Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “REINFORCEMENT”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18Linked to original sources
PubMed1999

The pharmacology of impulsive behaviour in rats VI: the effects of ethanol and selective serotonergic drugs on response choice with varying delays of reinforcement.

RATIONALE: Tolerance to delay of reinforcement has been proposed as an important facet of self-control in both animals and man. Poor self-control, leading to impulsive behaviour, can be a major problem if it reaches pathological levels. OBJECTIVES: The effects of five serotonergic drugs were compared to those of ethanol on a procedure for measuring tolerance to delay of reinforcement in rats in order to elucidate further the role of the serotonin systems in the regulation of impulsive behaviour. METHODS: Rats were trained to choose between a single food pellet (small reinforcer) delivered immediately or five food pellets (large reinforcer) delivered after programmed delays. At the start of each session, there was no delay between the response and delivery of the large reinforcer, but this was increased stepwise during the session to delays of 10, 20, 40 and 60 s. RESULTS: The rats showed consistent preference for the larger reinforcer when it was not delayed but showed a shift in preference as the session continued, so that they preferred the small reinforcer when the large was delayed by 40 or 60 s. Ethanol at a dose of 1.0 g/kg produced a significance increase in preference for the small, immediate reinforcer throughout the session, although there were marked individual differences in the size of the effect. A similar, but somewhat smaller effect was seen with the 5-HT(2) agonist, DOI, at a dose of 1.0 mg/kg. In contrast, the 5-HT(1A) agonist, 8-OH-DPAT (0.3 mg/kg) reduced preference for the large reinforcer at the start of the session, and reduced preference for the small reinforcer at the end of the session, i.e. produced a regression to indifference. Lower doses of these three drugs, and treatment with the 5-HT receptor subtype selective antagonists WAY-100635 (5-HT(1A): 0.01-0.1 mg/kg), ritanserin (5-HT(2): 0.1 and 0.3 mg/kg) and MDL-72222 (5-HT(3): 1.0 and 3.0 mg/kg) had no significant effects on reinforcer choice. CONCLUSION: These data show that ethanol and DOI increase preference for the immediate reinforcer, which can be construed as evidence of an increase in impulsive behaviour (reduction in self control), whereas selective blockade of the 5-HT(1A), 5-HT(2) or 5-HT(3) receptors using selective antagonists does not affect self-control.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2005

beta2-Subunit-containing nicotinic acetylcholine receptors are involved in nicotine-induced increases in conditioned reinforcement but not progressive ratio responding for food in C57BL/6 mice.

RATIONALE: Nicotine administration potentiates conditioned reinforcement in rats, an effect that persists for weeks after chronic exposure. Little is known regarding the nicotinic receptor subtypes that may mediate this effect. OBJECTIVE: The purpose of this study was to determine whether beta2-subunit-containing nicotinic acetylcholine receptors (beta2*nAChRs) are necessary for lasting effects of nicotine on conditioned and primary reinforcement in mice. METHODS: Beta2 knockout (beta2KO) and wild-type (WT) mice received 14 days of nicotine exposure (NIC, 200 microg/ml in 2% saccharin) or saccharin alone (SAC) in their drinking water. Five days later, mice received paired presentations of a conditioned stimulus (CS) with water unconditioned stimulus (US) or explicitly unpaired presentations of the CS and US during Pavlovian discriminative approach training. Training was followed by two conditioned reinforcement tests. Mice were subsequently tested for food-reinforced responding in the absence of explicit cues followed by a progressive ratio test. RESULTS: During conditioned reinforcement testing, only mice in the paired condition showed increased responding in the CS-reinforced aperture over inactive apertures. WT-NIC mice showed enhanced conditioned reinforcement compared to WT-SAC animals. beta2KO-SAC mice showed elevated conditioned reinforcement compared to WT-SAC subjects, but beta2KO-NIC and beta2KO-SAC mice did not differ in responding with conditioned reinforcement. Prior nicotine exposure did not alter food-reinforced responding but resulted in elevated break points for food in both genotypes. CONCLUSION: These data show that nicotine exposure enhances conditioned reinforcement in mice and indicate that beta2*nAChRs are necessary for nicotine-dependent enhancement of incentive aspects of motivation but not motivation for primary reinforcement measured by progressive ratio responding.

