Showing papers on "Reinforcement published in 1985"

Analysis of stress-strain, fracture, and ductility behavior of aluminum matrix composites containing discontinuous silicon carbide reinforcement

Abstract: Mechanical properties and stress-strain behavior were evaluated for several types of commercially fabricated aluminum matrix composites, containing up to 40 vol pct discontinuous SiC whisker, nodule, or particulate reinforcement. The elastic modulus of the composites was found to be isotropic to be independent of type of reinforcement, and to be controlled solely by the volume percentage of SiC reinforcement present. The yield/tensile strengths and ductility were controlled primarily by the matrix alloy and temper condition. Type and orientation of reinforcement had some effect on the strengths of composites, but only for those in which the whisker reinforcement was highly oriented. Ductility decreased with increasing reinforcement content; however, the fracture strains observed were higher than those reported in the literature for this type of composite. This increase in fracture strain was probably attributable to cleaner matrix powder, better mixing, and increased mechanical working during fabrication. Comparison of properties with conventional aluminum and titanium structural alloys showed that the properties of these low-cost, lightweight composites demonstrated very good potential for application to aerospace structures.

The role of observing and attention in establishing stimulus control

Abstract: Early theorists (Skinner, Spence) interpreted discrimination learning in terms of the strengthening of the response to one stimulus and its weakening to the other. But this analysis does not account for the increasing independence of the two performances as training continues or for increases in control by dimensions of a stimulus other than the one used in training. Correlation of stimuli with different densities of reinforcement produces an increase in the behavior necessary to observe them, and greater observing of and attending to the relevant stimuli may account for the increase in control by these stimuli. The observing analysis also encompasses errorless training, and the selective nature of observing explains the feature-positive effect and the relatively shallow gradients of generalization generated by negative discriminative stimuli. The effectiveness of the observing analysis in handling these special cases adds to the converging lines of evidence supporting its integrative power and thus its validity.

Contingency Effects with Maintained Instrumental Reinforcement

Abstract: In three experiments we investigated the effect on the performance of thirsty rats of varying the instrumental contingency between lever pressing and the delivery of a saccharin reinforcer. In Expe...

Human observing: maintained by negative informative stimuli only if correlated with improvement in response efficiency.

Abstract: Two experiments investigated the effect of observing responses that enabled college students to emit more efficient distributions of reinforced responses. In Experiment 1, the gains of response efficiency enabled by observing were minimized through use of identical low-effort response requirements in two alternating variable-interval schedules. These comprised a mixed schedule of reinforcement; they differed in the number of money-backed points per reinforcer. In each of three choices between two stimuli that varied in their correlation with the variable-interval schedules, the results showed that subjects preferred stimuli that were correlated with the larger average amount of reinforcement. This is consistent with a conditioned-reinforcement hypothesis. Negative informative stimuli--that is, stimuli correlated with the smaller of two rewards--did not maintain as much observing as stimuli that were uncorrelated with amount of reward. In Experiment 2, savings in effort made possible by producing S- were varied within subjects by alternately removing and reinstating the response-reinforcement contingency in a mixed variable-interval/extinction schedule of reinforcement. Preference for an uncorrelated stimulus compared to a negative informative stimulus (S-) decreased for each of six subjects, and usually reversed when observing permitted a more efficient temporal distribution of the responses required for reinforcement; in this case, the responses were pulls on a relatively high-effort plunger. When observing the S- could not improve response efficiency, subjects again chose the control stimulus. All of these results were inconsistent with the uncertainty-reduction hypothesis.

Sensitivity of pigeons to prereinforcer and postreinforcer delay

Abstract: Delay between choice and receipt of reinforcement (prereinforcer delay) and delay between receipt of reinforcement and the next opportunity to choose (postreinforcer delay) were varied in a discretetrials choice paradigm using four pigeons. The pigeons consistently chose the reinforcer with the smaller prereinforcer delay. Variations in postreinforcer delay did not affect choice unless prereinforcer delays were equal. The results support previous findings that prereinforcer delays contribute disproportionately to the effects of rate of reinforcer access on choice in pigeons.

