Responding for Sucrose and Wheel‐running Reinforcement: Effects of Sucrose Concentration and Wheel‐running Reinforcer Duration

Abstract

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.

Postreinforcement Pause Duration Varies Within a Session and With a Variable Response Requirement but Not as a Function of Prior Revolutions

“…The signaled reinforcers were opportunities to run for 10 s and 50 s. In contrast to Belke and Hancock's (2003) results, PRP duration varied as a function of the duration of the previous reinforcer but did not differ as a function of stimuli signaling different durations. PRP duration in this study was a function of inhibitory aftereffects, and there was no evidence for a difference in excitatory stimulus effects.…”

“…While minimal or very short pauses have been demonstrated on VR schedules using conventional reinforcers, they have yet to be shown with wheel-running reinforcement. With the exception of Premack, Schaeffer, and Hundt's (1964) study that used fixed-ratio (FR) schedules, most studies of wheel-running reinforcement have used fixed-interval (FI) schedules (e.g., Belke, 2000;Belke & Dunbar, 1998;Belke & Hancock, 2003;Collier & Hirsch, 1971) and response-initiated variable-interval (VI) schedules (e.g., Belke, 1997;Belke & Heyman, 1994). Response-initiated VI schedules have been used because the longer PRPs following the termination of wheel running would either time out or greatly reduce the programmed reinforcement interval, particularly in the case of short average-duration VI schedules (Belke & Dunbar, 1998).…”

“…Using a multiple-schedule procedure in which different stimuli signaled whether the upcoming reinforcer was sucrose or wheel running, Belke and Hancock (2003) found that as the wheel-running duration increased from 15 s to 90 s, PRPs increased in duration in the presence of a stimulus signaling wheel running but not in the presence of a stimulus signaling sucrose. This finding was attributed to a decrease in the excitatory effect of wheel running rather than an increase in inhibitory aftereffects because it occurred in the presence of a stimulus signaling an upcoming wheel-running reinforcer, but not when the previous reinforcer was wheel running and the signaled upcoming reinforcer was sucrose.…”

Concurrent schedules of wheel-running reinforcement: Choice between different durations of opportunity to run in rats

“…Wheel-running rate within a reinforcement period is typically higher earlier in the interval and declines as the interval elapses (Belke & Hancock, 2003;Belke & McLaughlin, 2005). This pattern means that wheel-running rate will vary with reinforcer duration simply because shorter durations represent higher rates earlier in the interval, whereas longer durations include both the higher earlier and the lower later rates.…”

“…This pattern means that wheel-running rate will vary with reinforcer duration simply because shorter durations represent higher rates earlier in the interval, whereas longer durations include both the higher earlier and the lower later rates. However, when wheel-running rates are measured across different reinforcer durations (see, e.g., Belke & Hancock, 2003), rates within shorter durations (e.g., a 15-sec reinforcer) differ from those observed over the same duration within longer reinforcers (e.g., the first 15 sec of a 90-sec reinforcer). Shorter durations engender higher rates.…”