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Effort discounting in rats These studies measured rats' sensitivity to the work costs of earning food. In Experiment 1, rats earned liquid food reinforcers on a discrete trial, adjusting amount procedure (Richards, Mitchell, de Wit & Seiden, 1997). On each trial, animals chose between the EASY side (a variable amount of sugar water earned by performing 0.01 N.s work) and the HARD side (150 ul sugar water earned by performing a specific amount of work that varied across conditions: 0.01, 0.15, 0.35, 0.60 and 0.90 N.s). Changes in reinforcer amount on the EASY side were recorded and used to calculate "indifference points". Hyperbolic discount functions were fitted to the indifference points for the work conditions (mean r2 = 0.85). In Experiment 2, the delay to reinforcer delivery on the hard side varied (0, 4 and 8 s). Preference for the HARD side declined as a function of the imposed delay. In Experiment 3, the concentration of the sugar water on the hard side varied (10% and 30% weigh-by-volume). Preference for the hard side was less at the lower concentration. These experiments demonstrate that rats discount the value of hard to obtain reinforcers. Further, effort discounting is influenced by reinforcer delay and quality. Keywords: choice, discounting, effort, self-control |
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