Sensitivity to delay is affected by magnitude of reinforcement in rats

• We studied if sensitivity to delay was affected by magnitude of reinforcement.
• We employed a multiple concurrent chains schedule with rats as experimental subjects.
• Sensitivity to delay was higher in the component with the larger reinforcer.
• The direction of the magnitude effect was different to the one observed in humans.
• Methodological factors might contribute to the inter-species difference.

Previous research has provided discrepant results about how reinforcement delay and magnitude are combined to determine the value of the alternatives in concurrent-chains schedules. In the present experiment, we analyzed a possible interaction between these characteristics of reinforcement, employing a two component concurrent-chains schedule, with rats as experimental subjects. Non-independent VI schedules were presented in the initial links of each component. In the terminal links, the following pairs of delays to reinforcement were presented in 4 conditions: 2-28, 6-24, 24-6, 28-2 s (fixed time schedules for a group, fixed interval schedules for the other). Magnitude of reinforcement was maintained constant within components: one pellet for one component, and four pellets for the other. The results indicated that in both groups, the sensitivity to delay – calculated according to the generalized matching law – was higher in the component with the larger reinforcer. This result is in contrast with those reported in the literature of temporal discounting with human participants.