Animals↗
PubMed2004

Food hedonics and reinforcement as determinants of laboratory food intake in smokers.

Both the hedonic ratings and the reinforcing value of food have been considered to be determinants of food intake. The objective of this study was to compare the pleasurable ratings and the reinforcing value of food as determinants of energy intake. Seventy-four smokers were studied in food consumption and reinforcing value of food tasks prior to enrolling in a smoking-cessation treatment program. For the food consumption task, the participants tasted and consumed food ad lib from eight snack foods. The reinforcing value of the food task assessed how hard subjects would work for a preferred snack food. Results showed that food reinforcement was related to laboratory food intake, with those high in food reinforcement consuming significantly more calories (+114.4 kcal, P<.01) than did the participants low in food reinforcement. Food reinforcement was related to food intake for the preferred food as well as to total energy intake. Hedonics for the preferred food was related to food reinforcement but not to either measure of laboratory energy intake. In multiple-regression models, food reinforcement and the interaction of food reinforcement by sex were significant predictors of energy intake for the preferred food and for total energy intake, along with baseline hunger. In conclusion, energy intake in smokers in a laboratory setting is more strongly related to food reinforcement than to the hedonic ratings of food.

Adult↗
PubMed1980

Differential reinforcement of correct responses to probes and prompts in picture-name training with severely retarded children.

A systematic sequence of prompt and probe trials was used to teach picture names to three severely retarded children. On prompt trials the experimenter presented a picture and said the picture name for the child to imitate; on probe trials the experimenter did not name the picture. A procedure whereby correct responses to prompts and probes were nondifferentially reinforced was compared with procedures whereby correct responses to prompts and probes were differentially reinforced according to separate and independent schedules of primary reinforcement. In Phase 1, correct responses to prompts and probes were reinforced nondifferentially on a fixed ratio (FR) 6 or 8 schedule; in Phase 2, correct responses to prompts were reinforced on the FR schedule and correct responses to probes were reinforced on an FR schedule of the same value; in Phase 3, correct responses to prompts were reinforced on the FR schedule and correct responses to probes were reinforced on a continuous reinforcement (CRF; every correct response reinforced) schedule; in Phase 4, correct responses to prompts were reinforced on a CRF schedule and correct responses to probes were reinforced on the FR schedule; in Phase 5, a reversal to the conditions of Phase 3 was conducted. For all three children, the FR schedule for correct responses to prompts combined with the CRF schedule for correct responses to probes (Phases 3 and 5) generated the highest number of correct responses to probes, the highest accuracy (correct responses relative to correct responses plus errors) on probe trials, and the highest rate of learning to name pictures.

Child, Preschool↗
PubMed1982

Reinforcement contingencies and signal detection.

Pigeons were trained to discriminate temporal stimuli in a discrete-trial signal-detection procedure. Pecks to one side key were reinforced intermittently after exposure to one duration, and pecks to the other side key were reinforced intermittently after exposure to a different duration. In Experiment I, the allocation of reinforcers was varied systematically for correct responses and for errors, using a procedure that controlled the obtained numbers of reinforcers. When reinforcers were allocated symmetrically, the level of discrimination decreased as the proportion of reinforcers for errors increased. When reinforcers were allocated asymmetrically, the decrease in discrimination was less systematic. Bias toward one or the other side key roughly matched the ratio of reinforcers obtained by pecks at those keys, independent of the level of discrimination. In Experiment II, the overall rate of reinforcement for correct responses was varied both within and between experimental conditions. The level of discrimination was positively related to the overall rate of reinforcement. The discrimination data of both experiments were interpreted in relation to the contingencies of reinforcement and nonreinforcement, characterized by the average difference in reinforcement probability for correct responses and errors.

Animals↗
PubMed1987

Choice between reliable and unreliable outcomes: mixed percentage-reinforcement in concurrent chains.

