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At least 343 records · Page 19Linked to original sources
PubMed2004

Repeated nicotine exposure enhances responding with conditioned reinforcement.

RATIONALE: Stimuli associated with a reinforcer (e.g., an addictive drug) can acquire conditioned reinforcing effects. Clinical observations indicate that smoking depends strongly upon conditioned reinforcement (i.e., cues support smoking behavior); however, little is known about the effects of repeated nicotine exposure on these processes. OBJECTIVE: This study investigated the consequences of prior repeated nicotine exposure on responding with conditioned reinforcement and on the potentiation of conditioned reinforcement by intra-NAc amphetamine infusion. METHODS: Rats received repeated saline or nicotine injections (0.35 mg/kg; 15 days) and were, following 3 days of withdrawal, trained to associate a tone + light stimulus with water reinforcement for 10 days. Animals were subsequently tested on acquisition of a new instrumental response with conditioned reinforcement (i.e., 14 days after the final nicotine injection). In additional experiments, animals received an infusion of amphetamine (10 microg per side) prior to the conditioned reinforcement test. RESULTS: Prior repeated nicotine exposure produced a behaviorally specific enhancement of responding with conditioned reinforcement. Furthermore, repeated nicotine pretreatment also augmented the potentiation of conditioned reinforcement by intra-NAc amphetamine. CONCLUSIONS: These findings demonstrate that prior repeated nicotine exposure augments the control over behavior by a conditioned reinforcer. Such long-lasting alterations in incentive motivational processes produced by repeated nicotine exposure may depend on drug-induced neuroadaptations in dopamine-regulated signaling within limbic-striatal brain regions that could underly persistent and compulsive aspects of addiction.

Adrenergic Uptake Inhibitors↗
PubMed1987

The competition of autistic stereotyped behavior with usual and specially assessed reinforcers.

This study was conducted to empirically assess a reinforcement theory of stereotyped behavior. Six students with autism were first presented with tasks, and no contingent reinforcers were provided for correct responding. Then, contingent reinforcers that were typically used with the students (usual reinforcers) were presented in a multiple baseline across subjects design. Three of the students evidenced decreases in stereotypy and increases in responding in the presence of usual reinforcers. The other three students required external suppression of stereotypy before increases in responding were shown. For these students, usual reinforcers and specially assessed reinforcers were then compared. The specially assessed reinforcers resulted in decreases in stereotypy and increases in responding and subjective measures of responsiveness. The results were discussed in terms of supporting a competing reinforcement hypothesis, such that powerful external reinforcers will successfully compete with and suppress reinforcers provided by stereotypy.

Adolescent↗
PubMed2006

The role of place of reinforcer delivery in the appearance of positive induction when rats respond for 1% sucrose.

Rats increase their rate of operant responding for 1% sucrose reinforcement in the first half of an experimental session if a high-valued reinforcer will be available in the second half. Previous research suggests that this induction effect occurs because the reinforcing value of the low-valued substance has increased. The present study investigated whether this increase may occur because of where the substances are delivered. Rats pressed a lever to earn 1% liquid-sucrose reinforcers in the first half of the session. In control conditions, they also pressed for 1% sucrose in the second half. In treatment conditions, they pressed for food-pellet (Experiment 1) or 32% sucrose (Experiment 2) reinforcers in the second half, with these reinforcers either being delivered to the same location as the 1% sucrose or to a different location. Upcoming food-pellet or 32% sucrose reinforcement increased rates of lever pressing for 1% sucrose in the first half of the session, with the largest increase observed when the high-valued reinforcer was delivered to the same location as the 1% sucrose. Qualitatively similar results were found with rates of consumption of 1% sucrose reinforcers in the first half of the session, which were measured in Experiment 2. The location to which reinforcers are delivered appears to be one of the factors that contributes to this induction effect. The present results may therefore identify one of the factors that determine whether differential conditions of reinforcement will lead to contrast or induction.

