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PubMed2005

Pitfalls in the use of acetabular reinforcement rings in total hip revision.

INTRODUCTION: For the reconstruction of acetabular bone defects different types of acetabular reinforcement rings are being used. In clinical practice, these implants showed to some extent good long-term results. In the present work pitfalls and complications after the implantation of acetabular reinforcement rings as well as possible solutions are being discussed. MATERIAL AND METHODS: In the first case recurrent dislocation was caused by the malposition of the acetabular component with an impingement of the protruding bone cement and the anterior edge of the acetabular ring as well as muscle insufficiency as a result of the shortening of the leg length. The second case revealed an impingement of the iliopsoas tendon due to a protruding acetabular reinforcement ring. During revision, bone cement was used to smoothen the protruding anterior edge of the acetabular reconstruction ring in order to obtain a relieved sliding of the tendon. Furthermore, we report on the case of a delayed neuropathy of the sciatic nerve after reconstruction of the acetabulum with an acetabular reinforcement ring. RESULTS: Intraoperatively an impingement of the sciatic nerve at the protruding dorsal edge of the acetabular reinforcement ring and the surrounding scar tissue was found. In a further case an aseptic loosening of an acetabular reinforcement ring caused the formation of an excessive granuloma with a large intrapelvic portion. The granuloma led to persisting senso-motoric deficits of the femoral nerve. In summary, based on these clinical cases possible pitfalls, associated with the use of acetabular reinforcement rings, are shown. The mal-positioning and the intra-operative re-shaping of the implant by the surgeon are pointed out as the substantial factors for the occurrence of an impingement phenomenon and total hip instability. Furthermore, in case of an adequate orientation of the cemented polyethylene insert an improper position of the acetabular ring which results in protruding edges has to be considered as a cause of a prosthetic impingement. CONCLUSION: The cases presented emphasize the necessity of prevention of such pitfalls intra-operatively as well as accurate analysis of implant failures. Furthermore, they suggest explicit preoperative planning before deciding on the strategy of revision surgery of acetabular reinforcement rings.

Acetabulum↗
PubMed2006

Functional comparison of staple line reinforcements in lung resection.

PURPOSE: Staple line reinforcement with bovine pericardium and expanded polytetrafluoroethylene during lung resections has shown reduction in air leak incidence and duration. Small intestinal submucosa and polyglycolic acid-trimethylene carbonate, have been introduced as new reinforcements for nonpulmonary staple lines. We hypothesize that reinforcement of staple lines in lungs with commercially available materials will decrease staple line leak at increased pressures. DESCRIPTION: We evaluated 8 staple lines per reinforcement material (4 groups) and a control group (n = 40) in healthy living pigs. After resections (up to four per animal), the lungs were tested sequentially using hand ventilation to increasing pressures (5-75 cm H2O). The occurrence of pressure at which leaks was recorded. EVALUATION: All reinforced staple lines exhibited higher mean leak threshold when compared with the controls; however only small intestinal submucosa achieved significance when compared with the controls. CONCLUSIONS: Commercially available reinforcements allow pulmonary staple lines to tolerate higher intrabronchial pressures without demonstrating air leak. In addition, reinforcement with small intestinal submucosa imparts a significant advantage to the other reinforcements in terms of pulmonary staple line leak rate.

Anastomosis, Surgical↗
PubMed2005

In vitro fracture resistance of four-unit fiber-reinforced composite fixed partial dentures.

OBJECTIVES: The aim of this in vitro study was to investigate the influence of glass fiber-reinforcement on the fracture resistance of four-unit composite fixed partial dentures (FPDs) in the posterior region. METHODS: A total of 70 FPDs were fabricated of the composites Sinfony, Vita Zeta and Targis. With each material, 10 FPDs were made without glass fiber-reinforcement and 10 were reinforced with the new glass fiber system EverStick. In addition, 10 FPDs were fabricated of the material combination Targis/Vectris. After thermocycling, all FPDs were loaded until failure in a universal testing machine. The FPDs were then cut and cross-sectional areas were examined by scanning electron microscopy (SEM). RESULTS: The load to fracture of the fiber-reinforced FPDs lay between 615 and 1191 N, which was significantly greater than the values found with unreinforced FPDs (between 178 and 307 N). The highest values were found with the combinations Targis/Vectris (1191 N) and Sinfony/EverStick (1137 N). SEM showed that the FPDs with EverStick reinforcement not only exhibited fracture lines in the fiber-composite interface, but also more often in the area of the fiber-reinforcement than was the case with the FPDs with Vectris reinforcement. The load to fracture was not significantly dependent on fiber quantity or course of fracture. SIGNIFICANCE: It may be concluded that the fracture resistance of four-unit composite FPDs can be significantly raised by glass fiber frameworks (p<0.05). The reinforcement effect of EverStick depended significantly on the composite used (p<0.05).

