Identification of drowsiness and alertness conditions by means of Spectral F-Test applied to pupillometric signals

The autonomous regulation of pupil size provides an objective physiological measure of alertness level. Pupil diameter decreases and its fluctuations increase during drowsiness. In this work, a statistical based technique in frequency domain, known as Spectral F-Test (SFT), was applied in order to compare the power of pupillometric signals measured in two conditions, wakefulness and sleepiness, from eleven volunteers. SFT was calculated based on Welch Periodograms of time series of pupil diameter (TSPD) signals. The median power for TSPD in two conditions and each volunteer at frequencies bellow 0.8 Hz were compared by means of the paired Wilcoxon signed-rank test. The percentages of volunteers for whom power during drowsiness were statistically higher than power during alertness achieved 100% for several frequencies bellow 0.2 Hz. For frequencies from 0.2 to 0.8 Hz, the percentages presented high variability, fluctuating from 40 to 90%. The Wilcoxon test indicated that median power of TSPD during drowsiness was higher than TSPD during alertness for frequencies bellow 0.2 Hz presented statistical difference. Hence, the SFT showed to be a suitable tool for drowsiness/alertness differentiation that could be applied to sleep studies.