Signal functions in delayed reinforcement

Three experiments were conducted with pigeons to examine the role of the signal in delay-of-reinforcement procedures. In the first, a blackout accompanying a period of nonreinforcement increased key-peck response rates maintained by immediate reinforcement. The effects of dissociating the blackout from the delay interval were examined in the second experiment. In three conditions, blackouts and unsignaled delays were negatively correlated or occurred randomly with respect to one another. A signaled delay and an unsignaled delay that omitted the blackouts were studied in two other conditions. All delay-of-reinforcement conditions generally produced response rates lower than those produced by immediate reinforcement. Signaled delays maintained higher response rates than did any of the various unsignaled-delay conditions, with or without dissociated blackouts. The effects of these latter conditions did not differ systematically from one another. The final experiment showed that response rates varied as a function of the frequency with which a blackout accompanied delay intervals. By eliminating a number of methodological difficulties present in previous delay-of-reinforcement experiments, these results suggest the importance of the signal in maintaining responding during delay-of-reinforcement procedures and, conversely, the importance of the delay interval in decreasing responding.     

Stimulus and reinforcer relativity in multiple schedules: Local and dimensional effects on sensitivity to reinforcement

Pigeons' responses in two successive components of multiple schedules were reinforced according to variable-interval schedules of reinforcement that varied over five different conditions. Within each session of all conditions, line orientations of 0°, 30°, or 45° in Component 1 alternated with orientations of 45°, 60°, or 90° in Component 2. Response rates were recorded in three successive subintervals of each component. Ratios were taken between the response rate in each Component 1 line orientation and the response rate in each Component 2 orientation. These ratios were found to be power functions of the corresponding ratios of obtained reinforcement rates. Sensitivity of response ratios to changes in reinforcer ratios, given by the value of the exponent of the power function, increased systematically with increasing disparity between the dimensional values of orientation stimuli. In addition, sensitivity decreased systematically over successive subintervals of components, that is, with increasing time since component alternation. Dimensional and local (subinterval) effects interacted in that sensitivity increased with stimulus disparity to a far greater extent in the first subinterval than later in components. The data could be described by a combination of rectangular hyperbolae which attributed the interaction between local and dimensional effects to limits set by local effects on the extent that stimulus differences could affect sensitivity.     

The effects of delayed reinforcement on free-operant responding

In previous studies of delayed reinforcement, response rate has been found to vary inversely with the response-reinforcer interval. However, in all of these studies the independent variable, response-reinforcer time, was confounded with the number of reinforcers presented in a fixed period of time (reinforcer frequency). In the present study, the frequency of available reinforcers was held constant, while temporal separation between response and reinforcer was independently manipulated. A repeating time cycle, T, was divided into two alternating time periods, t^D and t^Δ. The first response in t^D was reinforced at the end of the prevailing T cycle and extinction prevailed in t^Δ. Two placements for t^D were defined, an early t^D placement in which t^D precedes t^Δ and a late t^D placement in which t^D follows t^Δ. The duration of the early and late t^D was systematically decreased from 30 seconds (i.e., t^D = T) to 0.1 second. Manipulation of t^D placement and duration controlled the temporal separation between response and reinforcement, but it did not affect the frequency of programmed reinforcers, which was 1/T. The results show that early and late t^D placements of equal duration have similar overall effects upon response rate, reinforcer frequency, responses per reinforcer, and obtained response-reinforcer temporal separation. A stepwise regression analysis using log response rate as the dependent variable showed that the obtained delay was a significant first-step variable for six of eight subjects, with obtained reinforcer frequency significant for the remaining two subjects.     

Confirmation of linear system theory prediction: Changes in Herrnstein's k as a function of changes in reinforcer magnitude

Eight human subjects pressed a lever on a range of variable-interval schedules for 0.25¢ to 35.0¢ per reinforcement. Herrnstein's hyperbola described seven of the eight subjects' response-rate data well. For all subjects, the y-asymptote of the hyperbola increased with increasing reinforcer magnitude and its reciprocal was a linear function of the reciprocal of reinforcer magnitude. These results confirm predictions made by linear system theory; they contradict formal properties of Herrnstein's account and of six other mathematical accounts of single-alternative responding.     

