ASSESSMENT OF PREFERENCE FOR VARIED VERSUS CONSTANT REINFORCERS

One method that has been demonstrated to improve the effectiveness of reinforcement is stimulus (reinforcer) variation (Egel, 1980). Egel found that bar pressing increased and responding occurred more rapidly during varied reinforcement than during constant reinforcement when identical stimuli were used across phases for 10 individuals with autism. The purpose of the current investigation was to assess the preferences of 7 individuals for varied presentation of slightly lower quality stimuli relative to constant access to the highest quality stimulus. Varied presentation was preferred over constant reinforcer presentation with 4 participants, and the opposite was true for 2 participants. One participant did not demonstrate a preference. These results suggest that stimulus variation may allow less preferred reinforcers to compete effectively with a more highly preferred reinforcer for some individuals.     

The effects of constant versus varied reinforcers on preference and resistance to change

Previous research has demonstrated that factors such as reinforcer frequency, amount, and delay have similar effects on resistance to change and preference. In the present study, 4 boys with autism made choices between a constant reinforcer (one that was the same food item every trial) and a varied food reinforcer (one that varied randomly between three possible food items). For all 4 boys, varied reinforcers were preferred over constant reinforcers, and they maintained higher response rates than constant reinforcers. In addition, when a distraction (a video clip) was introduced, responding maintained by varied reinforcers was more resistant to distraction than responding maintained by constant reinforcers. Thus, the present experiment extended the generality of the relation between preference and resistance to change to variation in reinforcer quality.     

A comparison of displacement and reinforcer potency for typically developing children

Previous researchers found that individuals with intellectual and developmental disabilities tend to prefer edible over leisure stimuli, although leisure stimuli may still function as reinforcers. We replicated and extended previous research in a 2-part experiment with typically developing children. In Experiment 1, we evaluated 15 children's preference for leisure and edible stimuli. Five of 15 participants preferred edible over leisure stimuli, 3 of 15 participants preferred leisure over edible stimuli, and the remaining 7 of 15 participants did not show a preference for a stimulus class. In Experiment 2, we compared the reinforcer potency of the top-ranked stimulus from each class with 7 of the 8 participants who showed displacement of one stimulus class. Four of 7 participants allocated more responding to the task associated with the top-ranked stimulus and 3 of 7 participants showed no differences in responding to the task regardless of the stimulus rank.     

REINFORCER VARIATION: IMPLICATIONS FOR MOTIVATING DEVELOPMENTALLY DISABLED CHILDREN

Motivating developmentally disabled children to participate in educational activities can be very difficult. This is especially true for children diagnosed autistic. Because there is some evidence to suggest that stimulus variation may influence motivation, the present study investigated the effects of constant vs. varied reinforcer presentation on correct responding and on-task behavior. Results from a reversal design showed declining trends in both correct responding and on-task behavior when the same reinforcer was consistently presented, whereas, varying the reinforcers produced significantly improved and stable responding. The results are discussed in relation to the literature on stimulus variation and its effects on responsivity.     

Identification of olfactory stimuli as reinforcers in individuals with autism: a preliminary investigation

Preference for six olfactory stimuli was assessed via paired preference assessments with three adults with autism. Using a combination multielement and reversal design, a reinforcer assessment was then conducted to determine the extent to which three (high preference, medium preference, and low preference) of the six olfactory stimuli evaluated in the preference assessment functioned as reinforcers for responding in the context of a sorting task. Relative to baseline, all of the participants exhibited increased responding for access to their high preference olfactory stimulus. The utility of olfactory stimuli as components of behavior intervention plans is discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Assessing reinforcers under progressive schedule requirements.

Recent research findings suggest that reinforcing stimuli may be differentially effective as response requirements increase. We extended this line of research by evaluating responding under increasing schedule requirements via progressive‐ratio schedules and behavioral economic analyses. The differential effectiveness of preferred stimuli in treating destructive behavior maintained by automatic reinforcement also was examined. Results showed that one of two stimuli was associated with more responding under increasing schedule requirements for the 4 participants. Furthermore, stimuli associated with more responding under increasing schedule requirements generally were more effective in treating destructive behavior than stimuli associated with less responding. These data suggest that progressive‐ratio schedules and behavioral economic analyses may be useful for developing a new technology for reinforcer identification. From a clinical perspective, these results suggest that two reinforcers may be similarly effective for low‐effort tasks and differentially effective for high‐effort tasks.     