Composite Resins↗
PubMed2004

Conditioned reinforcing properties of stimuli paired with self-administered cocaine, heroin or sucrose: implications for the persistence of addictive behaviour.

Conditioned environmental stimuli are known to be important determinants of drug seeking. Traditional models of drug seeking under the control of conditioned stimuli have focused on the ability of conditioned reinforcers either to reinstate extinguished responding or to maintain prolonged chains of drug seeking under second-order schedules. These models have consistently suggested that it is the conditioned reinforcing, rather than other, effects of Pavlovian drug stimuli that most profoundly influence drug seeking. However, the impact of drug-associated conditioned reinforcers has not been studied directly and in isolation, not least because the instrumental seeking response is invariably the same as that which was previously reinforced with the drug itself. The purpose of the present study was, therefore, to investigate the conditioned reinforcing properties of drug-paired CSs using an acquisition of a new response procedure in which an animal learns to make a new instrumental response reinforced solely by the CS. It was found that CSs paired with either cocaine, heroin or sucrose supported the rapid acquisition of lever pressing for the CS that persisted over months of repeated, intermittent testing. Furthermore, rats did not acquire the lever press response when the CS was not paired with drug, suggesting that for this stimulus to acquire conditioned reinforcing properties, it must be predictively associated with the drug's effect. Moreover, lever pressing for the CS could not be explained as coincidental to an over-riding Pavlovian approach response to the location of the lever, since animals also acquired discriminated lever pressing when the CS was above the opposite, inactive lever. Extinction decreased responding with conditioned reinforcement, but only when the CS-US association was devalued prior to, and not after, acquisition of the lever press response, providing evidence for the establishment of habitual CS-maintained responding that may explain the persistence of drug-seeking responses in animal models of addiction and relapse.

Animals↗
PubMed2001

Three tests of 'anticipatory responding' as an account for induction produced by upcoming food-pellet reinforcement.

Previous research has demonstrated that rats' rates of lever pressing for low-concentration liquid-sucrose reinforcers are increased when food-pellet, rather than sucrose, reinforcement will be upcoming in the same session (i.e. induction). The present experiments were designed to determine whether this induction was the product of 'anticipatory responses' for the upcoming food pellets being added to the responses being made for the currently available sucrose reinforcement. Experiment 1 tested this idea by summing sucrose-reinforced responding and 'anticipatory responding' from different conditions and comparing the sum to responding from a third condition in which subjects responded for sucrose when food-pellet reinforcement was upcoming. The comparison yielded similar response rates. Experiment 2 employed a blackout, of different durations in different conditions, to delay the upcoming food-pellet reinforcement. Consistent with the anticipatory-responding account, the delay decreased the size of the induction. However, results from the blackouts were not entirely consistent with the anticipatory-responding explanation. Experiment 3 provided, in some conditions, sucrose and food-pellet reinforcement in the first and second halves of the session, respectively, for responding on separate levers. These conditions separated 'anticipatory responses' for the food pellets from responses for the sucrose reinforcers. However, induction in responding for sucrose was still present. Together, these experiments demonstrate that, although anticipatory responses may contribute to induction in some instances, they are not solely responsible for the effect.

Journal Article↗
PubMed2002

Self-control and impulsiveness with asynchronous presentation of reinforcement schedules.

IN DISCRETE TRIALS, PIGEONS WERE PRESENTED WITH TWO ALTERNATIVES: to wait for a larger reinforcer, or to respond and obtain a smaller reinforcer immediately. The choice of the former was defined as self-control, and the choice of the latter as impulsiveness. The stimulus that set the opportunity for an impulsive choice was presented after a set interval from the onset of the stimulus that signaled the waiting period. That interval increased or decreased from session to session so that the opportunity for an impulsive choice became available either more removed from or closer in time to the presentation of the larger reinforcer. In three separate conditions, the larger reinforcer was delivered according to either a fixed interval (FI) schedule, a fixed time (FT) schedule, or a differential reinforcement of other behavior (DRO) schedule. The results showed that impulsive choices increased as the opportunity for such a choice was more distant in time from presentation of the larger reinforcer. Although the schedule of the larger reinforcer affected the rate of response in the waiting period, the responses themselves had no effect on choice unless the responses postponed presentation of the larger reinforcer.

