Excitatory second-order conditioning using a backward first-order conditioned stimulus: A challenge for prediction error reduction.

Prével and colleagues reported excitatory learning with a backward conditioned stimulus (CS) in a conditioned reinforcement preparation. Their results add to existing evidence of backward CSs sometimes being excitatory and were viewed as challenging the view that learning is driven by prediction error reduction, which assumes that only predictive (i.e., forward) relationships are learned. The results instead were consistent with the assumptions of both Miller's Temporal Coding Hypothesis and Wagner's Sometimes Opponent Processes (SOP) model. The present experiment extended the conditioned reinforcement preparation developed by Prével et al. to a backward second-order conditioning preparation, with the aim of discriminating between these two accounts. We tested whether a second-order CS can serve as an effective conditioned reinforcer, even when the first-order CS with which it was paired is a backward CS that elicits no responding. Evidence of conditioned reinforcement was found, despite no conditioned response (CR) being elicited by the first-order backward CS. The evidence of second-order conditioning in the absence of excitatory conditioning to the first-order CS is interpreted as a challenge to SOP. In contrast, the present results are consistent with the Temporal Coding Hypothesis and constitute a conceptual replication in humans of previous reports of excitatory second-order conditioning in rodents with a backward CS. The proposal is made that learning is driven by "discrepancy" with prior experience as opposed to " prediction error."