Cam L. Melville

Within-session responding when different reinforcers are delivered in each half of the session

The present study investigated whether within-session responding was specific to the reinforcer currently being delivered and whether it was determined solely by retrospective factors. In four separate experiments, four rats pressed a lever on a multiple variable interval 60-s variable interval 60-s schedule during 60-min sessions. A different reinforcer (5% liquid sucrose or food pellets) was delivered in each half of the session. Rate of reinforcement in one half of the session varied across conditions. Response patterns in the second half of the session were unaffected by changes in the conditions of reinforcement of the other reinforcer in the first half of the session (specificity). Rate of responding was affected, however. The upcoming reinforcer influenced responding when sucrose was delivered in the first half of the session and food pellets were delivered in the second half, but not when their order was reversed. This effect makes contact with several other areas of research (e.g. behavioral contrast). They also suggest that the leading explanations for within-session changes in responding may be limited or incomplete.

Node-link-mapping-enhanced group treatment for pathological gambling

Two experiments evaluated a group treatment for pathological gambling that used node-link mapping techniques to enhance treatment effectiveness. In Experiment 1, 13 (8 female) pathological gamblers were randomly assigned to either a mapping group (n=4), a nonmapping group (n=4), or a wait-list control group (n=5). The treatments were conducted by Masters level counselors during 90-min sessions conducted twice per week for 8 weeks. Participants were assessed pre- and post-8 weeks and then 6 months later on Diagnostic and Statistical Manual of Mental Disorders 4th ed. (DSM-IV) pathological gambling criteria, three self-ratings of control of gambling, gambling expenditure, and gambling bout duration. Experiment 2 replicated the mapping (n=9; 8 female) and wait-list (n=10; 8 female) conditions of Experiment 1 and expanded the dependent measures to include assessment of changes in cooccurring depression and anxiety. The node-link-mapping-enhanced group treatment produced improvements in more of the dependent measures of pathological gambling than treatment without maps (Experiment 1) or an equivalent-length waiting period (Experiments 1 and 2). It also produced larger decreases in cooccurring depression and anxiety than an equivalent-length waiting period (Experiment 2). The results are consistent with previous treatment research with substance abusers.

The effect of second-half reinforcer type on responding for sucrose in the first half of the session

The present study investigated whether the sucrose-reinforced lever pressing of rats in the first half of a 50-min session would be sensitive to upcoming food-pellet reinforcement in the second half. In Experiment 1, the type of reinforcer in the first half of the session was always liquid sucrose and type of reinforcer in the second half (liquid sucrose or food pellets) varied across conditions. Sucrose concentration varied across groups (1, 5, or 25%). Results showed that rates and patterns of responding for 1%, and sometimes for 5%, sucrose reinforcers in the first half of the session were higher and steeper, respectively, when food-pellet, rather than sucrose, reinforcement occurred in the second half. Responding for 25% sucrose was not similarly affected. Experiment 2 replicated the results of Experiment 1 using a within-subjects design. Although the present results represent induction (i.e. the opposite of contrast), they are consistent with some results on consummatory contrast. They also further demonstrate that responding on interval schedules of reinforcement can be altered prospectively. By doing so, however, they pose potential problems for current theories for why operant response rates change within the session.

Delivering Different Reinforcers in Each Half of the Session: Effect of Reinforcement Rate

Previous research (Weatherly, Stout, Rue, & Melville, 2000) has shown that rats’ rates of lever pressing for low-concentration liquid-sucrose reinforcement in the first half of an experimental session are higher when food pellets, rather than the same sucrose reinforcers, are delivered in the second half of the session (i.e., induction). The present study investigated whether this effect was sensitive to changes in the rate of reinforcement in the first or second half of the session. Rats responded in 50-min sessions, with 1 % (Experiment 1) or 5% (Experiment 2) liquid-sucrose reinforcers delivered during the first half of the session. In different conditions, food pellets or the same sucrose served as the reinforcer in the second half of the session. Rate of reinforcement in either the first or second half of the session was varied across conditions. Results showed that induction was present in both experiments, although it was most reliable when subjects responded for 1 % sucrose. They also suggest that rate of sucrose reinforcement is not a determining factor of when induction will be observed. By doing so, the present results increase the generality of the present induction effect.

