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At least 19 recordsLinked to original sources
PubMed2006

Operant responding for conditioned and unconditioned reinforcers in rats is differentially enhanced by the primary reinforcing and reinforcement-enhancing effects of nicotine.

RATIONALE: Nicotine self-administration in rats is modest when response-contingent nicotine infusions are delivered alone (primary reinforcement) but robust when nicotine infusions are combined with a mildly reinforcing non-pharmacological stimulus. Furthermore, response-independent (non-contingent) nicotine administration also elevates responding for that same non-pharmacological stimulus, suggesting that in addition to primary reinforcement, nicotine can enhance the incentive value of other reinforcers. OBJECTIVES: In this study, we tested the hypothesis that the reinforcement-enhancing effects of non-contingent nicotine are more dependent on the reinforcing strength of the non-pharmacological stimulus than are the effects of contingent nicotine. MATERIALS AND METHODS: A weakly reinforcing light-tone stimulus was established as a conditioned reinforcer by repeated pairings with sucrose for some rats, or by delivery in an explicitly unpaired design with sucrose to other rats. Subsequently, both groups lever pressed for the stimulus with contingent nicotine, non-contingent nicotine (0.06 mg kg(-1) per infusion, freebase), or non-contingent saline, according to fixed ratio and progressive ratio reinforcement schedules. RESULTS: Compared to sucrose-unpaired training, repeated association with sucrose established the light-tone stimulus as a robust conditioned reinforcer. Contingent and non-contingent nicotine equally elevated responding for this conditioned stimulus. Conversely, for the less reinforcing (sucrose-unpaired) stimulus contingent nicotine more effectively elevated behavior compared to non-contingent nicotine. CONCLUSIONS: The reinforcement-enhancing effect of nicotine increases behavior controlled by both conditioned and unconditioned reinforcers; however, for less salient stimuli associative processes derived from the primary reinforcing effects of contingent nicotine may also be important. These data suggest that nicotine present in tobacco may differentially modulate stimulus-driven behavior in smokers.

Animals↗
PubMed2004

Nucleus accumbens neurons in the rat exhibit differential activity to conditioned reinforcers and primary reinforcers within a second-order schedule of saccharin reinforcement.

The nucleus accumbens has been associated with processing information related to primary reinforcement and reward. Most neurophysiological studies report that nucleus accumbens neurons are phasically excited in response to the onsets of salient events during the seeking of reinforcement and to the delivery of primary reinforcers. However, a minority of studies report inhibition during primary reinforcement. We recorded from 65 neurons in the nucleus accumbens whilst thirsty rats performed under a second-order schedule of saccharin reinforcement. This allowed us to analyse neural activity and behaviour during reinforcer-seeking in the presence of conditioned reinforcers (second-order stimuli, also called 'conditioned stimuli'), and during primary reinforcer consumption. Specifically, we sought to examine the valence of potential neural responses to primary reinforcement, to compare these responses to second-order stimulus-evoked responses, and to determine whether responses were differential to second-order stimuli presented at different time points within the schedule. Fifty out of 65 neurons we sampled responded to the second-order stimulus and/or consumption of the primary reinforcer. Most neurons in our sample exhibited excitation following the second-order stimulus and inhibition to the primary reinforcer, a pattern also present over the average response of the neural population. However, there was no systematic variation in neural responses evoked by second-order stimuli presented at different temporal proximities to primary reinforcement. Our results provide evidence that partially overlapping mechanisms within the nucleus accumbens differentially process conditioned reinforcers and primary reinforcers.

Action Potentials↗
PubMed1998

Humans' choice in a self-control choice situation: sensitivity to reinforcer amount, reinforcer delay, and overall reinforcement density.