Observation of the stress distribution in crushed glass with applications to soil reinforcement

Abstract: The research described in this dissertation follows on from the study made by Jewell (1980)into the effects of tensile reinforcement on the mechanical behaviour of sand. For this study Jewell used the direct shear test with reinforcement placed about the central plane as shown in fig. 1.1. The direct shear test was chosen for the following reasons. (1) The reinforcement variables could be better controlled and examined in a unit cell test than in modular field studies of soil reinforcement systems. (2) The pattern of deformation is similar to that experienced by soil in which a rupture band develops, with the principal axes of stress, strain and strain increment free to rotate as is the case in model and field structures. (3) The overall shear strength of the sample is measured directly at the boundaries of the apparatus. The direct shear tests were monitored by boundary measurements and internal measurements using a radiographic technique. The findings are outlined below with reference made to relevant observations by other researchers. 1) The optimum orientation for a relatively flexible steel grid was found to be approximately along the direction of principal tensile strains in the unreinforced sand, see fig.1.2. This indicated that the reinforcement functioned by limiting tensile strains in the sand. McGown et al. (1978) obtained a similar result for plane strain cell tests on sand containing a single layer of flexible reinforcement. However in both studies the reinforcement was observed to waken the sand. Jewell recognized weakening to occur when the steel grid was placed along the direction of principal compressive strains in the unreinforced sand. This was attributed to a reduction in vertical effective stress. McGown et al. observed weakening of the sand when the reinforcement orientation approached the rupture band which developed in the sand alone. This was recognized to be the direction of zero-extension in the unreinforced sand. The weakening was linked to a lower bond between soil and reinforcement than soil alone. 2) Internal strains determined by Jewell showed the tensile reinforcement modified strains in the sand over a well defined zone, see fig.1.3. This resulted in a significant rotation of principal axes of strain increment, with the bond of major strains which developed across the centre of the box in the unreinforced sand being prohibited from forming. This agreed with boundary measurements, indicating the reinforcement functioned by limiting tensile strains in the sand. Consequently a less favourable mode of failure took place. The limit of rotation of principal axes of strain increment was understood to be the alignment of a direction of zero-extension in the sand with the reinforcement. These findings agree with the ideas expressed by Basset and Last (1978) on the mode of action of tensile reinforcement, which in particular was related to the effect of tensile reinforcement on the strain field in a reinforced earth wall as shown in fig.1.4. 3) For efficient use of tensile reinforcement it was demonstrated that the bond with sand should be as high as possible. This could be achieved by roughening the surface. Alternatively, the bond was improved by introducing openings or apertures in the reinforcement, changing the shape to a grid. It appeared that the bond for a suitably proportioned grid could be as high as for a fully roughened surface. 4) The longitudinal stiffness of tensile reinforcement was observed to affect the magnitude and rate of increase in strength in the direct shear tests. The rupture strain of tensile reinforcement relative to maximum tensile strains of the soil, under the same operational stress conditions, have also been observed to influence the reinforcing effect in terms of its limiting behaviour, i.e. whether brittle or ductile (McGown, et al. 1978). With regards to the performance of reinforced earth walls, Al-Hussanini and Perry (1976) observed that steel reinforced strips produced a stiffer and stronger structure than a more extensible fabric reinforcement, even though surface roughness was less. The importance of reinforcement tensile stiffness is recognized in limit equilibrium designs for tensile reinforced soil structures by limiting the available reinforcement force to the tensile strains that can develop in the soil (e.g. Jewell 1985). For highly structured non-woven and composite geotextiles, McGown et al. (1982) demonstrated that the stress-strain behaviour can be significantly affected by soil confinement. Testing wider strips in isolation was not found to replicate the effects of soil confinement. Another factor which needs to be considered when assessing the tensile property of a polymer reinforcement is creep. McGown et al. (1984) illustrated an appropriate method of interpreting creep data using isochronous curves, which enable long term laboratory test data to be extrapolated to the design life of the soil structure. 5) The strain and hence stress fields in the reinforced direct shear tests have been shown to be complex and non-uniform. However Jewell successfully modelled the variation of reinforcing effect for tensile reinforcement at different orientations by using a simple limit equilibrium analysis, see fig.1.5. The effect of the tensile reinforcement force was represented as: - an increase in the normal effective stress acting on the central plane of the box due to the normal component of the force and - a reduction in the applied shear stress due to the parallel component of the force to the central plane. Subsequently this analysis has been applied to limit equilibrium design methods for reinforcing soil retaining walls and embankments, Jewell et al. 1984, and Jewell 1982 respectively. 6) A reduction in the reinforcing effect for individual reinforcement due to the presence of other reinforcement was observed in the shear box. This loss of efficiency of individual reinforcement was termed interference. Interference between tensile reinforcement has also been studied by Guilloux et al. (1979) for the pull-out resistance from soil. However interference between reinforcement has yet to be introduced into a limit equilibrium design method.

