Procrastination by pigeons with fixed-interval response requirements.

Two experiments studied the phenomenon of procrastination, in which pigeons chose a larger, more delayed response requirement over a smaller, more immediate response requirement. The response requirements were fixed-interval schedules that did not lead to an immediate food reinforcer, but that interrupted a 55-s period in which food was delivered at random times. The experiments used an adjusting-delay procedure in which the delay to the start of one fixed-interval requirement was varied over trials to estimate an indifference point--a delay at which the two alternatives were chosen about equally often. Experiment 1 found that as the delay to a shorter fixed-interval requirement was increased, the adjusting delay to a longer fixed-interval requirement also increased, and the rate of increase depended on the duration of the longer fixed-interval requirement. Experiment 2 found a strong preference for a fixed delay of 10 s to the start of a fixed-interval requirement compared to a mixed delay of either 0 or 20 s. The results help to distinguish among different equations that might describe the decreasing effectiveness of a response requirement with increasing delay, and they suggest that delayed reinforcers and delayed response requirements have symmetrical but opposite effects on choice.     

Response Form, Force, And Number: Effects On Concurrent-schedule Performance

Six hens responded on concurrent variable-interval (key-peck) variable-interval (door-push) schedules of reinforcement in which the second-order (fixed-ratio) requirements on the alternatives (Experiment 1) or the required door forces (Experiment 2) were varied. The key-peck and door-push response (measured as fixed-ratio completion) and time data were well described by the generalized matching law. However, the manipulations of fixed-ratio requirement and required response force differed in their effects. The manipulations of fixed-ratio size affected the response and time measures differently, producing fairly constant, multiplicative biases only in terms of response allocation. It was argued that variations in fixed-ratio size necessarily change the time allocated to that response unit, and thus changes in time bias were not necessarily a fundamental effect of changing the ratio. In contrast, the changes in response bias were a fundamental result of changes in ratio size. The response-force manipulations produced similar bias shifts in terms of response and time allocation, but they appeared to combine with relative reinforcement rate to affect choice interactively. Specifically, behavior appeared to be biased towards the least effortful (i.e., key-peck) response, but the increases in door force had a larger effect on bias when the hens were making this response infrequently (on a lean schedule). The different effects of the fixed-ratio and response-force manipulations on concurrent performance were partially accounted for by the differing times required to complete each response unit under those manipulations, but this would not account for the interaction. The interaction would be consonant with increased response effort decreasing the effective value of the associated reinforcement schedule.     

Ratio size and cocaine concentration effects on oral cocaine-reinforced behavior.

Monkeys were given a choice between cocaine solutions and water under concurrent fixed-ratio reinforcement schedules. The operant response was spout contact. Six rhesus monkeys served as subjects. The cocaine concentration was varied from 0.0125 to 0.8 mg/ml, and the fixed-ratio value was varied from 8 to 128. Cocaine maintained higher response rates than did water over a wide range of conditions. Response rate and number of cocaine deliveries per session were inverted U-shaped functions of concentration. These functions were shifted to the right as the fixed ratio was increased. The number of cocaine deliveries was more persistent as fixed-ratio value was increased when the unit dose was larger rather than smaller. Cocaine consumption was analyzed as a function of unit price (fixed-ratio value divided by cocaine concentration), and unit price accounted for between 77% and 92% of the variance in cocaine consumption for individual monkeys. The current data support the claim that a drug's reinforcing effects increase directly with dose and underscore the need to gather parametric data when examining the effects of experimental manipulations on a drug-reinforced baseline.     

Effects of unsignaled delay of reinforcement on preference and resistance to change

In Phase 1, pigeons were trained on a concurrent chain in which a 3-s unsignaled delay of reinforcement was imposed on responding in a terminal link in some conditions. Preference for that terminal link was always reduced in comparison with conditions in which there was no delay, substantially so for 3 of the 4 pigeons. In Phase 2, pigeons responded in a two-component multiple schedule. The scheduled rates of reinforcement were equal, but a 3-s unsignaled delay was imposed in one component. Resistance of responding to prefeeding and extinction was reduced in the delay component for the same 3 subjects for which the data had shown strong effects of delay on preference. Systematic observation revealed differences in response topography. In the delay component, subjects oriented more closely to the key and responses were less forceful compared with the no-delay component. Our results give further evidence that preference and resistance to change covary within subjects. However, they challenge the premise that the critical determiners of preference (i.e., terminal-link value) and resistance to change (behavioral mass) may be quantified purely in terms of stimulus—reinforcer relations.     

Conditioned reinforcement dynamics in three-link chained schedules.

