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When reinforcement schedules demand that rats depress a lever for a minimum period of time, most lever presses will meet reinforcer requirements, but others will be much shorter. This results in a bimodal distribution of lever-press durations, with one peak near the reinforced duration value, and a smaller peak at less than 1 s. We conducted an experimental and descriptive analysis of short-duration presses in rats responding under a schedule that delivered edible reinforcers for 10 s of lever depression. All rats emitted biting and idiosyncratic behavior that may have both added and subtracted to the downward force necessary to maintain lever depression for extended periods. Movement of the response levers due to vigorous biting and sniffing, as well as premature hopper entries were both responsible for response durations that fell short of reinforcer requirements. Maintenance of long lever-press durations during fixed-time schedules in two out of three rats suggested that timing failure was unlikely a factor underlying bimodal distributions of response durations. [ABSTRACT FROM AUTHOR]

The current study assessed whether the generalized matching law would provide an accurate description of behavior maintained by token reinforcement. A dependent-concurrent random interval 15 s schedule of token production maintained lever pressing in rats. Following delivery, each token could be immediately exchanged for sweetened condensed milk. In Experiment 1, the token ratio was either 1:3 or 1:9, depending upon condition, and the location of the rich schedule varied randomly across daily sessions. In Experiment 2, the token ratio varied randomly within each session (1:9, 1:6, 1:3, 1:1, 3:1, 6:1, and 9:1). Overall, the generalized matching law provided a good description of the data, revealing a high degree of undermatching. In Experiment 2, two of three rats tended to return to the just-productive lever following token delivery. The third subject showed this pattern only following left-token deliveries. Overall, the effects of token reinforcers on choice were similar to those observed with other reinforcers. [ABSTRACT FROM AUTHOR]

Background: Stimuli perfectly correlated with impending access to food have been shown to both attenuate response rates and to prevent response acquisition when they occur during delays to reinforcement. One explanation of these findings is that the stimulus better predicts food than the operant response itself, and therefore, 'blocks' learning of the response-reinforcer association. That such stimuli can abolish operant learning implies a breakdown in an organism's ability to detect causality between its own behavior and effects on the environment. Method: Two response acquisition experiments in which a stimulus preceded food delivery were conducted. In one experiment, an attempt was made to replicate the prevention of response acquisition using a non-resetting delay procedure that parallels those that result in overshadowing. In a second experiment, stimulus-food pretraining was given to provide a better parallel to typical respondent-conditioning blocking procedures. Results: Under neither circumstance was response acquisition prevented. Discussion: The generality and robustness of blocking the response-reinforcer association in operant response acquisition is questioned. [ABSTRACT FROM AUTHOR]

Responding on variable-ratio (VR) schedules of wheel-running and sucrose reinforcement was assessed using a within-session procedure. Six female Long Evans rats were exposed to schedules ranging from VR 3 to VR 40 in ascending and descending order within a session with sucrose (0.1 ml of 15 % solution) and wheel-running reinforcement (30 s). Within a session, 10 reinforcers were obtained on each schedule, with a 120 s inter-component interval between schedules. Results showed that local response rates generated by sucrose were higher and that the pattern of local response rates across the schedules differed substantively between reinforcer types. With sucrose, local rates decreased linearly as the ratio requirement increased. With wheel running, local rates did not differ except to decline on the highest ratio. Post-reinforcement pauses were longer with wheel-running reinforcement and longer on the highest ratio when this ratio occurred at the end of a session. In contrast, wheel-running rates were lower on the smallest ratio schedule when this schedule occurred at the beginning of a session. The implications of the marked difference in local response rates across these schedules were discussed. [ABSTRACT FROM AUTHOR]

Can rats discriminate between short (i.e., 10 s) and long (i.e., 50 s) intervals of opportunity to run in running wheels? Eight female Long- Evans rats were exposed to 50 opportunities to run in a wheel. Following each interval, rats made a response to identify the interval. A correct response produced 0.1 ml of 15% sucrose solution, while an incorrect response caused the chamber lights to flash on and off for 5 s. Five of 8 rats met the criterion of 5 successive sessions with 80% correct responses for both durations. Furthermore, the criterion of 80% correct responses in a session was met more often with the 10-s than with the 50-s duration. Rats can discriminate between opportunities to run for different durations, but the results cast doubt on the assumption that rats are timing the intervals. [ABSTRACT FROM AUTHOR]

The current study examined the variables that influence post-reinforcement pause (PRP) duration in rats when wheel running serves as the reinforcing consequence. The relationship between revolutions and PRP duration when revolutions were manipulated within a session and the effect of changing the response requirement from fixed to variable on PRP duration were evaluated. The operant was lever pressing and the reinforcer was the opportunity to run for a programmed number of revolutions. Results failed to show a positive correlation between revolutions run and PRP duration but did show that PRP duration was decreased by a variable response requirement. Analysis also revealed a within-session decrease in PRP duration. The implications of these findings for understanding the factors that influence PRP duration with wheel-running reinforcement are discussed. [ABSTRACT FROM AUTHOR]