Concurrent Schedules Research Articles

Lorcaserin maintenance fails to attenuate heroin vs. food choice in rhesus monkeys

BackgroundThe current opioid crisis has reinvigorated preclinical research in the evaluation of non-opioid candidate treatments for opioid use disorder (OUD). Emerging evidence suggests 5-HT2C receptor agonists may attenuate the abuse-related effects of opioids. This study evaluated effectiveness of 7-day treatment with the clinically available 5-HT2C agonist lorcaserin (Belviq®) on heroin-vs.-food choice in rhesus monkeys. Lorcaserin effects were compared to effects produced by 7-day saline substitution and by 7-day treatment with the opioid antagonist naltrexone. MethodsAdult male (1) and female (6) rhesus monkeys were trained to respond under a concurrent schedule of food delivery (1 g pellets, fixed-ratio 100 schedule) and intravenous heroin injections (0-0.032 mg/kg/injection, fixed-ratio 10 schedule) during daily 2 h sessions. Heroin choice dose-effect functions were determined daily before and following 7-day saline substitution or 7-day continuous treatment with naltrexone (0.0032-0.032 mg/kg/h, IV) or lorcaserin (0.032-0.32 mg/kg/h, IV). ResultsUnder baseline conditions, increasing heroin doses maintained a dose-dependent increase in heroin choice. Both saline substitution and 7-day naltrexone treatment significantly attenuated heroin choice and produced a reciprocal increase in food choice. Continuous lorcaserin (0.32 mg/kg/h) treatment significantly increased heroin choice. ConclusionsIn contrast to saline substitution and naltrexone, lorcaserin treatment was ineffective to reduce heroin-vs.-food choice. These preclinical results do not support the therapeutic potential and continued evaluation of lorcaserin as a candidate OUD treatment.

QoS-Aware Bandwidth Allocation and Concurrent Scheduling for Terahertz Wireless Backhaul Networks

In recent years, with the spectrum resources in low frequency bands becoming increasingly insufficient, the carrier frequency of wireless communication has started its evolution to the Terahertz (THz) frequency band, and meanwhile the THz communication system has become one of the research hot spots. In this paper, we investigate the problem of concurrent transmission scheduling for THz wireless backhaul network. To increase the weighted sum of completed flows with their quality of service (QoS) requirements satisfied in THz wireless backhaul network, we propose an algorithm of QoS-aware bandwidth allocation and concurrent scheduling (IHQB). Considering the priority of the flow, the reciprocal of the priority is taken as the weight of the flow. In this algorithm, QoS awareness and bandwidth allocation are exploited to achieve more successfully scheduled flows and higher network throughput. The concurrent scheduling with the maximum independent set (MIS) is allocated to different frequency bands. And the mentioned MIS is obtained from the conflict graph which has been established under the conditions of half-duplex and interference threshold. Simulation results show that IHQB performs better than other algorithms in terms of the weighted sum of completed flows and system throughput, especially compared with STDMA.

A Time Petri Net With Relaxed Mixed Semantics for Schedulability Analysis of Flexible Manufacturing Systems

Several semantics models are adopted by time Petri nets for different applications. Yet they have some limitations on schedulability analysis of flexible manufacturing systems. The scheduling scope of a strong semantics model is greatly limited because of the impact of strong timing requirements, perhaps keeping some optimal schedules out of the consideration. A weak semantics model cannot guarantee the scheduling timeliness as there lacks strong timing enforcement. A mixed semantics model cannot ensure that independent transitions with overlapping firing interval fire in an interleaving way, thus affecting the search for the optimal schedules. In this paper, we present a relaxed mixed semantics model for time Petri nets to address these problems by redefining the firability rules of transitions. In our model, the firability of a transition is determined by maximal concurrent sets containing the transition. This treatment not only extends the scheduling scope of TPN model greatly while avoiding the generation of invalid schedules, but also solves the problem of concurrent scheduling of independent transitions. A state class method is then proposed to support the verification and analysis of temporal properties. Finally, we apply the proposed model to schedulability analysis of a job shop scheduling problem, and compare the features of four semantics models.

