Performance on a progressive-ratio schedule of food reinforcement during concurrent access to a sucrose solution or tap water.

Seven food-deprived rats were observed on a progressive-ratio 5 schedule of food reinforcement under baseline conditions and during concurrent access to tap water, a 1 % sucrose solution, or a 5 % sucrose solution. Subjects responded for the alternative reinforcer primarily during the preratio pause. Responding for the alternative reinforcer caused a local increase in pause durations in all conditions, however, the mean pause duration for the session increased only when the 5 % sucrose solution was available. Otherwise, the increase in pause durations that accompanied responding for the alternative reinforcer was offset by reducing pausing at other times. Access to the 5 % sucrose solution changed the relation of ratio size to pause duration in several subjects in that the longest pause durations occurred before the end of the session rather than when the highest ratios were in effect. Breakpoints were largely unaffected by alternative reinforcement.