Analysis of Variance↗
PubMedDate not supplied

The effects of D-amphetamine on responding for candy and fruit drink using a fixed ratio and a progressive ratio schedule of reinforcer delivery.

The first purpose of this study was to compare the effects of D-amphetamine (AMPH) on operant responding reinforced under fixed ratio (FR) or progressive ratio (PR) schedules of reinforcement, testing the hypothesis that responding reinforced under a PR operant schedule would be disrupted by lower doses of AMPH than responding reinforced under a FR operant schedule. The second purpose of this study was to test the generalizability of the first hypothesis by comparing the effects of AMPH on responding reinforced by two different reinforcers under both FR and PR operant schedules. Rhesus monkeys had five to six candy and five to six fruit drink sessions per day, and could receive two reinforcers per session. Responding was initially reinforced under a PR procedure, such that the ratio size increased with each subsequent session. The parameters of the PR schedule were individually selected so that monkeys consumed a similar number of candy and fruit-drink reinforcers each day. The effects of oral AMPH (0.5, 0.75, 1.0 mg/kg) on responding were assessed. Responding was then stabilized using a FR schedule with parameters individually selected so that monkeys consumed a similar number of candy and fruit-drink reinforcers each day, and the effects of oral AMPH were again assessed. The PR breakpoint was significantly greater for candy than fruit-drink. AMPH produced dose-related decreases in both candy and fruit-drink intake, but each AMPH dose decreased the number of fruit-drink deliveries to a greater extent than the number of candy deliveries. The results failed to support the hypothesis that responding under PR schedules of reinforcement would be disrupted by lower doses of AMPH.

Animals↗
PubMed1997

Effects of rate of reinforcement and rate of change on choice behaviour in transition.

In two experiments with pigeons, a single variable-interval schedule assigned reinforcers to two response keys on a percentage basis. The percentage of reinforcers assigned to each key was changed every few sessions, and subjects' choice responses were recorded before and after each change. In Experiment 1, the overall rate of reinforcement was varied across conditions. The pigeons' choice responses adapted more quickly to a change in the reinforcement percentages when the overall reinforcement rates were higher, but acquisition rates varied by only about a factor of 3, whereas reinforcement rates were varied by about a factor of 9. In Experiment 2, the reinforcement percentages changed about every 8 sessions in Phases 1 and 3, but every 1 or 2 sessions in Phase 2. Pigeons' choice responses adapted to a change in reinforcement percentages more quickly in Phase 2 than in Phases 1 and 3. The results from both experiments pose difficulties for several prominent models of transitional choice behaviour. The results suggest that each successive reinforcer has more impact on a subject's subsequent choice behaviour when the overall rate of reinforcement is lower and when the reinforcement contingencies have changed frequently in the recent past.

Animals↗
PubMed2003

Reinforcement from pharmacological effects of ethanol in newborn rats.

BACKGROUND: The preweanling period in the rat is characterized by acceptance of substantial amounts of ethanol and susceptibility to its reinforcing effects. It has been unclear, however, whether the neurobiological basis of ethanol reinforcement properties at this age is in ethanol's olfactory, gustatory, or pharmacological effects. METHODS: The effectiveness of intraperitoneal (ip) ethanol as a reinforcer for newborn (3-hr-old) rats was tested toward separation of the orosensory and pharmacological sources of ethanol reinforcement. Responsiveness to a test nipple by pups given such pairings was compared with that of pups given unpaired presentations of the nipple and ethanol. RESULTS: Reinforcement was assessed in terms of response to a surrogate nipple 1 hr after a single pairing of a similar nipple providing water (conditioned stimulus) and ip injection of ethanol (0.125, 0.25, 0.50, or 0.75 g/kg; unconditioned stimulus). Significant effects of ethanol reinforcement occurred with the lower doses (0.125 and 0.25 g/kg); higher doses of ethanol (0.50 and 0.75 g/kg) had no significant reinforcement effect. A second experiment determined that for conditioning with ip ethanol as the unconditioned stimulus, a conditioned stimulus consisting of only ingesting water or only suckling on an empty nipple also yielded significant reinforcing effects of ethanol, although with less strength than their combination. Both reinforcing doses of ethanol, 0.125 and 0.25 g/kg, yielded detectable concentrations of ethanol in the blood 5 min after injection, which were sustained at a significantly lower level 60 min after administration. CONCLUSIONS: These data indicate that aside from possible, and likely weak, hematogenic sources of gustatory and olfactory attributes of ethanol, the basis of ethanol's reinforcement effect in neonatal rats is primarily pharmacological. For the pharmacological effects of ethanol to be reinforcing for the neonatal rat, concurrent appetitive activity on a nipple providing a fluid may be necessary for a substantial effect with this paradigm.