QoS-Oriented joint optimization of resource allocation and concurrent scheduling in 5G millimeter-wave network

With the mature application of massive MIMO, challenges for massive backhaul data and ubiquitous user access in future mobile communication are effectively coped with the potential technology of millimeter wave integrated backhaul and access network (mm-wave IBAN). In order to fully exploit mm-wave directional transmission gain, how to improve the concurrent transmission performance of mm-wave IBAN through effective scheduling scheme under the consideration of resource allocation between the backhaul and access link is an intractable issue. In this paper, an enhanced reverse-TDD frame is designed for mm-wave IBAN, and the QoS-oriented joint optimization problem of resource allocation and concurrent scheduling between backhaul and access link is deeply investigated, where the number of the QoS-satisfied transmission flows is maximized. To obtain a pragmatic solution, a joint resource allocation and concurrent scheduling algorithm is proposed. In the proposed algorithm, the whole transmission duration in each scheduling period is divided into several stages and the transmission flows are partitioned into groups according to the designed QoS-aware priority, then bandwidth resources between backhaul and access in each stage are allocated. The transmission duration of each scheduled flow is determined finally. Performance evaluation of proposed algorithm is verified with extensive simulations in 60 GHz mm-wave IBAN under various system parameters. It is demonstrated that significant enhancements in terms of the network throughput and the number of the successful transmission flows are achieved in the proposed algorithm when compared with other state-of-the-art schemes.

Behavioral Effects of Opioid Full and Partial Agonists During Chronic Buprenorphine Treatment.

Buprenorphine, a partial agonist at the μ-opioid receptor, is commonly prescribed for the management of opioid addiction. Notwithstanding buprenorphine's clinical popularity, the relationship between its effectiveness in attenuating relapse-related behavior and its opioid efficacy is poorly understood. Furthermore, changes in the antinociceptive potency or effectiveness of opioid drugs that might occur during buprenorphine treatment have not been characterized. Here, we address these questions by assessing the ability of daily buprenorphine treatment to protect against the reinstatement of drug-seeking behavior by six opioids differing in efficacy (methadone, heroin, oxycodone, buprenorphine, butorphanol, nalbuphine) and, in separate experiments, by determining how such treatment may modify their antinociceptive effects. In one set of experiments, squirrel monkeys were trained to respond under concurrent schedules (choice) of food or intravenous oxycodone presentations. The priming strength of different opioids during sessions in which saline, rather than oxycodone, was available for intravenous self-administration was determined before and during chronic buprenorphine treatment (0.1 or 0.32 mg/kg per day). In other subjects, antinociceptive effects of the different opioids were assessed using cumulative dosing procedures in a modified warm-water tail withdrawal procedure before and during buprenorphine treatment. Results show that, notwithstanding some tolerance, full agonists retain high efficacy in producing priming and antinociceptive effects. In contrast, both the priming strength and antinociceptive effectiveness of partial agonists were decreased. These results suggest that the utility of buprenorphine in the management of opioid addiction, and how it alters the analgesic effects of opioids, can vary depending on the efficacy of the abused or prescribed opioid. SIGNIFICANCE STATEMENT: Our findings indicate that the pharmacological efficacy of abused opioids may predict the ability of buprenorphine to attenuate their relapse-related priming and analgesia-related antinociceptive effects. This information can help inform physicians as to the effectiveness and limitations of buprenorphine as a pharmacotherapy for opioid addiction.

An implementation of punishment in the evolutionary theory of behavior dynamics.

An implementation of punishment in the evolutionary theory of behavior dynamics is proposed, and is applied to responding on concurrent schedules of reinforcement with superimposed punishment. In this implementation, punishment causes behaviors to mutate, and to do so with a higher probability in a lean reinforcement context than in a rich one. Computational experiments were conducted in an attempt to replicate three findings from experiments with live organisms. These are (1) when punishment is superimposed on one component of a concurrent schedule, response rate decreases in the punished component and increases in the unpunished component, (2) when punishment is superimposed on both components at equal scheduled rates, preference increases over its no-punishment baseline, and (3) when punishment is superimposed on both components at rates that are proportional to the scheduled rates of reinforcement, preference remains unchanged from the baseline preference. Artificial organisms animated by the theory, and working on concurrent schedules with superimposed punishment, reproduced all of these findings. Given this outcome, it may be possible to discover a steady-state mathematical description of punished choice in live organisms by studying the punished choice behavior of artificial organisms animated by the evolutionary theory.

