The effect of variable delays on self-control

Five pigeons served as subjects in an experiment that examined the effects of variable as opposed to fixed delays on preference in a self-control paradigm (choice between larger, more delayed and smaller, less delayed reinforcers). Nonindependent concurrent variable-interval schedules were used to measure choice. When delays to the larger, more delayed reinforcers were variable as opposed to fixed, the subjects showed an increased preference for that alternative (the self-control alternative). A series of regressions revealed that the hyperbolic decay model and incentive theory provided poor fits to the data, but a modified version of the generalized matching law provided an adequate fit. Together, consistent with a general prediction made by discounting models, the data supported the conclusion that variable delays can increase self-control. However, specific discounting models were not able to explain the present data well.     

Choice between reliable and unreliable reinforcement alternatives revisited: Preference for unreliable reinforcement

Pigeons' choices between a reliable alternative that always provided food after a delay (i.e., 100% reinforcement) and an unreliable one that provided food or blackout equally often after a delay (i.e., 50% reinforcement) was studied using a discrete-trials concurrent-chains procedure modified to prevent choice between alternatives following a blackout outcome. Initial links were fixed-ratio 1 schedules, and terminal links were fixed-time schedules. Stimuli presented during the terminal-link delays were correlated with the food and blackout outcomes. In Experiment 1, terminal-link durations were varied. With short terminal links (i.e., 10 s), 6 of 8 subjects showed strong preference for the 50% side. As terminal-link duration increased to 30 s, preference, regardless of direction, became less extreme. In Experiment 2, the side-key location of the 50% and 100% alternatives was reversed for 3 subjects. Preference for the 50% alternative reoccurred following the key reversal. When a 5-s separation was subsequently interposed between the initial and terminal links for both alternatives, all birds reversed to a preference for the 100% side. In general, the strong preference for the 50% side was qualitatively consistent with the expectation that the procedure enhanced the conditioned-reinforcement effectiveness of the food-associated terminal-link stimulus on the 50% side. Implications of the results for various accounts of choice of the 50% alternative are discussed.     

An eight-alternative concurrent schedule: foraging in a radial maze.

In two experiments conducted in an eight-arm radial maze, food pellets were delivered when a photocell beam was broken at the end of each arm via a nose poke, according to either fixed-interval or random-interval schedules of reinforcement, with each arm providing a different frequency of reinforcement. The behavior of rats exposed to these procedures was well described by the generalized matching law; that is, the relationships between log behavior ratios and log pellet ratios were approximated by linear functions. The slopes of these log-log functions, an index of sensitivity to reinforcement frequency, were greatest for nose pokes, intermediate for time spent in an arm, and least for arm entries. Similar results were obtained with both fixed-interval and random-interval schedules. Addition of a 10-s changeover delay in both experiments eliminated the slope differentials between nose pokes and time spent in an arm by reducing the slopes of the nose-poke functions. These results suggest that different aspects of foraging may be differentially sensitive to reinforcement frequency. With concurrent fixed-interval schedules, the degree of temporal control exerted by individual fixed-interval schedules was directly related to reinforcement frequency.     

Effects of two levels of procedural fidelity with constant time delay on children's learning

The purpose of this study was to compare the effects of constant time delay delivered with high procedural fidelity to constant time delay with high procedural fidelity on all variables except delivery of the controlling prompt (i.e., on a mean of 44% of the trials, the controlling prompt was not delivered when it should have been provided). Six preschool children with disabilities were taught to identify photographs in two alternating conditions (e.g., high procedural fidelity and low procedural fidelity). An adapted alternating treatments design was used to evaluate the instructional conditions on the effectiveness and efficiency of instruction. In addition, daily measures were taken of the teacher's implementation of each step of the constant time delay procedures which indicated that the two conditions were implemented as planned. The results indicate that both conditions were effective for four children; for three of these, the high procedural fidelity condition resulted in more efficient learning. For the fifth child, the high-fidelity condition resulted in criterion level responding, but the low fidelity condition did not. However, when the high fidelity procedure and trial-by-trial reinforcement were used for the low-fidelity stimuli, these also were acquired. For the sixth child, neither procedure was effective; thus, the high fidelity condition was used alone and resulted in learning. The results are discussed in terms of using the constant time delay procedure and studying the procedural fidelity of other strategies.     