Evaluation of absolute and relative reinforcer value using progressive-ratio schedules

We evaluated behavior exhibited by individuals with developmental disabilities using progressive-ratio (PR) schedules. High- and low-preference stimuli were determined based on the results of a paired-stimulus preference assessment and were evaluated in subsequent reinforcer and PR assessments using concurrent and single schedules of presentation. In Experiment 1, results showed that for 2 of 3 participants, stimuli determined to be low-preference functioned as reinforcers when evaluated independent of high-preference stimuli. Further, the results from Experiment 2 showed that low-preference stimuli also functioned as reinforcers under gradually increasing PR requirements. Results suggest that for cases in which a high-preference stimulus is unavailable or impractical, the contingent delivery of relatively less preferred stimuli may maintain appropriate behavior, even as schedule requirements increase.     

ON THE RELATIVE REINFORCING EFFECTS OF CHOICE AND DIFFERENTIAL CONSEQUENCES

Research on the reinforcing effects of providing choice-making opportunities to individuals with developmental disabilities (i.e., allowing them to choose reinforcers or tasks) has produced inconsistent results, perhaps because the mechanisms underlying such effects remain unclear. Choice may produce a reinforcement effect because it is correlated with differential consequences (i.e., choice may increase one's access to higher preference stimuli), or it may have reinforcement value independent of (or in addition to) the chosen stimulus. In Experiment 1, we used a concurrent-operants arrangement to assess preference for a choice condition (in which participants selected one of two available reinforcers) relative to a no-choice condition (in which the therapist selected the same reinforcers on a yoked schedule). All 3 participants preferred the choice option. In Experiment 2, we altered the schedules so that the participant selected one of two lower preference reinforcers in the choice condition, whereas the therapist selected a higher preference stimulus for the participant either half or all of the time in the no-choice condition. Participants typically allowed the therapist to select reinforcers for them (i.e., they allocated responding to the no-choice condition) when it resulted in greater access to higher preference stimuli.     

Reinforcement magnitude and pausing on progressive-ratio schedules

Rats responded under progressive-ratio schedules for sweetened milk reinforcers; each session ended when responding ceased for 10 min. Experiment 1 varied the concentration of milk and the duration of postreinforcement timeouts. Postreinforcement pausing increased as a positively accelerated function of the size of the ratio, and the rate of increase was reduced as a function of concentration and by timeouts of 10 s or longer. Experiment 2 varied reinforcement magnitude within sessions (number of dipper operations per reinforcer) in conjunction with stimuli correlated with the upcoming magnitude. In the absence of discriminative stimuli, pausing was longer following a large reinforcer than following a small one. Pauses were reduced by a stimulus signaling a large upcoming reinforcer, particularly at the highest ratios, and the animals tended to quit responding when the past reinforcer was large and the stimulus signaled that the next one would be small. Results of both experiments revealed parallels between responding under progressive-ratio schedules and other schedules containing ratio contingencies. Relationships between pausing and magnitude suggest that ratio pausing is under the joint control of inhibitory properties of the past reinforcer and excitatory properties of stimuli correlated with the upcoming reinforcer, rather than under the exclusive control of either factor alone.     

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

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

Responding for sucrose and wheel-running reinforcement: effects of sucrose concentration and wheel-running reinforcer duration

Six male albino rats were placed in running wheels and exposed to a fixed-interval 30-s schedule of lever pressing that produced either a drop of sucrose solution or the opportunity to run for a fixed duration as reinforcers. Each reinforcer type was signaled by a different stimulus. In Experiment 1, the duration of running was held constant at 15 s while the concentration of sucrose solution was varied across values of 0, 2.5. 5, 10, and 15%. As concentration decreased, postreinforcement pause duration increased and local rates decreased in the presence of the stimulus signaling sucrose. Consequently, the difference between responding in the presence of stimuli signaling wheel-running and sucrose reinforcers diminished, and at 2.5%, response functions for the two reinforcers were similar. In Experiment 2, the concentration of sucrose solution was held constant at 15% while the duration of the opportunity to run was first varied across values of 15, 45, and 90 s then subsequently across values of 5, 10, and 15 s. As run duration increased, postreinforcement pause duration in the presence of the wheel-running stimulus increased and local rates increased then decreased. In summary, inhibitory aftereffects of previous reinforcers occurred when both sucrose concentration and run duration varied; changes in responding were attributable to changes in the excitatory value of the stimuli signaling the two reinforcers.     