Human subjects were exposed to a concurrent-chains schedule in which reinforcer amounts, delays, or both were varied in the terminal links, and consummatory responses were required to receive points that were later exchangeable for money. Two independent variable-interval 30-s schedules were in effect during the initial links, and delay periods were defined by fixed-time schedules. In Experiment 1, subjects were exposed to three different pairs of reinforcer amounts and delays, and sensitivity to reinforcer amount and delay was determined based on the generalized matching law. The relative responding (choice) of most subjects was more sensitive to reinforcer amount than to reinforcer delay. In Experiment 2, subjects chose between immediate smaller reinforcers and delayed larger reinforcers in five conditions with and without timeout periods that followed a shorter delay, in which reinforcer amounts and delays were combined to make different predictions based on local reinforcement density (i.e., points per delay) or overall reinforcement density (i.e., points per total time). In most conditions, subjects' choices were qualitatively in accord with the predictions from the overall reinforcement density calculated by the ratio of reinforcer amount and total time. Therefore, the overall reinforcement density appears to influence the preference of humans in the present self-control choice situation.

Adolescent↗
PubMed2005

Dissociating the primary reinforcing and reinforcement-enhancing effects of nicotine using a rat self-administration paradigm with concurrently available drug and environmental reinforcers.

RATIONALE: Nicotine has two effects on reinforcement in traditional self-administration paradigms. It serves as a primary reinforcer by increasing the probability of behaviors that result in nicotine delivery. However, nicotine also potently enhances behaviors that result in the delivery of nonpharmacological reinforcers. OBJECTIVES: The present study sought to dissociate these two effects of nicotine on reinforcement. METHODS: For one group of rats (2 lever), a nonpharmacological reinforcer [visual stimulus (VS)] was available for pressing one lever. Nicotine infusions were available for pressing a different lever. A second group (NIC + VS) received more traditional self-administration training; both the VS and nicotine were delivered for pressing a single active lever. Control groups received either nicotine infusions (NIC only) or VS presentations (VS only) for pressing the active lever. RESULTS: Nicotine alone was a weak reinforcer; the VS alone was slightly more reinforcing than nicotine. When these two reinforcers were combined (NIC + VS), response rates were synergistically increased. For the 2-lever group, responding on the nicotine lever was weak, matching the response rates of rats receiving nicotine alone. However, responding on the VS lever was potently enhanced in this group; equaling the response rates for rats receiving both reinforcers for making a single response (NIC + VS). CONCLUSIONS: These data indicate that the reinforcement-enhancing effects of nicotine are very potent even when only moderate quantities of the drug are self-administered. Moreover, they provide the first demonstration that the reinforcement-enhancing and primary reinforcing effects of nicotine can be dissociated behaviorally.

Animals↗
PubMed1966

Concurrent schedules of interresponse time reinforcement: probability of reinforcement and the lower bounds of the reinforced interresponse time intervals.

Data were obtained with rats on the effects of interresponse time contingent reinforcement of the lever press response using schedules in which interresponse times falling within either of two temporal intervals could be reinforced. Some of the findings were (a) the mode of the interresponse time distribution generally occurred near the first lower bound when the maximum reinforcement rate for the two lower bounds was equal; this also frequently occurred even when the reinforcement rate was less for the first lower bound; (b) as is the case with schedules using a single interval of reinforced interresponse times the values of the lower bounds partially determined the location and spread of the distributions; but the particular pair of values used did not seem to influence the effects of the probabilities of reinforcement; (c) although the modal interresponse time was usually at the lower bound of one of the two intervals of reinforced interresponse times, no simple relation existed between either the probability or rate of reinforcement of interresponse times in these two intervals and the location of this mode.

Animals↗
PubMed2003

Every reinforcer counts: reinforcer magnitude and local preference.

