Within-session changes in responding during several simple schedules

Pigeons' key pecking was reinforced by food delivered by several fixed-interval, variable-ratio, and differential-reinforcement-of-low-rate schedules. Rate of responding, number of responses per reinforcer, length of postreinforcement pause, running response rate, and the time required to collect an available reinforcer changed systematically within sessions when the schedules provided high rates of reinforcement, but usually not when they provided low rates. These results suggest that the factors that produce within-session changes in responding are generally similar for different schedules of reinforcement. However, a separate factor may also contribute during variable-ratio schedules. The results question explanations for within-session changes that are related solely to the passage of time, to responding, and to one interpretation of attention. They support the idea that one or more factors related to reinforcement play a role.     

Reinforcer magnitude (sucrose concentration) and the matching law theory of response strength

This experiment investigated the relationship between reinforcer magnitude (sucrose concentration) and response rate. The purpose was to evaluate the behavior of two parameters of an equation that predicts absolute response rate as a function of reinforcement rate and two free parameters. According to Herrnstein's (1970) theory of reinforced behavior, one parameter of this "response-strength equation" measures the efficacy of the reinforcer maintaining responding and the other parameter measures motoric components of response rate, such as response duration. Seven rats served as subjects. Experimental sessions consisted of a series of five different variable-interval schedules of reinforcement, each in effect for 5 minutes. Within each session, obtained reinforcement rates varied over more than a 30-fold range, from about 20 per hour to 700 per hour. The reinforcer was sucrose solution, and, between sessions, its concentration was varied from 0.0 to 0.64 molar (0 to 21.9%). For sucrose concentrations of 0.16 to 0.64 m, response rate was a negatively accelerated function of reinforcement rate. Increases in sucrose concentration increased response rates maintained by low but not high reinforcement rates. This pattern of changes corresponds to a change in the reinforcement-efficacy parameter of the response-strength equation. In contrast, the motor-performance parameter did not change as a function of sucrose concentration. These findings are inconsistent with the results of a similar study (Bradshaw, Szabadi, & Bevan, 1978) but support Herrnstein's theory of reinforced behavior.     

The control of choice by its consequences

Five pigeons were trained on concurrent variable-interval schedules in which equal rates of reinforcement were always arranged for left- and right-key responses, but different overall rates were signaled by key colors. Sessions began with both keys lit yellow for the instrumental phase. If, after 20 s of this phase, the relative number of responses that had been made to the left key equaled or exceeded .75, both keys changed red for the contingent phase. The contingent phase arranged another concurrent variable-interval schedule for a further 20 s before the instrumental phase was reinstated. However, if preference in the instrumental phase did not exceed .75, the instrumental phase continued for a further 20 s before preference was again compared with the criterion. In Part 1, the reinforcer rate arranged in the instrumental phase was held constant at 4.8 reinforcers per minute, while the reinforcer rate arranged in the contingent phase was varied across conditions from 0 to 19.2 over five steps. In Part 2, reinforcer rates in the contingent phase were kept constant at 36 per minute, while reinforcer rates in the instrumental phase were varied from 0 to 36 over seven steps. Part 3 replicated Part 2 but used reinforcer rates in both phases that were one third of those arranged in Part 2. Measures of choice obtained by summing responses across presentations of the instrumental phase became more extreme toward the left key as the reinforcer rate obtained in the contingent phase was increased (Part 1) and as the reinforcer rate obtained in the instrumental phase was decreased (Parts 2 and 3). Changes in these measures of choice were accompanied by systematic changes in the relative frequency with which the criterion was exceeded. Changes in both these measures were correlated with changes in the relative frequency with which subjects responded exclusively to the left key. These results are discussed with respect to the two choices that were concurrently available in this procedure and the response alternatives that might constitute the concurrent operants in each choice.     

An evaluation of methylphenidate as a potential establishing operation for some common classroom reinforcers.

