interbeat interval

What Is the Interbeat Interval?

The interbeat interval (IBI) is the period between cardiac pulse waves, measured systole to systole. IBI shortens after stress onset (defence response) and lengthens during orienting responses. IBI and heart rate are reciprocals of each other.

Role in Polygraph Physiology

Understanding interbeat interval is part of the broader physiological knowledge base that supports polygraph science. The physiological responses the polygraph measures — changes in electrodermal activity, respiration, and cardiovascular function — are all products of the neural and physiological systems that include this concept. Examiners benefit from understanding these mechanisms to properly interpret the data they collect and to assess factors that might affect examination validity.

Clinical Considerations

Conditions or medications affecting this aspect of physiology may influence polygraph data quality. The pre-test interview and suitability assessment should identify relevant medical factors. When physiological conditions affect data quality in specific channels, the examiner evaluates whether the remaining channels provide sufficient information for a reliable diagnostic opinion.

Integration with Polygraph Channels

The polygraph simultaneously records three core physiological channels — electrodermal, respiratory, and cardiovascular — each capturing different aspects of the autonomic nervous system's response to psychologically significant stimuli. Validated scoring systems evaluate features from all three channels independently, then combine them for the overall diagnostic opinion. Understanding the physiological basis of each channel helps examiners interpret data accurately and identify factors that might affect specific channels.