Maximizing versus matching on concurrent variable-interval schedules

Maximization and matching predictions were examined for a time-based analogue of the concurrent variable-interval variable-ratio schedule. One alternative was a variable interval whose time base operated relatively independent of the schedule chosen, and the other was a discontinuous variable interval for which timing progressed only when selected. Pigeons switched between schedules by pecking a changeover key. The maximization hypothesis predicts that subjects will show a bias toward the discontinuous variable interval and undermatching; however the obtained results conformed closely to the predictions of the matching law. Finally, a quantitative comparison was made of the bias and sensitivity estimates obtained in published concurrent variable-interval variable-ratio analogue studies. Results indicated that only the ratio-based analogue of the concurrent variable interval variable ratio studied by Green, Rachlin, and Hanson (1983) produced significant bias toward the variable-ratio alternative and undermatching, as predicted by reinforcement maximization.     

Responding for sucrose and wheel-running reinforcement: effects of sucrose concentration and wheel-running reinforcer duration

Six male albino rats were placed in running wheels and exposed to a fixed-interval 30-s schedule of lever pressing that produced either a drop of sucrose solution or the opportunity to run for a fixed duration as reinforcers. Each reinforcer type was signaled by a different stimulus. In Experiment 1, the duration of running was held constant at 15 s while the concentration of sucrose solution was varied across values of 0, 2.5. 5, 10, and 15%. As concentration decreased, postreinforcement pause duration increased and local rates decreased in the presence of the stimulus signaling sucrose. Consequently, the difference between responding in the presence of stimuli signaling wheel-running and sucrose reinforcers diminished, and at 2.5%, response functions for the two reinforcers were similar. In Experiment 2, the concentration of sucrose solution was held constant at 15% while the duration of the opportunity to run was first varied across values of 15, 45, and 90 s then subsequently across values of 5, 10, and 15 s. As run duration increased, postreinforcement pause duration in the presence of the wheel-running stimulus increased and local rates increased then decreased. In summary, inhibitory aftereffects of previous reinforcers occurred when both sucrose concentration and run duration varied; changes in responding were attributable to changes in the excitatory value of the stimuli signaling the two reinforcers.     

Reinforcement value and substitutability of sucrose and wheel running: implications for activity anorexia

Choice between sucrose and wheel-running reinforcement was assessed in two experiments. In the first experiment, ten male Wistar rats were exposed to concurrent VI 30 s VI 30 s schedules of wheel-running and sucrose reinforcement. Sucrose concentration varied across concentrations of 2.5, 7.5, and 12.5%. As concentration increased, more behavior was allocated to sucrose and more reinforcements were obtained from that alternative. Allocation of behavior to wheel running decreased, but obtained wheel-running reinforcement did not change. Overall, the results suggested that food-deprived rats were sensitive to qualitative changes in food supply (sucrose concentration) while continuing to defend a level of physical activity (wheel running). In the second study, 15 female Long Evans rats were exposed to concurrent variable ratio schedules of sucrose and wheel-running, wheel-running and wheel-running, and sucrose and sucrose reinforcement. For each pair of reinforcers, substitutability was assessed by the effect of income-compensated price changes on consumption of the two reinforcers. Results showed that, as expected, sucrose substituted for sucrose and wheel running substituted for wheel running. Wheel running, however, did not substitute for sucrose; but sucrose partially substituted for wheel running. We address the implications of the interrelationships of sucrose and wheel running for an understanding of activity anorexia.     

Visual determinants of preferred adjective order

In referential communication, speakers refer to a target object among a set of context objects. The NPs they produce are characterized by a canonical order of prenominal adjectives: The dimensions that are easiest to detect (e.g., absolute dimensions) are commonly placed closer to the noun than other dimensions (e.g., relative dimensions). This stands in stark contrast to the assumption that language production is an incremental process. According to this incremental-procedural view, the dimensions that are easiest to detect should be named first. In the present paper, an alternative account of the canonical order effect is presented, suggesting that the prenominal adjective ordering rules are a result of the perceptual analysis processes underlying the evaluation of distinctive target features. Analyses of speakers’ eye movements during referential communication (Experiment 1) and analyses of utterance formats produced under time pressure (Experiment 2) provide evidence for the suggested perceptual classification account.     

Effects of High Doses of Naltrexone on Running and Responding for The Opportunity to Run in Rats: A Test of the Opiate Hypothesis

Previous research shows that low to moderate doses of opiate antagonists do not affect running whereas high doses decrease running. This decrease in running has been interpreted as a motivational effect; however, it may also be an effect of motoric impairment, malaise, or sedation. The purpose of the present study was to evaluate the effects of high doses of naltrexone on running and responding for the opportunity to run in rats. Seven male Wistar rats, trained to press levers for the opportunity to run for 30 s, were exposed to a series of tandem fixed-ratio 1 variable-interval (VI) schedules of reinforcement where the value of the VI schedule was varied. Four rats were exposed to a VI 60-, VI 30-, and VI 5-s schedule order and the remaining three were exposed to VI 5-, VI 30-, and VI 60-s schedule order. After 50 sessions, doses of 10, 20, or 40 mg/kg of naltrexone were administered prior to a session. Results showed that naltrexone significantly decreased rates of lever pressing and running and increased postreinforcement latency to respond. Within-session analyses showed that naltrexone significantly decreased responding and running during the first schedule of a session regardless of schedule value. The lack of interaction of the drug effect with the schedule of reinforcement is inconsistent with a motivational effect. Consequently, it was concluded that decreases in running caused by high doses of naltrexone are not motivational and should not be taken as evidence in support of the opiate hypothesis.

     

The general matching law describes choice on concurrent variable-interval schedules of wheel-running reinforcement.

Six male Wistar rats were exposed to concurrent variable-interval schedules of wheel-running reinforcement. The reinforcer associated with each alternative was the opportunity to run for 15 s, and the duration of the changeover delay was 1 s. Results suggested that time allocation was more sensitive to relative reinforcement rate than was response allocation. For time allocation, the mean slopes and intercepts were 0.82 and 0.008, respectively. In contrast, for response allocation, mean slopes and intercepts were 0.60 and 0.03, respectively. Correction for low response rates and high rates of changing over, however, increased slopes for response allocation to about equal those for time allocation. The results of the present study suggest that the two-operant form of the matching law can be extended to wheel-running reinforcement. 'I'he effects of a low overall response rate, a short Changeover delay, and long postreinforcement pausing on the assessment of matching in the present study are discussed.     

Effect of Light/Dark Cycle on Wheel Running and Responding Reinforced by the Opportunity to Run Depends on Postsession Feeding Time

The Psychological Record - Do rats run and respond at a higher rate to run during the dark phase when they are typically more active? to answer this question, Long Evans rats were exposed to a...