Animals↗
PubMed2006

Infrequent, but not frequent, reinforcers produce more variable responding and deficient sustained attention in young children with attention-deficit/hyperactivity disorder (ADHD).

BACKGROUND: The underlying behavioral/psychological processes of attention-deficit/hyperactivity disorder are unclear. Motivational factors, related to dopamine dysfunction, may play an important role in the development of the behavioral symptoms. Particularly, infrequent, but not frequent, reinforcers have been suggested to be associated with altered responding and deviant behavior in children with ADHD. The present study was designed to analyze the influence of reinforcement frequency on operationalized measures of hyperactivity, impulsiveness, sustained attention, and response variability. METHODS: Fifty-six boys, half of whom were diagnosed with ADHD, completed a computerized task presented as a game with two squares on the screen. One square was associated with reinforcement. The task required responses by the computer mouse under contingencies alternating between variable interval schedules of short (mean 2 s) and long (mean 20 s) durations. Reinforcers were cartoon pictures and small trinkets. RESULTS: Overall, there was no difference between children with ADHD and comparison children when reinforcers were given frequently. Statistically significant differences on measures of sustained attention and variability, but not hyperactivity and impulsiveness, were found during infrequent reinforcement only. Age effects interacted with group effects on sustained attention, showing that group differences were found in the young children only. Surprisingly, older comparison children showed increased response variability and no learning. CONCLUSIONS: When reinforcers are infrequent, children with ADHD show deficient sustained attention and increased variability in responding. Computer experience may have interfered with measures of hyperactivity and impulsiveness. The unexpectedly poor performance of the older comparison children may have been due to inefficient reinforcers or to verbally governed behavior overruling reinforcer effects. Reinforcer characteristics and experimental procedures are important factors influencing findings in studies investigating motivational factors. The study provides some support for the dynamic developmental theory of ADHD predicting relationships between neurobiological deficits, altered reinforcement mechanisms, and treatment recommendations.

Age Factors↗
PubMed2006

Two cases requiring external reinforcement in perceptual learning.

The role of external reinforcement is an issue of much debate and uncertainty in perceptual learning research. Although it is commonly acknowledged that external reinforcement, such as performance feedback, can aid in perceptual learning (M. H. Herzog & M. Fahle, 1997), there are many examples in which it is not required (K. Ball & R. Sekuler, 1987; M. Fahle, S. Edelman, & T. Poggio, 1995; A. Karni & D. Sagi, 1991; S. P. McKee & G. Westheimer, 1978; L. P. Shiu & H. Pashler, 1992). Additionally, learning without external reinforcement can occur even for stimuli that are irrelevant to the subject's task (A. R. Seitz & T. Watanabe, 2003). It has been thus hypothesized that internal reinforcement can serve a similar role as external reinforcement in learning (M. H. Herzog & M. Fahle, 1998; A. Seitz & T. Watanabe, 2005). This idea suggests that perceptual learning should occur in the absence of external reinforcement provided that easy exemplars are utilized as a basis for the subject to generate internal reinforcement. Here, we report results from two studies that show that this is not always the case. In the first study, subjects participated in two sessions of a motion direction discrimination task with low-contrast dots moving in directions separated by 90 degrees. In the second study, subjects participated in 12 orientation-discrimination sessions using oriented bars (oriented either 70 degrees or 110 degrees) that were masked by spatial noise. Trials of different signal levels (yielding psychometric functions ranging from chance to ceiling) were randomly interleaved. In both studies, subjects experiencing external reinforcement showed significant learning, whereas subjects receiving no external reinforcement failed to show learning. We conclude that while internal reinforcement is an important learning signal, the presence of easy exemplars is not sufficient to generate reinforcement signals.

