Simultaneous shifts in reward magnitude and level of food deprivation

Rats were employed in a 2 by 2 factorial design varying deprivation level (11 vs 20 g of food per day) and reward magnitude (1 vs 10 pellets) in Phase 1. In Phase 2, all groups were run to 10 pellets under low deprivation. Both Phase 1 deprivation level and Phase 1 reward magnitude exerted a significant effect on running speed in Phase 2. More importantly, the interaction of these two variables was not significant. The effect of Phase 1 reward magnitude decreased over the rewarded trials of Phase 2, while the effect of Phase 1 deprivation level did not. However, in a subsequent extinction phase, the effects of Phase 1 deprivation level disappeared.