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PubMed1968

Some factors controlling preference between fixed-ratio and variable-ratio schedules of reinforcement.

A multiple schedule of food reinforcement for key-pecking was arranged which consisted of nine fixed-ratios, each of which operated in the presence of a different stimulus. Pigeons could complete a given fixed-ratio within the multiple schedule or, by pecking a second key, could switch from the fixed-ratio schedule to a variable-ratio schedule consisting of the same nine ratios. Stable switching behavior was established which did not maximize simple probability or rate of reinforcement. Instead, the subjects showed a stable preference for the variable-ratio schedule of food reinforcement. Increasing the number of responses required to switch, and removing the occasions on which reinforcement was delivered after a single response in the variable schedule, decreased the number of switches to the variable schedule. Periods of delay interposed between a completed switch and the availability of reinforcement after one response in the variable schedule also decreased switching to the variable schedule, particularly at long delay intervals.

Journal Article↗
PubMed1989

Determinants of choice for pigeons and humans on concurrent-chains schedules of reinforcement.

Concurrent-chains schedules of reinforcement were arranged for humans and pigeons. Responses of humans were reinforced with tokens exchangeable for money, and key pecks of 4 birds were reinforced with food. Variable-interval 30-s and 40-s schedules operated in the terminal links of the chains. Condition 1 exposed subjects to variable-interval 90-s and variable-interval 30-s initial links, respectively. Conditions 2 and 3 arranged equal initial-link schedules of 40 s or 120 s. Experimental conditions tested the descriptive adequacy of five equations: reinforcement density, delay reduction, modified delay reduction, matching and maximization. Results based on choice proportions and switch rates during the initial links showed that pigeons behaved in accord with delay-reduction models, whereas humans maximized overall rate of reinforcement. As discussed by Logue and associates in self-control research, different types of reinforcement may affect sensitivity to delay differentially. Pigeons' responses were reinforced with food, a reinforcer that is consumable upon presentation. Humans' responses were reinforced with money, a reinforcer exchanged for consumable reinforcers after it was earned. Reinforcers that are immediately consumed may generate high sensitivity to delay and behavior described as delay reduction. Reinforces with longer times to consumption may generate low sensitivity to delay and behavior that maximizes overall payoff.

Animals↗
PubMed1998

The synergistic effects of combining cocaine and heroin ("speedball") using a progressive-ratio schedule of drug reinforcement.

The relative reinforcing value of cocaine/heroin combination ("speedball") was compared in the rat using a progressive-ratio (PR) reinforcement schedule. The initial training for all rats was a combined dose of 18 microg/kg/inj of heroin (H) plus 300 microg/kg/inj of cocaine (C). Break points for the training dose and individual component doses were determined for half and double the training dose. Of the three doses of each treatment, only C yielded the expected monotonic increase in break point as a function of dose. Also, break points for C (300 and 600 microg/kg/inj) was greater than for the combination of C and H (18 H/300 C and 36 H/600 C microg/kg/inj), suggesting a greater reward value for C alone. The doses for these three drug treatments that produced saline level break points were then determined. At these lower doses, significant break points were obtained with the H/C combination at which the respective doses of H or C had break points identical to those of saline. These lower dose results indicate that the combination is clearly synergistic and that the discrepancy with doses at the opposite end of the dose response curve suggest that the PR schedule is vulnerable to drug-induced motor effects.

Analysis of Variance↗
PubMed1994

Effects of reinforcement history on responding under progressive-ratio schedules of reinforcement.

