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Results for “REINFORCEMENT”

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At least 163 records · Page 9Linked to original sources

PubMed1978

Delayed reinforcement of fixed-ratio performance without mediating exteroceptive conditioned reinforcement.

The performance of pigeons was studied under conditions in which the completion of a fixed-ratio requirement was not contiguous with the presentation of a reinforcer. Timein and timeout periods alternated throughout the experimental sessions. Responses made by an experimental bird during the timein period were accumulated, and when a fixed-ratio requirement had been met, grain was presented to the experimental bird and a yoked control following their first response in the next timein period. Across most manipulations of the fixed-ratio requirement and of the duration of the timeout period, the response rates of the experimental birds were considerably higher than those of their controls, suggesting that the response-reinforcer dependency controlled the behavior of the experimental bird in the absence of a close temporal association between responding on the ratio schedule and reinforcer presentations.

Journal Article↗

PubMed1984

Graded differential reinforcement: Response-dependent reinforcer amount.

After key pecking had been autoshaped, six pigeons were exposed to a condition in which the duration of grain availability at the end of an 8-second trial depended on the number of responses emitted during the trial (0.25-second access to grain per response). This procedure, called correlated reinforcement, alternated across conditions with the automaintenance baseline in which the 8-second trial terminated with a constant 2.5-second access to grain. Two control procedures were run; in both, the reinforcer durations were yoked to those obtained in the last correlated session. In the yoked control no responses were required, but in the single-response yoked control at least one response was required to receive the yoked duration. The correlated condition maintained response rates above those produced by the two control conditions. These results may be accounted for by differential reinforcement.

Journal Article↗

PubMed1994

Precurrent contingencies: Behavior reinforced by altering reinforcement probability for other behavior.

The present study explored the effects of a precurrent contingency in which one (precurrent) activity increased the reinforcement probability for another (current) activity. Four human subjects responded on a two-key computer mouse. Each right-key press was reinforced (points exchangeable for money) with .02 probability. In one condition (no precurrent contingency), pressing the left key had no scheduled consequence; in another condition (precurrent contingency), pressing the left key increased the reinforcement probability for right-key responding to .08 for 15 s. Initial exposure to the precurrent contingency resulted in acquisition of precurrent left-key responding for 3 subjects, but for the 4th subject a special contingency was required. Right-key responding occurred at a high stable rate across the conditions. Changeovers to left-key responding dropped to near zero when the precurrent contingency was absent and were maintained at enhanced levels when the precurrent contingency was present. Contacts with the left key consisted of short response runs. Right-key responses were more frequently emitted within 15 s of a left-key response when the precurrent contingency was present, an efficient adaptation to the contingency. Continued research on precurrent behavior may produce insights into complex phenomena such as autoclitics and self-control.

Journal Article↗

PubMed1994

Choice between reliable and unreliable reinforcement alternatives revisited: Preference for unreliable reinforcement.

Pigeons' choices between a reliable alternative that always provided food after a delay (i.e., 100% reinforcement) and an unreliable one that provided food or blackout equally often after a delay (i.e., 50% reinforcement) was studied using a discrete-trials concurrent-chains procedure modified to prevent choice between alternatives following a blackout outcome. Initial links were fixed-ratio 1 schedules, and terminal links were fixed-time schedules. Stimuli presented during the terminal-link delays were correlated with the food and blackout outcomes. In Experiment 1, terminal-link durations were varied. With short terminal links (i.e., 10 s), 6 of 8 subjects showed strong preference for the 50% side. As terminal-link duration increased to 30 s, preference, regardless of direction, became less extreme. In Experiment 2, the side-key location of the 50% and 100% alternatives was reversed for 3 subjects. Preference for the 50% alternative reoccurred following the key reversal. When a 5-s separation was subsequently interposed between the initial and terminal links for both alternatives, all birds reversed to a preference for the 100% side. In general, the strong preference for the 50% side was qualitatively consistent with the expectation that the procedure enhanced the conditioned-reinforcement effectiveness of the food-associated terminal-link stimulus on the 50% side. Implications of the results for various accounts of choice of the 50% alternative are discussed.

Journal Article↗

PubMedDate not supplied

Probability of failure of veneered glass fiber-reinforced composites and glass-infiltrated alumina with or without zirconia reinforcement.

