Differential effects of expectancy and associative mechanisms on diminution of unconditioned response in electrodermal classical conditioning

The purpose of this experiment was to study whether conditioned diminution of the unconditioned response (UR) is a phenomenon with an associative basis. Twenty-five subjects received discrimination training with an interval between conditioned stimulus (CS) and unconditioned stimulus (US) of 5 s (differential conditioning group). The same stimuli were presented to another twenty-five subjects, but in an explicitly uncorrelated manner (non-conditioning group). After the acquisition phase, participants of each group were tested with seven presentations of CS+/US and CS-/US. The results of the acquisition phase showed that the UR amplitude was lower in the differential conditioning group than in the non-conditioning group. In the testing phase, CS+/US presentations elicited URs of lower amplitude than CS-/US in the differential conditioning group, but not in the non-conditioning-group. These findings are discussed as a result of expectancy and associative effects of conditioning processes.