Reinforcer specificity of the suppression of instrumental performance on a non-contingent schedule.

Hungry rats were trained to press one lever for a sucrose solution and another for food pellets on a concurrent schedule. The contingency between lever pressing and reinforcement was then reduced by delivering either free sucrose solution or free food pellets. The non-contingent schedule resulted in a greater reduction of pressing on the lever associated with the contiguous reinforcer that was the same as the free reinforcer. This finding suggests that the reduction in instrumental performance under a non-contingent schedule cannot be attributed solely to the development of competing responses.