PURPOSE: The probability of failure under flexural load of veneered specimens of a unidirectional glass fiber-reinforced composite (FibreKor/Sculpture), a bidirectional glass fiber-reinforced composite (Vectris/Targis), a glass-infiltrated alumina (In-Ceram Alumina/Vita alpha), and a zirconia-reinforced glass-infiltrated alumina (In-Ceram Zirconia/Vita alpha) was investigated; a metal-ceramic (PG200/Vita omega) system served as a control. MATERIALS AND METHODS: Ten uniform beams of the veneered core materials were fabricated for each system and subjected to a three-point bending test. The data were analyzed using the Weibull method. The failure load of specimens at a 10% probability of failure (B10 load) was compared. The mode of failure was analyzed. RESULTS: The B10 load of the systems investigated was not significantly different from that of the metal-ceramic system. FibreKor possessed significantly higher B10 load than Vectris, In-Ceram Alumina, and In-Ceram Zirconia. The B10 strength loads of Vectris, In-Ceram Alumina, and In-Ceram Zirconia were not significantly different from one another. CONCLUSION: The probability of FibreKor to fracture under a flexural load was significantly lower than that of Vectris, In-Ceram Alumina, or In-Ceram Zirconia.

Aluminum Oxide↗

PubMed1978

Drug effects on responding maintained by stimulus-reinforcer and response-reinforcer contingencies.

The effects of pentobarbital and d-amphetamine were assessed on key pecking by pigeons under conventional single-key multiple schedules and under two-key multiple schedules in which discriminative stimuli appeared on one key (stimulus key) while pecks on a second key (constant key) produced food. Pecks on the stimulus key had no scheduled consequences. A 60-second variable-interval schedule operated in one component of each multiple schedule: either extinction or a 60-second variable-time schedule operated in the alternate component. When the alternate-component schedule was extinction, a high rate of responding was maintained in the variable-interval component of the single-key schedule; responding on both keys was maintained in the variable-interval component of the two-key schedule. Pentobarbital increased responding in the variable-interval component of the single-key schedule and increased stimulus-key, but not constant-key responding in that component of the two-key schedule. When the alternate-component schedule was changed to variable time, responding declined in the variable-interval component of the single-key schedule; stimulus-key responding was no longer maintained under the two-key schedule. Pentobarbital decreased responding in the variable-interval component of both schedules. With an exception, d-amphetamine only decreased responding in the variable-interval component of the single- and two-key schedules both when the alternate-component schedule was extinction and when it was variable time. The results suggest that the effects of pentobarbital, but not d-amphetamine, depend on the nature of the contingency (stimulus-reinforcer, response-reinforcer) that maintains responding.

Animals↗

PubMed1989

A concurrently available nondrug reinforcer prevents the acquisition or decreases the maintenance of cocaine-reinforced behavior.

Lever-pressing responses of 55 rats were reinforced with IV-delivered cocaine (0.2 mg/kg) or saline under conditions of continuous access for 15 24-h sessions. The rats also responded on tongue-operated drinking devices for deliveries of a 3% (w/v) glucose + 0.125% (w/v) saccharin (G+S) solution or water. The effects of removing these substances on behavior maintained by G+S, water, cocaine, or saline were compared in 11 groups. Terminating cocaine access produced a decrease in G+S drinking and an increase in food and water intake. In contrast, a group of rats that did not initially self-administer G+S showed increases in G+S drinking when cocaine was removed, and G+S-maintained responding persisted when cocaine was reinstated. Substitution of water for G+S produced a nearly two-fold increase in cocaine-reinforced behavior but no change in IV-delivered saline self-administration in a control group. A group that did not initially self-administer cocaine increased its infusion rate to over 400 infusions per day as soon as G+S was replaced with water. The effect of presenting cocaine to a group that responded for G+S alone was to decrease G+S intake, but there was only a transient decrease in water intake in the control group. Likewise, presentation of G+S to a group of rats self-administering cocaine resulted in a decrease in infusions, but saline infusions did not change in a control group. Generally, there was an increase in food and water intake during cocaine removal, but food and water intake did not vary systematically with the removal or presentation of G+S.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Effects of alcohol on reinforced repetitions and reinforced variations in rats.

Six rats were rewarded with food pellets for repeating a particular sequence of four responses on two levers, namely left-left-right-right. Ethanol (0.75 g/kg and 2.0 g/kg injected IP) increased the variability of sequences under these "repeat" contingencies, resulting in fewer rewarded trials. Six other rats were rewarded only if their sequence of left and right responses in the current trial differed from each of the previous five trials. Ethanol had little effect on sequence variability and no effect on reward probability under these "vary" contingencies. The relative difficulties of the repeat and vary tasks were manipulated to show that task difficulty did not account for the results. Thus alcohol increased or maintained behavioral variability, thereby impairing reinforced repetitions but not reinforced variations. When previously reported results from rats in radial arm mazes were compared with a simulated random model, alcohol was found to increase behavioral variability under that procedure as well.