In two experiments rats were trained on three-link concurrent-chains schedules of reinforcement. In Experiment 1, additional entries to one terminal link were added during one of the middle links to a baseline schedule that was otherwise equal for the two chains, and, depending on the condition, these additional terminal-link presentations ended either in food or in no food. When food occurred, preference was always in favor of the chain with the additional terminal-link presentations (which also entailed a higher rate of reinforcement). When no food occurred at the end of the additional terminal links, the outcome depended on the nature of the stimuli associated with these additional terminal links. When stimuli different from the reinforced baseline terminal links were used for the no-food terminal links, preference was against the choice alternative that led to the extra periods of extinction. When the same stimulus was used for the two kinds of terminal links, preference was near indifference, that is, significantly greater than when different stimuli were used. In Experiment 2, rats learned repeated reversals of a simultaneous discrimination under a three-link concurrent-chains schedule, in which the food or no-food choice outcomes were delayed until the end of the chain. Different conditions were defined by the point in the chain at which differential stimuli occurred. When the middle and terminal links provided no differential stimuli, discrimination was acquired more slowly than when differential stimuli occurred in both links. When differential stimuli occurred in the middle but not the terminal links, acquisition rates were intermediate. Both experiments together show that the effects of stimuli in a chain schedule are due partly to the time to food correlated with the stimuli and partly to the time to the next conditioned reinforcer in the sequence.     

Nonstable concurrent choice in pigeons

Six pigeons were trained on concurrent variable-interval schedules in which the arranged reinforcer ratios changed from session to session according to a 31-step pseudorandom binary sequence. This procedure allows a quantitative analysis of the degree to which performance in an experimental session is affected by conditions in previous sessions. Two experiments were carried out. In each, the size of the reinforcer ratios arranged between the two concurrent schedules was varied between 31-step conditions. In Experiment 1, the concurrent schedules were arranged independently, and in Experiment 2 they were arranged nonindependently. An extended form of the generalized matching law described the relative contribution of past and present events to present-session behavior. Total performance in sessions was mostly determined by the reinforcer ratio in that session and partially by reinforcers that had been obtained in previous sessions. However, the initial exposure to the random sequence produced a lower sensitivity to current-session reinforcers but no difference in overall sensitivity to reinforcement. There was no evidence that the size of the reinforcer ratios available on the concurrent schedules affected either overall sensitivity to reinforcement or the sensitivity to reinforcement in the current session. There was also no evidence of any different performance between independent and nonindependent scheduling. Because of these invariances, this experiment validates the use of the pseudorandom sequence for the fast determination of sensitivity to reinforcement.     

A multicomponent approach to thinning reinforcer delivery during noncontingent reinforcement schedules

We evaluated a noncontingent reinforcement procedure that involved initially providing three subjects with signaled, continuous access to the functional reinforcer for aggression and slowly increasing the amount of time subjects were exposed to the signaled unavailability of the reinforcer. Additionally, alternative potential reinforcers were available throughout the sessions. Results showed immediate and substantial reductions in aggression for all three subjects. The clinical utility of this intervention is discussed, and future research directions are recommended.     

Functional analysis and treatment of problem behavior related to mands for rearrangement

This study is a systematic replication of a functional analysis (FA) of the relation between mands and problem behavior. We extended treatment approaches for this problem behavior function, and describe the treatment of problem behavior related to mands for rearrangement demonstrated by a 12‐year‐old girl with autism spectrum disorder and Smith‐Magenis syndrome. The mands consisted of requests for others to change their body positioning or proximity, or rearrange items back to their original position. An FA confirmed the relation between problem behavior and mand compliance, and functional communication training with extinction decreased problem behavior and increased functional communication responses. Problem behavior remained low as gradually longer nonreinforcement periods were introduced using a multiple schedule.     

Divided stimulus control: Which key did you peck,or what color was it?

Responding on concurrent schedules produced a conditional discrimination (Phases 1 and 2), asking either which peck produced the event, or which color the keys were when the event was produced. In Phases 3 and 4, reinforcer delivery or a delay in blackout was interpolated between responding and the conditional discrimination. In Phase 1, location versus color discrimination accuracy was controlled by the relative reinforcer frequency for correct responses to these questions (divided stimulus control). In Phases 2 to 4, relative reinforcer frequency for correct responses to these questions was .5, and the relative frequency with which concurrent‐schedule responses produced the questions was varied. This variation had no clear effect on the accuracy of reporting Location or Color. These results are consistent with the model of divided control suggested by Davison and Elliffe (2010). Arranging a 3‐s reinforcer between responding and choice decreased both color and location accuracy, but a 3‐s delay only decreased location accuracy. Thus, in concurrent‐schedule performance, both ambient stimuli prior to a reinforcer and the location of the just‐reinforced response are available as discriminative stimuli following the reinforcer. Control of postreinforcer responding is divided between these according to their association with the relative frequency of subsequent reinforcers.     

Effects of Interspersing Briefer Mathematics Problems on Assignment Choice in Students with Learning Disabilities

Within- and between-series designs were combined and used to evaluate the effects of interspersing briefer math problems (i.e., one-digit by one-digit multiplication, 1 × 1) with more time-consuming problems (i.e., two-digit by one-digit multiplication, 2 × 1) on time allocation to one of two concurrent computer-delivered mathematics computation assignments in four high school students with specific learning disabilities in mathematics. The computer presented students with a choice of 2 × 1 problems with 1 × 1 problems interspersed every third problem (i.e., experimental assignment) or 2 × 1 problems without interspersal (i.e., control assignment). Visual and statistical analysis showed that students allocated a greater percentage of their time to the interspersal assignments. These results support previous research on the matching law and problem completion rates and suggest that students' preference for assignments can be improved through the interspersal technique. Discussion focuses on future research and applied educational implications for curricula construction and task sequencing.