Undergraduate Honors Theses

Thesis Defended

Spring 2011

Document Type



Integrative Physiology

First Advisor

Dr. Kenneth Wright


Driver safety is of utmost importance in the US, a country with approximately 208 million licensed drivers (Our Nation’s Highways, 2010). Driving while distracted or drowsy decreases performance and endangers lives. Yet in today’s bustling society, driving when distracted and/or sleepy is unfortunately more often the norm than the exception. In order to construct appropriate countermeasures to drowsy and distracted driving, it is important to understand how distraction and sleepiness affect driving. Therefore, we examined how objective markers of physiological sleepiness and simulated driving performance were influenced by time awake and cognitive distraction (referred to in this thesis as cognitive engagement) by using a 30-min driving simulation during 28-hrs of continuous wakefulness. Thirty-four healthy subjects (17 males [21.8 ± 3.8 years; mean ± SD) were studied in a modified constant routine protocol. Participants were deemed healthy based on a physical exam, sleep, psychological and medical histories, and blood chemistries. Subjects were also drug free based on urine toxicology and alcohol breath tester. After an 8-hour sleep opportunity, seven driving simulations were given beginning at approximately 1.25 hours awake and every 4 hours thereafter until approximately 25.25 hours of wakefulness. Subjects were randomized into the quiet driving (QD) (18 subjects [10 males]) or cognitive engagement (CE) (16 subjects [7 males]) condition. Subjects in the CE condition completed working memory tasks (N-back and serial subtraction) as well as trivia questions during all drives. Visual identification of markers of physiological sleepiness— slow eye movements (SEMs) and microsleep (MS) event number and duration— allowed for mean calculations of physiological sleepiness for each drive. Also for each drive, simulated driving performance was determined by mean crash events and absolute values of speed deviations (kph) and lane deviations (cm). All variables were analyzed in a mixed model ANOVA, with paired t-tests for planned comparisons, and a modified Bonferroni correction for multiple comparisons. A significant main effect of hours awake (HA) was observed for all markers of physiological sleepiness (PS) and measures of driving performance. Additionally, effects of condition were seen for all PS markers and speed deviations (p < 0.048). Compared to the QD condition, CE subjects showed significantly increased speed deviations at 9.25 and 13.25 HA, and significantly reduced PS markers at 5.25, 13.25, 17.25, 21.25 and 25.25 HA. In general, increased markers of physiological sleepiness and decreased driving performance were associated with increased time awake. Our results suggest that during extended wakefulness, CE worsens driving performance during the day but reduces markers of physiological sleepiness beginning in the afternoon and through the early morning. Therefore, reducing physiological sleepiness through cognitive engagement may prevent episodes of falling asleep at the wheel and/or catastrophic accidents late at night. These findings support the need for further research regarding the influence of cognitive engagement on sleepiness during driving.