Pigeons' choices between alternatives that provided different percentages of reinforcement in mixed schedules were studied using the concurrent-chains procedure. In Experiment 1, the alternatives were terminal-link schedules that were equal in delay and magnitude of reinforcement, but that provided different percentages of reinforcement, with one schedule providing, reinforcement twice as reliably as the other. All pigeons preferred the more reliable schedule, and their level of preference was not systematically affected by variation in the absolute percentage values, or in the magnitude of reinforcement. In Experiment 2, preference for a schedule providing 100% reinforcement over one providing 33% reinforcement increased systematically with increases in the duration of the terminal links. In contrast, preference decreased systematically with increases in the duration of the initial links. Experiment 3 examined choice with equal percentages of reinforcement but unequal delays to reinforcement. Preference for the shorter delay to reinforcement was not systematically affected by variation in the absolute percentage of reinforcement. The overall pattern of results supported predictions based on an extension of the delay-reduction hypothesis to choice procedures involving mixed schedules of percentage reinforcement.

Animals↗
PubMed1988

Self-control in mentally retarded adolescents: choice as a function of amount and delay of reinforcement.

Three severely mentally retarded adolescents were studied under discrete-trial procedures in which a choice was arranged between edible reinforcers that differed in magnitude and, in some conditions, delay. In the absence of delays the larger reinforcer was consistently chosen. Under conditions in which the smaller reinforcer was not delayed, increasing the delay to delivery of the larger reinforcer decreased the percentage of trials in which that reinforcer was chosen. All subjects directed the majority of choice responses to the smaller reinforcer when the larger reinforcer was sufficiently delayed, although the value at which this occurred differed across subjects. Under conditions in which the larger reinforcer initially was sufficiently delayed to result in preference for the smaller one, progressively increasing in 5-s increments the delay to both reinforcers increased percentage of trials with the larger reinforcer chosen. At sufficiently long delays, 2 of the subjects consistently chose the larger, but more delayed, reinforcer, and the 3rd subject chose that reinforcer on half of the trials. These results are consistent with the findings of prior studies in which adult humans responded to terminate noise and pigeons responded to produce food.

Adolescent↗
PubMed1994

Effects of qualitatively different reinforcers on the parameters of the response-strength equation.

This experiment examined the relationship between two qualitatively different reinforcers and the parameters of a quantitative model of reinforced responding, referred to as the response-strength equation or the Herrnstein equation. A group of rats was first food deprived and later water deprived. An 11.5% sucrose solution served as the reinforcer in the food-deprivation condition, and water was the reinforcer in the water-deprivation condition. Each experimental session consisted of a series of seven variable-interval schedules, providing reinforcement rates that varied between 20 and 1,200 reinforcers per hour. The response rates increased in a negatively accelerating function in a manner consistent with the response-strength equation. This equation has two fitted parameters, k and Re. According to one theory, the k parameter is a measure of motor performance, and Re is indicative of the relative reinforcement efficacy of the background uncontrollable sources of reinforcement in relation to the experimentally arranged reinforcer. In this study, k did not change as a result of the different reinforcers, but Re was significantly larger in the sucrose-reinforcement condition. These results are consistent with the interpretation that k and Re measure two independent and experimentally distinguishable parameters and provide further evidence that absolute response rate is a function of relative reinforcement rate, as implied by the derivation of the response-strength equation based on the matching law.

Animals↗
PubMed2003

Establishing preference for unreliable reinforcement in adults with dual diagnoses.

We evaluated the choice responding of three adults dually diagnosed with developmental and psychiatric disabilities using concurrent schedules of reinforcement. Specifically, participants were given a choice between a response option resulting in reliable reinforcement and a response option resulting in unreliable reinforcement. Our primary purpose was to shift preference from reliable to unreliable reinforcement via the systematic presentation of stimuli during delay intervals. A second purpose was to evaluate the effectiveness of intervening stimuli in shifting preference at differing delay-to-reinforcement intervals. Preference for unreliable reinforcement was first examined in the absence of stimulus presentations during delays, at three different delay values. Next, we aimed to establish preference for unreliable reinforcement by presenting pictures of reinforcers during delays preceding unreliable reinforcement. Preference was again examined at three different delay values. In the absence of stimulus presentations during delays, participants were shown to prefer reliable reinforcement, particularly at the longer delay value. When stimuli were presented during the delays, two of the three participants preferred unreliable reinforcement, particularly the longer the delay value. These results suggest that the presentation of intervening stimuli during delays may help facilitate tolerance for unreliable reinforcement.

Adult↗
PubMed2004

Release of chlorhexidine digluconate and flexural properties of glass fibre reinforced provisional fixed partial denture polymer.

