Abstract
After the performances of two pigeons had stabilized on an FR 100 grain reinforcement schedule, response-contingent shock was introduced in the form of a block counter. When shock intensity increased in successive thirds of the ratio, duration of post-reinforcement pauses increased and local rate in an advanced part of the ratio declined. With decrements of shock intensity in successive thirds of the ratio, running rate was not consistently affected but pauses after reinforcements were longer than those under the increasing counter. The results are interpreted in terms of the interaction among some controlling variables operating in the behavioral chain.