Scheduling Concurrent Visual Feedback in Learning a Continuous Balance Task

This investigation held concurrent visual feedback frequency at 50% in the acquisition phase and manipulated three different feedback schedules while comparing those to a 0% feedback frequency. In an assessment of dynamic postural stability, young, healthy adults performed 20 acquisition trials and four retention trials 48-hr later on a circular platform that moved in the anterior/posterior and medial/lateral axes simultaneously. Three concurrent feedback schedules were manipulated: a fade schedule consisting of high relative frequency of concurrent feedback early in the acquisition phase which was systematically reduced throughout acquisition (e.g., 100%, 75%, 50%, 25%, 0%), a constant schedule consisting of a uniform scheduling of concurrent feedback on every other acquisition trial, and a reverse fade group consisting of a schedule exactly opposite to that of the fade group. A no concurrent feedback group was also utilized to determine if feedback was necessary to learn the balance task. Acquisition and retention results revealed the concurrent groups performed with significantly greater accuracy and stability than the no concurrent feedback group. There were no significant differences between the three concurrent feedback schedules. Results indicate that manipulating concurrent feedback scheduling did not produce similar results to those investigations manipulating knowledge of results scheduling.

Adding concurrency to smart contracts

Modern cryptocurrency systems, such as the Ethereum project, permit complex financial transactions through scripts called smart contracts. These smart contracts are executed many, many times, always without real concurrency. First, all smart contracts are serially executed by miners before appending them to the blockchain. Later, those contracts are serially re-executed by validators to verify that the smart contracts were executed correctly by miners. Serial execution limits system throughput and fails to exploit today’s concurrent multicore and cluster architectures. Nevertheless, serial execution appears to be required: contracts share state, and contract programming languages have a serial semantics. This paper presents a novel way to permit miners and validators to execute smart contracts in parallel, based on techniques adapted from software transactional memory. Miners execute smart contracts speculatively in parallel, allowing non-conflicting contracts to proceed concurrently, and “discovering” a serializable concurrent schedule for a block’s transactions, This schedule is captured and encoded as a deterministic fork-join program used by validators to re-execute the miner’s parallel schedule deterministically but concurrently. We have proved that the validator’s execution is equivalent to miner’s execution. Smart contract benchmarks run on a JVM with ScalaSTM show that a speedup of 1.39$$\times $$ can be obtained for miners and 1.59$$\times $$ for validators with just three concurrent threads.

Is increased sensitivity to punishment a common characteristic of attention deficit/hyperactivity disorder? An experimental study of response allocation in Japanese children

Research on motivational processes in attention deficit/hyperactivity disorder (ADHD) focuses on reward. Studies with punishment are limited and findings mixed. This study evaluated the effects of punishment on response allocation in Japanese children with and without ADHD. Thirty-four children meeting DSM-IV criteria for ADHD and 59 typically developing control-group children completed an operant task in which they choose between playing two simultaneously available games. Reward was arranged symmetrically across the games under concurrent variable interval schedules. Asymmetric punishment schedules were superimposed with responses on one game punished four times as often as responses on the other. Children with ADHD showed greater behavioral sensitivity to punishment than controls. They allocated significantly more responses to the less frequently punished alternative and were more likely to play this game on consecutive trials and responded more slowly to the more punished game. Control group children allocated their responses evenly across games. Punishment exerted greater control over the behavior of Japanese children with ADHD than controls, similar to findings with children from Western countries, suggesting this is a common characteristic of the disorder. The behavior of typically developing Japanese children, while demonstrating awareness of punishment, was not controlled by the frequency of its occurrence.

Device-to-Device Communications Enabled Multicast Scheduling for mmWave Small Cells Using Multi-Level Codebooks

Heterogeneous cellular networks with small cells in the millimeter wave (mmWave) band densely deployed have become one of promising candidates for future wireless networks due to huge bandwidth available in the mmWave band. To overcome high path loss in the mmWave band, the beamforming technique of directional antennas is adopted. Consequently, concurrent transmissions of links can be enabled to improve network capacity. On the other hand, multicast services can support many applications like popular content downloading and broadcast communication services. In user intensive region where multicast services usually happen, device-to-device (D2D) communications in physical proximity provide better channel conditions, and can improve multicast efficiency. In this paper, we develop an efficient multicast scheduling scheme for mmWave small cells, referred to as CONMD2D, where both concurrent transmissions and D2D communications are exploited based on a multi-level antenna codebook to optimize network performance. In CONMD2D, the multicast group is partitioned into subgroups, and D2D transmission paths are established between subgroups. Then, a concurrent scheduling algorithm schedules the multicast links concurrently into the transmission stage. Performance evaluation under various system parameters demonstrates CONMD2D achieves significant improvement in network throughput and energy efficiency compared with other state-of-the-art schemes.