The effects of experimental history on responding under a progressive-ratio schedule of reinforcement were examined. Sixteen pigeons were divided into four equal groups. Groups 1 to 3 were trained to peck a key for food under a fixed-ratio, variable-ratio, or differential-reinforcement-of-low-rate schedule of reinforcement. After training, these pigeons were shifted to a progressive-ratio schedule, later were shifted back to their original schedule (with decreased rates of reinforcement), and finally were returned to the progressive-ratio schedule. Pigeons in Group 4 (control) were maintained on the progressive-ratio schedule for the entire experiment. To test for potential "latent history" effects, pigeons responding under the progressive-ratio schedule were injected with d-amphetamine and given behavioral-momentum tests of prefeeding and extinction. Experimental histories affected responding in the immediate transition to the progressive-ratio schedule; response rates of pigeons with variable-ratio and fixed-ratio histories were higher than rates of pigeons with differential-reinforcement-of-low-rate and progressive-ratio-only histories. Pigeons with differential-reinforcement-of-low-rate histories, and to a lesser degree pigeons with variable-ratio and fixed-ratio histories, also had shorter postreinforcement pauses than pigeons with only a progressive-ratio history. No consistent long-term effects of prior contingencies on responding under the progressive-ratio schedule were evident. d-Amphetamine and resistance-to-change tests failed to reveal consistent latent history effects. The data suggest that history effects are sometimes transitory and not susceptible to latent influences.

Animals↗
PubMed1970

The response-reinforcement dependency in fixed-interval schedules of reinforcement.

Pigeons were exposed to four different schedules of food reinforcement that arranged a fixed minimum time interval between reinforcements (60 sec or 300 sec). The first was a standard fixed-interval schedule. The second was a schedule in which food was presented automatically at the end of the fixed time interval as long as a response had occurred earlier. The third and fourth schedules were identical to the first two except that the first response after reinforcement changed the color on the key. When the schedule required a peck after the interval elapsed, the response pattern consisted of a pause after reinforcement followed by responding at a high rate until reinforcement. When a response was not required after the termination of the interval, the pattern consisted of a pause after reinforcement, followed by responses and then by a subsequent pause until reinforcement. Having the first response after reinforcement change the color on the key had little effect on performance. Post-reinforcement pause duration varied with the minimum interreinforcement interval but was unaffected by whether or not a response was required after the interval elapsed.

Journal Article↗
PubMed1991

Behavioral manifestations of prolonged lead exposure initiated at different stages of the life cycle: I. Schedule-controlled responding.

While early development represents a period of particular sensitivity to the neurotoxic effects of lead (Pb), much less is known about CNS effects at later stages of the life cycle. It is conceivable that old age represents an additional period of vulnerability given the neurodegenerative processes that are the inevitable accompaniment of advanced age. The experiments described here examined that possibility. The effects of prolonged low-level Pb exposures were assessed in young (21 day old), adult (8 mon old) and old (16 mon old) F-344 rats performing on Fixed-Interval (F1) and Variable-Interval (VI) schedules of reinforcement, two behavioral baselines previously shown to be sensitive to Pb exposure in young rats. The profile of Pb effects within each age group was remarkably uniform across both reinforcement schedules, while the direction of effect differed by age group. Pb exposure was associated with shifts toward increased VI and FI response rates in both young and old rats. In contrast, adult rats exposed to Pb exhibited decreased rates of responding on both FI and VI schedules. Both patterns of response rate changes can be indicative of less efficient performance. Of the two reinforcement schedules, the FI appeared to be the more sensitive, as marginally significant behavioral effects were observed at both the 2 and 10 mg Pb/kg/day doses on the FI, while only occurring in response to the 10 mg/kg dose of Pb on the VI. The differential pattern of Pb effects across age groups does not appear to reflect a rate-dependency phenomenon, but its exact basis awaits further investigation. The detection of primarily marginally significant response rate changes here as compared to previous studies using similar Pb exposure levels suggests that the F-344 strain of rats is less sensitive to Pb than is the Long-Evans rat strain.

Aging↗
PubMed1991

The effects of schedule history and the opportunity for adjunctive responding on behavior during a fixed-interval schedule of reinforcement.