The objective of this study was to determine the flexural properties and the release of chlorhexidine digluconate (CHX) of CHX laced unidirectional E-glass fibre reinforced provisional fixed partial denture polymer. Bar shaped test specimens (3.3 x 10.0 x 65.0 mm) were fabricated from provisional fixed partial denture polymer (mixture of poly[ethylmethacrylate] powder and n-poly[butyl methacrylate] monomer liquid) with E-glass fibre reinforcements. Poly(methyl methacrylate) preimpregnated continuous unidirectional glass fibre reinforcement was laced with CHX. The glass fibre reinforcements were incorporated into the polymer and the polymerised to the form of test specimens. In addition test specimens without CHX in glass fibre reinforcement were made for comparison. Control specimens did not contain glass fibres in the test specimens. Flexural strength and modulus of test specimens (n = 6) was tested with three-point bending test after storing the specimens dry or in water (two weeks). Released CHX was determined with high performance liquid chromatography during 180 days water immersion. In dry conditions, the flexural strength and the modulus of the polymer was 43 MPa and 1.7 GPa, and with glass fibre reinforcement 96 MPa and 3.5 GPa. With the reinforcement laced with CHX, the strength was 92 MPa and the modulus was 3.2 GPa. The water storage of test specimens did not weaken the reinforced polymer. The majority of the CHX released from the glass fibre reinforced polymer during the first days of storage in water. Flexural properties of provisional fixed partial denture polymer were increased using glass fibre reinforcement. The fibre reinforcement that was laced with CHX resulted in similar reinforcing effect.

Adhesives↗
PubMed1987

The effects of fibre reinforcement and gold plating on the flexural and tensile strength of PGA/PLA copolymer materials in vitro.

Changes in the flexural and/or tensile strength of plates and rods made of PGA/PLA copolymer submerged in water for a period of 4 wk were investigated. During this time, the effects of PGA/PLA fibre self-reinforcement, carbon fibre reinforcement and gold plating on tensile and/or flexural strength were examined. The results were used for evaluation of the surgical applications of PGA/PLA copolymer and its composites. The initial tensile strength of non-reinforced material was 45 Mpa and its flexural strength was 150 MPa: the flexural strength of self-reinforced material was 265 MPa. The tensile strength of carbon fibre reinforced material was 90 MPa and its flexural strength 190 MPa. The initial strengths of plated and unplated samples were the same but plating delayed the loss of the mechanical strength of carbon fibre reinforced samples. After 4 wk the flexural strength of self-reinforced and carbon fibre reinforced samples was decreased to the level of cancellous bone (10-20 MPa) while the flexural strength of non-reinforced samples was below that level (less than or equal to 5 MPa). The results suggested that self-reinforced PGA/PLA composites may be used for the treatment of fractures in cancellous bone. Positive animal experiments led to clinical studies in vivo. These studies showed that there was no difference in outcome between 2 groups of patients with displaced fractures of the ankle treated with metallic implants or PGA/PLA fibre self-reinforced implants, respectively. Self-reinforced biodegradable implants are now used routinely in Helsinki University Central Hospital.

Biocompatible Materials↗
PubMed2001

Effect of polyaramid fiber reinforcement on the strength of 3 denture base polymethyl methacrylate resins.

PURPOSE: The interactive effects of synthetic polyaramid reinforcement fibers on the transverse strength of intact and repaired heat-polymerized denture base acrylic resins were investigated. MATERIALS AND METHODS: Three polymethylmethacrylate (PMMA) polymers were tested: Acron MC (GC International Corp, Scottsdale, AZ), Lucitone 199 (Dentsply International Inc, York, PA), and Microlon (The Hygienic Corp, Akron, OH). With each polymer, there were 2 controls and 4 experimental groups (n = 9 per group). The treatment groups were intact heat-polymerized PMMA control, PMMA with unreinforced repair, PMMA with polyaramid reinforced repair, intact polyaramid reinforced heat-polymerized PMMA control, polyaramid reinforced PMMA with unreinforced repair, and polyaramid reinforced PMMA with polyaramid reinforced repair. The transverse fracture strengths of the samples were measured with a 3-point bending test on a Zwick Universal Testing Machine (Zwick of America, Inc, East Windsor, CT). RESULTS: The highest mean strength at fracture was recorded with intact polyaramid reinforced heat-polymerized PMMA controls for all resins. Analysis of variance showed significant differences in transverse strength (p < .05) by experimental group, by material, and by interaction of group and material. Tukey HSD (honestly significant difference) Multiple Comparisons Test (alpha = 0.05) showed that intact polyaramid reinforced heat-polymerized PMMA controls were significantly stronger than intact heat-polymerized PMMA controls and all the other treatment groups. Use of polyaramid reinforcement in repair of unreinforced PMMA or polyaramid reinforced PMMA did not result in significantly increased transverse strength. CONCLUSIONS: Polyaramid reinforcement significantly increased the transverse strength of intact heat-polymerized PMMA. Polyaramid fibers did not significantly increase strength to reinforce PMMA repairs.