Comparing the effects of static and dynamic signals during multiple schedules

The extent to which multiple schedules are an effective schedule thinning method following functional communication training (FCT) relies on the control the schedule-correlated stimuli exert over behavior. Thus, the stimuli used to signal the schedule in place (e.g., reinforcement and extinction) in a multiple schedule arrangement require special attention. To date, the majority of the research on multiple schedules has evaluated the use of different arbitrary signals as schedule-correlated stimuli (e.g., poster boards). These signals are considered static as they lack movement. More recently, some studies have successfully used dynamic signals, which include movement or animation, within multiple schedule arrangements. However, the extent to which one type of signal may result in faster stimulus control over behavior has not been evaluated. Thus, the purpose of this study was to compare the use of static and dynamic signals as schedule-correlated stimuli in multiple schedules used within the context of FCT. Four children diagnosed with autism spectrum disorder participated in the study. The results suggest that no differences in discriminated manding were observed for three out of four participants. Only dynamic signals resulted in discriminated manding for one participant.     

About Skinner and time: behavior-analytic contributions to research on animal timing

The article discusses two important influences of B. F. Skinner, and later workers in the behavior-analytic tradition, on the study of animal timing. The first influence is methodological, and is traced from the invention of schedules imposing temporal constraints or periodicities on animals in The Behavior of Organisms, through the rate differentiation procedures of Schedules of Reinforcement, to modern temporal psychophysics in animals. The second influence has been the development of accounts of animal timing that have tried to avoid reference to internal processes of a cognitive sort, in particular internal clock mechanisms. Skinner's early discussion of temporal control is first reviewed, and then three recent theories-Killeen & Fetterman's (1988) Behavioral Theory of Timing; Machado's (1997) Learning to Time; and Dragoi, Staddon, Palmer, & Buhusi's (2003) Adaptive Timer Model-are discussed and evaluated.     

Roger T. Kelleher, behavior analyst

Roger T. Kelleher, rightly known as one of the foremost contributors to behavioral pharmacology, also made many important contributions to the experimental analysis of behavior. He participated significantly in the development of the discipline, through both his research and his editorial contributions to thisjournal. This article summarizes his contributions to the field of behavior analysis. His most significant empirical and conceptual contributions to behavior analysis came in two domains-conditioned reinforcement and the power of schedules of reinforcement. His accomplishments in these two domains still serve as principal foundations for modern research and theory.     

Brief presentations are sufficient for pigeons to discriminate arrays of same and different stimuli

Four pigeons first learned to discriminate 16-item arrays of same from different pictorial stimuli. They were then tested with reduced exposure to the pictorial arrays, brought about by changes in the stimulus viewing requirement under fixed-ratio (FR) and fixed-interval (FI) schedules. Increasing the FR requirement enhanced discriminative performance up to 10 pecks; increasing the FI requirement enhanced discriminative performance up to 5 s. Exposures to the stimulus arrays averaging only 2 s supported reliable discrimination. Pigeons thus discriminate same from different stimuli with considerable speed, suggesting that same-different discrimination behavior is of substantial adaptive significance.     

Concurrent schedules: short- and long-term effects of reinforcers

Five pigeons were trained on concurrent variable-interval schedules in a switching-key procedure. The overall rate of reinforcement was constant in all conditions, and the ratios of reinforcers obtainable on the two alternatives were varied over seven levels. Each condition remained in effect for 65 sessions, and the last 50 sessions of data from each condition were analyzed. The most recently obtained reinforcer had the largest effect on current preference, but each of the eight previously obtained reinforcers had a small measurable effect. These effects were larger when the reinforcer ratio was more extreme. A longer term effect of reinforcement was also evident, which changed as a function of the reinforcer ratio arranged. More local analyses showed regularities at a reinforcer-by-reinforcer level and large transient movements in preference toward the just-reinforced alternative immediately following reinforcers, followed by a return to stable levels that were related to the reinforcer ratio in effect. The present data suggest that the variables that control choice have both short- and long-term effects and that the short-term effects increased when the reinforcer ratios arranged were more extreme.