Differential effects of midazolam and pentylenetetrazole on behavioral repetition and variation

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.

Response-reinforcer dependency and resistance to change

The effects of the response-reinforcer dependency on resistance to change were studied in three experiments with rats. In Experiment 1, lever pressing produced reinforcers at similar rates after variable interreinforcer intervals in each component of a two-component multiple schedule. Across conditions, in the fixed component, all reinforcers were response-dependent; in the alternative component, the percentage of response-dependent reinforcers was 100, 50 (i.e., 50% response-dependent and 50% response-independent) or 10% (i.e., 10% response-dependent and 90% response-independent). Resistance to extinction was greater in the alternative than in the fixed component when the dependency in the former was 10%, but was similar between components when this dependency was 100 or 50%. In Experiment 2, a three-component multiple schedule was used. The dependency was 100% in one component and 10% in the other two. The 10% components differed on how reinforcers were programmed. In one component, as in Experiment 1, a reinforcer had to be collected before the scheduling of other response-dependent or independent reinforcers. In the other component, response-dependent and -independent reinforcers were programmed by superimposing a variable-time schedule on an independent variable-interval schedule. Regardless of the procedure used to program the dependency, resistance to extinction was greater in the 10% components than in the 100% component. These results were replicated in Experiment 3 in which, instead of extinction, VT schedules replaced the baseline schedules in each multiple-schedule component during the test. We argue that the relative change in dependency from Baseline to Test, which is greater when baseline dependencies are high rather than low, could account for the differential resistance to change in the present experiments. The inconsistencies in results across the present and previous experiments suggest that the effects of dependency on resistance to change are not well understood. Additional systematic analyses are important to further understand the effects of the response-reinforcer relation on resistance to change and to the development of a more comprehensive theory of behavioral persistence.

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.

Reaparecimento de sequências com diferentes números de respostas em contextos de extinção e de variação

RESUMO O reaparecimento de uma resposta previamente extinta quando os reforços para uma resposta alternativa são descontinuados é denominado ressurgência. Foram investigados os efeitos de três variáveis sobre o reaparecimento de sequências de respostas: probabilidade da sequência (alta e baixa), contexto de teste (extinção e variação operante) e número de respostas por sequência (três e cinco). Sequências muito prováveis reapareceram mais frequentemente que sequências pouco prováveis, o reaparecimento da sequência alvo foi mais frequente no contexto de extinção do que de variação e o reaparecimento da sequência alvo variou inversamente ao número de respostas por sequência. O reaparecimento da sequência alvo, entretanto, não foi conceitualizado como ressurgência, uma vez que sua frequência foi menor que a das sequências controle.