Sex differences in opioid reinforcement under a fentanyl vs. foodchoice procedure in rats.

Clinical evidence suggest that men are more sensitive than women to the abuse-related effects of mu-opioid agonists. In contrast, preclinical studies suggest the opposite sex difference. The aim of the present study was to clarify this discrepancy using a fentanyl vs. diluted Ensure® choice procedure to assess sex differences in opioid reinforcement. Sex differences in intravenous (IV) fentanyl self-administration were examined under a fixed-ratio (FR5) schedule, a multi-day progressive-ratio (PR) schedule for behavioral economic analysis, and a concurrent (choice) schedule of fentanyl and diluted Ensure® reinforcement in Sprague-Dawley male and female rats. The fentanyl dose-effect function under the FR5 schedule was significantly shifted upward in females compared to males. Similarly, the reinforcing effectiveness of both fentanyl (3.2 and 10 µg/kg per injection, IV) and diluted Ensure® (18 and 56%) were greater in females than in males as assessed using behavioral economic analysis, irrespective of dose or concentration. However, under a fentanyl vs. foodchoice procedure, males chose 3.2 µg/kg per injection fentanyl injections over 18%, but not 56%, diluted Ensure® at a higher percentage compared to females. Overall, these results suggest that the expression of sex differences in opioid reinforcement depends upon the schedule of reinforcement and that preclinical opioid vs. food choice procedures provide a translationally relevant measure (i.e., behavioral allocation) consistent with the direction of sex differences reported in the clinical literature.

Temporal and Effort cost Decision-making in Healthy Individuals with Subclinical Psychotic Symptoms

The value people attribute to rewards is influenced both by the time and the effort required to obtain them. Impairments in these computations are described in patients with schizophrenia and appear associated with negative symptom severity. This study investigated whether deficits in temporal and effort cost computations can be observed in individuals with subclinical psychotic symptoms (PS) to determine if this dysfunction is already present in a potentially pre-psychotic period. Sixty participants, divided into three groups based on the severity of PS (high, medium and low), performed two temporal discounting tasks with food and money and a concurrent schedule task, in which the effort to obtain food increased over time. We observed that in high PS participants the discounting rate appeared linear and flatter than that exhibited by participants with medium and low PS, especially with food. In the concurrent task, compared to those with low PS, participants with high PS exerted tendentially less effort to obtain snacks only when the required effort was high. Participants exerting less effort in the higher effort condition were those with higher negative symptoms. These results suggest that aberrant temporal and effort cost computations might be present in individuals with subclinical PS and therefore could represent a vulnerability marker for psychosis.

Relay Assisted Concurrent Scheduling to Overcome Blockage in Full-Duplex Millimeter Wave Small Cells

The millimeter wave (mmWave) has been extensively utilized for its rich spectrum resource. With the development of self-interference (SI) cancellation technology, full-duplex (FD) communications have become possible recently. In order to get larger network capacity, we introduce FD communications into mmWave wireless network. However, mmWave links are easily blocked by obstacles, and the blockage makes some flows fail to be transmitted directly. For the communication problems of shadow coverage area, a relay path selection algorithm is proposed to select optimal multi-hop paths for these blocked flows. This proposed algorithm not only can relay the blocked flows by other unblocked links, but also select the appropriate relay paths to minimize transmission time of the entire transmission process. To further improve the system transmission efficiency, we develop a concurrent scheduling algorithm by using FD communications. The scheduling algorithm continuously schedules the links until the throughput requirements of flows are accommodated. Through extensive simulations at 60 GHz mmWave wireless network, the proposed scheme can solve the problem for a certain degree of blocked flows and complete the transmission with the least time consumption. Compared with other existing schemes, the proposed scheme shows superior performances on relaying capability and scheduling duration.

Concurrent and Overlapping Surgery: Perspectives From Parents of Adolescents Undergoing Spinal Posterior Instrumented Fusion for Idiopathic Scoliosis.