The effects of schedule history and the availability of an adjunctive response (polydipsia) on fixed-interval schedule performance were investigated. Two rats first pressed levers under a schedule of food reinforcement with an interresponse time greater than 11 s, and 2 others responded under a fixed-ratio 40 schedule. All 4 were then exposed to a fixed-interval 15-s schedule. Water was continuously available under these conditions, but after responding became stable on the fixed-interval schedule, access was experimentally manipulated. With water freely available, subjects did not display characteristic fixed-interval response rates and patterns (i.e., scalloping or break-and-run). Instead, they exhibited predictable, stable patterns of behavior as a function of their schedule histories: Subjects with the interresponse-time history exhibited low response rates, and those with the fixed-ratio history exhibited high rates. Manipulating the amount of water available resulted in marked changes in response rates for rats with the interresponse-time history but not for those with the fixed-ratio history. The results illustrate the multiple causation of behavior by its previous and current schedules of reinforcement and other concurrent factors.

Animals↗
PubMed1978

Time allocation in concurrent schedules: the effect of signalled reinforcement.

The responses of five pigeons were reinforced on concurrent variable-interval variable-interval reinforcement schedules in which changeover key responses changed the stimulus and reinforcement schedules associated with the food key. While the reinforcement availability in one component remained unchanged throughout the experiment, the reinforcement availability in the other component was, during several conditions, signalled by the onset of an additional discriminative stimulus. During unsignalled conditions, both the relative frequency of responding and the relative time spent in each component approximated the obtained relative reinforcement frequency in each component. The effect of signalling reinforcer availability in one component was to (1) reduce responding in the signalled component to near-zero levels, and (2) increase the relative time in the unsignalled component, without a corresponding increase in the obtained relative reinforcement frequency. The magnitude of the increase in relative time in the unsignalled component decreased as the overall frequency of reinforcement increased. This deviation in the matching relation between relative time and the obtained relative reinforcement frequency was eliminated if the overall reinforcement frequency was increased before the signal was introduced and then, without removing the signal, gradually reduced.

Journal Article↗
PubMed1985

Comparing autistic and normal children along the dimensions of reinforcement maximization, stimulus sampling, and responsiveness to extinction.

The purpose of this study was to assess autistic children's ability to maximize reinforcement, sample among available stimuli, and respond to extinction. Responding to five concurrent reinforcement schedules (CRF, FR 2, FR 4, FR 7, and FR 11) was monitored and compared to groups of mental age-matched and chronological age-matched normal children. When a given child consistently selected a given schedule of reinforcement, it was then put on extinction, and both perseveration and responding to the remaining (intact) schedules of reinforcement were monitored. The results showed, first, that while normal children selected the richest schedule of reinforcement, autistics did not maximize reinforcement, typically selecting one of the thinner schedules available. Second, the autistic children sampled less, and less efficiently, than the normal children. Third, the autistic children proved to be much less responsive to extinction, perseverating longer than the normal children before switching to a new reinforcement schedule. Fourth, whenever extinction proved to be a problem in the autistics, it was quickly achieved by a simple change in the stimulus conditions. These results are discussed as possible "keystone" deficits, which may be causally related to many of the behavioral deficits of autism and which might be important target behaviors for treatment.

Adolescent↗
PubMed1995

Sucrose, ethanol, and sucrose/ethanol reinforced responding under variable-interval schedules of reinforcement.

Adding sweeteners to ethanol solutions is a common method of inducing rats to consume ethanol. However, it has usually been assumed that it is the sweet taste and/or the calories contained in the sweet solution that controls consumption. The present experiment examined the role of ethanol in controlling responding reinforced by ethanol or an ethanol/sucrose mixture compared with sucrose solutions of various concentrations. After initiation to self-administer 10% (v/v) ethanol using the sucrose-substitution method, rats were trained to respond under a concurrent VI 5" VI 5" schedule. During one condition, responding on one lever was reinforced by the presentation of 10% ethanol, and responding on a second lever was reinforced by water or one of the following sucrose solutions: 1% (w/v), 1.5%, 2%, 2.5%, 3%, and 5%. During a subsequent condition, responding reinforced by a 10% ethanol/2% sucrose mixture was compared under the concurrent schedule with responding reinforced by water, 2%, 2.5%, 3%, 5%, or 10% sucrose (w/v). The results indicated that the ethanol or ethanol/sucrose mixture maintained more responding than did sucrose solutions that were sweeter. Data support the conclusion that, after initiation, the taste and/or pharmacological effects of ethanol had become an important component of the reinforcing stimulus independent of the sweetener.