Response-independent milk delivery enhances persistence of pellet-reinforced lever pressing by rats

If, during training, one stimulus is correlated with a higher rate of reinforcement than another, responding will be more resistant to extinction in the presence of that higher rate signal, even if many of the reinforcers have been presented independently of responding. For the present study we asked if the response-independent reinforcers must be the same as the response-dependent reinforcers to enhance the response's persistence. Twelve Long-Evans hooded rats obtained 45-mg food pellets by lever pressing (variable-interval 100-s schedules) in the presence of two discriminative stimuli (blinking vs. steady lights) that alternated every minute during daily sessions. Also, in the presence of one of the stimuli (counterbalanced across rats), the rats received additional response-independent deliveries of sweetened condensed milk (a variable-time schedule). Extinction sessions were exactly like training sessions except that neither pellets nor milk were presented. Lever pressing was more resistant to extinction in the presence of the milk-correlated stimulus when (a) the size of the milk deliveries during training (under a variable-time 30 s schedule) was 0.04 ml (vs. 0.01 ml) and (b) 120-s or 240-s blackouts separated components. Response-independent reinforcers do not have to be the same as the response-dependent reinforcers to enhance persistence.     

Equivalence classification by California sea lions using class-specific reinforcers

The ability to group dissimilar stimuli into categories on the basis of common stimulus relations (stimulus equivalence) or common functional relations (functional equivalence) has been convincingly demonstrated in verbally competent subjects. However, there are investigations with verbally limited humans and with nonhuman animals that suggest that the formation and use of classification schemes based on equivalence does not depend on linguistic skills. The present investigation documented the ability of two California sea lions to classify stimuli into functional classes using a simple discrimination reversal procedure. Following the formation of functional classes in this context, the second experiment showed transfer of the relations that emerged between class members to a matching-to-sample procedure. The third experiment demonstrated that the functional classes could be expanded through traditionally defined equivalence relations. In these three experiments, appropriate within-class responding produced class-specific food reinforcers. Experiment 3 addressed the role of these reinforcers in equivalence classification and showed that the class-specific reinforcers were sufficient to relate new stimuli to the functional classes. These findings show that sea lions can form equivalence classes in simple and conditional discrimination procedures, and that class-specific reinforcers can become equivalence class members.     

Reinforcer frequency and restricted stimulus control.

Stimulus control was evaluated in 3 individuals with moderate to severe mental retardation by delayed identity matching-to-sample procedures that presented either one or two discrete forms as sample stimuli on each trial. On pretests, accuracy scores on one-sample trials were uniformly high. On two-sample trials, the correct stimulus (i.e., the one that subsequently appeared in the comparison array) varied unpredictably, and accuracy scores were substantially lower, suggesting that both sample stimuli did not exert stimulus control on every trial. Subjects were then given training sessions with the one-sample task and with a new set of four stimuli. For two of the stimuli, correct matching responses were followed by reinforcers on a variable-ratio schedule that led to a high reinforcer rate. For the other two stimuli, correct responses were followed by reinforcers on a variable-ratio schedule that led to a substantially lower reinforcer rate. Results on two-sample tests that followed showed that (a) on trials in which comparison arrays consisted of one high reinforcer-rate and one low reinforcer-rate stimulus, subjects most often selected the high-rate stimulus; and (b) on trials in which the comparison arrays were either two high reinforcer-rate stimuli or two low reinforcer-rate stimuli and the samples were one high reinforcer- and one low reinforcer-rate stimulus, accuracy was higher on trials with the high-rate comparisons. These results indicate that the frequency of stimulus control by high reinforcer-rate samples was greater than that by low reinforcer-rate samples. Following more training with the one-sample task and reversed reinforcement schedules for all stimuli, the differences in stimulus control frequencies on two-sample tests also reversed. These results demonstrate experimental control by reinforcement contingencies of which of two sample stimuli controlled selections in the two-sample task. The procedures and results may prove to be relevant for understanding restricted stimulus control and stimulus overselectivity.     

Establishing preference for unreliable reinforcement in adults with dual diagnoses

We evaluated the choice responding of three adults dually diagnosed with developmental and psychiatric disabilities using concurrent schedules of reinforcement. Specifically, participants were given a choice between a response option resulting in reliable reinforcement and a response option resulting in unreliable reinforcement. Our primary purpose was to shift preference from reliable to unreliable reinforcement via the systematic presentation of stimuli during delay intervals. A second purpose was to evaluate the effectiveness of intervening stimuli in shifting preference at differing delay-to-reinforcement intervals. Preference for unreliable reinforcement was first examined in the absence of stimulus presentations during delays, at three different delay values. Next, we aimed to establish preference for unreliable reinforcement by presenting pictures of reinforcers during delays preceding unreliable reinforcement. Preference was again examined at three different delay values. In the absence of stimulus presentations during delays, participants were shown to prefer reliable reinforcement, particularly at the longer delay value. When stimuli were presented during the delays, two of the three participants preferred unreliable reinforcement, particularly the longer the delay value. These results suggest that the presentation of intervening stimuli during delays may help facilitate tolerance for unreliable reinforcement.     