Prospective cross-sectional survey. To determine the perspectives of parents of patients undergoing posterior instrumented fusion for adolescent idiopathic scoliosis (AIS) regarding simultaneous surgery and trainee participation. Simultaneous ("at the same time") surgery is under scrutiny by the public, government, payers, and the medical community. The objective of this study is to determine the perspectives of parents of patients undergoing posterior instrumented fusion for adolescent idiopathic scoliosis. Our goal is to inform the national conversation on this subject with real patient and family voices. A survey was prospectively administered to 31 consecutive parents of patients undergoing posterior instrumented fusion for adolescent idiopathic scoliosis at a large academic medical center. "Overlapping" was defined as simultaneity during "noncritical" parts of an operation. "Concurrent" was defined as simultaneity that includes "critical" part(s) of an operation. Participants were asked to provide levels of agreement with overlapping and concurrent surgery and anesthesia, as well as with trainee involvement. On average, respondents "strongly agree" with the need to be informed about overlapping or concurrent surgery. They "disagree" with both overlapping and concurrent scheduling, and "disagree" with trainees operating without direct supervision, even for "noncritical" parts. Informing parents about the presence of a back-up surgeon or research demonstrating safety of simultaneous surgery did not make them agreeable to simultaneous scheduling. Parents have a strong desire to be informed of simultaneous spinal surgery and anesthesia as part of consent on behalf of their children. Their disagreement with simultaneous surgery, as well as with trainees operating without direct supervision, suggests discordance with current guidelines and practice and should inform the national conversation moving forward. N/A.

Energy-Efficient Full-Duplex Concurrent Scheduling Based on Contention Graph in mmWave Backhaul Networks

In the fifth generation (5G) era, dense deployment of small cells and full-duplex (FD) technology applications are two key features of millimeter-wave (mmWave) wireless communication systems, which offer the opportunity to meet the explosive growth of data service requirements. It is the beamforming and advances in analog as well as digital self-interference (SI) cancellation schemes that improve the network capacity in mmWave wireless backhaul networks. To achieve power saving and further network performance optimization, we propose a FD concurrent transmission mechanism employed in a mmWave backhaul network. Contention graph is constructed in consideration of multi-user interference (MUI), SI, and FD transmission constraints. Then flow-grouping and power control algorithms are proposed based on the contention graph. We evaluate the performance of the proposed algorithm in terms of energy consumption, achievable network throughput, and energy efficiency. The impact of the interference threshold on the system performance is also investigated when the distribution of base stations (BSs), traffic loads, and maximum transmission powers change. Simulation results illustrate that with proper SI cancellation and interference threshold, the proposed concurrent mechanism outperforms time-division multiple access (TDMA), half-duplex (HD) concurrent transmission, and FD concurrent transmission without power control.

Stimulus comparison: Effects of the pre-exposure schedule and instructions for perceptual learning and attention

This study aimed to test the effects of the preexposure schedule and certain kinds of verbal instructions for pre-exposure in perceptual learning and attention to the distinctive features of the stimuli. For this, in two experiments adult human participants received concurrent or blocked pre-exposure to two stimuli, and were then required to judge them as same or different in a target identification task. During pre-exposure, participants could receive unspecific instructions to look only at the stimuli (Experiments 1 and 2), asking for “same/different” judgments (Experiments 1 and 2), or only for “different” or “same” judgments (Experiment 2), whilst the dwell time on the distinctive and common features of the stimuli was also recorded. Regardless of the instructions, Experiment 1 found a clear benefit of the concurrent schedule relative to the blocked schedule in the ability to differentiate the stimuli, accompanied by a preference to look at the distinctive features of the stimuli. In the concurrent preexposure condition, the instructions asking for same/different judgments boosted stimulus differentiation in general, along with an attentional shift, while a clear effect of instructions was not found for the blocked preexposure conditions. Experiment 2 further found that whilst such effects of the instructions for the concurrent schedule might appear when the participants were asked uniquely whether the stimuli were the same, these were stronger when the instructions asked explicitly whether the stimuli were different. According to these novel findings, the benefit of the concurrent preexposure schedule for human perceptual learning might arise from an attentional shift toward the distinctive elements; the instructions encouraging the search for stimulus differences are not needed for either stimulus differentiation or an attentional shift during concurrent preexposure, even though such instructions might enhance both effects. Several valuable implications of these findings for human and non-human perceptual learning are discussed.

