He created and validated the psychomotor vigilance test (PVT), which is among the most widely used assays for behavioral alertness relative to sleep and circadian dynamics biology. His has conducted seminal experiments on the effects of chronic sleep restriction in healthy adults living in a specially-equipped laboratory in the Hospital of the University of Pennsylvania. His laboratory’s current experiments focus on the nature of recovery dynamics from sleep loss; phenotypic differences in vulnerability to the effects of sleep loss; and the development of novel behavioral, physiological and technological ways to detect, manage and mitigate the effects of sleep loss. He and his colleagues also conduct naturalistic and interventional field research on healthy adults living near and/or working in safety-sensitive occupations that induce sleep disturbance, sleep loss, and circadian misalignment (e.g., astronauts, civilian and military pilots, health care professionals, commercial truck drivers, etc.). He has also conducted studies on the International Space Station, and in various space analog environments (Mars 500, NEEMO, HERA). His research findings are often used in public policy areas relative to work hours, prevention and detection of fatigue, and standards for health and safety.