Scond-order excitation mediated by a backward conditioned inhibitor

Conditioned suppression studies with rats explored the informational content of a backward conditioned inhibitor. Pairings of an unconditioned stimulus (US) and Stimulus 1 (US->S1) established SI as an inhibitor in Experiment 1. Pairing the inhibitor SI with a novel S2 (S2->S1) promoted excitatory second-order conditioning (SOC) to S2, which suggested SI was well associated with the US. Degrading presumed SI-US associations in Experiment 2 by SI- (extinction) treatment eliminated S2's excitation while preserving Si's inhibition. Experiments 3 and 4 converged in showing that S2 was not an excitor when Pavlovian conditioned inhibition (CI) was the inhibitory treatment prior to the SOC phase, but instead acted as a second-order inhibitor. Results are discussed in relation to the temporal coding hypothesis, the SOP (sometimes opponent process) and Rescorla-Wagner models of conditioning, and the associative structure of SOC. Also, the data suggest that backward inhibition is special and that not all forms of CI are equal. Coovrieht 1996 bv the American Psvcholoeical Association. Inc.