Abstract
Five groups of pigeons were food reinforced on various schedules. Half of each group were extinguished in the normal manner; the others were presented with a stimulus change, previously paired with reinforcement, each time they completed their respective fixed ratios. Response rate in training was an increasing negatively accelerated function of the FR. Increasing the FR produced transitory rate changes, the amount of which yielded a quantitative index of ratio strain. Cumulative records of extinction performance revealed that the stimulus change exerted discriminative control by maintaining the cohesiveness of FR response units. Nevertheless, neither the absolute number of extinction responses nor extinction response units differed appreciably for the two extinction procedures.