Mental Stress Analysis using the Power Spectrum of fNIRS Signals

Mental stress is one of the major health problems in modern societies. Detecting mental stress at its early stage and developing a method of stress mitigation is very important for safety, health and quality of life. In this study, we employed a modified Stroop Color Word Task (SCWT) with time constrains and negative feedback about the performance, together with Binaural Beats Stimulation (BBs), to induce three varied levels of mental stress. Level one was based on SCWT alone and level two was based on SCWT+time-pressure and level three was by utilizing SCWT+time-pressure+BBs. We then quantified the level of stress using a NASA TLX questionnaire and functional near-infrared spectroscopy (fNIRS). The fNIRS signals were then analyzed using the Welch power spectrum density (PSD) to investigate the discrepancy in brain activity across the three levels of mental stress. We found that the mean PSD value in the frequency range of 0.2 to 0.5 Hz has significantly changed between the three stress levels. These findings indicate that the fNIRS power spectrum analysis method could be used as a robust marker for mental stress.