Animals↗

PubMed1971

Signaled reinforcing brain stimulation facilitates operant behavior under schedules of intermittent reinforcement.

When single, rewarding brain stimulations were mnade predictable by preceding them with a brief warning signal, operant behavior was established and maintained under fixed ratio 200, variable ratio 30, fixed interval 3-minute, variable interval 2-minute, and differential reinforcement of low rate 20-second schedules of intermittent reinforcement. When the warning signal was removed, overall response rate declined in all but the fixed ratio schedules and then returned to the previous rate when the signal was reinstated.

Animals↗

PubMed1998

Competing motivations: drug reinforcement vs non-drug reinforcement.

A behavioral pharmacological conceptualization of drug abuse is summarized, which views drug abuse as learned operant behavior that is reinforced by positive effects produced by drugs of abuse. In this view drug abuse may be better characterized as involving attraction rather than compulsion. Incentive-based treatments may be useful for overcoming and competing with the reinforcing effects of drugs of abuse. Illustrative examples of incentive-based treatments for drug abuse, and their results, are described. The efficacy of incentive-based treatments indicates that many substance abusers possess the necessary skills to achieve abstinence and suggests that motivational interventions alone may be sufficient in many cases. Areas for further research are discussed that relate to refining and developing incentive-based therapies and to improving their practical utility and public acceptability.

Behavior Therapy↗

PubMed1990

Conditioned reinforcement versus time to reinforcement in chain schedules.

Pigeons were trained on three-component chain schedules in which the initial component was either a fixed-interval or variable-interval schedule. The middle and terminal components were varied among fixed-interval fixed-interval, variable-interval variable-interval, and an interdependent variable-interval variable-interval schedule in which the sum of the durations of the two variable-interval components was always equal to the sum of the fixed-interval fixed-interval components. At issue was whether the response rate in the initial component was controlled by its time to primary reinforcement or by the temporal parameters of the stimulus correlated with the middle terminal link. The fixed-interval initial-link schedule maintained much lower response rates than the variable-interval initial-link schedule regardless of the schedules in the middle and terminal links. Nevertheless, the intervening schedules played some role: With fixed-interval schedules in the initial links, response rates were consistently highest with independent variable-interval schedules in the middle and terminal links and intermediate with the interdependent variable-interval schedules; these initial-link differences were predicted by the response rates in the middle link of the chain. With variable-interval schedules in the initial links, response rates were lowest with the fixed-interval fixed-interval schedules following the initial link and were not systematically different for the two types of variable-interval variable-interval schedules. The results suggest that time to reinforcement itself accounts for little if any variance in initial-link responding.

Animals↗

PubMed1990

Bombesin improves rats' operant responding maintained by a differential-reinforcement-of-low-rates schedule of food reinforcement.

The present study examined rats' responding on a differential-reinforcement-of-low-rates schedule of food reinforcement following intraperitoneal injections of various doses of bombesin (4, 6, 8, 16, 32 micrograms/kg). Analyses indicated that only the 6 micrograms/kg dosage improved DRL responding. The findings are consistent with prior research examining bombesin's effect on operant behavior and support the notion that bombesin induces satiety rather than malaise.

Animals↗

PubMed2000

Delay of reinforcement effects: timing of reinforcement or narrow goal-box confinement.

The present experiment investigated whether narrow goal-box confinement in studies of delay of reinforcement in the runway may have had aversive or punishing effects. Analysis showed no difference in performance between groups of rats who were either confined in a narrow goal-box or a large compartment while receiving their delay of reinforcement. The results suggest that narrow goal-box confinement does not have aversive characteristics.

Animals↗

PubMedDate not supplied

Bacterial adherence to self-reinforced polyglycolic acid and self-reinforced polylactic acid 96 urological spiral stents in vitro.

The aim of this study was to evaluate the bacterial adherence to biodegradable self-reinforced polyglycolic acid (SR-PGA) and self-reinforced poly-DL-lactic acid (SR-PLA 96) spiral stents in vitro. They are used as temporary urethral stents in urology. Gold-plated metal wire, polyurethane and latex were used as controls. Materials were incubated up to 28 days in artificial urine, after which a bacterial suspension was added. After detaching by sonication the adhesive bacteria were analysed as colony forming units (CFUs) and by scanning electron microscopy (SEM) analysis. Adhesion was more significantly correlated to stent bacterial type than to the tested material in both assays. No encrustation was seen on SR-PGA or SR-PLA 96. SR-PGA and SR-PLA 96 had no effect on the bacterial growth. In conclusion, the bacterial properties are equally or more important than the material properties in the adhesion process.

