Crespi effect Wikipedia
The Crespi effect (Leo P(aul) Crespi (1916–2008)) is a behavioural phenomenon observed in rats. In a repeatedly carried out task such as finding food in a maze, the running speed of the rat is proportional to the size of the reward it obtained on the previous trial. The more food reward that was given to it last time upon completion of the task, the faster it will run when attempting to complete the same task. The effect also works in reverse.
It is important to note that the size of the reward has little or no influence on the speed of learning, but that it does have an influence on the performance of tasks already learned.