Effect of initial-link length on the sensitivity of the post-reinforcer delay

For a long time, post-reinforcer delays have been considered to have no effect on choice. The most influential choice models therefore do not consider such delays. Recently, however, some studies reported that post-reinforcer delays affect choice behavior in pigeons. One such study (Mazur, 2006) concluded that a short initial link increases the sensitivity to post-reinforcer delays in concurrent-chains schedules. However, this study did not use typical concurrent-chains schedule procedures, in which the number of reinforcements differs between alternatives, and did not systematically analyze the effect of the systematic post-reinforcer delay. The current study therefore examined whether the length of the initial link modulates the post-reinforcer delay effect on choice with standard concurrent-chains schedules and by systematically varying both the initial link and the post-reinforcer delay. As the results, the shorter the initial link length, the larger the effect of the post-reinforcer delay. Models with post-reinforcer delays predicted choice behavior better than models without, but pigeons were more insensitive to delays than the model prediction for long initial links. These findings provide important information for models on choice, and suggest that experiments should be designed with more caution with regards to post-reinforcer delays.

Research on self-control: An integrating framework

The tendency to choose a larger, more delayed reinforcer over a smaller, less delayed one has frequently been termed “selfcontrol.” Three very different research traditions – two models emphasizing the control of local contingencies of reinforcement (Mischel's social learning theory and Herrnstein's matching law) and molar maximization models (specifically optimal foraging theory) – have all investigated behavior within the self-control paradigm. A framework is proposed to integrate research from all three research areas. This framework consists of three parts: a procedural analysis, a causal analysis, and a theoretical analysis. The procedural analysis provides a common procedural terminology for all three areas. The causal analysis establishes that, in all three research traditions, self-control varies directly with the current physical values of the reinforcers; that is, choices increase with reinforcer amount and decrease with reinforcer delay. But self-control also varies according to past events to which a subject has been exposed, and according to current factors other than the reinforcers. Each of the three models has therefore incorporated these indirect effects on self-control by postulating unobservable mechanisms. In all three cases, these mechanisms represent a subject's behavior as a function of a perceived environment. The theoretical analysis demonstrates that evolutionary theory can encompass the research from all three areas by considering differences in the adaptiveness of self-control in different situations. This integration provides a better and more predictive description of self-control.