Journal Article↗
PubMed2002

Voucher-based reinforcement of opiate abstinence during methadone detoxification.

Methadone detoxification is often used in the treatment of opiate dependence. This procedure, however, is frequently associated with continued opiate use, and high rates of attrition and relapse. In this study, a 90-day methadone detoxification was enhanced by adding voucher-based reinforcement of opiate abstinence before, during and after the dose tapering schedule. After 4 weeks of standard methadone maintenance (baseline), subjects were randomized to either the abstinence (n=26), or attendance reinforcement (n=22) condition. During the remaining 22 weeks of the study, the abstinence reinforcement group could receive vouchers with monetary value three times per week for providing opiate-negative urine specimens, while subjects in the attendance reinforcement group received vouchers of equal value for attending the clinic, regardless of urinalysis results. Methadone maintenance continued during weeks 5-10, dose tapering was implemented during weeks 11-23, and during weeks 24-26 the voucher schedule remained in effect but no medication was provided. Fifty percent of clients in both groups completed dose tapering, and 40% completed the vouchers-only phase. Subjects in the abstinence as compared with the attendance reinforcement group had lower rates of opiate use during the maintenance and detoxification phases, and longer periods of opiate abstinence during the detoxification phase. Cocaine use was also lower in the abstinence than the attendance reinforcement group during the maintenance and detoxification phases. In addition, abstinence as compared with attendance reinforcement subjects reported significantly fewer intravenous injections during the detoxification phase. Voucher-based reinforcement procedures could be useful for successfully transitioning patients into opiate antagonist therapy, or drug-free treatments.

Adult↗
PubMed1976

Self- versus investigator-administered presumed fluency reinforcing stimuli.

The effects of self-administered and investigator-administered presumed fluency reinforcing monetary rewards for perceived fluency increases on the disfluency frequency rate of 17 adult stutterers were studied. Subjects read aloud during 11 one-minute segments under three conditions: one in which no reinforcer was administered at the end of each one-minute segment, a self-administered reinforcement condition, and an investigator-administered reinforcement condition. Although less stuttering was found in the two experimental conditions (with significantly less stuttering occurring in the self-administered fluency reinforcing condition than in the control condition), an increase in stuttering was observed in those reading segments which followed the administration of presumed fluency reinforcing stimuli. These results were interpreted to suggest that although the concept of self-reinforcement may be clinically useful, the operant learning paradigm may be insufficient in providing an adequate description of the events taking place following the administration of fluency contingent reinforcing or punishing stimuli.

Adolescent↗
PubMed2001

Orthodontic bracket bonding with a plasma-arc light and resin-reinforced glass ionomer cement.

Developments in light-curing technology have led to the introduction of a plasma-arc light-curing unit that delivers high-intensity output for faster curing. The purposes of this study were to determine the shear bond strengths of light-cured resin-reinforced glass ionomer cement cured with a plasma-arc light-curing unit and to evaluate the durability of the resultant bond strength with thermal cycling. Comparisons were made between light-cured resin-reinforced glass ionomer cement and light-cured composite resin. Two light-curing units were used in this study: a plasma-arc light-curing unit and a conventional light-curing unit. The mean shear bond strengths of light-cured resin-reinforced glass ionomer cement with the plasma-arc and the conventional light-curing units were 20.3 MPa and 26.0 MPa, respectively. An analysis of variance showed no statistically significant differences between the plasma-arc and the conventional light-curing units. Light-cured resin-reinforced glass ionomer cement and light-cured composite resin demonstrated similar bond strengths and exhibited no statistical differences. There was no statistical difference in bond strength between the teeth that were thermal cycled and those that were not. Failure sites for the brackets bonded with light-cured resin-reinforced glass ionomer cement appeared to be predominantly at the bracket-adhesive interface. The SDs of light-cured composite resin were high for both light-curing units. Whereas the coefficients of variation for light-cured resin-reinforced glass ionomer cement ranged from 20% to 30%, those of light-cured composite resin ranged from 40% to 60%. The bond strength of light-cured resin-reinforced glass ionomer cement cured with either a conventional light-curing unit or a plasma-arc light-curing unit surpassed the clinically required threshold. The plasma-arc light-curing unit may be an advantageous alternative to the conventional light-curing unit for orthodontic bracket bonding with both light-cured resin-reinforced glass ionomer cement and light-cured composite resin.