Alcohol Drinking↗
PubMed2000

Firing rate of nucleus accumbens neurons is dopamine-dependent and reflects the timing of cocaine-seeking behavior in rats on a progressive ratio schedule of reinforcement.

The progressive ratio (PR) schedule of reinforcement is used to determine the reinforcing properties of rewards such as drugs of abuse. In this schedule, the animal is required to press a lever a progressively increasing number of times to receive a reward; the highest ratio obtained before the animal ceases responding is termed "breakpoint." We recorded neuronal spike activity from cells in the nucleus accumbens (NAc) of rats responding on a PR schedule for cocaine reinforcement. A common subtype of NAc cells demonstrated firing rates that varied according to the time between cocaine deliveries. The firing rate was inversely related to the NAc cocaine level predicted by a pharmacokinetic model. At higher response-to-reward ratios, inter-reward intervals were increased, resulting in a decrease in modeled cocaine level and a concomitant increase in firing rate over the session. The final increase in firing rate above a threshold value suggests a neural correlate of breakpoint. The effects of preadministration of dopamine D1 or D2 antagonists on the animals' behavior were similar in that both reduced breakpoint; however, each antagonist had markedly different effects on NAc cell firing. The D1 antagonist SCH23390 reduced firing rates, even at low cocaine levels, whereas the D2 antagonist eticlopride induced a rightward shift in the dose dependence of NAc cell firing relative to modeled cocaine level. Our results suggest that the firing of NAc cells reflects changes in cocaine levels and thereby contributes to the temporal spacing of self-administration and to the cessation of responding at breakpoint.

Animals↗
PubMed1962

Some effects of response cost upon human operant behavior.

Three experiments are reported which investigated the effects of cost (point loss per response) upon human-observer responses maintained by VI and FI schedules of reinforcement (acquisition of points via critical-signal detections). (I) Cost attenuated VI response rates without substantially disturbing the constancy of responding, regardless of the presentation sequence of the no-cost and cost conditions. (II) FI scalloping appeared only under cost conditions. Under no cost, a constant rate of responding (similar to VI performance) characterized inter-reinforcement intervals. Exposure to cost did not prevent the recovery of previously established no-cost baselines. (III) FI irregularities, analogous to those commonly observed under FI reinforcement schedules, may be produced by different temporal presentations of the no-cost and cost conditions. The results of all three experiments emphasize the importance of cost as a factor in the maintenance of human behavior on schedules of positive reinforcement.

Learning↗
PubMed2000

Effects of reinforcement magnitude and ratio values on behaviour maintained by a cyclic ratio schedule of reinforcement.

In Experiments 1 and 2, lever pressing by rats was reinforced on a cyclic ratio schedule of food reinforcement, comprising a repeated sequence of fixed-ratio component schedules. Reinforcement magnitude was varied, on occasional sessions in Experiment 1 and across blocks of sessions in Experiment 2, from one to two or three 45-mg food pellets. In the one-pellet condition, post-reinforcement pauses increased with component schedule value. At higher magnitudes, post-reinforcement pauses increased, and overall response rates declined. Response rate on component schedules was a decreasing linear function of the obtained rate of reinforcement in all conditions. Plotted against component schedule value, response rate increased exponentially to an asymptote that decreased when reinforcement magnitude increased. These findings are consistent with regulatory accounts of food-reinforced behaviour. In Experiment 3, rats were trained under a cyclic ratio schedule comprising fixed-ratio components including higher values, and some inverted U-shaped response functions were obtained. Those rats that did not show this relationship were trained on cyclic ratios with even higher values, and all showed inverted U-shaped response functions. This suggests that behaviour on cyclic ratio schedules can reflect activating of reinforcement as well as the satiating effects seen in Experiments 1 and 2.

