Cardiac reactions to two psychological stressors, acting in combination

56 student volunteers (mean age 21 yr.) participated in a study designed to assess how the Stroop procedure and delayed auditory feedback affect cardiac activity when they are used individually as well as when they are combined in the same task. In a preliminary study, listening to tape-recorded instructions on how to relax produced a significant decrease in cardiac activity. In the major study, when used individually, both the Stroop procedure and delayed auditory feedback produced significant increases in cardiac activity. The largest increase, however, occurred with systolic blood pressure and was induced by delayed auditory feedback. When the Stroop procedure was used in combination with delayed auditory feedback, systolic blood pressure again increased, but this effect was no greater than when delayed auditory feedback was used alone. This pattern of results implies that, when combined, the Stroop procedure and delayed auditory feedback have largely independent effects on cardiac activity and that, when tested under similar conditions, delayed auditory feedback has the larger effect.