The effect of prefeeding on fixed-ratio pausing is jointly determined by past and upcoming reinforcer magnitudes.

Pausing within multiple fixed-ratio schedules differing in reinforcer magnitude is jointly controlled by both past and upcoming conditions of reinforcement. Abrupt shifts from a just-received large reinforcer to a signaled upcoming small reinforcer (i.e., a negative incentive shift) produce marked disruptions in responding, as indexed by extended pausing. The purpose of this experiment was to determine if reducing the level of food deprivation via prefeeding enhanced these disruptive effects. Five Long Evans rats lever-pressed according to a fixed-ratio schedule. Half of the components ended in a relatively large reinforcer (three 45-mg food pellets) and half ended in a relatively small reinforcer (one pellet). Components alternated irregularly, yielding four transitions between reinforcers: small-small, small-large, large-small (the negative incentive shift), and large-large. During five, 1-session prefeeding probes, rats were given 12 g of food in their home cages 1h prior to the start of the session. Under steady-state conditions, negative incentive shifts engendered the longest pausing. Prefeeding produced large absolute and relative increases in pausing during negative incentive shifts, and small increases in pausing in the other transitions. The results are interpreted within a resistance to change framework.