Environment tracking and signal following in a reinforcer-ratio reversal procedure

Several studies suggest that the degree of control by reinforcer ratios (environment tracking) and by exteroceptive stimuli that signal future reinforcer availability (signal following) depends on environmental certainty: As reinforcers become more likely at one location, environmental contingencies exert stronger control and exteroceptive stimuli exert weaker control. This research has not yet been extended to environments in which reinforcer availability changes across time, even though such changes are present in most natural environments. Thus, in the present experiment, we examined environment tracking and signal following in a concurrent schedule in which the reinforcer ratio reversed to its reciprocal 30 s after a reinforcer delivery and keylight-color stimuli signaled the likely or definite time or location of the next reinforcer. Across conditions, we manipulated environmental certainty by varying the probability of reinforcer deliveries on the locally richer key. This made the location of future reinforcers at a particular time more or less certain, but did not change the overall reinforcer ratio. Changes in local environmental certainty had little to no effect on environment tracking and signal following; in all conditions, keylight-color stimuli strongly controlled choice and reinforcer ratios exerted weak control. The present findings suggest that the extent of environment tracking and signal following is primarily determined by global, not local, environmental certainty.

Will work less for food: Go/No-Go training decreases the reinforcing value of high-caloric food

Consistently inhibiting responses to palatable food stimuli increases motor suppression for those stimuli and reduces their hedonic value, suggesting a close link between motor inhibition and food reward. The current study aimed to investigate whether GNG training also reduces the motivational, reinforcing value of palatable, high-calorie food. Participants completed either GNG training for high-calorie food or a control task. This was followed by a Concurrent Schedules Task (CST) to measure the reinforcing value of high-calorie food. As hypothesized, participants in the GNG condition showed reduced high-caloric food reinforcement, as indexed by the number of key presses participants were willing to execute to obtain the food, compared to the control condition. This difference between GNG and control, however, was only significant when the response requirement to obtain high-calorie food was high. These results suggest that GNG training not only reduces hedonic food value but also the motivational, reinforcing value of food.

Pre-exposure Schedule Effects on Generalization of Taste Aversion and Palatability for Thirsty and Not Thirsty Rats.

The study reported four experiments aiming to test the effects of the pre-exposure schedule and water deprivation on the generalization of a conditioned taste aversion in rats, with a particular focus on testing whether or not the concurrent schedule might enhance generalization. In two experiments, non-water-deprived rats received concurrent, intermixed, or blocked exposure to a sweet-acid solution and a salty-acid solution before conditioning of one of these compounds and testing of both flavors. During pre-exposure, the rats consumed a greater amount of the sweet-acid solution than the salty-acid solution (Experiments 1 and 2), consumption of the former increasing during pre-exposure while consumption of the latter decreased (Experiment 1). Furthermore, consumption of the salty-acid solution was lower during concurrent than intermixed or blocked pre-exposure (Experiment 1 and 2) while consumption of the sweet-acid solution was greater during intermixed than concurrent or blocked pre-exposure (Experiment 1). It is discussed whether the pre-exposure schedule might modify stimulus perception beyond the mere enhancement of stimulus differentiation, by, for instance, affecting the palatability of gustatory stimuli. Evidence for enhanced generalization after concurrent pre-exposure was not found for either deprived (Experiments 1, 2, and 3) or non-deprived rats (Experiments 3 and 4), with deprivation leading to a general increase in consumption of both the conditioned and test flavors. This then raised the question of whether or not concurrent pre-exposure to flavors always increases generalization between them. The present study highlights the importance of this issue for various accounts of perceptual learning.

Functional Communication Training and Demand Fading Using Concurrent Schedules of Reinforcement

Demand fading, a schedule thinning procedure for escape-maintained behaviors, typically includes an escape extinction component. The purpose of this study was to examine the effectiveness of demand fading with alternative reinforcement utilizing concurrent reinforcement schedules without extinction. During demand fading, aggression and requests emitted prior to meeting the task completion criterion were reinforced with short, low-quality breaks, but requests emitted following the task completion criterion were reinforced with long, high-quality breaks. Results suggest that concurrent schedules of reinforcement may be an effective alternative to extinction as a component of demand fading.