Abstract
Pecks at a first (left) key were reinforced by a partial movement (advance) of the voltmeter behind the key toward the maximum position. When the meter reached maximum deflection, pecks at a second key were continuously reinforced with food. The schedule of reinforcement by which pecking the first key produced a deflection, as well as the size of the deflection, were varied in a series of experiments. The rate of responding on the first key was more affected by changes in the number of steps required to move the meter to the maximum position (the size of the deflection) than by the value of the variable-interval schedule by which pecking produced a meter deflection. The rate at which the bird pecked was low when the meter was near the null position, and high as the meter approached the maximum deflection.