The effects of type of reinforcer, schedule of reinforcement, sex and personality on response rates of mentally retarded children.
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Pigeons were trained on a discrete-trials, simultaneous discrimination procedure, with confusable stimuli such that asymptotic performance was about 85% correct. Trials were terminated if no response occurred within 2 sec of stimulus onset, so that probability of responding was free to vary. The schedule of reinforcement for correct responses was varied, with the following results: (1) there was no relation between frequency of reinforcement and accuracy of responding. (2) In extinction, the probability of responding fell to low levels, but accuracy remained roughly constant. (3) When reinforcement was available after a fixed number of trials or after a fixed number of correct responses, the probability of responding increased with successive trials after reinforcement, but accuracy was generally constant. (4) When every fifth correct response was reinforced, accuracy decreased immediately after reinforcement if the birds were required to respond on every trial.
The response rate of an educably mentally retarded male on a folder assembly task and for two types of self-stimulatory behavior was measured under fixed ratio, variable ratio, and fixed ratio pacing schedules of reinforcement. Higher work rates were maintained by the variable ratio and fixed ratio pacing schedule than by the simple fixed ratio schedule. The rate of self-stimulatory behavior associated with each reinforcement schedule and with a medication termination was also reported.
Positive behavioral contrast was assessed in two experiments with young infants using multiple conjugate reinforcement schedules. Reinforcement was produced by footkicks which activated the objects of an overhead crib mobile in a manner proportional to the vigor and rate of responding. Distinctive color/pattern cues on the sides of the objects served as discriminative stimuli for components of the multiple schedule. In Experiment 1, infants were trained with one cue (S+) only before insertion of S+ into a multiple schedule with an extinction component. A control group received S+ throughout all sessions. In Experiment 2, a multiple schedule was introduced at the outset, and responses in both components were reinforced before the introduction of extinction in the second component. In a final phase, reinforcement was reintroduced into the second component. Positive behavioral contrast occurred in both experiments. Response reduction in the extinction component was seen only in individual relative response curves. In both experiments, negative emotional behaviors accompanied the extinction component, and in Experiment 1, cooing accompanied presentations of S+.
Traditional strategies for determining whether a reinforcer schedule enhances the occurrence of an activity are reviewed and critically evaluated. A basic assumption underlying these strategies is that it is possible to isolate the effect of reinforcer intermittency on schedule induction. It is concluded that this is not, in fact, possible. An alternative approach is proposed that emphasizes the inductive effects of the reinforcer schedule as a unit and the effects of particular aspects of the reinforcer schedule (e.g., interreinforcer interval, repetition of the reinforcer, reinforcer magnitude).
Rats maintained at 80% of their ad lib body weight were trained on a two bar concurrent fixed ratio 8-fixed ratio 8 schedule with sucrose solutions presented at schedule completion. When the solutions were available on the same schedule of reinforcement, rats consistently responded more on the lever associated with the higher sucrose concentration over either less concentrated sucrose solutions or water. However, when a preferred 20% sucrose solution was placed on a high fixed ratio requirement (FR64) and a less preferred 2% sucrose solution remained on the lower ratio requirement (FR8), the rats were observed to increase their responding on the lever associated with presentation of the 2% sucrose solution. Response rates for the low concentrated sucrose solution increased to levels comparable to those seen when that solution was paired with water. These results were compared to prior studies using ethanol and sucrose as the available fluids.
The effects of a variable-ratio schedule of reinforcement on pedaling a a stationary exercise bicycle were examined. Three obese and three nonobese 11-year-old boys were individually tested five times weekly for approximately 12 weeks. A changing-criterion design was used in which each successive criterion was increased over mean performance rate in the previous phase by approximately 15%. The contingencies of the successive criteria resulted in systematic increases in rate of exercise for all children. Final variable-ratio rates were higher than those under fixed ratios found in previous research, with rates for 2 of the 3 obese boys approximating those of the nonobese.
Rats were either undernourished from birth to 43 days and thereafter well fed (previously undernourished, PU) or well nourished throughout. When behaviour was tested in adulthood it was found that significant differences between the groups in rate of lever-pressing for food occurred when they were tested under a variable-interval 60-sec schedule of reinforcement, but not when reward was delivered according to a fixed-interval 60-sec or variable-ratio ten schedule. The results of a second experiment suggested that the rate difference might reduce or disappear with extended exposure to the schedule. The third experiment exposed rats to fixed-interval 60-sec and mixed fixed-interval 10-sec fixed-interval 110 sec schedules. Response rate differences between the PU and control groups occurred only under the mixed schedule, a result interpreted as showing that temporal irregularity of reward delivery plays some role in the genesis of more rapid operant responding in PU rats. When rats received a larger variable-ratio schedule, requiring 40 responses for reward, no significant rate differences between the groups were found over the whole experimental condition. It is suggested that schedules on which there are significant differences have some special characteristic, possibly sensitivity to differences in food motivation between the groups.