Acrylic Resins↗
PubMed1982

An invariant relation between changing over and reinforcement.

Although concurrent schedules may arrange reinforcers irregularly, relatively large numbers of reinforcers are obtained when an animal changes from one schedule to the other. This paper proposes a quantitative relation that predicts the proportion of reinforcers obtained when an animal is working on a schedule and the proportion when the animal changes over to a schedule. Basically the relation states that the number of reinforcers obtained while an animal works on a schedule varies directly with the relative amount of time spent working on that schedule; and the number of reinforcers obtained when an animal changes to a schedule varies directly with the relative amount of time spent on the alternate schedule. An important aspect of this relation is that when relative reinforcement rates are less than .50, more reinforcers are obtained just after an animal changes to a schedule than at all other times when this schedule is engaged. Data obtained both from a stat-bird and a live pigeon were in close agreement with the quantitative predictions. The relation between changing over and reinforcement held across several procedural changes that included changes in relative reinforcement rate, changes from independent to interdependent scheduling procedures, and changes in the variable-interval reinforcement distributions. The results are discussed in terms of the effects of the local distribution of reinforcement on responding. The local reinforcement distribution can affect local response rates and affects the resulting matching relation. This arrangement has implications for explanations of choice.

Journal Article↗
PubMed1985

A parametric description of amphetamine's effect on response rate: changes in reinforcement efficacy and response topography.

A mathematical model was used to describe the effects of amphetamine on the rate of a reinforced response in the rat. The model provides measures of reinforcement efficacy and response topography for behavior maintained by variable-interval reinforcement schedules. In this study the measured behavior was a lever press, the reinforcer was water, and the variable-interval schedules provided five different rates of reinforcement, ranging from about 20 to 660/h. In each session the rats were exposed to each of the five schedules, and as reinforcement rate increased, the rate of lever pressing increased in a negatively accelerated manner that was closely approximated by the equation for a rectangular hyperbola. Amphetamine changed response rate and the parameters of the best-fitting hyperbolas. The 0.25-1.0-mg/kg doses increased response rate, and the parameter changes supported the interpretation that the increases were due primarily to an increase in reinforcement efficacy. The 2.0- and 3.0-mg/kg doses decreased response rates maintained by low reinforcement rates and increased response rates maintained by high reinforcement rates, and the parameter changes supported the interpretation that at higher doses amphetamine produced counteracting changes in reinforcement efficacy and response topography: reinforcement efficacy decreased, whereas response topography changed so as to increase response rates.

Animals↗
PubMed2006

Some effects of overall rate of earning reinforcers on run lengths and visit durations.

In a concurrent schedule, responding at each alternative is controlled by a pair of schedules that arrange reinforcers for staying at that alternative and reinforcers for switching to the other alternative. Each pair of schedules operates only while at the associated alternative. When only one pair of stay and switch schedules is presented, the rates of earning reinforcers for staying divided by the rates of earning reinforcers for switching controls the mean number responses in a visit and the mean duration of visits. The purpose of the present experiment was to see whether the sum of the rates of earning stay and switch reinforcers changed the way that run length and visit duration were affected by the ratio of the rates of stay to switch reinforcers. Rats were exposed to pairs of stay and switch schedules that varied both the ratio of the rates of earning stay and switch reinforcers and the sum of the rates of earning stay and switch reinforcers. Run lengths and visit durations were joint functions of the ratio of the rates of earning stay and switch reinforcers and the sum of the rates of earning stay and switch reinforcers. These results shows that the effect of the ratio of the sum of the rates of earning stay and switch reinforcers results from processes operating at the alternative, rather than from processes operating at both alternatives.