Acrylic Resins↗
PubMed2006

Effect of continuous longitudinal glass fiber reinforcement on the cantilever beam strength of particulate filler composites.

OBJECTIVE: The objective of this in vitro study was to investigate the effect of continuous longitudinal glass fibers on the bending properties of particulate filler composite resins. MATERIAL AND METHODS: Four particulate filler composite resins (Tetric Ceram, Point 4, Z250, P60) and one continuous longitudinal glass fiber material (everStick) as reinforcement were selected. Three groups of beam specimens (5 x 5 x 25 mm) for each material were fabricated. For group I, specimens were not reinforced with fibers and were tested as the control group. For group II, specimens were reinforced with 2 layers of the fiber (6.5 vol%), and for group III with 3 layers (9.8 vol%). The specimens were stored at 37 degrees C for 30 days. One end of the beam specimen (14 mm) was fixed in a device, while the other (11 mm) was left free. Cantilever beam strength was measured using a universal testing machine, loading at a distance of 10 mm from the upright support through a steel ball of 2 mm diameter. The loads and deflection at initial failure and at final failure for each specimen were recorded. The data were statistically analyzed using one-way ANOVA and the multiple comparison Scheffé test (alpha = 0.05). RESULTS: The bending moments of particulate filler composite at final failure, when reinforced with 3 layers of the glass fibers (272.4-325.2 Ncm), were significantly higher than for the composites without fibers. However, the materials reinforced with 3 layers of fibers were not significantly different from the materials reinforced with 2 layers of fibers (234.1-282.6 Ncm). The materials reinforced with 3 layers of fibers exhibited severe deflection at final failure, ranging from 2.8 mm to 3.4 mm. The bending moments of the particulate composites increased linearly with the weight fraction of the fillers, but there was no linear correlation between them when reinforced with fibers. CONCLUSIONS: The cantilever beam strength of the particulate filler composites increased significantly when layers of fibers were added and as the weight fraction of filler increased, but a higher fiber volume fraction did not lead to a significantly higher cantilever beam strength.

Composite Resins↗
PubMed1996

Speciation by reinforcement: a model derived from studies of Drosophila.

Reinforcement is an increase in premating reproductive isolation between taxa resulting from selection against hybrids. We present a model of reinforcement with a novel type of selection on female mating behavior. Previous models of reinforcement have focused on the divergence of female mating preferences between nascent species. We suggest that an increase in the level of female mating discrimination can yield reinforcement without further divergence of either male characters or female preferences. This model indicates that selection on mating discrimination is a viable mechanism for reinforcement and may allow speciation under less stringent conditions than selection on female preference. This model also incorporates empirical results from genetic studies of hybrid fitness determination in Drosophila species. We find that the details of inheritance, which include sex-linked transmission, sex-limited fertility reduction, and X-autosome epistasis, have important effects on the likelihood of reinforcement. In particular, X-autosome epistasis for hybrid fitness determination facilitates reinforcement when hybrid fertility reduction occurs in males, but hinders the process when it occurs in females. HALDANE's rule indicates that hybrid sterility will generally evolve in males prior to females within nascent species. Thus, HALDANE's rule and X-autosome epistasis provide conditions that are surprisingly favorable for reinforcement in Drosophila.

Animals↗
PubMed1994

Operant ethanol-reinforced behavior in P, NP, HAD, and LAD rats bred for high versus low ethanol preference.

