Some parameters of the second-order conditioning of fear in rats.

The effects of CS1 duration, partial reinforcement, and trace conditioning on second-order conditioned suppression were investigated, employing 64 rats as Ss. In Experiment 1, the clearest second-order conditioning was obtained when CS1 duration was the same during both the firstand the second-order conditioning phases of the experiment. In Experiment 2, somewhat better second-order conditioning was obtained when first-order conditioning had been under conditions of partial reinforcement, delay CS-US pairing. In neither experiment were CS1 suppression and CS2 suppression during second-order testing well correlated. This aspect of the results raised the question of the influence of nonclassical conditioning factors on the conditioned suppression measure of emotional conditioning. The purpose of the present research was to investigate the effects of several parameters on second-order conditioning in rats. Recently, Davenport (1966) and Kamil (1968) have demonstrated that secondorder conditioning can be obtained readily, using the conditioned suppression technique. In these experiments, a multistage paradigm has been employed. Following the establishment of a steady state of operant responding on a partial reinforcement schedule, two stimuli are separately preexposed with no programmed consequences. In the next stage, first-order conditioning (FOC), one of these stimuli, CS1, is paired with the US, electric shock. After conditioned suppression (a reduction in response rate during the CS) is established, the second stimulus, CS2, is again preexposed. Finally, during second-order conditioning (SOC), CS2 is paired with CS1 (no US presented) and second-order suppression to CS2 measured. The present research represents an attempt to initiate parametric investigation into secondorder conditioned suppression.