Animals↗
PubMed2004

Validation of a questionnaire measure of the relative reinforcing value of food.

The traditional method of measuring the relative reinforcing value of food provides subjects a choice of food and non-food alternatives, and defines the relative reinforcing value of food based on the allocation of responses for the two alternatives as the schedules of reinforcement for the alternatives change. Greater allocation of responses for one alternative versus another reflects the relative reinforcing value of the alternatives. This method was designed for laboratory use, but methods are needed to extend measurement of reinforcing value to applied research environments. Two experiments were conducted to assess the validity of a questionnaire measure of the relative reinforcing value of food in normal weight university samples. Study 1 (n=39) assessed the relationship between the relative reinforcing value of snack food versus fruits and vegetables (condition 1) or enjoyable sedentary behaviors (condition 2) as measured by the questionnaire and standardized computerized concurrent schedules criterion. A significant relationship (Pearson r=0.49, p<0.01; Guttman's MU2=0.69) across the two conditions between the two methods of measuring food reinforcement was observed. Experiment 2 (n=10) utilized a within-subject counterbalanced design to manipulate food deprivation and hunger levels to determine if food deprivation increased the reinforcing value of snack food as measured by the questionnaire to provide an index of validity of the questionnaire. Results showed that food deprivation increased the relative reinforcing value of snack food. Results from both studies suggest that the questionnaire has good validity, and may represent an efficient and reliable method of assessing the relative reinforcing value of food.

Adolescent↗
PubMed1968

A quantitative analysis of the responding maintained by interval schedules of reinforcement.

Interval schedules of reinforcement maintained pigeons' key-pecking in six experiments. Each schedule was specified in terms of mean interval, which determined the maximum rate of reinforcement possible, and distribution of intervals, which ranged from many-valued (variable-interval) to single-valued (fixed-interval). In Exp. 1, the relative durations of a sequence of intervals from an arithmetic progression were held constant while the mean interval was varied. Rate of responding was a monotonically increasing, negatively accelerated function of rate of reinforcement over a range from 8.4 to 300 reinforcements per hour. The rate of responding also increased as time passed within the individual intervals of a given schedule. In Exp. 2 and 3, several variable-interval schedules made up of different sequences of intervals were examined. In each schedule, the rate of responding at a particular time within an interval was shown to depend at least in part on the local rate of reinforcement at that time, derived from a measure of the probability of reinforcement at that time and the proximity of potential reinforcements at other times. The functional relationship between rate of responding and rate of reinforcement at different times within the intervals of a single schedule was similar to that obtained across different schedules in Exp. 1. Experiments 4, 5, and 6 examined fixed-interval and two-valued (mixed fixed-interval fixed-interval) schedules, and demonstrated that reinforcement at one time in an interval had substantial effects on responding maintained at other times. It was concluded that the rate of responding maintained by a given interval schedule depends not on the overall rate of reinforcement provided but rather on the summation of different local effects of reinforcement at different times within intervals.

Animals↗
PubMed1986

Choice between single and multiple delayed reinforcers.

Pigeons chose between alternatives that differed in the number of reinforcers and in the delay to each reinforcer. A peck on a red key produced the same consequences on every trial within a condition, but between conditions the number of reinforcers varied from one to three and the reinforcer delays varied between 5 s and 30 s. A peck on a green key produced a delay of adjustable duration and then a single reinforcer. The green-key delay was increased or decreased many times per session, depending on a subject's previous choices, which permitted estimation of an indifference point, or a delay at which a subject chose each alternative about equally often. The indifference points decreased systematically with more red-key reinforcers and with shorter red-key delays. The results did not support the suggestion of Moore (1979) that multiple delayed reinforcers have no effect on preference unless they are closely grouped. The results were well described in quantitative detail by a simple model stating that each of a series of reinforcers increases preference, but that a reinforcer's effect is inversely related to its delay. The success of this model, which considers only delay of reinforcement, suggested that the overall rate of reinforcement for each alternative had no effect on choice between those alternatives.

Animals↗