Influences of delay and rate of reinforcement on discrete-trial choice.

Abstract: An adjusting procedure was used to measure pigeons' preferences among alternatives that differed in the duration of a delay before reinforcement and of an intertrial interval (ITI) after reinforcement. In most conditions, a peck at a red key led to a fixed delay, followed by reinforcement, a fixed ITI, and then the beginning of the next trial. A peck at a green key led to an adjustable delay, reinforcement, and then the next trial began without an ITI. The purpose of the adjusting delay was to estimate an indifference point, or a delay that made a subject approximately indifferent between the two alternatives. As the ITI for the red key increased from 0 s to 60 s, the green-key delay at the indifference point increased systematically but only slightly. The fact that there was some increase showed that pigeons' choices were controlled by more than simply the delay to the next reinforcer. One interpretation of these results is that besides delay of reinforcement, rate of reinforcement also influenced choice. However, an analysis that ignored reinforcement rate, but considered the delays between a choice response and the reinforcers on subsequent trials, was able to account for most of the obtained increases in green-key delays. It was concluded that in this type of discrete-trial situation, rate of reinforcement exerts little control over choice behavior, and perhaps none at all.

Probability and delay of reinforcement as factors in discrete-trial choice.

Abstract: Pigeons chose between two alternatives that differed in the probability of reinforcement and the delay to reinforcement. A peck on the red key always produced a delay of 5 s and then a possible reinforcer. The probability of reinforcement for responding on this key varied from .05 to 1.0 in different conditions. A response on the green key produced a delay of adjustable duration and then a possible reinforcer, with the probability of reinforcement ranging from .25 to 1.0 in different conditions. The green-key delay was increased or decreased many times per session, depending on a subject's previous choices. The purpose of these adjustments was to estimate an indifference point, or a delay that resulted in a subject's choosing each alternative about equally often. In conditions where the probability of reinforcement was five times higher on the green key, the green-key delay averaged about 12 s at the indifference point. In conditions where the probability of reinforcement was twice as high on the green key, the green-key delay at the indifference point was about 8 s with high probabilities and about 6 s with low probabilities. An analysis based on these results and those from studies on delay of reinforcement suggests that pigeons' choices are relatively insensitive to variations in the probability of reinforcement between .2 and 1.0, but quite sensitive to variations in probability between .2 and 0.

Predictive Accuracy and the Effects of Partial Reinforcement on Serial Autoshaping

Abstract: A series of five experiments examined the influence of partial reinforcement on serial autoshaping with pigeons. In Experiment l Group AB+A ° received two sequences of events: A followed by B followed by food, or A alone. Group AB +/° always received the AB sequence, reinforcement being presented on 50% of the trials. Subjects responded more rapidly during A in Group AB+A °. Experiment 2 replicated this finding and confirmed that it was not due to differences in the density of the conditioning trials. A similar outcome was observed in Experiment 3, which also indicated that the differences between the groups were not due to differences in the reinforcing properties of B. The results throughout are interpreted in terms of the Pearce-Hall theory, which states that responding during A in the AB+A ° group is high because this stimulus is an inaccurate predictor of its immediate consequences. The results from the final two experiments support and extend this analysis. A common assumption of many theories of Pavlovian learning is that the repeated pairing of a conditioned stimulus (CS) and unconditioned stimulus (US) results in the growth of an association between internal representations of these events. The strength of conditioned responding is then held to be directly related to the magnitude of this association (e.g., Rescorla & Wagner, 1972). A further claim of these theories is that continuous reinforcement will result in the development of a stronger CS-US association than will partial reinforcement and, in general, the experimental evidence supports this conclusion (see Mackintosh, 1974, for a review). There are, in contrast, a number of studies showing that partial reinforcement may actually result in a higher asymptote of conditioned responding than continuous reinforcement. Using the pigeon autoshaping procedure, Gibbon, Farrell, Locurto, Duncan, and Terrace (1980), Picker and Poling (1982), and Rashotte (198 l) all re

Specific anti-aggressive effects of fluprazine hydrochloride.

