Effects of past and upcoming response-force requirements on fixed-ratio pausing.

Four rats obtained food by pressing a lever 30 times in each component of a two-component multiple schedule. Across conditions, the force required to press the lever was increased in one component and held constant in the other. Pausing at the outset of each component was controlled by both the past and upcoming force requirements: Pauses were longer when the upcoming requirement was high and this effect was intensified when the past requirement was low. In concert with previous research, the results support the general proposition that behavior is disrupted by abrupt, discriminable transitions from favorable to unfavorable schedule conditions, across a range of subjects and operational definitions of favorability.