On the discriminability of stimulus duration.

The performance of pigeons trained to detect differences in the duration of stimuli was analysed using a matching model of signal detection. Two white stimuli, S1 and S2, differing in duration, were arranged with equal probability on the center key of a three-key chamber. S1 was systematically varied from 5 seconds to 25 seconds while S2 remained constant at 30 seconds. On completion of the center-key stimulus, a peck on the center key turned on the two red side keys. A left-key response was "correct" when S1 had been in effect on the center key and a right-key response was "correct" on S2 trials. A correct response produced a 3-second magazine light accompanied intermittently by food. Incorrect responses produced 3-second blackouts. Detection performance was measured under two procedures. In the first, the obtained reinforcement ratio was uncontrolled by allowing the number of food reinforcements obtained for correct left- and right-key responses to vary as the stimuli were changed. In the second procedure, the presentation of food reinforcement was controlled by holding the obtained reinforcement ratio constant. Discriminability changed as a function of stimulus differences under both procedures. No such trend was found in response bias.     

Choice and reinforcement delay

Previous studies of choice between two delayed reinforcers have indicated that the relative immediacy of the reinforcer is a major determinant of the relative frequency of responding. Parallel studies of choice between two interresponse times have found exceptions to this generality. The present study looked at the choice by pigeons between two delays, one of which was always four times longer than the other, but whose absolute durations were varied across conditions. The results indicated that choice is not uniquely determined by the relative immediacy of reinforcement, but that absolute delays are also involved. Models for concurrent chained schedules appear to be more applicable to the present data than the matching relation; however, these too failed to predict choice for long delays.     

The effects of a response cost treatment tactic on hyperactive children

In a pilot study, a multielement design was used to assess the effectiveness of a response cost procedure on a 7-year-old child's hyperactive behavior and academic performance across days. The procedure was effective in reducing off-task behavior and in increasing academic assignment completion. In Experiment 2, three strategies were compared to a no-treatment baseline in treating an 8-year-old hyperactive child: drug (Ritalin) alone, response cost alone, and drug plus response cost. The cost program alone and the cost program combined with medication were effective in reducing off-task behavior and in increasing academic performance. In both studies, the procedure was viewed by the teachers as practical and effective for use in a classroom setting. The subjects liked the cost system and believed that they completed more academic work when it was operative.     

Context dependent changes in the reinforcing strength of schedule-induced drinking.

Previous experiments show that the opportunity to engage in schedule-induced responding is reinforcing. In this experiment, the reinforcing strength of schedule-induced drinking was measured. Four rats were trained on a concurrent-chain schedule. The two terminal links provided food pellets on identical fixed-time schedules. In addition, one terminal link also provided the opportunity to press a button that operated a water dipper. In this link, the rats showed polydipsic drinking. Button-pressing rate for polydipsic drinking was a bitonic function of pellet rate, and it was possible to describe the relationship with a slightly modified version of the matching equation for primary reinforcement. This equation also closely fit the data from other studies. Initial-link response rates, however, did not appear to be influenced by the availability of water in the terminal links. Control conditions suggested that the reinforcing strength of polydipsia was strongly bound to the context provided by periodic food reinforcement.     

Follow-up on welfare benefits received by Job Club clients

A follow-up was made of the welfare payments received by AFDC clients who had received job-finding counseling. At the 6th-month follow-up, welfare payments had been reduced by about one-half for the Job Club clients vs 15% for the control group.     

REINFORCER VARIATION: IMPLICATIONS FOR MOTIVATING DEVELOPMENTALLY DISABLED CHILDREN

Motivating developmentally disabled children to participate in educational activities can be very difficult. This is especially true for children diagnosed autistic. Because there is some evidence to suggest that stimulus variation may influence motivation, the present study investigated the effects of constant vs. varied reinforcer presentation on correct responding and on-task behavior. Results from a reversal design showed declining trends in both correct responding and on-task behavior when the same reinforcer was consistently presented, whereas, varying the reinforcers produced significantly improved and stable responding. The results are discussed in relation to the literature on stimulus variation and its effects on responsivity.     

Conditioned inhibition of fear: Evidence for a competing response mechanism

In two experiments, inhibitory conditioning was attempted by presenting a discrete CS in a neutral stimulus environment shortly following the termination of either shock (Experiment 1) or a second discrete CS which had been paired in a forward manner with shock (Experiment 2). Evidence of successful inhibitory conditioning was mixed in Experiment 1, where the properties of the CS were assessed within an escape-from-fear procedure. Postresponse presentations of the CS enhanced performance, whereas the presentation of the CS prior to responding did not have the expected degrading effect on performance. In Experiment 2, the inhibitory properties of the CS were assessed by combining this stimulus with an excitatory CS and presenting the compound to rats engaged in a water-reinforced licking response. Less response suppression was found in reaction to this compound relative to three separate comparison conditions, thus witnessing the success of the inhibitory-conditioning procedure used. The common assumption that inhibitory conditioning results from the nonreinforcement of a CS in a situation where reinforcement is expected, i.e., one which contains previously reinforced cues, is not supported by these data, for no previously reinforced cues were simultaneously presented with the CS during inhibitory training. The data are in agreement with a conditioned antagonistic-response interpretation of inhibitory conditioning.     

The following schedule of reinforcement as a fundamental determinant of steady state contrast in multiple schedules

Two experiments investigated whether steady-state interactions in multiple schedules depend exclusively on the following schedule of reinforcement. Experiment 1 used a four-component multiple schedule in which two components were associated with the same constant schedule of reinforcement, and where rate of reinforcement was varied in the component that followed one of these. Contrast effects were reliable only in the component that preceded the point of reinforcement variation, although some contrast did occur otherwise. In those instances where contrast other than the following-schedule effect did occur, it was accounted for by the effect of the preceding schedule, an effect for which there were consistent individual differences among subjects, and which varied with component duration. Experiment 2 used a three-component schedule, in which reinforcement rate was varied in the middle component. The results were consistent with Experiment 1, as the following-schedule effect was the only consistent effect that occurred, although an effect of the preceding schedule did occur for some subjects under some conditions, and was especially evident early in training. The conclusion from both experiments is that there is no general effect of relative rate of reinforcement apart from the sum of the effects of the preceding and following schedules, and that the following-schedule effect is the fundamental cause of steady-state interactions.