variable-interval 60-s schedules of food reinforcement in two components of a multiple schedule, and brief response-dependent keylight-color changes were added to one or both components. Although relative response rates were not systematically affected in either experiment, relative resistance to presession feeding and extinction were. In Experiment 1, adding stimuli on a variable-interval schedule to one component of a multiple schedule either at a low rate (1 per min) for one group or at a high rate (4 per min) for another group similarly increased resistance to disruption in the components with added stimuli. When high and low rates of stimuli were presented across components (i.e., within subjects) in Experiment 2, however, relative resistance to disruption was greater in the component presenting stimuli at a lower rate. These results suggest that stimuli uncorrelated with food reinforcement do not strengthen responding in the same way as primary reinforcers.

Nicotine's enhancing effects on responding maintained by conditioned reinforcers are reduced by pretreatment with mecamylamine, but not hexamethonium, in rats

Several studies have indicated that nicotine increases responding maintained by conditioned reinforcers. We assessed the effects of subcutaneous injections of 0.3 mg/kg nicotine and two nicotinic antagonists on responding maintained by conditioned and primary reinforcers and responding during extinction in 8 Long Evans rats. Mecamylamine, a central and peripheral nicotinic antagonist, and hexamethonium, a peripheral nicotinic antagonist, were administered prior to a subset of the experimental sessions. Nicotine selectively increased responding maintained by conditioned reinforcers and mecamylamine, but not hexamethonium, attenuated this effect. These results suggest that nicotine's enhancing effect on responding maintained by conditioned reinforcers is mediated in the central nervous system.

Conditioned reinforcement and response strength

Stimuli associated with primary reinforcers appear themselves to acquire the capacity to strengthen behavior. This paper reviews research on the strengthening effects of conditioned reinforcers within the context of contemporary quantitative choice theories and behavioral momentum theory. Based partially on the finding that variations in parameters of conditioned reinforcement appear not to affect response strength as measured by resistance to change, long-standing assertions that conditioned reinforcers do not strengthen behavior in a reinforcement-like fashion are considered. A signposts or means-to-an-end account is explored and appears to provide a plausible alternative interpretation of the effects of stimuli associated with primary reinforcers. Related suggestions that primary reinforcers also might not have their effects via a strengthening process are explored and found to be worthy of serious consideration.

Behavioral Momentum: Translational Research in Intellectual and Developmental Disabilities

Behavioral momentum theory (Nevin, 1992, Nevin & Grace, 2000) describes the relation between the characteristic level of reinforcement within a context and behavioral resistance to change within that context. This paper will describe the multiple-schedule-disrupter paradigm for basic behavioral momentum research and illustrate it with two representative examples from the literature with non-human subjects. The remainder of the paper will provide a review of translational research in human populations with intellectual and developmental disabilities (IDD) employing the multiple-schedule-disrupter paradigm and closely related variations. The results of this research show that the reinforcer-rate effects predicted by behavioral momentum theory are widely replicated in IDD populations. The intended audience for this paper is the practitioner interested in learning about the current status of translational research in behavioral momentum as a foundation for considering ways in which behavioral momentum theory may be relevant to clinical issues.

The generality of nicotine as a reinforcer enhancer in rats: effects on responding maintained by primary and conditioned reinforcers and resistance to extinction

RATIONALE

Nicotine may enhance the reinforcing value of other reinforcers. It is unclear whether nicotine enhances responding maintained by all reinforcers or whether there are limits to this role.

OBJECTIVE

The objective of the study is to test the generality of nicotine-induced increases in reinforced responding by using an observing response procedure, which generated measures of responding maintained by food reinforcers, conditioned reinforcers, and responding during extinction. We also examined whether nicotine increased resistance to extinction and whether nicotine's effects could be characterized as rate-dependent.

MATERIALS AND METHODS

Rats received presession subcutaneous injections of Vehicle (n=5), 0.3 (n=6), or 0.56 (n=6) mg/kg nicotine for 70 sessions. Resistance to extinction was also assessed by removing food for five sessions.

RESULTS

Nicotine did not consistently affect food or extinction responding. Both doses of nicotine produced increases in responding maintained by conditioned reinforcers, but did not increase resistance to extinction. Predrug response rates accounted for a small but significant percentage of the variance in the drug effect.

