 The Psychomotor Vigilance Self Test on the International Space Station (Reaction Self Test) provides the crewmembers with feedback on neurobehavioral changes in vigilant attention, state stability, and impulsivity.It aids crewmembers to objectively identify when their performance capability is degraded by various fatigue-related conditions that can occur as a result of ISS operations and time in space (e.g., acute and chronic sleep restriction, slam shifts, extravehicular activity (EVA), and residual sedation from sleep medications).The test is ideal for use in space flight because unlike other cognitive tests, it is brief while being free of learning effects and aptitude difference that make interpretation of other measures difficult, as it has been successfully deployed in three NASA missions.