Adult↗
PubMed2000

Facilitating tolerance of delayed reinforcement during functional communication training.

Few clinical investigations have addressed the problem of delayed reinforcement. In this investigation, three individuals whose destructive behavior was maintained by positive reinforcement were treated using functional communication training (FCT) with extinction (EXT). Next, procedures used in the basic literature on delayed reinforcement and self-control (reinforcer delay fading, punishment of impulsive responding, and provision of an alternative activity during reinforcer delay) were used to teach participants to tolerate delayed reinforcement. With the first case, reinforcer delay fading alone was effective at maintaining low rates of destructive behavior while introducing delayed reinforcement. In the second case, the addition of a punishment component reduced destructive behavior to near-zero levels and facilitated reinforcer delay fading. With the third case, reinforcer delay fading was associated with increases in masturbation and head rolling, but prompting and praising the individual for completing work during the delay interval reduced all problem behaviors and facilitated reinforcer delay fading.

Adult↗
PubMed1997

An analysis of reinforcer substitutability using object manipulation and self-injury as competing responses.

The concept of reinforcer substitutability proposes a continuum of interactions among reinforcers in a given situation. At one end of this continuum, reinforcers are substitutable, with one reinforcer being readily traded for another. We conducted an analysis of reinforcers that were substitutable with those produced by self-injurious behavior (SIB). Three individuals with profound developmental disabilities, whose SIB appeared to be maintained by automatic reinforcement, participated. Results of three experiments showed that (a) object manipulation and SIB were inversely related when leisure materials and SIB were concurrently available, with participants showing almost complete preference for object manipulation; (b) attempts to reduce SIB using the preferred objects as reinforcers in differential reinforcement contingencies were unsuccessful for all 3 participants; and (c) participants' preferences for SIB or object manipulation systematically changed when reinforcer cost (the amount of effort required to obtain the object) was varied. Results of the three experiments illustrate the importance of examining interactions among concurrently available reinforcers when conducting reinforcer assessments.

Adult↗
PubMed2005

Motivational influences on performance maintained by food reinforcement.

In Study 1, we examined the independent effects of reinforcer consumption during sessions and meal consumption prior to sessions on performance maintained by food reinforcement. Nine individuals with developmental disabilities participated. On alternate days, a preferred edible item was delivered during (a) seven sessions conducted before lunch (repeated-reinforcement condition) versus (b) one session each conducted before and after lunch (pre- and postmeal conditions). Results for 7 of 9 participants showed decreased response rates across sessions in the repeated-reinforcement condition; results for 3 of 9 participants showed decreased rates during postmeal relative to premeal conditions. Two participants who did not show a decrement in responding during either comparison participated in Study 2, in which reinforcer consumption during sessions, combined with meal consumption prior to sessions, also had no effect on their performance. In Study 3, we determined whether (a) choice of reinforcers, (b) increased break time between sessions, (c) varied reinforcers, or (d) intermittent reinforcement schedules mitigated the satiation effects observed for the 7 participants in Study 1. Presession choice of reinforcers resulted in maintained performance for 2 of 6 participants exposed to this condition. Varied reinforcement resulted in maintained performance for only 1 of 5 participants exposed to this condition. Neither the increased break between sessions nor the intermittent reinforcement schedule was effective in maintaining performance for the participants who were exposed to these conditions.

