Risk-sensitive foraging: changes in choice due to reward quality and delay

Past risk-sensitive foraging studies commonly manipulated delay to reward and reward magnitude, but recent risk-sensitive foraging research revealed that changes in reward quality resulted in changes in a forager's preference for a variable or fixed return. However, no studies have investigated the effects of changes in reward quality and delay to reward on risk sensitivity. Therefore, the current experiment was designed to explore rats' preference for a variable or fixed option when delay to reward and reward quality were manipulated. Using a within-subjects, ABACADA design, rats (N = 10) choose between a variable and constant option that delivered six food pellets but the amount of sugar (i.e. reward quality) and delay to reward differed per condition. In each baseline condition, pellets were 100% sugar and delivered after a 2 s mean delay. Subjects displayed a significant preference for the variable option in all baseline conditions. In condition B, pellets were 20% sugar, delivered after a 2 s mean delay, and rats were risk indifferent. In condition C, rats displayed a significant preference for the variable option when delay was 10 s and reward quality was 100%. Finally, in condition D, subjects showed the strongest variable option responses among all treatments when both reward quality and delay to reward were manipulated (i.e. 20% sugar pellets and 10 s mean delay). Preference was assessed relative to the daily energy budget rule, the scalar utility theory and the sequential choice model. The sequential choice model provided the most comprehensive and accurate prediction of subjects' preferences.