Mental Fatigue Measurement Based on the Changes in Flicker Perception Threshold using Consumer Mobile Devices

Abstract

We developed a technique to evaluate mental fatigue quantitatively by measuring perceptual performance of visually presented flicker;namely, the flicker-perception threshold (FPT), on consumer devices. Frequency domain flicker-perception threshold (FD-FPT) or critical fusion frequency (CFF), defined as a frequency at which intermittency of light disappears into a steady state for a human observer, is known to decrease as mental fatigue increases. Although FD-FPT has a long history as a reliable index of mental fatigue in the laboratory setting, it requires a dedicated device to measure, which impedes the use of this method by the general public. Additionally, arbitrariness and subjectivity of subject responses in the conventional flicker test present a significant problem for robust measurements of mental fatigue in everyday situations. This issue is especially important under such conditions where there is no supervision for users on how to respond to the ongoing flicker stimuli. We developed (a) a new method to control the subjective flickering sensation by changing the contrast of the visual stimuli instead of changing the temporal frequency, and (b) a new paradigm in which forced-choice task performance is used to determine FPT to eliminate arbitrariness of subject responses. The proposed techniques were implemented as application software, which enables persons to measure mental fatigue quantitatively using consumer mobile devices such as smart phones and PCs.