The effects of signaling the US in backward conditioning: A shift from excitatory to inhibitory learning

The associative effects of “backward” US-CS pairings were compared when the pairing occasions were either consistently preceded by a well-trained CS+ or were unannounced. The investigation employed a conditioned emotional response procedure with rats, under conditions in which all subjects received the same schedule of shock USs, some signaled and others not, and the back-ward CS was arranged to follow either the former or the latter, in separate groups. The major finding was that although the backward CS became excitatory when it followed unsignaled USs, it became inhibitory when it followed signaled USs. This outcome, which is in line with prior findings of Wagner and Terry (1975), is in accordance with a “sometimes-opponent-process” model proposed by Wagner (1981). It is contrary to data reported by Fowler, Kleiman, and Lysle (1984) that may have resulted from a confounding of the different circumstances of backward conditioning with differences in the predictability of the US in the experimental context.