Conditioned reinforcement and backward association

In the present study, excitatory backward conditioning was assessed in a conditioned reinforcement paradigm. The experiment was conducted with human subjects and consisted of five conditions. In all conditions, US reinforcing value (i.e. time reduction of a timer) was assessed in phase 1 using a concurrent FR schedule, with one response key leading to US presentation and the other key leading to no-US. In phase 2, two discrete stimuli, S+ and S−, were paired with US and no-US respectively using an operant contingency. For three groups, backward contingencies were arranged, and two of these were designed to rule out a trace (forward) conditioning interpretation of the results. The two other groups served as control conditions (forward and neutral conditions). Finally, in phase 3 for all groups the CSs were delivered in a concurrent FR schedule similar to phase 1, but with no US. Responding during phase 3 showed conditioned reinforcement effects and hence excitatory backward conditioning. Implications of the results for conditioned reinforcement models are discussed