Six pigeons were trained on concurrent variable-interval schedules. Sessions consisted of seven components, each lasting 10 reinforcers, with the conditions of reinforcement differing between components. The component sequence was randomly selected without replacement. In Experiment 1, the concurrent-schedule reinforcer ratios in components were all equal to 1.0, but across components reinforcer-magnitude ratios varied from 1:7 through 7:1. Three different overall reinforcer rates were arranged across conditions. In Experiment 2, the reinforcer-rate ratios varied across components from 27:1 to 1:27, and the reinforcer-magnitude ratios for each alternative were changed across conditions from 1:7 to 7:1. The results of Experiment 1 replicated the results for changing reinforcer-rate ratios across components reported by Davison and Baum (2000, 2002): Sensitivity to reinforcer-magnitude ratios increased with increasing numbers of reinforcers in components. Sensitivity to magnitude ratio, however, fell short of sensitivity to reinforcer-rate ratio. The degree of carryover from component to component depended on the reinforcer rate. Larger reinforcers produced larger and longer postreinforcer preference pulses than did smaller reinforcers. Similar results were found in Experiment 2, except that sensitivity to reinforcer magnitude was considerably higher and was greater for magnitudes that differed more from one another. Visit durations following reinforcers measured either as number of responses emitted or time spent responding before a changeover were longer following larger than following smaller reinforcers, and were longer following sequences of same reinforcers than following other sequences. The results add to the growing body of research that informs model building at local levels.

Animals↗
PubMed2001

Sensitivity to relative reinforcer rate in concurrent schedules: independence from relative and absolute reinforcer duration.

Twelve pigeons responded on two keys under concurrent variable-interval (VI) schedules. Over several series of conditions, relative and absolute magnitudes of reinforcement were varied. Within each series, relative rate of reinforcement was varied and sensitivity of behavior ratios to reinforcer-rate ratios was assessed. When responding at both alternatives was maintained by equal-sized small reinforcers, sensitivity to variation in reinforcer-rate ratios was the same as when large reinforcers were used. This result was observed when the overall rate of reinforcement was constant over conditions, and also in another series of concurrent schedules in which one schedule was kept constant at VI ached 120 s. Similarly, reinforcer magnitude did not affect the rate at which response allocation approached asymptote within a condition. When reinforcer magnitudes differred between the two responses and reinforcer-rate ratios were varied, sensitivity of behavior allocation was unaffected although response bias favored the schedule that arranged the larger reinforcers. Analysis of absolute response rates ratio sensitivity to reinforcement occurrred on the two keys showed that this invariance of response despite changes in reinforcement interaction that were observed in absolute response rates on the constant VI 120-s schedule. Response rate on the constant VI 120-s schedule was inversely related to reinforcer rate on the varied key and the strength of this relation depended on the relative magnitude of reinforcers arranged on varied key. Independence of sensitivity to reinforcer-rate ratios from relative and absolute reinforcer magnitude is consistent with the relativity and independence assumtions of the matching law.

Animals↗
PubMed1988

Reinforcement schedules: Retroactive and proactive effects of reinforcers inserted into fixed-interval performances.

The responding maintained by a reinforcer depends on the relation of the reinforcer not merely to the response that produces it but also to other preceding responses. Early responses in a sequence that ends in a reinforcing consequence make smaller contributions to later response rates than more recent ones, by virtue of the longer delays that separate them from the reinforcer. This study shows that the relation between a response and a later reinforcer contributes to responding only if no other reinforcers intervene; in other words, each reinforcer blocks responses that precede it from the effects of later reinforcers. Pigeons' pecks were maintained by fixed-interval (FI) schedules of food reinforcement. When FI 60-s (short) and FI 75-s (long) schedules began simultaneously within constant 150-s cycles, long FIs did not affect short-FI performances, but short FIs eliminated the first 60 s of long-FI performances. Removing either short-FI reinforcers or short-FI stimuli showed that short-FI reinforcers and not short-FI stimuli blocked the first 60 s of the long-FI performance from the retroactive effects of the long-FI reinforcer. With FI 15-s and FI 75-s schedules, the short-FI reinforcer was followed by reduced long-FI responding, but a schedule that prevented discrimination based on time since a reinforcer eliminated this proactive effect of the short-FI reinforcer. In other words, the retroactive effects were reinforcer effects whereas the proactive effects were discriminative effects. Quantitative descriptions of variable-interval performances, in which reinforcer effects may operate in the absence of temporal discriminative effects, can be derived from these relations.

Journal Article↗
PubMed2003

Fracture resistance of fiber-reinforced vs. non-fiber-reinforced composite molar crowns.

