Rats don’t always respond faster for more food: The paradoxical incentive effect

Abstract

Rats' leverpressing was reinforced on variable-ratio (VR) schedules. As ratio values increased, response rates initially increased with them, then eventually decreased. In Experiment 1, rates were uniformly higher with one-pellet reinforcers than with two-pellet reinforcers-the paradoxical incentive effect. Killeen's (1994) mathematical principles of reinforcement (MPR) described the data quantitatively but failed to predict the advantage for the one-pellet condition. In Experiment 2, rats receivedone-, two-, and three-pellet reinforcers with counterbalanced preloads of pellets; the continued superiority of the smaller reinforcers ruled out a satiation explanation. Experiment 3 introduced a 20-sec intertrial interval (ITI), and Experiment 4 filled the ITI with an alternate response to test a memorial/overshadowing explanation. In Experiment 5, the rats received one or two standard grain pellets or one sucrose pellet as reinforcers over an extended range of ratios. Once again, rates were higher for one than for two pellets at short to moderate VR values; thereafter, two pellets supported higher response rates. The diminution of the effect in Experiment 3 and its reversal in Experiment 4 and in Experiment 5 at large ratios provided evidence for overshadowing and reconciled the phenomenon with MPR.

Effect of orexin-B-saporin-induced lesions of the lateral hypothalamus on performance on a progressive ratio schedule

“…Running rate was calculated by dividing the number of responses by the 'run-time' (i.e. the time taken to complete the ratio, excluding the postreinforcement pause: Bizo et al, 2001). The data were analysed as described above.…”

“…A recent study of the effect of reinforcer size on progressive-ratio schedule performance (Rickard et al, 2009) revealed that while Equation 1 provided a good description of overall response rate, its fit to the 'running' response rate (response rate calculated after exclusion of the post-reinforcement pause: Bizo et al, 2001) was less satisfactory. Running response rate was, however, well described by the logistic function:…”

A clozapine-like effect of cyproheptadine on progressive ratio schedule performance

“…Running rate was calculated by dividing the number of responses by the "run-time" (i.e. the time taken to complete the ratio, excluding the post-reinforcement pause: Bizo et al 2001). The data were analysed as described Because the number of ratios completed within a session under a progressiveratio schedule differs among individual subjects, analyses of variance of the raw response rates included only those ratios that were completed by at least 75% of the rats in each group under each treatment condition (ratios up to and including 62 in the case of the haloperidol series and up to and including 118 in the case of all other drugs), missing values being filled using the value obtained in the highest ratio completed by the subject in question (Rickard et al 2009).…”

Does satiation close the open economy?

“…It can happen because the third and fourth reinforcers (or the third and fourth seconds of the same reinforcing event) are more remote from the target response than are the first and second events (or seconds; Killeen, 1985). It can also happen because extended reinforcement epochs block the reinforcement of responses by the subsequent reinforcers (Bizo, Kettle, & Killeen, 2001). These are behavioral mechanisms that can be tested with behavioral arrangements.…”