The temporal organization of behavior on periodic food schedules.

Various theories of temporal control and schedule induction imply that periodic schedules temporally modulate an organism's motivational states within interreinforcement intervals. This speculation has been fueled by frequently observed multimodal activity distributions created by averaging across interreinforcement intervals. We tested this hypothesis by manipulating the cost associated with schedule-induced activities and the availability of other activities to determine the degree to which (a) the temporal distributions of activities within the interreinforcement interval are fixed or can be temporally displaced, (b) rats can reallocate activities across different interreinforcement intervals, and (c) noninduced activities can substitute for schedule-induced activities. Obtained multimodal activity distributions created by averaging across interreinforcement intervals were not representative of the transitions occurring within individual intervals, so the averaged multimodal distributions should not be assumed to represent changes in the subject's motivational states within the interval. Rather, the multimodal distributions often result from averaging across interreinforcement intervals in which only a single activity occurs. A direct influence of the periodic schedule on the motivational states implies that drinking and running should occur at different periods within the interval, but in three experiments the starting times of drinking and running within interreinforcement intervals were equal. Thus, the sequential pattern of drinking and running on periodic schedules does not result from temporal modulation of motivational states within interreinforcement intervals.     

Bouts of responding on variable-interval schedules: effects of deprivation level

Rats obtained food pellets on a variable-interval schedule of reinforcement by nose poking a lighted key. After training to establish baseline performance (with the mean variable interval set at either 60, 120, or 240 s), the rats were given free access to food during the hour just before their daily session. This satiation operation reduced the rate of key poking. Analysis of the interresponse time distributions (log survivor plots) indicated that key poking occurred in bouts. Prefeeding lengthened the pauses between bouts, shortened the length of bouts (less reliably), and had a relatively small decremental effect on the response rate within bouts. That deprivation level affects mainly between-bout pauses has been reported previously with fixed-ratio schedules. Thus, when the focus is on bouts, the performances maintained by variable-interval schedules and fixed-ratio schedules are similarly affected by deprivation.     

An inverse relationship between baseline fixed-interval response rate and the effects of a tandem response requirement.

Previous experiments examining the effects of adding a tandem fixed-ratio response requirement on fixed-interval schedule performance have reported inconsistent results. One variable that may account for such inconsistencies is the baseline response rate in the fixed-interval condition. This possibility was investigated in the present study. Rats were given histories with either interresponse times greater than 11 s or fixed-ratio 40 schedules of reinforcement, which engendered either relatively low or high rates of responding, respectively, in the subsequent fixed-interval condition. A tandem ratio response requirement (fixed-ratio 9) was then introduced. The effects of adding this tandem response requirement were inversely related to the baseline fixed-interval response rates; low rates of responding in the fixed-interval condition were markedly increased, whereas high rates of responding were relatively unaffected. This inverse relationship appears to be similar to the rate-dependent relations observed in behavioral pharmacology. These results may provide an explanation for the inconsistent findings reported in previous studies on tandem fixed-interval fixed-ratio schedules and suggest that principles of behavioral pharmacology research may be applicable to the study of the effects of nonpharmacological variables on schedule-controlled behavior.     

The effects of morphine on fixed-interval patterning and temporal discrimination

Changes produced by drugs in response patterns under fixed-interval schedules of reinforcement have been interpreted to result from changes in temporal discrimination. To examine this possibility, this experiment determined the effects of morphine on the response patterning of 4 pigeons during a fixed-interval 1-min schedule of food delivery with interpolated temporal discrimination trials. Twenty of the 50 total intervals were interrupted by choice trials. Pecks to one key color produced food if the interval was interrupted after a short time (after 2 or 4.64 s). Pecks to another key color produced food if the interval was interrupted after a long time (after 24.99 or 58 s). Morphine (1.0 to 10.0 mg/kg) decreased the index of curvature (a measure of response patterning) during fixed intervals and accuracy during temporal discrimination trials. Accuracy was equally disrupted following short and long sample durations. Although morphine disrupted temporal discrimination in the context of a fixed-interval schedule, these effects are inconsistent with interpretations of the disruption of response patterning as a selective overestimation of elapsed time. The effects of morphine may be related to the effects of more conventional external stimuli on response patterning.     

On the effects of food deprivation and component reinforcer rates on multiple-schedule performance

Six pigeons were used to investigate the effects of varying body weight and component reinforcer rates in two-component multiple variable-interval variable-interval schedules. In Parts 1 and 3 of the experiment, unequal component reinforcer rates were arranged, and body weights were respectively increased and decreased. At 80% ad lib weight, response-rate ratios were closer to unity than reinforcer-rate ratios, but at 100% or more of ad lib weight, response-rate ratios generally equaled reinforcer-rate ratios. In Part 2, component reinforcer-rate ratios were varied over five conditions with the subjects maintained at 100% or more of their ad lib weights, and response-rate ratios matched reinforcer-rate ratios. The data thus support the empirical finding that response allocation in multiple schedules is a function of deprivation. Although this qualitative result is predicted by three models of multiple-schedule performance, only a model that assumes no direct component interaction adequately describes the data.     

Effects of chlordiazepoxide and cocaine on concurrent food and avoidance-of-timeout schedules.

