Timberlake's behavior systems: A paradigm shift toward an ecological approach.

Timberlake's Behavior Systems model constitutes a discontinuity in theoretical and empirical consequences of traditional approaches to the experimental study of behavior, such as operant as well as classical conditioning. Here we consider the synergy of an animal-centered approach and acknowledge that niche-related behaviors as functional activities create synergy with Gibson's ecological approach, in at least three terms. These are: an ecological stance for learning and behavior, hierarchical organization of behavior systems, and affordances implied in the process of tuning experimental procedures. The ideas expressed herein favor a paradigm shift toward an ecological approach to behavioral science.

Discrete and continuous stimulus control in the A-not-B sandbox task.

In behavior-analytic studies of generalization, stimulus control appears to be discrete rather than continuous: after two behavior patterns R1 and R2 are trained in the presence of stimuli A and B, respectively, tests of intermediate stimuli evoke R1 and R2 in varying proportions rather than an actual mix of R1 and R2. By contrast, theories and data from developmental psychology suggest that spatial searches in the A-not-B sandbox task may be continuous: after burying an object at position A and then at position B, children may search the sand surface at positions that are actually intermediate between A and B. The published evidence so far has been ambiguous, however, because researchers typically report group means rather than response distributions, and group means intermediate between A and B might be statistical artefacts of averaging across subjects. Here we report two A-not-B sandbox studies designed to address this issue. In Experiment 1, which employed a purely motor A-not-B procedure, stimulus control was found to be continuous. In Experiment 2, which used a purely observational A-not-B procedure, stimulus control was basically discrete but also exhibited continuous aspects. These findings are discussed in relation to cognitive and behavior-analytic approaches to stimulus control.

An affordance analysis of unconditioned lever pressing in rats and hamsters.

Two experiments were conducted to assess the effect of lever height on lever pressing that was not explicitly reinforced - i.e., operant-level responding. Two rodent species were used as subjects, rats (Experiment 1) and hamsters (Experiment 2), aiming to compare the behavioral support offered by one lever at various heights relative to the subjects' body size. Results showed that lever height had a substantial effect on response rate. The rate of lever pressing varied similarly for rats and hamsters as a function of lever height, when lever height was re-scaled relative to body size. The distribution of inter-response times showed that lever pressing was organized in bouts separated by pauses. This pattern of responding was accurately described in both experiments by a mixture of two exponential distributions. These findings support an analysis of affordances in non-human species.

The effect of methylphenidate and rearing environment on behavioral inhibition in adult male rats.

RATIONALE: The ability to withhold reinforced responses-behavioral inhibition-is impaired in various psychiatric conditions including Attention Deficit Hyperactivity Disorder (ADHD). Methodological and analytical limitations have constrained our understanding of the effects of pharmacological and environmental factors on behavioral inhibition. OBJECTIVES: To determine the effects of acute methylphenidate (MPH) administration and rearing conditions (isolated vs. pair-housed) on behavioral inhibition in adult rats. METHODS: Inhibitory capacity was evaluated using two response-withholding tasks, differential reinforcement of low rates (DRL) and fixed minimum interval (FMI) schedules of reinforcement. Both tasks made sugar pellets contingent on intervals longer than 6 s between consecutive responses. Inferences on inhibitory and timing capacities were drawn from the distribution of withholding times (interresponse times, or IRTs). RESULTS: MPH increased the number of intervals produced in both tasks. Estimates of behavioral inhibition increased with MPH dose in FMI and with social isolation in DRL. Nonetheless, burst responding in DRL and the divergence of DRL data relative to past studies, among other limitations, undermined the reliability of DRL data as the basis for inferences on behavioral inhibition. CONCLUSIONS: Inhibitory capacity was more precisely estimated from FMI than from DRL performance. Based on FMI data, MPH, but not a socially enriched environment, appears to improve inhibitory capacity. The highest dose of MPH tested, 8 mg/kg, did not reduce inhibitory capacity but reduced the responsiveness to waiting contingencies. These results support the use of the FMI schedule, complemented with appropriate analytic techniques, for the assessment of behavioral inhibition in animal models.

Effects of reinforcer quality and step size on rats' performance under progressive ratio schedules.

The Mathematical Principles of Reinforcement (MPR) model accurately predicts performance in fixed ratio (FR) schedules of reinforcement. The aim of the present study was to assess the generality of MPR with rats responding under progressive ratio (PR) schedules of different step sizes (PR1 or PR3) that provided either food or saccharin pellets. The results showed that the rats responding for saccharin pellets produced higher breakpoints (i.e., completed higher ratios) than those responding for food pellets. In terms of theoretical parameters, one finding unanticipated on the basis of MPR was that the a parameter (specific activation) was higher for the PR3 schedules. This finding suggests that specific activation may be affected indirectly by motor parameters of the task.