Discriminative control of variability: effects of successive stimulus reversals

Effects of variability requirements on difficult sequence learning

The present study investigated the effects of variability requirements on learning difficult target sequences in humans. Twenty university students emitted five-response sequences. For the experimental groups, 30 nontarget sequences were reinforced according to the Lag-10 variation criterion or the Lag-3 repetition criterion across conditions. For the control groups, the probability of reinforcers for nontarget sequences was yoked to that obtained by the experimental groups. In addition, for both groups, two difficult target sequences were continuously reinforced. U values were higher with the Lag-10 variation criterion than with the Lag-3 repetition criterion for the experimental groups and were unsystematic for the control groups. Higher U values ​​were accompanied by a random pattern in the emission of nontarget sequences for all groups. Higher levels of variability, regardless of whether they were directly produced by reinforcement or were contingency induced, facilitated learning of difficult target sequences.

An investigation of resurgence of reinforced behavioral variability in humans

The present study examined resurgence of reinforced variability in college students, who completed a 3-phase computer-based variability task. In the first phase, baseline, points were delivered for drawing rectangles that sufficiently differed from previous rectangles in terms of a target dimension (size or location, counterbalanced) but were sufficiently similar in terms of the alternative dimension. In the second phase, alternative, points were only delivered for rectangles that were sufficiently different in terms of the alternative dimension, but repetitive in terms of the target dimension. In the third phase, extinction, no points were delivered. In baseline, participants made rectangles that were highly varied in terms of the target dimension and less varied in terms of the alternative dimension, and vice versa in the alternative phase. During extinction, levels of variability increased for the target dimension, providing evidence for resurgence of reinforced variability of a specific dimension of behavior. However, levels of variability also remained high for the alternative dimension, indicating that extinction-induced response variability may also have impacted the results. Although future research is needed to explore other explanations, the results of this study replicate prior research with pigeons and provide some support for the notion of variability as an operant.

A Critical Review of the Support for Variability as an Operant Dimension

There is abundant evidence that behavioral variability is more predominant when reinforcement is contingent on it than when it is not, and the interpretation of direct reinforcement of variability suggested by Page and Neuringer, Journal of Experimental Psychology: Animal Behavior Processes, 11(3), 429-452 (1985) has been widely accepted. Even so, trying to identify the underlying mechanisms in the emergence of stochastic-like variability in a variability contingency is intricate. There are several challenges to characterizing variability as directly reinforced, most notably because reinforcement traditionally has been found to produce repetitive responding, but also because directly reinforced variability does not always relate to independent variables the same way as more commonly studied repetitive responding does. The challenging findings in variability experiments are discussed, along with alternative hypotheses on how variability contingencies may engender the high variability that they undeniably do. We suggest that the typical increase in behavioral variability that is often demonstrated when reinforcement is contingent on it may be better explained in terms of a dynamic interaction of reinforcement and extinction working on several specific responses rather than as directly reinforced.

Choice for reinforced behavioral variability in children with autism spectrum disorder

Although individuals with autism spectrum disorder (ASD) tend to behave repetitively, certain reinforcement contingencies (e.g., lag schedules) can be used to increase behavioral variability. In a lag schedule, reinforcers only follow responses that differ from recent responses. The present study was designed to promote variable play behavior in preschoolers with ASD interacting with playsets and figurines and to assess preference for variability and repetition contingencies. Data have shown a preference for variability in pigeons and college students, but this effect has not been explored in clinical populations. In this experiment, preschoolers with ASD were taught to discriminate between variability and repetition contingencies. Only play behaviors that met a lag schedule were reinforced in the presence of one color, and only repetitive behaviors were reinforced in the presence of another. After differential performance was established, participants experienced a concurrent chains schedule. Participants chose between the colors taught in training and then completed a play session with the selected contingency. One participant selected variability and repetition equally. The other participants showed a slight preference for variability. These results indicate that some individuals with ASD may play repetitively, not because they prefer repetition, but because they require additional teaching to play variably.

