Overmatching in rats: The barrier choice paradigm

The barrier choice paradigm was used to impose a cost on rats' behavior of traveling between two levers: Pressing on two levers was reinforced with fo od on concurrent random-interval schedules, but rats had to climb over a ba rrier to move from one lever to another The height of the barrier separatin g the levers was increased from 30.5 to 45.7 cm across two phases that invo lved various pairs of random-interval schedules. With the 30.5-cm barrier, the generalized matching law showed slopes equal to or slightly above 1.0 f or response and time allocation. With the 45.7-cm barrier, the generalized matching law showed slopes above 1.2 for responses, indicating that sensiti vity to reinforcement increased with increasing barrier height. For time al location the slopes remained close to 1.0; sensitivity to reinforcement did not seem to increase with increasing barrier height. The role of locomotio n effort in choice situations is discussed.