Both sleep deprivation and loss of situation awareness (SA) have been cited as primary causal factors contributing to the accident and injury rate in the military and civilian sector (e.g., transportation). Despite the numerous references to both factors as causal in nature, much of the literature on the effects of sleep deprivation on executive function is anecdotal. Research has produced mixed results regarding the nature and extent of performance degradation on a variety of lower-level and executive function tasks. Similarly, although SA has been cited as a significant contributor to operational performance, there is still considerable debate over the definition and construct validity of SA. Thus, a 29-hour hour sleep deprivation study was conducted to analyze the effects of sleep deprivation on both lower-order cognitive tasks (e.g., attention and working memory) and executive function tasks (e.g., reasoning, planning, decision making, and SA). In conjunction with the sleep deprivation analysis, the relationships among lower level cognition, executive function, and situation awareness were analyzed to form hypotheses about the SA construct and its relationship to complex task performance.

Forty-eight participants were administered a series of cognitive tasks during baseline and sleep deprived testing sessions. Paired t-tests and additional post hoc analyses were conducted to determine the effects of sleep deprivation on cognition. Regression and factor analysis were used analyze the relationship among lower-order cognition, executive function, situation awareness, and complex task performance. Paired t-test results showed degraded vigilance in response to sleep deprivation, but did not indicate degraded executive function. Results of additional post-hoc analyses on executive function data indicated a trend toward degraded decision making and a trend toward increased planning errors in response to sleep deprivation. The results of the regression and factor analyses provided initial support for a dynamic, process definition of SA and illustrated the importance of considering SA as part of information processing as a whole in order to improve performance prediction. Based on the results of this dissertation, engineering recommendations were made for developing an "ideal" SA measurement technique and improving existing SA measurement techniques. Additionally, future sleep deprivation and situation awareness research directions were suggested.