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.

The effect of lever height on the microstructure of operant behavior.

The effect of lever height on the temporal organization of reinforced lever pressing was examined. Lever pressing was reinforced on a variable-interval 30-s schedule in rats, with lever height manipulated across six successive conditions. Parameters of the organization of responses in bouts (bout length distribution, bout-initiation rate, within-bout rate, and sequential dependency) were estimated. These estimates revealed (1) a qualitative change in the distribution of IRTs and their sequential dependency when the lever was too high, (2) a mixture of geometrically-distributed bout lengths at all lever heights, and (3) longer bouts at lower and intermediate lever heights. In accordance with previous data, these findings suggest that lower and intermediate lever heights favored lever pressing with longer bout lengths, faster bout initiation, faster within-bout responding, and more sequentially dependent timing. These results underscore the disociability of motoric capacity in operant performance, and may reflect the influence of the body size on the temporal organization of the operant.

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.