Efficacy of constant time delay implemented by peer tutors in general education classrooms

We evaluated the effects of teaching 13 typically developing children to use constant time delay when tutoring three of their peers who had substantial disabilities. We measured the extent to which the tutors used the constant time delay procedure correctly and the tutees' correct performance on the skills being taught. A multiple probe design across behaviors was used. The results indicated that (a) the tutors used each step of the constant time delay with a high degree of procedural fidelity; (b) the students with disabilities acquired the skills that were taught during peer tutoring; and (c) modifications of the procedure were required for 2 of the 3 students with disabilities, and the peers tutors were able to implement the modifications. Implications for practice and future research are described.     

Body weight and response acquisition with delayed reinforcement.

The relation between body weight and responding established with unsignaled delayed reinforcement was investigated. In three experiments, naive rats were deprived to either 70%, 80%, or 90% of ad libitum weight and were then exposed to tandem variable-interval 15-s differential-reinforcement-of-other-behavior 30-s schedules. The tandem schedule defined a resetting unsignaled delay-of-reinforcement procedure. In the first experiment, speed of magazine training, acquisition of lever pressing, and final rate of lever pressing were related to body weight. In the next experiment, lever pressing was established and maintained in rats that were magazine trained at 70% of ad libitum weight but that were then exposed to the delay procedure at 90% of ad libitum weight. Responding did not change consistently either across or within subjects in subsequent conditions in which body weight was manipulated. In the final experiment, lever pressing was established and maintained with delayed reinforcement in the absence of magazine training for each of 2 rats at 70% and for 1 of 2 rats at 90% of ad libitum weight. The results further illuminate the conditions under which responding can be established in the absence of training and when such responses are reinforced only following an unsignaled delay period.     

Delayed signal detection, differential reinforcement, and short-term memory in the pigeon.

In two discrete-trial delayed-detection experiments, six pigeons were trained on dependent concurrent variable-interval schedules. Pecking a red side key was reinforced when the brighter of two white lights (S1) had been presented on the center key, and pecking a green side key was reinforced when the duller of two white lights (S2) had been presented on the center key. Incorrect responses were red side-key pecks following S2 presentations and green side-key pecks following S1 presentations; these resulted in three-second blackouts. In Experiment 1, the time between presentation of S1 or S2 on the center key and the onset of the red and green side keys was varied nonsystematically from 0.06 seconds to 19.69 seconds across experimental conditions. Stimulus discriminability decreased as the stimulus-choice delay increased. A rectangular-hyperbolic function better described this decrease in discriminability over time than did a negative-exponential function. In Experiment 2, at each of three stimulus-choice delays (0.06, 3.85, and 10.36 seconds), relative reinforcer frequency for correct responses to the red and green side keys was varied by changing the values of the dependent concurrent variable-interval schedules. The sensitivity of choice to relative reinforcer frequency was independent of the decrease in stimulus discriminability with increasing stimulus-choice delay.     

Teaching chained skills in a non-school setting using a divided half instructional format

This investigation evaluated the use of dyadic instructional arrangements in teaching chained skills to four students with moderate mental retardation. Each instructional dyad consisted of two students. Each of the three cooking skills was divided into two equal parts, and each student in a dyad received direct instruction on one part of the task analysis during each instructional session. During the following session, the two parts were reversed and a student received instruction on the second part. A constant time delay procedure was used to teach the targeted skills in an off-campus setting. A multiple probe design across skills and replicated across students evaluated the effectiveness of the instructional procedure and teaching arrangement. Results indicate that each of the four students learned the three cooking skills. Implications for future research are discussed.     

Memory for two stimulus-response items in pigeons

Six pigeons served in a discrete-trial experiment on short-term memory. Combinations of three key positions and two ordinal positions, yielding six possible sequences of stimulus-response pairs, were used as lists of items. A retention interval separated list presentation from the test phase in which two (for Group 1) or three (for Group 2) keys were illuminated with either red or green light. A reinforcer was delivered if a subject pecked the key of the first item on a red trial and the key of the second item on a green trial. When the retention interval was lengthened from one to five or nine seconds, a systematic loss of stimulus control resulted. Lengthening the interval between items from one to eight seconds had a much smaller effect for the birds in Group 1, whereas a systematic loss of stimulus control was found in red trials for the birds in Group 2. The functional relations between choice accuracy and delay provided an empirical basis for analysis of what relations among temporal events can become discriminative stimuli.     

Choice and the relative immediacy of reinforcement

The relative immediacy of reinforcement in concurrent-chain schedules was varied while the relative reduction in the overall average time to reinforcement associated with terminal-link entry was held constant. For each of four pigeons, choice did not vary with relative immediacy of reinforcement. Subsequently, choice by the same subjects was shown to be sensitive to relative reduction in average time to reinforcement.