A Test of the Aversive Transition Account: Extended Pausing Following Signaled Rich-Lean Transitions on Multiple Fixed-Ratio Schedules in Fischer 344 and Lewis Rats

Abstract

On multiple schedules ending in two different magnitudes of reinforcement, a signaled transition from a preceding large (rich) to an upcoming small (lean) reinforcer occasions long post-reinforcer pauses compared to transitions from lean to rich, or when magnitude is constant (e.g., rich-rich and lean-lean transitions). A behavioral process that may underlie extended pausing at signaled rich-lean transitions is that these transitions are aversive and set the occasion for escape in the form of extended pausing. The present study evaluated this hypothesis by examining pausing at signaled rich-lean transitions in two inbred strains of rats putatively differing in sensitivity to aversive stimulation. Fischer 344 rats are more sensitive to aversive stimuli and so should pause longer than Lewis rats at the signaled transition from large to small reinforcers. Pausing was assessed at four different signaled transitions (rich-lean, rich-rich, lean-rich, and lean-lean) across a range of fixed-ratio values (1, 25, 50, 75, and 100). Consistent with the aversive transition hypothesis, Fischer 344 rats paused longer than Lewis rats at signaled rich-lean transitions at most ratio values. Control procedures suggest this difference is not due to motoric differences between rat strains.