Adult↗
PubMed1990

Alternative reinforcement increases resistance to change: Pavlovian or operant contingencies?

Two multiple-schedule experiments with pigeons examined the effect of adding food reinforcement from an alternative source on the resistance of the reinforced response (target response) to the decremental effects of satiation and extinction. In Experiment 1, key pecks were reinforced by food in two components according to variable-interval schedules and, in some conditions, food was delivered according to variable-time schedules in one of the components. The rate of key pecking in a component was negatively related to the proportion of reinforcers from the alternative (variable-time) source. Resistance to satiation and extinction, in contrast, was positively related to the overall rate of reinforcement in the component. Experiment 2 was conceptually similar except that the alternative reinforcers were contingent on a specific concurrent response. Again, the rate of the target response varied as a function of its relative reinforcement, but its resistance to satiation and extinction varied directly with the overall rate of reinforcement in the component stimulus regardless of its relative reinforcement. Together the results of the two experiments suggest that the relative reinforcement of a response (the operant contingency) determines its rate, whereas the stimulus-reinforcement contingency (a Pavlovian contingency) determines its resistance to change.

Animals↗
PubMed1991

Conditioned reinforcement value and choice.

The delay-reduction hypothesis of conditioned reinforcement states that the reinforcing value of a food-associated stimulus is determined by the delay to primary reinforcement signaled by the onset of the stimulus relative to the average delay to primary reinforcement in the conditioning situation. In contrast, most contemporary models of conditioned reinforcement strength posit that the reinforcing strength of a stimulus is some simple function only of the delay to primary reinforcement in the presence of stimulus. The delay-reduction hypothesis diverges from other conditioned reinforcement models in that it predicts that a fixed-duration food-paired stimulus will have different reinforcing values depending on the frequency of its presentation. In Experiment 1, pigeons' key pecks were reinforced according to concurrent-chains schedules with variable-interval 10-second and variable-interval 20-second terminal-link schedules. The initial-link schedule preceding the shorter terminal link was always variable-interval 60 seconds, and the initial-link schedule requirement preceding the longer terminal link was varied between 1 second and 60 seconds across conditions. In Experiment 2, the initial-link schedule preceding the longer of two terminal links was varied for each of three groups of pigeons. The terminal links of the concurrent chains for the three groups were variable-interval 10 seconds and 20 seconds, variable-interval 10 seconds and 30 seconds, and variable-interval 30 seconds and 50 seconds. In both experiments, preference for the shorter terminal link was either a bitonic function or an inverse function of the initial-link schedule preceding the longer terminal-link schedule. Consistent with the predictions of the delay-reduction hypothesis, the relative values of the terminal-link stimuli changed as a function of the overall frequency of primary reinforcement. Vaughan's (1985) melioration model, which was shown to be formally similar to Squires and Fantino's (1971) delay-reduction model, can be modified so as to predict these results without changing its underlying assumptions.

Animals↗
PubMed1995

Behavioral economics of concurrent ethanol-sucrose and sucrose reinforcement in the rat: effects of altering variable-ratio requirements.