CONCLUSION

Although there was a tendency for nicotine to increase low predrug response rates (i.e., response rates just prior to nicotine administration), 0.3 and 0.56 mg/kg nicotine systematically increased responding maintained by conditioned reinforcers. The results are consistent with a reinforcer-enhancing role of nicotine. However, nicotine did not increase resistance to extinction, nor did it increase food-maintained responses. Nicotine may selectively increase responding maintained by moderately reinforcing stimuli, such as the conditioned reinforcers used in the present study.

Conditioned reinforcement value and resistance to change

Three experiments examined the effects of conditioned reinforcement value and primary reinforcement rate on resistance to change using a multiple schedule of observing-response procedures with pigeons. In the absence of observing responses in both components, unsignaled periods of variable-interval (VI) schedule food reinforcement alternated with extinction. Observing responses in both components intermittently produced 15 s of a stimulus associated with the VI schedule (i.e., S+). In the first experiment, a lower-valued conditioned reinforcer and a higher rate of primary reinforcement were arranged in one component by adding response-independent food deliveries uncorrelated with S+. In the second experiment, one component arranged a lower valued conditioned reinforcer but a higher rate of primary reinforcement by increasing the probability of VI schedule periods relative to extinction periods. In the third experiment, the two observing-response components provided similar rates of primary reinforcement but arranged different valued conditioned reinforcers. Across the three experiments, observing-response rates were typically higher in the component associated with the higher valued conditioned reinforcer. Resistance to change was not affected by conditioned reinforcement value, but was an orderly function of the rate of primary reinforcement obtained in the two components. One interpretation of these results is that S+ value does not affect response strength and that S+ deliveries increase response rates through a mechanism other than reinforcement. Alternatively, because resistance to change depends on the discriminative stimulus-reinforcer relation, the failure of S+ value to impact resistance to change could have resulted from a lack of transfer of S+ value to the broader discriminative context.

Signals, resistance to change, and conditioned reinforcement in a multiple schedule

The effect of signals on resistance to change was evaluated using pigeons responding on a three-component multiple schedule. Each component contained a variable-interval initial link followed by a fixed-time terminal link. One component was an unsignaled-delay schedule, and two were equivalent signaled-delay schedules. After baseline training, resistance to change was assessed through (a) extinction and (b) adding free food to the intercomponent interval. During these tests, the signal stimulus from one of the signaled-delay components (SIG-T) was replaced with the initial-link stimulus from that component, converting it to an unsignaled-delay schedule. That signal stimulus was added to the delay period of the unsignaled-delay component (UNS), converting it to a signaled-delay schedule. The remaining signaled component remained unchanged (SIG-C). Resistance-to-change tests showed removing the signal had a minimal effect on resistance to change in the SIG-T component compared to the unchanged SIG-C component except for one block during free-food testing. Adding the signal to the UNS component significantly increased response rates suggesting that component had low response strength. Interestingly, the direction of the effect was in the opposite direction from what is typically observed. Results are consistent with the conclusion that the signal functioned as a conditioned reinforcer and inconsistent with a generalization-decrement explanation.

Quantitative analyses of observing and attending

We review recent experiments examining whether simple models of the allocation and persistence of operant behavior are applicable to attending. In one series of experiments, observing responses of pigeons were used as an analog of attending. Maintenance of observing is often attributed to the conditioned reinforcing effects of a food-correlated stimulus (i.e., S+), so these experiments also may inform our understanding of conditioned reinforcement. Rates and allocations of observing were governed by rates of food or S+ delivery in a manner consistent with the matching law. Resistance to change of observing was well described by behavioral momentum theory only when rates of primary reinforcement in the context were considered. Rate and value of S+ deliveries did not affect resistance to change. Thus, persistence of attending to stimuli appears to be governed by primary reinforcement rates in the training context rather than conditioned reinforcing effects of the stimuli. An additional implication of these findings is that conditioned "reinforcers" may affect response rates through some mechanism other than response-strengthening. In a second series of experiments, we examined the applicability of the matching law to the allocation of attending to the elements of compound stimuli in a divided-attention task. The generalized matching law described performance well, and sensitivity to relative reinforcement varied with sample duration. The bias and sensitivity terms of the generalized matching law may provide measures of stimulus-driven and goal-driven control of divided attention. Further application of theories of operant behavior to performance on attention tasks may provide insights into what is referred to variously as endogenous, top-down, or goal-directed control of attention.