Choice behavior under a concurrent VR-FR schedule of reinforcement was investigated in two experiments to test a molar theory of maximization. Hunger-motivated albino rats pressed two bars, one on an FR10 and the other on a VR10 schedule, for a food reward. With the total number of experiences with each bar equated and interalternative switching eliminated during training, the study showed that during the choice test, the animals made significantly more responses to the VR than to the FR alternative, allocating about 75% of their responses to the VR alternative. The results suggest that, given an equal return of reward in the long run, the animals preferred a variable to a constant alternative in a choice situation. The findings are discussed in terms of a molar theory of maximization and a schedule-appropriate behavior interpretation of choice.
The effects of subcutaneous injections of methadone hydrochloride (0.75mg, 1.5mg and 2.5mg/kg) on lever pressing maintained by fixed ratio schedules of reinforcement were examined in C57BL/6J and DBA/2J mice. Response output over a 30 min session decreased as a function of increasing drug dose when reinforcement was delivered for every 5 responses. Increasing the response to reinforcement ratio from 5 to 20 in a second experiment doubled and nearly quadrupled responding by DBA and C57 mice, respectively. Injecting animals maintained on this schedule with methadone reduced responding to the same extent as that observed in the first experiment when response rates were lower. Hence, these experiments provide no support for the effect of methadone being rate-dependent. In both experiments methadone disrupted responding of DBA more than that of C57 mice. This finding is consistent with a previous report that other narcotic analgesics were more potent analgesics for DBA than for C57 mice. From these studies it appears that the opposite changes in locomotor activity upon an exposure to narcotic analgesics does not generalize to behavior under control of reinforcing stimuli; and that both the effects obtained in the present study and the analgesic action are dissociated from the effects of these drugs on locomotor activity.
Behavior controlled by various schedules of reinforcement is useful for characterizing drugs as well as for analyzing the mechanisms of action of their effects on behavior. Conditioned avoidance techniques have been useful for studying neuroleptics and for predicting their clinical antipsychotic acitivity; the possible involvement of dopaminergic mechanisms in the effect of neurolpetics on avoidance behavior is discussed. Tricyclic antidepressant agents have been studied in assays involving interactions with other agents, such as cocaine, amphetamine and tetrabenazine. One type of operant behavior, Sidman avoidance, has been used as particularly sensitive assay for such drug interactions. Another schedule, in which "observing" responses in pigeons are measured. seems to provide a method for studying antidepressants without involving drug interaction phenomena. For tricyclic compounds, facilitation of observing responses and weak potency of conditioned avoidance inhibition constitute a pharmacological profile that seems to have some predictive value for clinical imipramine-like antidepressant activity. "Conflict (punishment) schedules have been useful for predicting antianxiety activity in man. Although the degree of anticonflict effect observed is consistent with Dew's rate dependency hypothesis, this principle does not fully account for the observed drug effects. In the conflict model, the actions of benzodiazepines differ in drug-naive versus drug-experienced animals. Experiments with parachlorophenylalnine have not yet provided clear support for the postulated role of serotonin in related phenomena.
The effects of reinforcement schedules on rats' choice behavior in extinction were studied. In a free-operant chamber equipped with two retractable bars, the experimental animals were trained to press the bars separately for a food reward. One bar delivered the reward on a continuous reinforcement (CRF) schedule, and the other delivered the reward on a partial reinforcement (PRF) schedule. Control animals earned the reward from both bars with the same reinforcement schedule, either a CRF or a PRF. When both bars were simultaneously available during extinction, the experimental animals responded more frequently to the CRF than to the PRF alternative, demonstrating a reversed within-subjects partial reinforcement extinction effect (PREE). A conventional between-subjects PREE was replicated in the control subjects. The results of this study were inconsistent with both Amsel's (1962, 1967) frustration hypothesis and Capaldi's (1966, 1967) sequential hypotheses.
The objective of this exploratory investigation was to determine the interactive effects of fixed-ratio scheduling of microwave reinforcement in tandem with changes in microwave intensity. Nine albino rats were conditioned to regulate their thermal environment with microwave radiation while living in a Skinner (operant conditioning) Box in which the ambient temperature was about 27.13 degrees F at the beginning of the session. Each rat obtained a 6-sec. exposure of microwave radiation on a fixed-ratio schedule of MW reinforcement, the values of which varied from FR-1 to FR-30. Intensities of MW radiation were 62.5 W, 125 W, 250 W, and 437.5 W. Sessions lasted for 8 to 9 hr. over an approximate 13-mo. period. The effects of the intensity of microwave reinforcement varied as a function of the ratio value of the schedule used. Continuous reinforcement (FR-1) produced the lowest over-all rates, whereas FR-15, and FR-25 produced the highest over-all rates. Relatively higher thermal-behavior rates occurred under 62.5 W than under any of the other MW intensities for FR-1, FR-15, and FR-25, whereas FR-10 and FR-30 ratios produced intermediate rates of thermal responding which were constant for all values of MW intensity. These data are explained in terms of interactive effects between the "local" satiation or deprivation properties of the MW intensity and the ratio requirements of the schedule of MW reinforcement.