We conducted reinforcer assessments for 3 boys with a diagnosis of attention deficit hyperactivity disorder who alternately received either placebo or previously prescribed methylphenidate. Our purpose was to evaluate whether methylphenidate altered the relative reinforcing effectiveness of various stimuli that are often used in classroom-based behavioral treatment programs (e.g., activities, tangible items). Results showed clear differences for some stimuli between reinforcer assessments conducted when participants had received methylphenidate compared to placebo. Results suggest that methylphenidate might act as an establishing operation for some common classroom reinforcers. Implications for the development and evaluation of behavioral treatments are discussed.     

ASSESSMENT OF PREFERENCE FOR VARIED VERSUS CONSTANT REINFORCERS

One method that has been demonstrated to improve the effectiveness of reinforcement is stimulus (reinforcer) variation (Egel, 1980). Egel found that bar pressing increased and responding occurred more rapidly during varied reinforcement than during constant reinforcement when identical stimuli were used across phases for 10 individuals with autism. The purpose of the current investigation was to assess the preferences of 7 individuals for varied presentation of slightly lower quality stimuli relative to constant access to the highest quality stimulus. Varied presentation was preferred over constant reinforcer presentation with 4 participants, and the opposite was true for 2 participants. One participant did not demonstrate a preference. These results suggest that stimulus variation may allow less preferred reinforcers to compete effectively with a more highly preferred reinforcer for some individuals.     

EFFECTS OF REINFORCER QUALITY ON BEHAVIORAL MOMENTUM: COORDINATED APPLIED AND BASIC RESEARCH

The high-probability (high-p) instructional sequence has been an effective treatment for noncompliance. However, treatment failures have also been reported. We hypothesized that the efficacy of the high-p treatment may be improved by using higher quality reinforcers for compliance to high-p instructions. The resistance of compliance to change was tested by varying reinforcer quality in two applied studies and a basic laboratory experiment. Experiment 1 tested the hypothesis that an increase in reinforcer quality for high-p compliance will increase the effectiveness of the high-p treatment when it fails to increase compliance. Experiment 2 assessed the effects of reinforcer quality on resistance of compliance to change by presenting successive low-p requests following the high-p treatment. A basic laboratory study (Experiment 3) was conducted to further isolate the relation between reinforcer quality and behavioral momentum. Two different liquid reinforcers (sucrose and citric acid solutions) were presented in a two-component multiple variable-interval variable-interval schedule followed by a single extinction test session. Results of all three experiments showed a generally consistent relationship between reinforcer quality and behavioral momentum.     

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.     

An integrative model for the study of behavioral momentum.

Behavioral momentum is the product of response rate and resistance to change. The data on relative resistance to change are summarized for pigeons responding on single-key two-component multiple schedules, in the initial links of two-key multiple chained schedules, and in equivalent components of two-key serial schedules. For single-key procedures, the ratio of resistance to change in two schedule components is shown to depend on the ratio of reinforcer rates obtained in the presence of the component stimuli. For two-key procedures, the ratio of resistance to change in equivalent components is shown to depend on the ratio of reinforcer rates correlated with key locations. A model based on stimulus-reinforcer contingencies that combines the reinforcer rates in schedule components summed over key locations and reinforcer rates correlated with key locations summed over components, each expressed relative to the session average reinforcer rate, gives a good account of the data. An extension of the relative law of effect for multiple schedules fails to provide a complete account of resistance to change, but both approaches are needed for a comprehensive understanding of behavioral momentum.     

Effects of reinforcer duration on responding in two-link chained interval schedules

Each of five pigeons was exposed to two or more durations of access to mixed grains on two-link, chained, interval schedules in which both links were identical fixed-interval or variable-interval schedules. Response rates were an increasing function of reinforcer duration for both initial and terminal links. For both types of interval schedules, initial-link response rates were more sensitive to reinforcer duration than were terminal-link response rates. The present results, together with prior ones, suggest that chaining and choice procedures are each sufficient for demonstrating substantial sensitivity of responding to changes in reinforcer duration.