Academic journal article The Psychological Record

Local Response Rates on Variable-Ratio Schedules of Wheel-Running Reinforcement Are Relatively Invariant Compared to Sucrose

Academic journal article The Psychological Record

Local Response Rates on Variable-Ratio Schedules of Wheel-Running Reinforcement Are Relatively Invariant Compared to Sucrose

Article excerpt

There is less known about the properties of wheel running as a reinforcer than more conventional reinforcers such as food or water. The importance of investigating these properties is to determine similarities and differences compared to more conventional reinforcers. Unlike food or water, wheel running does not involve the ingestion of a substance important for survival. Wheel running involves the expenditure rather than acquisition of calories. Additionally, unlike the case with food or water, it is unclear whether duration of access can be equated to magnitude of reinforcement (Belke 1997, 2006, 2007). However, like food, the efficacy of wheel running as a reinforcer is enhanced when food is withheld and body weight decreases (Belke 1996, 2004). While wheel running generates longer post-reinforcement pauses (PRP), these pauses largely do not appear to be a function of fatigue (Belke 2000a)--the factor that most readily comes to mind. In terms of efficacy, the opportunity to run appears to generate responding roughly equivalent to a 2.5 % sucrose solution (Belke and Hancock 2003; Belke et al. 2006), a relatively weak reinforcer. The role of the greater temporal extension of the opportunity to run relative to the opportunity to eat a small bit of food has yet to be elucidated. Furthermore, rates of operant responding may be affected by changes in the rate of wheel running (Belke 2000b). Further investigation into the bases of these differences is required to determine whether they are informative about the nature of reinforcement in general or are specific to the physical parameters of this particular behavior.

The objective of the current study was to add to the growing literature on wheel-running reinforcement by investigating how response rates vary when the opportunity to run as a reinforcer is programmed to occur contingent upon different VR schedule requirements. With few exceptions (BeIke 2010, 2011; BeIke and Pierce 2009; BeIke et al. 2006; Collier and Hirsch 1971; Iversen 1993; Premack et al. 1964), investigations of wheel running as a reinforcer have used interval and response-initiated interval schedules.

Recent research using concurrent ratio schedules has clearly demonstrated differences between sucrose and wheel-running reinforcement. BeIke et al. (2006) showed that wheel running substituted less well for itself than did sucrose. Belke (2010) showed that as the ratio requirement on one alternative on concurrent ratio schedules was increased, responding quickly shifted to near exclusive preference for the unchanged alternative when the reinforcer was sucrose, but not when it was wheel running. With wheel running, preference shifted to the unchanged alternative, but responding was maintained on the alternative with the increasing ratio, leading to a much greater difference between the ratios to produce near exclusive preference for the unchanged alternative. Although these anomalous results are from concurrent rather than single schedules, they serve as an impetus for further investigation of the relationship between response and reinforcement rates on ratio schedules.

With respect to prior research, Premack et al. (1964) investigated the effect of varying the fixed-ratio (FR) requirement for the opportunity to run for 20 s across ratios of 5, 10, 15, 20, 40, 60, 200, and 300 responses. Session duration was constant at 20 minutes, and the operant was licks recorded by a drinkometer. The results demonstrated that as the ratio requirement increased, the frequency of licks increased while the frequency of wheel turns decreased. Response rate was noted as an overall rate (licks per session); however, there was no calculation of a local rate of licking (licks per minute of time spent licking, exclusive of PRP). With session duration held constant, one would expect that as the ratio requirement increased, rats would engage in more licks and fewer total revolutions, as fewer reinforcers would be obtained per session. …

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