These experiments examined the own-price and cross-price elasticities of a drug (ethanol mixed with 10% sucrose) and a nondrug (10% sucrose) reinforcer. Rats were presented with ethanol-sucrose and sucrose, both available on concurrent independent variable-ratio (VR) 8 schedules of reinforcement. In Experiment 1, the variable ratio for the ethanol mix was systematically raised to 10, 12, 14, 16, 20, and 30, while the variable ratio for sucrose remained at 8. Five of the 6 rats increased ethanol-reinforced responding at some of the increments and defended baseline levels of ethanol intake. However, the rats eventually ceased ethanol-reinforced responding at the highest variable ratios. Sucrose-reinforced responding was not systematically affected by the changes in variable ratio for ethanol mix. In Experiment 2, the variable ratio for sucrose was systematically increased while the ethanol-sucrose response requirement remained constant. The rats decreased sucrose-reinforced responding and increased ethanol-sucrose-reinforced responding, resulting in a two- to 10-fold increase in ethanol intake. Experiment 3 examined the substitutability of qualitatively identical reinforcers: 10% sucrose versus 10% sucrose. Increases in variable-ratio requirements at the preferred lever resulted in a switch in lever preference. Experiment 4 examined whether 10% ethanol mix substituted for 5% ethanol mix, with increasing variable-ratio requirements of the 5% ethanol. All rats eventually responded predominantly for the 10% ethanol mix, but total amount of ethanol consumed per session did not systematically change. In Experiment 5, the variable-ratio requirements for both ethanol and sucrose were simultaneously raised to VR 120; 7 of 8 rats increased ethanol-reinforced responding while decreasing sucrose-reinforced responding. These data suggest that, within this ethanol-induction procedure and within certain parameters, demand for ethanol-sucrose was relatively inelastic, and sucrose consumption was independent of ethanol-sucrose consumption. Demand for sucrose, on the other hand, was relatively elastic, and ethanol-sucrose readily substituted for it. The results are discussed in terms of applying a behavioral economic approach to relationships between drug and nondrug reinforcers.

Alcohol Drinking↗
PubMed2001

The role of the primate amygdala in conditioned reinforcement.

Conditioned reinforcement refers to the capacity of a conditioned stimulus to support instrumental behavior by acquiring affective properties of the primary reinforcer with which it is associated. Conditioned reinforcers maintain behavior over protracted periods of time in the absence of, and potentially in conflict with, primary reinforcers and as such may play a fundamental role in complex social behavior. A relatively large body of evidence supports the view that the amygdala (and in particular the basolateral area) contributes to conditioned reinforcement by maintaining a representation of the affective value of conditioned stimuli. However, a recent study in primates (Malkova et al., 1997), using a second-order visual discrimination task, suggests that the amygdala is not critical for the conditioned reinforcement process. In the present study, excitotoxic lesions of the amygdala in a new world primate, the common marmoset, resulted in a progressive impairment in responding under a second-order schedule of food reinforcement. In addition, the responding of amygdala-lesioned animals was insensitive to the omission of the conditioned reinforcer, unlike that of control animals, for which responding was markedly reduced. In contrast, lesioned animals were unimpaired when responding on a progression of fixed-ratio schedules of primary reinforcement. These data confirm that the amygdala is critical for the conditioned reinforcement process in primates, and taken together with other recent work in monkeys, these results suggest that the contribution of the amygdala is to provide the affective value of specific reinforcers as accessed by associated conditioned stimuli.

Acoustic Stimulation↗
PubMed1992

Signalling and incentive processes in instrumental reinforcer devaluation.

We have previously reported that conditioning an aversion to the reinforcer using an isotonic lithium chloride (LiCl) solution following instrumental training reduces performance in a subsequent extinction test only if animals are re-exposed to the reinforcer prior to the test. Rescorla (1992), in contrast, reported an immediate devaluation effect using a hypertonic LiCl solution that did not depend upon re-exposure. In two experiments we examined the effect of using a hypertonic LiCl solution to condition the aversion to the reinforcer on subsequent instrumental performance in extinction, with and without re-exposure. In Experiment 1 thirsty rats were trained to press a lever for a sucrose solution before being injected with 0.6 M LiCl either immediately or after a delay. Half of the immediate and delay groups were then re-exposed to the sucrose in the absence of the lever, with the remainder being exposed to water. Contrary to the previously reported effects of isotonic LiCl, a hypertonic solution induced a reinforcer devaluation effect in all the immediately poisoned animals, which did not depend upon re-exposure to the reinforcer. In Experiment 2 the possibility that this devaluation effect was induced by the discomfort associated with the hypertonicity of the solution was assessed by replicating Experiment 1 but, in addition, using two immediately poisoned groups given the LiCl injection under anaesthesia. In the absence of anaesthesia, the devaluation effect observed without re-exposure to the reinforcer in Experiment 1 was replicated. When the injection was given under anaesthesia, however, a reinforcer devaluation effect was observed only in animals that were re-exposed to the reinforcer prior to the extinction test. These results were interpreted as evidence that a reinforcer devaluation effect induced by pairing the reinforcer with illness depends upon a process of incentive learning, whereas a devaluation effect mediated by learning a signalling relationship between the reinforcer and somatic discomfort does not.