Exploring the interoceptive stimulus effects of nicotine and varenicline

Learning processes associated with nicotine influence the development of addiction to tobacco products. In the present report, we are interested in the interoceptive stimulus effects of nicotine acquiring control over appetitive behaviors - specifically, reward seeking. Also of interest is the current smoking cessation drug, varenicline (Chantix®). Varenicline, with its nicotine-like stimulus effects, can decrease withdrawal and cravings for a subset of individuals addicted to nicotine, though relapse is still common. We trained rats (N = 48) with nicotine (0.4 mg/kg, SC) as an excitatory stimulus (i.e., paired with sucrose) in a drug-discriminated goal-tracking (DGT) task. There was no access to sucrose on interspersed saline days. After acquisition of the initial nicotine-saline discrimination, rats were separated into four groups to test discrimination reversal and drug substitution. The control group maintained nicotine as the excitatory stimulus (NIC+). The substitution group had varenicline (1 mg/kg) replace nicotine as the stimulus paired with sucrose (VAR+). One reversal group had nicotine signal the absence of sucrose (i.e., now available on intermixed saline sessions; NIC-). The last group was similar to the NIC- group except varenicline replaced nicotine on non-reinforced sessions (VAR-). We found that varenicline fully substituted as the training stimulus when the drug-sucrose relation remained in place (VAR+). Both reversal groups acquired the new discrimination, albeit slowly and more variable for the VAR- group in comparison to NIC-. There was an effect of group during substitution testing. Specifically, nicotine fully substituted for varenicline regardless of condition. However, varenicline only partially substituted for the nicotine stimulus. At the start of extinction, responding mimicked that of the rats training condition. However, by extinction session 12, all groups maintained similarly low levels of responding. These findings show nicotine and varenicline share stimulus elements, yet the conclusion of partial to full substitution depends on the nature of the testing protocol.

An analysis of procedures that affect response variability

Response variability is sensitive to antecedent and consequent manipulations. Researchers have investigated inducement, direct production through reinforcement, and stimulus control of response variability. Recently, researchers have shown that lag reinforcement schedules reliably increase variability but may also produce higher-order stereotypy. There has been limited investigation of appropriate variability levels and alternation between repetition and variation. In a three-part study, we evaluated levels of variability across a group of children, the effects of various procedures on producing response variability and novelty, and the use of schedule-correlated stimuli for producing rapid alternation between repetition and variation. In Study 1, there was a nearly bimodal distribution of children emitting either low or high variability. In Study 2, for most children, fixed lag 4 and variable lag 4 schedules produced the highest levels of variability and novelty. In Study 3, responding was brought under control of schedule-correlated stimuli, allowing for rapid alternation between repetition and variation.

Differential effects of 3,4-methylenedioxymethamphetamine, methamphetamine, meta-Chlorophenylpiperazine, and scopolamine on behavioral repetition versus variation in rats

Acute administration of drugs of abuse, such as MDMA and methamphetamine, disrupts performance on many operant tasks, for example, those used to study memory. This might occur in part because drugs make behavior, in general, more repetitive or more variable, or because they produce a more global disruption to performance. The current study explored this across two experiments by employing Neuringer's 'reinforced variability' procedure. Varied behavior was reinforced at some times during the session and repetitive behavior at other times; lights signalled the behavior required. This procedure allowed an investigation of whether a particular drug made behavior more variable (affected behavior when repetition was required), more repetitive (affected behavior when variability was required), or produced a global disruption (affected both components). In Experiment 1, MDMA increased variability while methamphetamine affected both components. In Experiment 2, m-CPP affected both components while scopolamine affected both components at lower doses and increased variability at higher doses. These results indicate both that the reinforced variability procedure can be used to isolate the specific effects of drugs of abuse on the variability of behavior, and that the specific impact of a given drug needs to be considered when interpreting pharmacological disruptions to operant task performance.

Controlling and Predicting Unpredictable Behavior

Behaving predictably can be advantageous in some situations, but unpredictability can also be advantageous in some competitive situations like sports, games, and war. Can, however, unpredictable behavior be conditioned? If a contingency of reinforcement based upon the predictability of behavior generates unpredictable responding, is it possible to conclude that predictability is itself a reinforceable dimension of behavior? In this paper, I address these questions by examining the concept and measures of predictability and the procedures generally used to increase unpredictable responding. I discuss the hypothesis that contingencies based on response frequency shape the generalized operant "to vary" and an alternative hypothesis that such contingencies generate unpredictable responding by balancing the strength of each alternative response over time. I discuss the findings that support the balance hypothesis as well as its limitations. I conclude that the two alternative hypotheses may be complementary in explaining unpredictable responding.

Operant variability: a conceptual analysis

Some researchers claim that variability is an operant dimension of behavior. The present paper reviews the concept of operant behavior and emphasizes that differentiation is the behavioral process that demonstrates an operant relation. Differentiation is conceived as change in the overlap between two probability distributions: the distribution of reinforcement probability as a function of some response property (S distribution) and the probability distribution of the response property itself (R distribution). This concept implies that the differentiation process can be measured only if S distribution and R distribution are both established on the same response property. To determine whether the differentially reinforced behavioral variability fits the proposed concept of operant behavior, I examine the main procedures (lag n and threshold procedures) and the main dependent variable (U value) employed in the studies of operant variability. Because lag n and threshold procedures establish their S distributions on properties distinct from U value, differentiation cannot be measured over the change in U value. I conclude that studies of operant variability have failed to provide a direct demonstration that variability is an operant dimension of behavior. Hence, studies in which measures of variability provide a basis to measure differentiation can better support the claim that variability is an operant dimension of behavior.