UNLABELLED: This study compared fracture resistance of fiber-reinforced and non-fiber-reinforced composite molar crowns under simulated oral stress conditions. Three groups of fiber-reinforced composite crowns were constructed using one polyethylene fiber (belleGlass/Connect) and two glass fiber reinforcement systems (Sculpture/FiberKor, Targis/Vectris). The non-fiber-reinforced crowns based on the facing material alone: Sculpture, Targis or belleGlass. Additionally, crowns were made of the non-reinforced composite Artglass. Each group consisted of eight crowns. All crowns were luted to human molars and exposed to thermal cycling and mechanical loading (6000 x 5 degrees C/55 degrees C; 1.2 x 10(6x)50 N; 1.66 Hz). The fracture resistance was measured using a Zwick universal testing machine. RESULTS: The non-reinforced Artglass crowns demonstrated the highest fracture resistance, significantly higher than the resistance shown with belleGlass, belleGlass/Connect or Targis. Artglass showed an extremely wide distribution of values, however. No statistically significant differences were found between the reinforced and non-reinforced composite crowns of Vectris/Targis, FiberKor/Sculpture or Connect/belleGlass although the reinforced crowns showed a tendency towards higher values. The fracture resistance values scattered markedly more for the reinforced crowns, and their lowest fracture values also reached the level of the lowest non-reinforced crowns. The small distribution of fracture values for the non-reinforced crowns indicates that they will be less susceptible for manufacturing faults and more reliable under clinical conditions. CONCLUSIONS: RESULTS of this study suggest that single molar composite crowns (tested in this study) do not benefit from fiber-reinforcement.

Analysis of Variance↗
PubMed1995

Contrast and reallocation of extraneous reinforcers as a function of component duration and baseline rate of reinforcement.

Four pigeons responded on multiple schedules arranged on a "main" key in a two-key experimental chamber. A constant schedule component was alternated with another component that was varied over conditions. On an extra response key, conjoint schedules of reinforcement that operated in both components were arranged concurrently with the multiple schedule on the main key. On the main key, changes in reinforcement rate in the varied component were inversely related to changes in response rates in the constant component (behavioral contrast). On the extra key, some reinforcers were reallocated between components, depending on the schedules in effect on the main key in the varied component. In the varied component, the obtained rates of reinforcement on the extra key were inversely related to main-key reinforcement rate. In the constant component, extra-key reinforcer rates were positively related to main-key reinforcer rates obtained in the varied component, and were not a function of response rates on the extra key. In two comparisons, the rate at which components alternated and the value of the main-key schedule in the constant component were varied. Consistent with earlier work, long components reduced the extent of contrast. Reductions in contrast as a function of component duration were accompanied by similar reductions in the extent of reinforcer reallocation on the extra key. In the second comparison, lowering the rate of reinforcement in the constant component increased the rate at which extra-key reinforcers were obtained, reduced the extent of reinforcer reallocation, and reduced contrast. Overall, the results are consistent with the suggestion that some contrast effects are due to the changes in extraneous reinforcement during the constant component, and that manipulations of component duration, and manipulations of the rate of reinforcement in the constant component, affect contrast because they influence the extent of extraneous reinforcer real-location.

Journal Article↗
PubMed1992

Effects of reinforcer rate and reinforcer quality on time allocation: Extensions of matching theory to educational settings.

We examined how 3 special education students allocated their responding across two concurrently available tasks associated with unequal rates and equal versus unequal qualities of reinforcement. The students completed math problems from two alternative sets on concurrent variable-interval (VI) 30-s VI 120-s schedules of reinforcement. During the equal-quality reinforcer condition, high-quality (nickels) and low-quality items ("program money" in the school's token economy) were alternated across sessions as the reinforcer for both sets of problems. During the unequal-quality reinforcer condition, the low-quality reinforcer was used for the set of problems on the VI 30-s schedule, and the high-quality reinforcer was used for the set of problems on the VI 120-s schedule. Equal- and unequal-quality reinforcer conditions were alternated using a reversal design. Results showed that sensitivity to the features of the VI reinforcement schedules developed only after the reinforcement intervals were signaled through countdown timers. Thereafter, when reinforcer quality was equal, the time allocated to concurrent response alternatives was approximately proportional to obtained reinforcement, as predicted by the matching law. However the matching relation was disrupted when, as occurs in most natural choice situations, the quality of the reinforcers differed across the response options.