Stereotypic behavior is one of the more common disturbed behaviors displayed by people who are developmentally disabled. This study evaluated the indirect effects on stereotypic frequency when the value of a concurrent fixed-interval reinforcement schedule for adaptive behavior was varied. Three profoundly mentally retarded adults performed a simple adaptive task reinforced under a fixed-interval schedule. The reinforcement schedule value was varied from fixed-interval 15 to 90, and 180 seconds after schedule control under each condition was demonstrated. The dependent measure was the frequency of stereotypic behavior. Stereotypic behavior increased in direct relation to the interval length. The theoretical and practical implications of treating stereotypies as an adjunctive behavior partially controlled by the reinforcement frequency for adaptive behaviors are discussed.
The present investigation developed and tested a new percentile reinforcement schedule suited to study pattern variability, whose main feature was the relative dissociation it provided between the variability requirement defining criterional responses and overall probability of reinforcement. In a discrete-trials procedure, pigeons produced patterns of four pecks on two response keys. If the pattern emitted on the current trial differed from the N preceding patterns, reinforcement was delivered with probability mu. The schedule continuously adjusted the criterion N such that the probability of a criterional response, estimated from the subject's recent behavior, was always constant. In these circumstances, the criterion corresponded to an invariant percentile in the distribution of recent responses. Using a between-subjects design, Experiment 1 manipulated the variability requirement--the percentile--while keeping overall reinforcement probability constant. The degree of variability varied directly with the requirement. In addition, an inverse relationship existed between the requirement and within-group variance. Experiment 2 manipulated probability of reinforcement while maintaining the variability requirement constant. No consistent relationship was found between variability and reinforcement probability. A tentative hypothesis was advanced ascribing the operant conditioning of behavioral variability to a process of probability-dependent selection.
The effects of several different schedules of primary reinforcement were compared in a picture-naming task with retarded children. In Experiment I, number of correct responses and learning rate were higher under fixed-ratio schedules than under continuous reinforcement. In Experiment II, number of correct responses and learning rate tended to be greater under in intermediate than under low or high fixed-ratio schedules. In Experiment III, number of correct responses was higher under interlocking schedules, in which the response requirement increased with time following the previous reinforcement, than under comparable fixed-ratio schedules. Learning rates were generally low and, perhaps because of this, not very different under the two types of schedules in this experiment. Accuracy (i.e., proportion of trials on which correct responses occurred) was typically high and insensitive to variations in schedule and schedule parameter throughout each experiment.
One of the most effective treatments for children with Attention Deficit Disorder with Hyperactivity (ADDH) has been the prescription of methylphenidate (MPH). While laboratory-based evidence indicates that MPH effects may be rate-dependent, little is known about changes evinced in operant behavior controlled by complex reinforcement schedules. The present study examined the effects of several doses of MPH on the operant key-pressing behavior of 20 children with ADDH who were favorable responders to the drug. Following a drug-free training period, each child performed the task across all doses in a randomly assigned sequence under double-blind placebo control conditions. Rate-dependent effects were found for both high- and low-rate reinforcement schedules. The strength of these effects varied across dose. These results have implications for the nature of rate-dependent phenomena in humans and investigations of treatment parameters in the pharmacotherapy of children with ADDH.
Task interspersal procedures have been quite effective in increasing autistic children's motivation to learn. These procedures have typically demonstrated that the inclusion of reinforced maintenance tasks (previously learned tasks) increases responding to new acquisition tasks because more reinforcers, in general, are available. However, studies have not specifically addressed the effects of various schedules of reinforcement, used in conjunction with task interspersal procedures, upon response acquisition. In the present study, a multiple baseline design across subjects was used to assess different reinforcement schedules. Five autistic children participated in learning sessions, during which trials of an acquisition task were interspersed with trials of three maintenance tasks. Correct responses to acquisition tasks were continuously reinforced throughout all conditions, while the reinforcement schedule for competent performance of maintenance tasks differed systematically. Results indicated that all children learned the new tasks when food reinforcers were presented only for acquisition tasks. Results are discussed in terms of behavioral contrast and improving the effectiveness of motivation-enhancing procedures for autistic children.