The discounting-by-interruptions hypothesis: model and experiment

Experimental animals often prefer small but immediate rewards even when larger-delayed rewards provide a higher rate of intake. This impulsivity has important implications for models of foraging and cooperation. Behavioral ecologists have hypothesized that animals discount delayed rewards because delay imposes a collection risk. According to this long-standing hypothesis, delay reduces value because an interruption that occurs while an animal is waiting may prevent it from collecting the delayed reward. Although there have been many experimental demonstrations of animal preferences for immediacy, none have included any interruptions. This paper develops a simple model of discounting by interruptions and then tests this model experimentally. The model considers the effects of interruption rate and duration on choice behavior. The experiment tests the effects of interruptions on the choice behavior of captive blue jays (Cyanocitta cristata) using a factorial design that manipulates the rate and duration of interruptions. The results do not support the discounting-by-interruptions hypothesis. This represents one of several lines of evidence suggesting that investigators should seek alternative explanations of the animal impulsivity. Copyright 2008, Oxford University Press.