Journal Article↗
PubMed1977

Associative interaction: joint control of key pecking by stimulus-reinforcer and response-reinforcer relationships.

The joint control of rate of key pecking in pigeons by stimulus-reinforcer and response-reinforcer relationships was studied in the context of a two-component multiple schedule of reinforcement. Food presentation was always associated with one component and extinction with the other. The stimulus-reinforcer relationship was manipulated by varying the relative durations of the two components. In the food-presentation component, a fixed rate of reinforcement, independent of rate of responding, was generated by a schedule referred to as "T*". One aspect of the response-reinforcer relationship, contiguity, was manipulated by varying the percentage of delayed reinforcers. With the multiple T* extinction schedule, stimulus-reinforcer and response-reinforcer relationships could be varied independently of one another. Rate of key pecking was sensitive to manipulations of both relationships. However, significant differential effects due to either the stimulus-reinforcer or response-reinforcer relationship were obtained only when the other relationship was weak: stimulus-reinforcer and response-reinforcer relationships interacted in the joint control of responding.

Journal Article↗
PubMed2006

Investigations of timing during the schedule and reinforcement intervals with wheel-running reinforcement.

Across two experiments, a peak procedure was used to assess the timing of the onset and offset of an opportunity to run as a reinforcer. The first experiment investigated the effect of reinforcer duration on temporal discrimination of the onset of the reinforcement interval. Three male Wistar rats were exposed to fixed-interval (FI) 30-s schedules of wheel-running reinforcement and the duration of the opportunity to run was varied across values of 15, 30, and 60s. Each session consisted of 50 reinforcers and 10 probe trials. Results showed that as reinforcer duration increased, the percentage of postreinforcement pauses longer than the 30-s schedule interval increased. On probe trials, peak response rates occurred near the time of reinforcer delivery and peak times varied with reinforcer duration. In a second experiment, seven female Long-Evans rats were exposed to FI 30-s schedules leading to 30-s opportunities to run. Timing of the onset and offset of the reinforcement period was assessed by probe trials during the schedule interval and during the reinforcement interval in separate conditions. The results provided evidence of timing of the onset, but not the offset of the wheel-running reinforcement period. Further research is required to assess if timing occurs during a wheel-running reinforcement period.

Analysis of Variance↗
PubMed1998

Multiple variable interval schedule behaviour in humans: effects of ethanol, mood, and reinforcer size on responding maintained by monetary reinforcement.

Ethanol is an effective reinforcer but, in common with other drugs of abuse, it may derive some of its reinforcing properties from the effects it has on behaviour maintained by other reinforcers. However, any assessment of ethanol's hypothesized effect on behaviour maintained by other reinforcers must take into account the fact that ethanol may have multiple mechanisms of action. In order to address this problem the experiments reported herein used a procedure based upon Herrnstein's Matching Law which allowed joint assessment of subjects' motor capacity and reinforcer sensitivity. The effect of ethanol (0, 0.3, and 0.6 g/kg) on motor capacity and reinforcer sensitivity was assessed by studying behaviour maintained by monetary reinforcement. In the first experiment the procedure was validated by showing that the behaviour of subjects was sensitive to changes in reinforcer value and in the second experiment 0.6 g/kg ethanol reduced motor capacity but did not affect reinforcer sensitivity. As a secondary hypothesis we also studied the effect of mood on reinforcer sensitivity and motor capacity. It was found that lower mood scores (lower hedonic tone) were associated with reduced reinforcer sensitivity and that male subjects showed higher motor capacity than females. However, there was also a mood by sex interaction, which indicated that higher motor capacity in males was only found in the presence of lower mood scores. The results are discussed in relation to the mechanisms of ethanol's dopaminergic effects, interactions between ethanol and other drugs of abuse, and the changes in reinforcer sensitivity which are thought to occur in depression.