Abstract: Two experiments were performed with adult male rats of the Long-Evans strain to determine the specificity of fluprazine hydrochloride in decreasing offensive attack. Both 4 and 8 mg/kg doses (IP) significantly reduced offense by resident males selected for high or medium levels of aggression when tested with intruders 30 min postinjection. No reliable differences in other social or nonsocial behaviors were observed. Drug treatment resulted in an overall reduction in offensive behavior of more than 70% in both groups. Actual biting and wounding of intruders by treated subjects was decreased by as much as 98%. A second experiment assessed the drug's influence on defense in the "shock-elicited aggression" paradigm. While duration of boxing to multiple intermittent shocks was significantly suppressed by drug administration (4 and 8 mg/kg), the same doses had no effect on postshock duration of boxing, or sonic and ultrasonic vocalizations following several high intensity (1.5 mA) shocks. These findings are consistent with other research on this and related phenylpiperazine compounds, indicating that its action is specific in reducing offense with minimal influence on social or defensive behavior.

Selection of Consequences: Adaptive Behavior from Random Reinforcement

Abstract: The behavior of subjects in a human operant conditioning experiment was “shaped” using a random reinforcement contingency. Bar-press responses kept a moving cursor near a target although the conseq...

Nonaversive Procedures in the Treatment of Classroom Behavior Problems

Abstract: Athough a number of previous narrative reviews have found reinforcement to be effective in the management of classroom behavior problems, lack of a statistical methodology for analyzing singe-case design has prevented precise comparisons of many of the parameters of reinforcement. This investigation uses a regression approach to generate effect sizes for a quantitative synthesis of single-case studies. Five parameters of reinforcement approaches in classroom behavior management were investigated: type of treatment, topography of behavior treated, administrative arrangements, agent administering the treatment, and setting. Although few main effect differences were found within any one parameter, significant, robust interaction effects were found between the presence of reinforcement and topography, reinforcement and setting, and setting and administrative arrangements. Implications for both practice and research methodology are discussed.

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

Abstract: 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 responser 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.

The effects of pimozide on the establishment of conditioned reinforcement as a function of the amount of conditioning.

Abstract: In an attempt to understand some inconsistent findings, the present experiment investigated the effects of pimozide, a dopamine (DA) receptor blocker, on the establishment of conditioned reinforcement as a function of the amount of conditioning. In Experiment 1, rats received three phases of training in a two-lever box. The pre-exposure phase measured the operant rates of pressing the levers; one produced a 3-s tone and the other turned the lights off for 3 s. In the conditioning phase, with the levers absent, the light-off stimulus was paired with food for two or four sessions. The test phase again measured the rate of pressing the levers. Conditioned reinforcement was shown by a relative increase in responding on the light lever during the test. Of the groups receiving four conditioning sessions, pimozide (0.5, 1.0, 2.0 and 4.0 mg/kg) produced a dose-dependent attenuation of conditioned reinforcement, those rats treated with 4.0 mg/kg failing to demonstrate a significant effect. When 2 conditioning days were employed, pimozide treatment also produced a dose-dependent attenuation; however, in these less conditioned animals 2.0 mg/kg blocked the effect. The possibility that pimozide produced a conditioned taste aversion to the food was ruled out in Experiment 2. These data suggest that DA transmission may be necessary for the establishment of conditioned reinforcement and that the effects of receptor blockade may be related to the amount of conditioning.

Applications of Behavior Modification to Community Health Education: The Case of Heart Disease Prevention

Abstract: Principles of behavior modification increasingly have been applied to community health education and offer considerable promise for public health in general. Behavior modification procedures can be conceptualized in a 2 X 2 framework with desired goals being either to increase and strengthen or decrease and weaken behavior, and procedures producing essentially positive or negative consequences. Modifying specific behavioral risk factors for the prevention of heart disease may include the use of positive reinforcement, shaping, differential reinforcement, negative reinforcement, and "punishment." The use of an adequate "behavior analytic" history, highly acceptable interventions, observable effects, inexpensive materials and procedures, community-owned programs, and other practical guidelines can help optimize the effectiveness of behavior modification for health education in the community.