Effects of concurrent schedules on human fixed-interval performance

Young adults performed a lever-pressing task for money on two schedules of reinforcement: concurrent fixed-interval 1 min-differential-reinforcement-of-low-rate 20-sec, and concurrent fixed-interval 1-min-fixed ratio 100 responses. All subjects were trained on both schedules. Fixed-interval performance concurrent with the differential reinforcement procedure was characterized by high constant rates with no post-reinforcement pauses. Fixed-interval performance concurrent with fixed ratio was characterized by low rates and lengthy post-reinforcement pauses. These results differ from those obtained in prior studies on the effects of conditioning history upon subsequent fixed-interval performance. The prior work, using non-concurrent procedures, had shown that fixed-interval performance following differential reinforcement of low rates was characterized by post-reinforcement pauses and low rates, while fixed-interval performance following fixed ratio exhibited high constant rates and no post-reinforcement pause. The present results suggest that alternative concurrent contingencies are another major determinant of human fixed-interval performance.