Effects of CS-US Interval on Unconditioned Response Diminution in Human Heart Rate Classical Conditioning

This experiment studies the role of the conditioned response (CR) in explaining the unconditioned response (UR) diminution phenomenon in heart rate (HR) classical conditioning. In order to analyze the implication of the different CR components on UR diminution, the interstimulus interval (ISI) was varied. Sixty volunteer subjects received discrimination training with an interval between conditioned stimulus (CS) and unconditioned stimulus (US; aversive white noise) of 8 s. After the discrimination training phase, subjects were randomized into three different groups according to an ISI of 1, 5, or 8 s. The subjects of each group were then tested with five presentations of CS+/US. The results showed that UR amplitude as well as the deceleration immediately before this response (pre-UR deceleration) were significantly lower in the 5 s and 8 s ISI groups than in the 1 s ISI group. In addition, UR amplitude and pre-UR deceleration were statistically the same in the 5 s and 8 s ISI groups. These findings are discussed in terms of the adaptative role of the CR in classical conditioning.