These studies examined the reinforcing effects of ethanol in rats selectively bred for high versus low ethanol drinking in a two-bottle choice preference task, namely the Preferring (P), Non-Preferring (NP), High Alcohol Drinking (HAD), and Low Alcohol Drinking (LAD) rats. The results substantiate findings suggesting that genetic factors are significant in determining whether ethanol will come to serve as a reinforcer. P rats exhibited high levels of responding for ethanol compared with the water vehicle, NP and HAD rats exhibited more moderate levels of responding for ethanol, and the behavior of LAD rats suggested that ethanol served only inconsistently as a reinforcer for these rats. Overall, the results suggest the existence of distinct, biologically influenced components of ethanol drinking behavior. Preference appears to measure an inherent facilitative factor allowing animals to initiate ethanol drinking. The operant chamber paradigm appears to measure factors related to whether and to what extent ethanol will serve as a positive reinforcer following conditioned exposure to the drug. Although preferring animals generally find ethanol reinforcing there seems to be little quantitative relationship between degree of preference and whether ethanol will serve as a reinforcer. Lack of preference does not seem to be predictive of lack of reinforcement. Thus, it appears that preference for ethanol and reinforcement from ethanol are somewhat overlapping, but distinct factors that contribute to ethanol drinking. These results suggest the existence of multiple components of behavior mediated by multiple mechanisms that contribute to ethanol drinking.

Alcohol Drinking↗
PubMed1996

Surgicel reinforced resection lines in left-sided hepatectomy with linear stapling device. An experimental study on pigs.

Fourteen pigs underwent left-sided hepatectomy. The resection was performed with a linear stapling device and the pigs were randomised to either Surgicel reinforced resection lines or not. The median time required for resection was 25 min (range 17-30) in the Surgicel reinforced group compared to 30 min (range 21-41) in the stapled group. This difference was, however, not statistically significant (p = 0.053). The postoperative haemoglobin value was lower in the stapled group compared to the Surgicel reinforced group 69 g/l (range 42-85) versus 82 g/l (range 78-90) (p = 0.018). The estimated blood losses by weighing the compresses were 287 ml (range 166-379) for the stapled group and 204 ml (range 152-264) for the Surgicel reinforced group (p = 0.053). The median number of additional haemostatic sutures in the Surgicel reinforced group was 7 (range 3-11) and in the stapled group 10 (range 5-15) (p = 0.038). The haemoglobin value was similar in the two groups 1 week postoperatively; 100 g/l (range 87-104) and 102 g/l (range 95-114), p = 0.27, in the stapled group and the Surgicel reinforced group, respectively. In the stapled group reinforced with the Surgicel there was one postoperative death. In the solely stapled group there was no postoperative death (p = 0.5). Four out of six pigs in the Surgicel group had massive adhesions to the resection lines. One of these six pigs was sacrificed postoperatively as it was ill and had small bowel obstruction secondary to Surgicel induced adhesions. On the other hand, no adhesions were seen in the solely stapled pigs (p = 0.09). At this point, we can not recommend the use of Surgicel to reinforce resection lines at stapled liver resection in the clinical situation, because of the high frequency of adhesions this material creates.

Animals↗
PubMed2003

The effect of fiber reinforcement type and water storage on strength properties of a provisional fixed partial denture resin.

Fracture resistance of provisional restorations is an important clinical concern. This property is directly related to transverse strength. Strengthening of provisional fixed partial dentures may result from reinforcement with various fiber types. This study evaluated the effect of fiber type and water storage on the transverse strength of a commercially available provisional resin under two different conditions. The denture resin was reinforced with either glass or aramid fiber or no reinforcement was used. Uniform samples were made from a commercially available autopolymerizing provisional fixed partial denture resin. Sixteen bar-shaped specimens (60 x 10 x 4 mm) were reinforced with pre-treated epoxy resin-coated glass fibers, with aramid fibers, or with no fibers. Eight specimens of each group, with and without fibers, were tested after 24 h of fabrication (immediate group), and after 30-day water storage. A three-point loading test was used to measure the transverse strength, the maximal deflection, and the modulus of elasticity. The Kruskal-Wallis Analysis of Variance was used to examine differences among the three groups, and then the Mann-Whitney U Test and Wilcoxon Signed Ranks Test were applied to determine pair-wise differences. The transverse strength and the maximal deflection values in the immediate group and in the 30-day water storage group were not statistically significant. In the group tested immediately, the elasticity modulus was found to be significant (P = 0.042). In the 30-day water storage group, all the values were statistically insignificant. The highest transverse strength was displayed by the glass-reinforced resin (66.25MPa) in the immediate group. The transverse strength value was 62.04MPa for the unreinforced samples in the immediate group. All the specimens exhibited lower transverse strength with an increase in water immersion time. The transverse strength value was 61.13 MPa for the glass-reinforced resin and was 61.24 MPa for the unreinforced resin. The aramid-reinforced resin decreased from 62.29 to 58.77 MPa. The addition of fiber reinforcement enhanced the physical properties (the transverse strength, the maximal deflection, the modulus of elasticity) of the processed material over that seen with no addition of fiber. Water storage did not statistically affect the transverse strength of the provisional denture resin compared to that of the unreinforced resin. The transverse strength was lowered at water storage but it was not statistically significant. The transverse strength was enhanced by fiber addition compared to the unreinforced resin. The glass fiber was superior to the other fiber. Also the modulus of elasticity was enhanced by fiber addition compared to the unreinforced resin.

