Analysis of 1/f Fluctuation of Keystroke Dynamics and Heart Rate Variability

Mental stress has been an issue in modern society. Several studies have investigated the detection of mental stress using physiological indices. However, measurement of these indices would itself impart a certain level of stress to subjects. The temporal dynamics of key typing are called "keystroke dynamics". Keystroke dynamics show variations with psychological subtlety. The objective of this study was to develop a technique for ambient, unconscious measurement of mental stress based on keystroke dynamics. The relationship between fluctuations in keystroke dynamics and cardiac activity, in the form of heart rate variability, was analyzed. Intervals between key strokes were measured while using a computer under conditions of auditory stimulus or cognitive stress was determined. Power exponent beta of the regression curve of the power spectrum for the time series of inter-stroke time (IST), and the power spectrum density of the high-frequency component (HF) for the time series of the R-R interval extracted from electrocardiography were calculated. As a result, the power spectrum of IST approached 1/f with auditory stimulus or cognitive stress, and a significant correlation existed between beta and HF.