Animals↗
PubMed2006

Effect of fiber architecture on flexural characteristics and fracture of fiber-reinforced dental composites.

OBJECTIVE: The aim of this study was to compare and elucidate the differences in damage mechanisms and response of fiber-reinforced dental resin composites based on three different brands under flexural loading. The types of reinforcement consisted of a unidirectional E-glass prepreg (Splint-It from Jeneric/Petron Inc.), an ultrahigh molecular weight polyethylene fiber based biaxial braid (Connect, Kerr) and an ultrahigh molecular weight polyethylene fiber based leno-weave (Ribbond). METHODS: Three different commercially available fiber reinforcing systems were used to fabricate rectangular bars, with the fiber reinforcement close to the tensile face, which were tested in flexure with an emphasis on studying damage mechanisms and response. Eight specimens (n=8) of each type were tested. Overall energy capacity as well as flexural strength and modulus were determined and results compared in light of the different abilities of the architectures used. RESULTS: Under flexural loading unreinforced and unidirectional prepreg reinforced dental composites failed in a brittle fashion, whereas the braid and leno-weave reinforced materials underwent significant deformation without rupture. The braid reinforced specimens showed the highest peak load. The addition of the unidirectional to the matrix resulted in an average strain of 0.06mm/mm which is 50% greater than the capacity of the unreinforced matrix, whereas the addition of the braid and leno-weave resulted in increases of 119 and 126%, respectively, emphasizing the higher capacity of both the UHM polyethylene fibers and the architectures to hold together without rupture under flexural loading. The addition of the fiber reinforcement substantially increases the level of strain energy in the specimens with the maximum being attained in the braid reinforced specimens with a 433% increase in energy absorption capability above the unreinforced case. The minimum scatter and highest consistency in response is seen in the leno-weave reinforced specimens due to the details of the architecture which restrict fabric shearing and movement during placement. SIGNIFICANCE: It is crucial that the appropriate selection of fiber architectures be made not just from a perspective of highest strength, but overall damage tolerance and energy absorption. Differences in weaves and architectures can result in substantially different performance and appropriate selection can mitigate premature and catastrophic failure. The study provides details of materials level response characteristics which are useful in selection of the fiber reinforcement based on specifics of application.

Composite Resins↗
PubMed2003

Mathematical principles of reinforcement and resistance to change.

Although Killeen's mathematical principles of reinforcement (MPR) apply to the asymptotic rate of a free operant after extended exposure to a single schedule of reinforcement, they can be extended to resistance to change in multiple schedules via alterations in the parameter representing the activating effects of reinforcers. MPR's predictions of resistance to change in relation to reinforcer rate on variable-interval (VI) schedules are empirically correct and agree with behavioral momentum theory (BMT). However, both MPR and BMT encounter problems in accounting for the effects of delayed reinforcement on resistance to change, relative to immediate reinforcement at the same rate. Further problems are raised by differences in resistance to change between variable-ratio (VR) and variable-interval performances maintained by the same reinforcer rate. With both delayed versus immediate reinforcement and variable-ratio versus variable-interval reinforcement, differential resistance to change is negatively correlated with the log ratios of baseline response rates when reinforcer rates are equated. Cases where resistance to change varies despite equated reinforcer rates, and the correlations among behavioral measures, provide challenges and opportunities for both MPR and BMT.

Journal Article↗