Acrylic Resins↗
PubMed1973

The effect of vicarious reinforcement on attentive behavior in the classroom.

The effect of social reinforcement delivered to target subjects on the attentive behavior of adjacent peers was examined in a classroom setting. In a combined reversal and multiple baseline design, two pairs of mentally retarded children were sequentially exposed to three reinforcement phases. After baseline rates of attentive behavior were obtained, praise was delivered to the target subject in each subject pair for attentive behavior. After a reversal phase, praise was delivered contingently to target subjects for inattentive behavior. In a final phase, contingent praise for attentive behavior was reinstated for the target subjects. Throughout the study, nontarget subjects received no direct reinforcers. The results indicated a vicarious reinforcement effect. Reinforcing attentive behavior of target subjects increased this behavior in adjacent peers. However, reinforcing inattentive behavior of target subjects also increased the attentive behavior of adjacent peers. The effects obtained through vicarious reinforcement were considered to reflect the discriminative stimulus properties of reinforcement, which may serve as a cue for the performance of nonreinforced peers.

Journal Article↗
PubMed1981

Generalization of the effects of teacher- and self-administered token reinforcers to nontreated students.

Ten, black, second-grade boys served in a series of single-subject studies. They were from poor families, did not do well in arithmetic, were deficient in sustained attention, and presented behavior problems at school. One boy was a therapeutic confederate. Of the remaining nine nontreated students, three observed the confederate reinforced by a teacher, three observed the confederate self-reinforce without having an opportunity to use "self-reinforcement" themselves, and three observed self-reinforcement while having an opportunity to use "self-reinforcement." The target behavior was attending. Other measures of outcome were glancing, academic achievement, and accuracy of reinforcement. The basic experimental design consisted of an ABAB withdrawal applied to the confederate while the nontreated students remained on baseline. Generalization was expressed as a ratio (i.e., percent change in the generalization measure divided by percent change in the target behavior). Teacher-administered reinforcers to the confederate did not produce generalization of any kind. Both arrangements of self-administered reinforcers to the confederate produced across-subjects generalization and subject-response generalization. Additionally, the confederate manifested response generalization.

Attention↗
PubMed1982

Token reinforcement during the instatement and shaping of fluency in the treatment of stuttering.

The value of token reinforcement in the instatement and shaping of fluency was examined in an intensive treatment program for adult stutterers. Experiment 1 examined the effect of removing the tangible back-up reinforcers for the token system and found that clients' performance in the program was equally good with or without these back-up reinforcers, suggesting that a strict token economy may not be crucial to rapid progress through treatment. Experiment 2 compared contingent and noncontingent taken reinforcement, while controlling for some variables that may have confounded the results of earlier research, and found no difference in clients' performance. Experiment 3 examined the effect of the entire removal of token reinforcement. Performance was found to be no worse under a "no tokens" system than under a system of tokens with back-up reinforcers. It is argued that in a highly structured treatment program where many other reinforcers are operating, token reinforcement may be largely redundant. Clinical and theoretical implications of the findings are discussed.

Adult↗
PubMed1971

Percentage reinforcement of fixed-ratio and variable-interval performances.

Twenty to seventy per cent of the reinforcements scheduled for pigeons' fixed-ratio 80 performances were replaced by a 4-sec timeout. Pauses after reinforced ratios were unchanged at 80% reinforcement, but were lengthened at lower reinforcement percentages. Pauses after nonreinforced ratios were shorter than post-reinforcement pauses. When 50% of the reinforcements arranged by a variable-interval 60-sec schedule were replaced by a 4-sec timeout, pauses after reinforcement omission increased. Both frustrative nonreward and reinforcement aftereffects notions can explain the fixed-ratio results; neither easily explains the variable-interval data.

Journal Article↗