Investigation of Intraindividual Difference in Vigilance Index of Saccade Based on Rated Facial Sleepiness

Abstract

Proposal of a method for assessing human vigilance levels is desired to prevent traffic accidents caused by drowsy drivers. However many research groups encounter an issue in proving validity of their proposed approaches, because there is no gold standard for estimating vigilance levels. Our research group has focused on dynamic characteristics of saccadic eye movement (saccade: SC) as a candidate of vigilance index and has challenged to demonstrate its validity by analyzing correlations between the characteristics of SC and a number of vigilance indices. As a result, an acceleration property of the SC showed significant correlations to rated facial sleepiness (FS). However, some of the subjects showed low correlations in these articles. In order to reveal causality of the low correlations and to improve certainty of the vigilance estimation method, we investigate intraindividual difference in the vigilance index of SC based on the FS during simulated driving. As the result of correlation coefficients, variations of FS and PV/D showed correlation of average 0.70. But six repetition of the measurement for one subject revealed wide intraindividual differences (up to 0.35) in correlation coefficient between FS and PV/D. As the result of analysis for repeatability of SC, even high correlation coefficient group, there is significant difference at FS3. And PV/D values are high at FS4 and low at FS2 in low correlation coefficient group.