Adolescent↗
PubMed2003

Effects of reinforcer consumption and magnitude on response rates during noncontingent reinforcement.

Results of previous research on the effects of noncontingent reinforcement (NCR) have been inconsistent when magnitude of reinforcement was manipulated. We attempted to clarify the influence of NCR magnitude by including additional controls. In Study 1, we examined the effects of reinforcer consumption time by comparing the same magnitude of NCR when session time was and was not corrected to account for reinforcer consumption. Lower response rates were observed when session time was not corrected, indicating that reinforcer consumption can suppress response rates. In Study 2, we first selected varying reinforcer magnitudes (small, medium, and large) on the basis of corrected response rates observed during a contingent reinforcement condition and then compared the effects of these magnitudes during NCR. One participant exhibited lower response rates when large-magnitude reinforcers were delivered; the other ceased responding altogether even when small-magnitude reinforcers were delivered. We also compared the effects of the same NCR magnitude (medium) during 10-min and 30-min sessions. Lower response rates were observed during 30-min sessions, indicating that the number of reinforcers consumed across a session can have the same effect as the number consumed per reinforcer delivery. These findings indicate that, even when response rate is corrected to account for reinforcer consumption, larger magnitudes of NCR (defined on either a per-delivery or per-session basis) result in lower response rates than do smaller magnitudes.

Adult↗
PubMed1994

Increasing and signaling background reinforcement: effect on the foreground response-reinforcer relation.

Herrnstein's (1970) hyperbolic matching equation describes the relationship between response rate and reinforcement rate. It has two estimated parameters, k and Re. According to one interpretation, k measures motor performance and Re measures the efficacy of the reinforcer maintaining responding relative to background sources of reinforcement. Experiment 1 tested this interpretation of the Re parameter by observing the effect of adding and removing an additional source of reinforcement to the context. Using a within-session procedure, estimates of Re were obtained from the response-reinforcer relation over a series of seven variable-interval schedules. A second, concurrently available variable-interval schedule of reinforcement was added and then removed from the context. Results showed that when the alternative was added to the context, the value of Re increased by 107 reinforcers per hour; this approximated the 91 reinforcers per hour obtained from this schedule. Experiment 2 investigated the effects of signaling background reinforcement on k and Re. The signal decreased Re, but did not have a systematic effect on k. In general, the results supported Herrnstein's interpretation that in settings with one experimenter-controlled reinforcement source, Re indexes the strength of the reinforcer maintaining responding relative to uncontrolled background sources of reinforcement.

Animals↗
PubMed2002

Effects of reinforcer magnitude on responding under differential-reinforcement-of-low-rate schedules of rats and pigeons.

Experiment I investigated the effects of reinforcer magnitude on differential-reinforcement-of-low-rate (DRL) schedule performance in three phases. In Phase 1, two groups of rats (n = 6 and 5) responded under a DRI. 72-s schedule with reinforcer magnitudes of either 30 or 300 microl of water. After acquisition, the water amounts were reversed for each rat. In Phase 2, the effects of the same reinforcer magnitudes on DRL 18-s schedule performance were examined across conditions. In Phase 3, each rat responded unider a DR1. 18-s schedule in which the water amotnts alternated between 30 and 300 microl daily. Throughout each phase of Experiment 1, the larger reinforcer magnitude resulted in higher response rates and lower reinforcement rates. The peak of the interresponse-time distributions was at a lower value tinder the larger reinforcer magnitude. In Experiment 2, 3 pigeons responded under a DRL 20-s schedule in which reinforcer magnitude (1-s or 6-s access to grain) varied iron session to session. Higher response rates and lower reinforcement rates occurred tinder the longer hopper duration. These results demonstrate that larger reinforcer magnitudes engender less efficient DRL schedule performance in both rats and pigeons, and when reinforcer magnitude was held constant between sessions or was varied daily. The present results are consistent with previous research demonstrating a decrease in efficiency as a function of increased reinforcer magnituide tinder procedures that require a period of time without a specified response. These findings also support the claim that DRI. schedule performance is not governed solely by a timing process.

Animals↗