Bacterial Adhesion↗

PubMed2002

In vitro study of fracture strength and marginal adaptation of polyethylene-fibre-reinforced-composite versus glass-fibre-reinforced-composite fixed partial dentures.

This in vitro study was carried out in order to estimate the clinical usability of adhesively luted three-unit posterior fixed partial dentures (FPD) made of a polyethylene-fibre-reinforced-composite system (PFRC) in comparison with a glass-fibre-reinforced-composite system (GFRC). Therefore the fracture strength and marginal adaptation were examined. A total of 16 FPDs of each material combination were manufactured and adhesively luted to human molars. Before and after an artificial ageing process by thermal cycling and mechanical loading (TCML) the quality of the marginal adaptation was examined by evaluating epoxy replicas in a scanning electron microscope (SEM). After TCML the fracture strength of eight FPDs of each series was tested by mechanical loading them to failure. With the remaining eight FPDs the quality of deeper layers of the luting was examined with a dye penetration technique. The calculated median fracture strength values (25/75% percentiles) were 830 N (643/982) for the PFRC and 884 N (684/1,113) for the GFRC. The SEM analysis showed at least 80% of perfect marginal areas for both material combinations in dentine as well as in enamel before and after TCML. Looking at the cement-tooth interfaces the dye penetration technique showed statistically significant better results for the enamel finishing lines than for those in dentine. With finishing lines in dentine the two material combinations showed statistically significant differences for this interface. Fracture force results as well as marginal quality encourage further clinical investigations on both systems although the GFRC performed slightly better than the PFRC.

Cementation↗

PubMed2005

Fixation of distal femoral osteotomies with self-reinforced poly(L/DL)lactide 70:30 and self-reinforced poly(L/DL)lactide 70: 30/bioactive glass composite rods. an experimental study on rabbits.

Two self-reinforced poly(L/DL)lactide 70:30 or self-reinforced poly (L/DL)lactide 70:30/ bioactive glass (SR-P(L/DL)LA/bioactive glass) composite rods (2 mm x 40 mm) were implanted into the dorsal subcutaneous tissue and osteotomies of the distal femur were fixed with these rods (2 mm x 26 mm) in 36 rabbits. The follow-up times varied from 3 to 100 weeks. After the animals were killed, three-point bending and shear tests and molecular weight measurements were performed for subcutaneously placed rods. Radiological, histological, histomorphometrical, microradiographic and oxytetracycline-fluorescence studies of the osteotomized and intact control femora were performed. After 12 weeks the SR-P(L/DL)LA rods had fragmented into pieces and the mechanical properties could not be measured. The SR-P(L/DL)LA/bioactive glass rods lost their mechanical properties slower, and at 24 weeks the bending strength had decreased by 39% and the shear strength by 50%. After that the mechanical properties of the SR-P(L/DL)LA/bioactive glass rods could not be measured. All osteotomies healed well, and no gross signs of inflammatory reactions were observed. One slight displacement was seen in the three-week follow-up group with SR-P(L/DL)LA rods. Signs of resorption of the implants were seen after 48 weeks in the SR-P(L/DL)LA group and after 24 weeks in the SR-P(L/DL)LA/bioactive glass group. The SR-P(L/DL)LA/bioactive glass rods were almost totally resorbed from the bone at 100 weeks. The present investigation showed that the mechanical strength and fixation properties of the SR-P(L/DL)LA and the SR-P(L/DL)LA/bioactive glass composite rods are suitable for fixation of cancellous bone osteotomies in rabbits.

Animals↗

PubMed2000

Effects of choice of stimuli as reinforcement for task responding in reinforcement for task responding in preschoolers with and without developmental disabilities.

The effects of choice and no choice of stimuli as reinforcement for task responding were investigated across preschoolers with and without disabilities. Five less preferred stimuli were identified for each participant using a stimulus preference assessment. No differences were found for choice and no-choice conditions when the less preferred stimuli were used as reinforcers.

Behavior Therapy↗

PubMed1981

Differential responding without differential reinforcement: Intensity difference, continuum position, and reinforcement density effects.

The response rates of five groups of rats were observed during exposure to different intensities of a four kilohertz tone within a two-component multiple schedule of nondifferential reinforcement. Response rates were found to be higher during the multiple schedule component which contained the higher intensity tone. Larger differences in response rates between the two multiple schedule components occurred with greater intensity separations (30 versus 20 decibels). At the 30 decibel separation a low absolute magnitude produced larger response rate differences than a high absolute magnitude, while at the 20 decibel separation a high absolute magnitude produced larger response rate differences. Increases in reinforcement density were accompanied by decreases in response rate differences between high and low intensity components only when over-all response rates also increased.

Journal Article↗