Within-session responding as a function of force required for lever press

Four male Sprague-Dawley rats pressed a lever for food reinforcers delivered by a multiple variable interval 1-min variable interval 1-min schedule. Components alternated every 5 min. The force required to move the lever was 0.25, 0.15, 1.10, 0.75, and 0.50 N in different conditions. Changes in the force requirement did not alter the within-session pattern of responding. These results are consistent with other experiments suggesting that muscle warm-up and fatigue are not sufficient explanations for the within-session pattern of responding.

Within-session patterns of responding when rats run in a T-maze.

Free-operant responding changes systematically within experimental sessions, usually increasing and then decreasing, even when the contingencies of reinforcement remain constant within the session. The present study extended this finding to running times in a T-maze. In Experiment 1, running times changed significantly within the session. Furthermore, the within-session pattern of running times changed with changes in the amount or rate of reinforcement. In Experiment 2, the within-session change in running times was found to be independent of the accuracy of responding. In Experiment 3, manipulating whether responding and/or reinforcement occurred early in the session did not affect the pattern of running times later in the session. The present results increase the generality of within-session changes in responding to a discrete-trials procedure. Furthermore, within-session patterns of running times usually changed in a similar manner as within-session patterns of free-operant responding when similar factors were manipulated. Thus, the same factors may be producing the changes in both situations.

Behavioral contrast with changes in duration and rate of reinforcement

Behavioral contrast can be defined as an inverse relation between rate of responding in one component of a multiple schedule and conditions of reinforcement in the other components. The present study was an attempt to produce contrast with changes in duration of reinforcement. Pigeons pecked a key for mixed grain delivered by a multiple variable-interval variable-interval schedule. In Experiment 1, the reinforcer duration in the second component was decreased or increased, for different subjects, by a factor of two, four, and six from that delivered during baseline. These changes usually produced contrast. In Experiment 2, rate, duration, or rate and duration of reinforcement varied in the second component. Contrast was usually observed when only one variable was manipulated. When both variables were manipulated in the same condition, but in opposite directions, responding in the constant component usually changed inversely with the change in rate of reinforcement, not the change in reinforcer duration. The results demonstrate that changes in duration of reinforcement can produce contrast. They also increase the empirical base for which a successful theoretical account of contrast must encompass and the generality of contrast, which increases its potential practical implications.

Behavioral contrast using different reinforcers: effect of baseline rate of reinforcement.

The present study determined whether behavioral contrast would occur when different reinforcers were delivered in the different components and whether its size would vary at different baseline rates of reinforcement. Pigeons pecked keys on a multiple variable-interval schedule. Mixed grain was the reinforcer in one component and wheat was the reinforcer in the other component. In contrast conditions, the rate of wheat reinforcement was increased or decreased, from the baseline delivery rate, by a factor of four. Contrast was studied at four different baseline rates of reinforcement. Contrast was usually observed and its size almost always varied directly with the programmed baseline rate of reinforcement. The present results indicate that changes in the condition of reinforcement of a different reinforcer can produce contrast. They also broaden the potential implications of behavioral contrast.

Academic performance in reading a text as related to course grades: Student performance when studying is impossible

The discrepancy model of Stock, Winston, Behrens, and Harper-Marinick (1989) is based on the effects of student expectation of how well they should do, feedback about actual performance, and subsequent student behavior to keep the discrepancy within acceptable bounds. Students can, for example, study to improve their grades if the grades fall below the acceptable level. However, there is another way to explain student performance that does not involve the student’s studying or working to achieve better. This perspective says that much academic achievement may be due to how good or poor the student is, and that this can be shown by testing the student in a situation in which no studying is possible. This was done with 68 students who read texts as part of the study and were then tested on what they had read. Their final course grades were compared with their performance on the test of text reading, and it was found that students who made As tended to recall over 70% of the text, whereas students who made Bs, Ds, Fs, or Ws (withdrew from the course) recalled less than 70% of the text. Since study of the text material was impossible, the results suggest that the scores on the text reading test were due to some general ability factor, and not always controlled by feedback, discrepancy, studying, or the like.