Comparing stimulus preference and response force in a conjugate preparation

Researchers used a conjugate preparation to evaluate how response force changed based on participants' preferences for visual stimuli. First, researchers used a verbal preference assessment to evaluate each participant's preference for viewing for five object categories of visual stimuli; this process identified high preference (HP) stimuli and low preference stimuli for most participants. Thereafter, researchers exposed each participant to the five stimulus categories in a randomized order while using a force dynamometer to measure their response force to increase visual clarity of each stimulus. Results indicate the majority of participants' HP stimuli corresponded to the stimulus category for which they exerted the highest mean force. These preliminary findings suggest conjugate preparations involving response force may provide another option for measuring the relative value of some stimulus events.     

Negative behavioral contrast on multiple treadle-press schedules

Eight pigeons pressed treadles for food reinforcers delivered by several multiple variable-interval schedules. The rate of reinforcement for responding during one component schedule was held constant at 30 reinforcers per hour. The rate of reinforcement for responding during the other component varied from 0 to 120 or 240 reinforcers per hour. The schedules were presented in different orders for different subjects. The rate of responding emitted during the variable component schedule varied directly with the rate of reinforcement it provided. The rate of responding during the constant component did not increase consistently when the rate of reinforcement obtained from the variable component decreased from 30 to 0 reinforcers per hr. The rate of responding emitted during the constant component decreased when the rate of reinforcement obtained from the variable component increased from 30 reinforcers per hour to a higher rate. That is, negative but not positive behavioral contrast occurred. The failure to find positive contrast is consistent with one of the predictions of the additive theories of behavioral contrast. Finding negative contrast has ambiguous implications for the additive theories.     

Stimulus control and compounding with ambient odor as a discriminative stimulus on a free-operant baseline

Previous experiments have demonstrated that the simultaneous presentation of independently established discriminative stimuli can control rates of operant responding substantially higher than the rates occasioned by the individual stimuli. This "additive summation" phenomenon has been shown with a variety of different reinforcers (e.g., food, water, shock avoidance, cocaine, and heroin). Discriminative stimuli previously used in such studies have been limited to the visual and auditory sensory modalities. The present experiment sought to (1) establish stimulus control on a free-operant baseline with an ambient olfactory discriminative stimulus, (2) compare olfactory control to that produced with an auditory discriminative stimulus, and (3) determine whether compounding independently established olfactory and auditory discriminative stimuli produces additive summation. Rats lever pressed for food on a variable-interval schedule in the presence of either a tone or an odor, with comparable control developed to each stimulus. In the absence of these stimuli responding was not reinforced. During stimulus compounding tests, the tone-plus-odor compound occasioned more than double the responses occasioned by either the tone or odor presented individually. Thus, the current study (1) established stimulus control with an ambient olfactory discriminative stimulus in a traditional free-operant setting and (2) extended the generality of stimulus-compounding effects by demonstrating additive summation when olfactory and auditory discriminative stimuli were presented simultaneously.     

Evaluating Open-Ended Parent Reports and Direct Preference Assessments to Identify Reinforcers for Young Children With Autism

Little research has evaluated open-ended parent reports to identify reinforcers for children with autism. This study evaluated open-ended parent reports and direct preference assessments for six young children with autism in home-based therapy. Results indicated little correspondence between parent reports and direct assessment assessments for all but one child. However, a follow-up reinforcer assessment with two children showed that the top ranked stimulus from both assessments functioned as reinforcers, with one child demonstrating higher levels of responding for the top ranked stimulus from the parent report. Results tentatively support open-ended parent reports to identify reinforcers for young children with autism.     

A test of the reinforcing properties of stimuli correlated with nonreinforcement

The information hypothesis of conditioned reinforcement predicts that a stimulus that “reduces uncertainty” about the outcome of a trial will acquire reinforcing properties, even when the stimulus reliably predicts nonreinforcement. Four pigeons' key pecks produced one of two 5-sec stimuli with 0.50 probability according to a discriminated variable-interval schedule. One stimulus was followed by reinforcement; a second stimulus was followed by blackout. To the same extent, therefore, both stimuli reduced uncertainty about the possibility that food would arrive at the termination of the schedule interval. When a second key in the chamber was lighted, each peck on it could produce the stimulus preceding reinforcement, the stimulus preceding nonreinforcement, a novel stimulus, or no stimulus, across separate conditions. The stimulus preceding food maintained responding at substantial levels on the second, stimulus-producing, key. Such responding was not maintained by other stimuli. These data, replicated when the stimuli were reversed on the variable-interval schedule, do not support the prediction that uncertainty-reducing stimuli are necessarily conditioned reinforcers.