Effect of unsignaled delays between stimuli in a chain schedule on responding and resistance to change

Behavioral momentum theory is an evolving theoretical account of the strength of behavior. One challenge for the theory is determining the role of signal stimuli in determining response strength. This study evaluated the effect of an unsignaled delay between the initial link and terminal link of a two-link chain schedule on resistance to change using a multiple schedule of reinforcement. Pigeons were presented two different signaled delay to reinforcement schedules. Both schedules employed a two-link chain schedule with a variable interval 120-s initial link followed by a 5-s fixed time terminal link schedule. One of the schedules included a 5-s unsignaled delay between the initial link and the terminal link. Resistance to change was assessed with two separate disruption procedures: extinction and adding a variable time 20-s schedule of reinforcement to the inter-component interval. Baseline responding was lower in the schedule with the unsignaled delay but resistance to change for the initial link was unaffected by the unsignaled delay. The results suggest that not all unsignaled delays are equal in their effect on resistance to change.

Disruption of responding maintained by conditioned reinforcement: alterations in response-conditioned-reinforcer relations

An observing procedure was used to investigate the effects of alterations in response-conditioned-reinforcer relations on observing. Pigeons responded to produce schedule-correlated stimuli paired with the availability of food or extinction. The contingency between observing responses and conditioned reinforcement was altered in three experiments. In Experiment 1, after a contingency was established in baseline between the observing response and conditioned reinforcement, it was removed and the schedule-correlated stimuli were presented independently of responding according to a variable-time schedule. The variable-time schedule was constructed such that the rate of stimulus presentations was yoked from baseline. The removal of the observing contingency reliably reduced rates of observing. In Experiment 2, resetting delays to conditioned reinforcement were imposed between observing responses and the schedule-correlated stimuli they produced. Delay values of 0, 0.5, 1, 5, and 10 s were examined. Rates of observing varied inversely as a function of delay value. In Experiment 3, signaled and unsignaled resetting delays between observing responses and schedule-correlated stimuli were compared. Baseline rates of observing were decreased less by signaled delays than by unsignaled delays. Disruptions in response-conditioned-reinforcer relations produce similar behavioral effects to those found with primary reinforcement.

Effect of signaling reinforcement on resistance to change in a multiple schedule

This study evaluated the effect of a signal on resistance to change using a multiple schedule of reinforcement. Experiment 1 presented pigeons with three schedules: a signaled delay to reinforcement schedule (a two-link chain schedule with a variable-interval 120-s initial link followed by a 5-s fixed-time schedule), an unsignaled delay schedule (a comparable two-link tandem schedule), and an immediate, zero-delay variable-interval 125-s schedule. Two separate disruption procedures assessed resistance to change: extinction and adding a variable-time 20-s schedule of reinforcement to the inter-component interval. Resistance to change tests were conducted twice, once with the signal stimulus (the terminal link of the chain schedule) present and once with it absent. Results from both disruption procedures showed that signal absence reduced resistance to change for the pre-signal stimulus. In probe choice tests subjects strongly preferred the signal stimulus over the unsignaled stimulus and exhibited no reliable preference when given a choice between the signal stimulus and immediate stimulus. Experiment 2 presented two equal signaled schedules where, during resistance to change tests, the signal remained for one schedule and was removed for the second. Resistance to change was consistently lower when the signal was absent.

Matching and conditioned reinforcement rate

Attempts to examine the effects of variations in relative conditioned reinforcement rate on choice have been confounded by changes in rates of primary reinforcement or changes in the value of the conditioned reinforcer. To avoid these problems, this experiment used concurrent observing responses to examine sensitivity of choice to relative conditioned reinforcement rate. In the absence of observing responses, unsignaled periods of food delivery on a variable-interval 90-s schedule alternated with extinction on a center key (i.e., a mixed schedule was in effect). Two concurrently available observing responses produced 15-s access to a stimulus differentially associated with the schedule of food delivery (S+). The relative rate of S+ deliveries arranged by independent variable-interval schedules for the two observing responses varied across conditions. The relation between the ratio of observing responses and the ratio of S+ deliveries was well described by the generalized matching law, despite the absence of changes in the rate of food delivery. In addition, the value of the S+ deliveries likely remained constant across conditions because the ratio of S+ to mixed schedule food deliveries remained constant. Assuming that S+ deliveries serve as conditioned reinforcers, these findings are consistent with the functional similarity between primary and conditioned reinforcers suggested by general choice theories based on the concatenated matching law (e.g., contextual choice and hyperbolic value-added models). These findings are inconsistent with delay reduction theory, which has no terms for the effects of rate of conditioned reinforcement in the absence of changes in rate of primary reinforcement.