The relationship between objectively measured sleepiness and driving ability

Abstract

The complex task of driving requires driver vigilance, attention and ability to perceive, comprehend, react and adapt. While it appears self-evident that most, if not all, of these functions are affected by fatigue and drowsiness, little direct, concrete proof exists. Therefore, the aim of the present study was to examine the relationship between objectively measured sleepiness and driving ability. Twelve adults (mean age 24.5 ± 1.4 years: 6 males, 6 females) participated in the study. During the entire study period (24 h of continuous awakening) participants were tested every three hours with a battery of computerized tests (Vienna Test System) known to significantly correlate with accident involvement and with the Pupillographic Sleepiness Test (PST) that objectively measures sleepiness. The PST consists of an 11-minute recording by infrared video pupillography of the sitting participant’s pupil diameter, followed by automated data analysis. Spontaneous pupillary oscillations provide objective and quantitative measures of tonic central nervous activation, which is a precondition for higher level mental performance. In sleepy subjects the pupil shows spontaneous oscillations with a predominantly low frequency component and amplitudes reaching several millimeters. Analysis revealed significant difference between day and night tests in mean motor reaction time [ t (11) = 3.61; p < 0.01], in distribution reaction time [ t (11) = 2.89; p < 0.05], and in the percentage of wrong responses [ t (11) = −1.80; p < 0.001]. Likewise, analysis revealed a significant correlation between PST Index and mean motor reaction time ( r = 0.94; p < 0.01), between PST Index and distribution reaction time (r = 0.84; p < 0.05), and between PST Index and percentage of wrong responses ( r = 0.80; p < 0.005). The results suggest that driving ability is directly and highly related to fatigue and sleepiness. This exploratory study can shed light on the role fatigue plays in decreased driving skills and increased road accidents. The authors thank Paula S. Herer for assisting in the statistical analysis.