Sensitivity of primary phasic heart rate deceleration to stimulus repetition in an habituation procedure: influence of a subjective measure of activation/arousal on the evoked cardiac response.

The post-stimulus primary bradycardia--sometimes labelled as the first evoked cardiac response, ECR1--is regarded as a response which is independent of the stimulus novelty factor. Despite this however, in our previous research we have observed a noticeable variation of this response, which made us suspect that there could be some additional factor influencing it. To test this, we designed a habituation procedure to measure susceptibility of the ECR1 to stimulus repetition. In our experimental design, we also included a measure of the level of activation (arousal) as a possible additional factor influencing the time-course of the cardiac response. The level of arousal over the study was measured by the Activation-Deactivation Adjective Check List (AD ACL). Our results show that mere stimulus repetition does not influence the time-course of ECR1. However, another pattern of results appeared when one of the dimensions of AD ACL, namely Tense Arousal, was taken into account. We observed different ECR time-courses during the initial stimulus presentations for subjects with high and low levels of Tense Arousal. These results are interpreted within the framework of Preliminary Process Theory in terms of the different attentional patterns in subjects with high and low levels of Tense Arousal.