Animals↗
PubMed2005

Effects of reinforcement history on response rate and response pattern in periodic reinforcement.

Several researchers have suggested that conditioning history may have long-term effects on fixed-interval performances of rats. To test this idea and to identify possible factors involved in temporal control development, groups of rats initially were exposed to different reinforcement schedules: continuous, fixed-time, and random-interval. Afterwards, half of the rats in each group were studied on a fixed-interval 30-s schedule of reinforcement and the other half on a fixed-interval 90-s schedule of reinforcement. No evidence of long-term effects attributable to conditioning history on either response output or response patterning was found; history effects were transitory. Different tendencies in trajectory across sessions were observed for measures of early and late responding within the interreinforcer interval, suggesting that temporal control is the result of two separate processes: one involved in response output and the other in time allocation of responding and not responding.

Animals↗
PubMed1977

Undermatching: a reappraisal of performance on concurrent variable-interval schedules of reinforcement.

The extant data for pigeons' performance on concurrent variable-interval schedules were examined in detail. Least-squares lines relating relative pecks and time to the corresponding relative reinforcements were obtained for four studies. The between-study group slopes for time and pecks and five of seven within-study group slopes from individual studies were less than 1.00. This suggested the generality that pigeons respond less to the richer reinforcement schedule than predicted by matching. For pecks, a nonparametric test for distribution of points also supported this concept of undermatching (to the richer reinforcement schedule). In addition, using mean squared error as the criterion, a cubic curve fit the peck proportion data better than any line or other polynomial. This indicates that the relation between peck and reinforcement proportions may be nonlinear.

Journal Article↗
PubMed1996

Intravenous self-administration of cocaine under concurrent VI schedules of reinforcement.

Under concurrent VI (conc VI) schedules of reinforcement, organisms match the proportion of responses to the proportion of reinforcers obtained from the available options. This result is the basis of the matching law, a major theoretical view of the control of choice between and among available reinforcers. The present experiment examined the extent to which i.v. cocaine self-administration by monkeys under conc VI schedules of reinforcement was predicted by the matching law. One group of rhesus monkeys (n = 4) was prepared with chronic indwelling i.v. catheters and allowed to respond in a two-lever situation under conc VI schedules of reinforcement for cocaine injections. Three doses of cocaine (0.025, 0.05 and 0.1 mg/kg per injection) were made available under various conc VI schedules with an average inter-injection interval of 3 min. The same injection was available for each response, the difference between the options being the schedule of reinforcement. Each dose and schedule condition was in effect for at least ten consecutive sessions and until responding was stable. In a second group of monkeys (n = 3), a comparable experiment was conducted with responding maintained by the delivery of 1-g food pellets. Overall response rate maintained by cocaine was inversely related to dose. In addition, response rate decreased over the course of a session, apparently due to accumulation of cocaine. With regard to choice, more responding was maintained by the schedule that arranged more frequent injections. Choice was well predicted by the matching law, with a consistent tendency toward undermatching but no consistent bias toward one or the other option. Results were similar for behavior maintained by food, though two of three monkeys showed an unexplained bias toward the left lever. With regard to drug self-administration, these results demonstrate that in a choice situation, with all other variables being equal, injections that are available more frequently in time maintain behavior more strongly than less frequently available injections. Undermatching implies that the relative proportion of behavior maintained by the two options is somewhat less than the relative proportion of injections obtained. The finding that choice maintained by cocaine under conc VI schedules was comparable to choice maintained by food extends the generality of the conclusion that drugs and non-drug reinforcers control behavior by similar mechanisms.

Animals↗