"Justification of effort" in rats: effects of physical and discriminative effort on reward value.

The justification of effort is the tendency for humans to justify the amount of work they have put into an achievement by increasing the perceived value of that achievement after the effort has been expended. A positive effect of effort on reward value has also been reported for pigeons and starlings. The present study examined the effects of different amounts of required physical and discriminative effort on primary reward value in rats. On each day of training, rats underwent one high-effort training session and one low-effort training session in an operant chamber to earn either a grape-flavored reward pellet or a bacon-flavored reward pellet. Half of the rats exerted high effort to earn the grape pellets and low effort to earn the bacon pellets, with the arrangement reversed for the other half. On each test trial, each rat had the opportunity to consume 3 pellets of each flavor at the choice point in a T-maze. Analysis indicated no significant difference between the frequency of high-effort flavor choices and low-effort flavor choices. A positive effect of effort on reward value was not demonstrated in this experiment.