Reinforcement of spaced responding in a simultaneous discrimination.

Pigeons were exposed to three stimuli simultaneously with responses reinforced according to differential-reinforcement-of-low-rate schedules. Responses to one stimulus (the positive stimulus) that were spaced appropriately resulted in food presentation. The variables manipulated were the time parameter of the schedule (5, 10, 20, 30 sec) and the consequences of responding to the other two stimuli (the negative stimuli). The percentage of the total responses that occurred to each stimulus was independent of the schedule value but was dependent on the consequences of responding to the negative stimuli. If responses to both reset the schedule timer, responding was confined largely to the positive stimulus. If responses to neither had scheduled effects, the birds were more likely to respond to those stimuli. Responding to one negative stimulus could be selectively attenuated by having responses to that stimulus alone reset the timer. With the schedule time value held constant, the absolute rate of responding to the positive stimulus was either stable or decreased with maintained exposure; it did not change as a function of increases or decreases in responding to the negative stimuli. Rather than interacting and affecting each other, responses to the three stimuli were controlled independently by their relation to reinforcement. There was no evidence that responses to the negative stimuli mediated the spacing of responses to the positive stimulus.