A Magnitude Effect in Temporal discounting with Hens

Abstract

This study aimed to determine whether a magnitude effect could be obtained in temporal discounting with brown shaver hens. Subjects responded in a classic self-control situation for the choice between a smaller-sooner reward (1-s access to food, after a 2 s delay) or a larger-later reward (4.5-s access to food, after a 28 s delay). Hens responded in a multiple concurrent-chain procedure on concurrent variable-interval (VI-30s, VI 30-s) schedules in the choice phase (initial links), and a fixed interval (FI) schedule, ranging from FI 2-s to FI 28-s in the outcome phase (terminal links). The outcome phase then resulted in reinforcement of either 1-s access to grain or 4.5-s access to grain. The results replicated the findings of a previous study by Grace, Sargisson & White (2012), who obtained evidence of a magnitude effect in temporal discounting with pigeons, in which subjects demonstrated a greater preference for the larger reward compared to the small reward over increasing time delay. The findings indicate that the magnitude effect is not unique to humans, as previous studies have suggested. Data was applied the Generalized Matching Law (GML) and the Contextual Choice Model (CCM) equations to determine if the data was comparable with models of behavioural choice.