Effects of CS-US interval modification on diminution of the unconditioned response in electrodermal classical conditioning

The purpose of this experiment was to study whether interstimulus interval (ISI) modification differentially affects the amplitude of the unconditione d response (UR amp.). Seventy-five volunteer subjects received discriminati on training with an interval between conditioned stimulus (CS) and uncondit ioned stimulus ((US; aversive white noise) of 8 s. After the discrimination training phase, subjects exhibiting discriminative control were randomized into three groups that differed according to the ISI, of 1, 5 or 8 s. The subjects of each group were then tested with five presentations of CS + /US . The results demonstrate that the UR showed a greater amplitude when an IS I of 8 s was used than with ISIs of 1 or 5 s. No significant differences we re found between the UR amp. of the 1- and 5-s ISI groups. These findings a re discussed as a result of a hypothetical experimentally induced blend of the anticipatory CRs with the UR. (C) 1999 Elsevier Science B.V. All rights reserved.