Five rats were trained on a concurrent schedule in which responses on one lever produced a food pellet on a random-interval 30-s schedule during 10 s of food availability associated with distinctive exteroceptive stimuli. Responses on another lever postponed for 20 s the presentation of a 50-s timeout, during which all stimuli were extinguished and the schedule contingencies on the food lever were suspended. The response rates maintained by the random-interval schedule exceeded those maintained by the avoidance contingency, but both provided a stable baseline to assess the behavioral effects of different drugs. Low doses of cocaine hydrochloride (1 and 3 mg/kg) did not affect food-reinforced responding or avoidance response rates. Intermediate doses (5.6, 10, and 13 mg/kg) produced a dose-dependent decrease in food-maintained and avoidance response rates, and both types of responding were virtually eliminated after administration of the highest doses (17 and 30 mg/kg) of cocaine. Low doses of chlordiazepoxide (1 and 3 mg/kg) increased food-maintained and avoidance response rates, and both rates decreased systematically after 10 and 30 mg/kg of this drug. The effects of cocaine and chlordiazepoxide on response rates maintained by avoidance of timeout from food presentation were unlike those reported when subjects responded to avoid shock presentation. The results of this experiment thus provide evidence to suggest that the effects of drug administration on avoidance behavior may be a function of the nature of the consequent event to be avoided.     

The effects of fixed‐interval schedules on variability of pigeons' pecking location

Many studies that have investigated performance under reinforcement schedules have measured response rate or interresponse time, which reflect the temporal dimension of responding; however, relatively few studies have examined other dimensions. The present study investigated the effects of fixed‐interval schedules on the location of pigeons' pecking response. A circular response area 22.4 cm in diameter was used so that the pecking responses were effective over a wide range. Pigeons were exposed to a fixed‐interval schedule whose requirement was systematically varied between conditions. Response location moved closer to the location of the last reinforced response as time elapsed in each trial. Additionally, as the fixed‐interval duration requirement increased, response locations shifted to the border of the response area and the variability of response locations increased. These results suggest that fixed‐interval schedules systematically control response location.     

Optimism as a predictor of the effects of laboratory‐induced stress on fears and hope

The objective of the current study is to explore optimism as a predictor of personal and collective fear, as well as hope, following laboratory‐induced stress. Students (N = 107; 74 female, 33 male) were assigned randomly to either the experimental (stress—political violence video clip) or the control group (no‐stress—nature video clip). Questionnaires of fear and hope were administered immediately after the experiment (Time 1) and 3 weeks later (Time 2). Structural equation modeling indicated the following: (a) Optimism significantly predicted both fear and hope in the stress group at Time 1, but not in the no‐stress group. (b) Optimism predicted hope but not fear at Time 2 in the stress group. (c) Hope at Time 1 significantly predicted hope at Time 2, in both the stress and the no‐stress groups. (d) Gender did not predict significantly fear at Time 1 in the stress group, despite a significant difference between genders. This study supports previous studies indicating that optimism plays an important role in people's coping with stress. However, based on our research the data raise the question of whether optimism, by itself, or environmental stress, by itself, may accurately predict stress response.     

Interactions between the effects of food and water motivating operations on food‐ and water‐reinforced responding in mice

Two experiments examined interactions between the effects of food and water motivating operations (MOs) on the food‐ and water‐reinforced operant behavior of mice. In Experiment 1, mice responded for sucrose pellets and then water reinforcement under four different MOs: food deprivation, water deprivation, concurrent food and water deprivation, and no deprivation. The most responding for pellets occurred under food deprivation and the most responding for water occurred under water deprivation. Concurrent food and water deprivation decreased responding for both reinforcers. Nevertheless, water deprivation alone increased pellet‐reinforced responding and food deprivation alone likewise increased water‐reinforced responding relative to no deprivation. Experiment 2 demonstrated that presession food during concurrent food and water deprivation increased in‐session responding for water relative to sessions where no presession food was provided. Conversely, presession water during concurrent food and water deprivation did not increase in‐session responding for pellets. These results suggest that a) the reinforcing value of a single stimulus can be affected by multiple MOs, b) a single MO can affect the reinforcing value of multiple stimuli, and c) reinforcing events can also function as MOs. We consider implications for theory and practice and suggest strategies for further basic research on MOs.     

Ease‐of‐retrieval effects on procedural justice judgements under conditions of informational and personal uncertainty

This study tests whether individuals' reliance on ease‐of‐retrieval processes when forming procedural justice judgements are moderated by informational and personal uncertainty. In Studies 1 and 2 we examined the predicted effects of informational uncertainty. Results indicated that participants in information‐uncertain conditions relied on ease‐of‐retrieval, whereas those in information‐certain conditions relied on content information to make procedural justice judgements. In Study 3 we examined the combined effects of informational uncertainty and personal uncertainty on reliance on ease‐of‐retrieval when forming procedural justice judgements. The findings of Study 3 indicated that personal uncertain participants who were in informational certain conditions based their procedural justice judgements on content information, whereas all other participants based their procedural justice judgements on ease‐of‐retrieval. This is the first paper to demonstrate that the joint effect of informational uncertainty and personal uncertainty on reliance on ease‐of‐retrieval is different from the two uncertainties acting alone.     

Evaluating the effects of discriminability on behavioral persistence during and following time‐based reinforcement

With four children with autism we evaluated a refinement to time‐based reinforcement designed to reduce response persistence when we simultaneously introduced time‐based reinforcement and extinction. We further evaluated whether this refinement mitigated response recurrence when all reinforcer deliveries ceased during an extinction‐only disruptor phase. The refinement involved increasing the saliency of the contingency change from contingent reinforcement (during baseline) to time‐based reinforcement by delivering different colored reinforcers during time‐based reinforcement. Behavioral momentum theory predicts that increasing the discriminability of the change from variable‐interval to variable‐time reinforcement should lead to faster reductions in responding. We present data on four participants, three of whom displayed response patterns consistent with the predictions of behavioral momentum theory during time‐based reinforcement. However, the participants showed more varied patterns of recurrent behavior during extinction. We discuss these results within a translational research framework focusing on strategies used to mitigate treatment relapse for severe destructive behavior, as time‐based reinforcement is one of the most commonly prescribed interventions for destructive behavior displayed by individuals with intellectual and developmental disabilities.