A comparison of phasic cardiac responses derived from the electrocardiogram and the peripheral pulse

In recent years, psychophysiologists have increasingly used the peripheral pulse as a more convenient source of cardiac information than the electrocardiogram. We explored some of the measurement problems associated with this choice by comparing estimates, produced by both data sources, of the cardiac response evoked by innocuous visual stimuli. The most important difference is that pulse transit time results in the immediately-prestimulus beat of a significant proportion of pulse-derived responses being mislabelled as the following beat, shifting the entire apparent response by one beat. This reduces correlations between the data streams, and has implications for the adequate measurement of evoked cardiac responses.